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AUTHOR Vogt, Gregory L., Ed.; Wargo, Michael J., Ed.TITLE Microgravity: A Teacher's Guide with Activities.

Secondary Level.INSTITUTION National Aeronautics and Space Administration,

Washington, D.C.REPORT NO EP-280PUB DATE Jul 92NOTE 64p.; Photographs will not reproduce clearly.AVAILABLE FROM Education Division, NASA Headquarters, Code FET,

Washington, DC 20277-2028.PUB TYPE Guides Classroom Use Teaching Guides (For

Teacher) (052)

EDRS PRICE MF01/PC03 Plus Postage.DESCRIPTORS Experiential Learning; *Gravity (Physics); Science

Activities; *Science Instruction; ScientificConcepts; Secondary Education; Secondary SchoolScience; Space Sciences; *Space Utilization

IDENTIFIERS *Microgravity

ABSTRACT

A microgravity environment is one that will impart toan object a net acceleration that is small compared with thatproduced by Earth at its surface. In practice, such acceleration willrange from about one percent of Earth's gravitational acceleration tobetter than one part in a million. this teacher's guide presents anintroduction to microgravity, a microgravity primer discusses thefluid state, combustion science, materials science, biotechnology,and microgravity and space flight, and 12 microgravity activities(free fall demonstration; falling water, gravity and acceleration,inertial balance--2 parts, gravity driven fluid flow, candle flames,candle drop, contact angle, fiber pulling, crystal growth andmicroscopic observation of crystal growth). Each activity contains:the objective, background, procedure and materials needed. Someactivities also includes suggested questions and further research.These activities used metric units of measure. A one-page glossarydefines words used in microgravity research and 22 microgravityreferences are provided. The guide is amply illustrated with blackand white photographs, diagrams, and drawings. (PR)

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EDUCATIONAL RESOURCES INFORMATIONCENTER (ERIC)

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National Aeronautics anc:Space Administration

The Cover

The National Aeronautics and Space Administrationuses a variety of technologies to create microgravityenvironments for research. Pictured is the SpaceShuttle Orbiter positioned with its tail pointed towardsEarth to obtain the lowest possible gravity levels. Inthis orientation, called a gravity gradient attitude,the vehicle's position is maintained primarily bynatural forces. This reduces the need for orbiterthruster firings that disturb acceleration-sensitiveexperiments.

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MicrogravityA Teacher's Guide With Activities

Secondary Level

Microgravity Science and Applications DivisionOffice of Space Science and Applications

Education DivisionOffice of Human Resources and Education

National Aeronautics and Space Administration

This publication may be reproduced.EP-280 July 1992

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Acknowledgments

The Microgravity Teacher's Guide was developed for the National Aeronautics and SpaceAdministration with the guidance, support, and cooperation of many individuals and groups.

NASA Headquarters, Washington DCOffice of Space-Science and Applications

Microgravity Science and Applications DivisionOffice of Human Resources and Education

Education Division

Johnson Space Center, Houston, TXEducation Working Group

Marshall Space Flight Center, Huntsville, ALEducation Branch

Editors Production

Gregory L. Vogt, Ed.D.Crew Educational Affairs LiaisonJohnson Space Center

Michael J. Wargo, Sc.D.Visiting Senior ScientistMicrogravity Science and ApplicationsDivisionNASA Headquarters

on leave from:Materials Processing CenterDepartment of Materials Science andEngineeringMassachusetts Institute ofTechnology

ii

Managing EditorCheryl A. ManningTechnology and Evaluation BranchEducation DivisionNASA Headquarters

Cover DesignAnother Color, Inc.

Activity Contributors

Free Fall DemonstratorFalling Water CupInertial Balance, Part 1Inertial Balance, Part 2Candle DropGregory L. Vogt, Ed.D.Crew Educational Affairs LiaisonJohnson Space Center

Gravity-Driven Fluid FlowCharles E. Bugg, Ph.D.DirectorCenter for Macromolecular CrystallographyUniversity of Alabama at Birmingham

Craig D. Smith, Ph.D.ManagerX-Ray Crystallography LaboratoryCenter for Macromolecular CrystallographyUniversity of Alabama at Birmingham

Contact AnglePaul Concus Ph.D.Senior ScientistLawrence Berkeley LaboratoryAdjunct Professor of MathematicsUniversity of California, Berkeley

Robert Finn, Ph.D.Professor of MathematicsStanford University

Gravity and AccelerationRichard De Lombard, M.S.E.E.Project ManagerSpace Acceleration Measurement SystemNASA Lewis Research Center

iii

Crysta! GrowthRoger L. Kroes, Ph.D.ResearcherMicrogravity Science DivisionNASA Marshall Space Flight Center

Donald A. Reiss, Ph.D.ResearcherMicrogravity Science DivisionNASA Marshall Space Flight Center

Microscopic Observation of CrystalGrowthDavid Mathiesen, Ph.D.Senior Research AssociateCase Western Reserve University

Fiber PullingRobert J. Naumann, Ph.D.ProfessorOffice of the Dean, College of ScienceThe University of Alabama in Huntsville

andProgram ManagerConsort Rocket FlightsConsortium for MaterialsDevelopment in SpaceThe University of Alabama in Huntsville

Candle FlamesHoward D. Ross, Ph.D.ChiefMicrogravity Combustion BranchNASA Lewis Research Center

Table of Contents Acknowledgments i i

INTRODUCTION 1

What Is Microgravity? 1

Gravity 2Creating Microgravity 3

MICROGRAVITY PRIMER 8The Fluid State 8Combustion Science 11

Materials Science 12Biotechnology 16Microgravity and Space Flight 17

ACTIVITIES 22Free Fall Demonstrator 23Falling Water 25Gravity and Acceleration 27Inertial Balance, Part 1 29Inertial Balance, Part 2 31Gravity-Driven Fluid Flow 33Candle Flames 35Candle Drop 38Contact Angle 40Fiber Pulling 42Crystal Growth 44Microscopic Observation of Crystal Growth 47

GLOSSARY 50

MICROGRAVITY REFERENCES 51

NASA EDUCATIONAL RESOURCES 52

IntroductionThere are many reasons for space flight.Space flight carries scientific instruments,and sometimes humans, high above theground, permitting us to see Earth as aplanet and to study the complex interac-tions of atmosphere, oceans, land, energy,and living things. Space flight lofts scientificinstruments above the filtering effects of theatmosphere, making the entire electromag-netic spectrum available and allowing us tosee more clearly the distant planets, stars,and galaxies. Space flight permits us totravel directly to other worlds to see themclose up and sample their compositions.Finally, space flight allows scientists toinvestigate living processes and the funda-mental states of mattersolids, liquids, andgasesand the forces that affect them in amicrogravity environment. The study of thestates of matter and their interactions inmicrogravity is an exciting opportunity toexpand the frontiers of science. Investiga-tions include materials science, combus-tion, fluids, and biotechnology. Microgravityis the subject of this teacher's guide.

What Is Microgravity?

The presence of Earth creates a gravita-tional field that acts to attract objects with aforce inversely proportional to the square ofthe distance between the center of theobject and the center of Earth. Whenmeasured on the surface of Earth, theacceleration of an object acted upon onlyby Earth's gravity is commonly referred toas one g or one Earth gravity. This accel-eration is approximately 9.8 meters/secondsquared (m/s2).

G

1

The term microgravity (kg) can be inter-preted in a number of ways depending uponcontext. The prefix micro - (ii) is derivedfrom the original Greek mikros, meaning"small." By this definition, a microgravityenvironment is one that will impart to anobject a net acceleration small comparedwith that produced by Earth at its surface.In practice, such accelerations will rangefrom about one percent of Earth's gravita-tional acceleration (aboard aircraft in para-bolic flight) to better than one part in amillion (for example, aboard Earth-orbitingfree flyers).

Another common usage of micro- is found inquantitative systems of measurement, suchas the metric system, where micro- meansone part in a million. By this second defini-tion, the acceleration imparted to an objectin microgravity will be one-millionth (10-6) ofthat measured at Earth's surface.

The use of the term microgravity in thisguide will correspond to the first definition:small gravity levels or low gravity. As wedescribe how low-acceleration environmentscan be produced, you will find that thefidelity (quality) of the microgravity environ-ment will depend on the mechanism used tocreate it. For illustrative purposes only, wewill provide a few simple quantitative ex-amples using the second definition. Theexamples attempt to provide insight intowhat might be expected if the local accelera-tion environment would be reduced by sixorders of magnitude from 1g to 10-6g.

If you stepped off a roof that was five metershigh, it would take you just one second toreach the ground. In a microgravity environ-ment equal to one percent of Earth's gravita-tional pull, the same drop would take 10seconds. In a microgravity environmentequal to one-millionth of Earth's gravitationalpull, the same drop would take 1,000seconds or about 17 minutes!

2Microgravity can be createdin two ways. Because gravi-tational pull diminishes withdistance, one way to create amicrogravity environment isto travel away from Earth. Toreach a point where Earth'sgravitational pull is reduced toone-millionth of that at thesurface, you would have totravel into space a distance of6.37 million kilometers fromEarth (almost 17 times fartheraway than the Moon). Thisapproach is impractical,except for automated space-craft, since humans have yetto travel farther away fromEarth than the distance to theMoon. However, a morepractical microgravity envi-ronment can be createdthrough the act of free fall.

Normalweight

Heavierthan normal

Figure 1. Acceleration and weight

o".

Lighterthan normal

Microgravity

The person in the stationary elevator car experiences normalweight. In the car immediately to the right, weight increases slightlybecause of the upward acceleration. Weight decreases slightly inthe next car because of the downward acceleration. No weight ismeasured in the last car on the right because of free fall.

We will use a simple example to illustratehow free fall can achieve microgravity.Imagine riding in an elevator to the top floorof a very tall building. At the top, the cablessupporting the car break, causir.j the carand you to fall to the ground. (In this ex-ample, we discount the effects of air frictionon the falling car.) Since you and the eleva-tor car are falling together, you will floatinside the car. In other words, you and theelevator car are accelerating downward atthe same rate. If a scale were present, yourweight would not register because the scalewould be falling too. (Figure 1)

Gravity

Gravitational attraction is a fundamentalproperty of matter that exists throughout theknown universe. Physicists identify gravityas one of the four types of forces in theuniverse. The cthers are the strong and

weak nuclear forces and the electromag-netic force.

More than 300 years ago the great Englishscientist Sir Isaac Newton published theimporter); generalization that mathematicallydescribes this universal force of gravity.Newton was the first to realize that gravityextends well beyond the domain of Earth.This realization was based on the first ofthree laws he had formulated to describe themotion of objects. Part of Newton's first law,the law of inertia, states that objects inmotion travel in a straight line at a constantvelocity unless acted upon by a net force.According to this law, the planets in spaceshould travel in straight lines. However, asearly as the time of Aristotle, the planetswere kown to travel on curved paths.Newton reasoned that the circular motionsof the planets are the result of a net forceacting upon each of them. That force, heconcluded, is the same force that causes anapple to fall to the groundgravity.

Newton's experimental research into theforce of gravity resulted in his elegant math-ematical statement that is known today asthe Law of Universal Gravitation. Accord-ing to Newton, every mass in the universeattracts every other mass. The attractiveforce between any two objects is directlyproportional to the product of the twomasses being measured and inverselyproportional to the square of the distanceseparating them. If we let F represent thisforce, r the distance between the centers ofthe masses, and mi and m2 the magnitudeof the two masses, the relationship statedcan be written symbolically as:

M1M2F a

r 2

(a is defined mathematically to mean "isproportional to.") From this relationship, wecan see that the greater the masses of theattracting objects, the greater the force ofattraction between them. We can also seethat the farther apart the objects are fromeach other, the less the attraction. It isimportant to note the inverse square rela-tionship with respect to distance. In otherwords, if the distance between the objects isdoubled, the attraction between them isdiminished by a factor of four, and if thedistance is tripled, the attraction is only one-ninth as much.

Newton's Law of Universal Gravitation waslater quantified by eighteenth-century En-glish physicist Henry Cavendish who actu-ally measured the gravitational force be-tween two one-kilogram masses separatedby a distance of one meter. This attractionwas an extremely weak force, but its deter-mination permitted the proportional relation-ship of Newton's law to be converted into anequation. This measurement yielded theuniversal gravitational constant or G.

Deep In Space

The inverse square relattonship, with respectto distance, of the Lawl)f Gravitation can beused to determine how far to move a micro-gravity laboratory from Earth to achieve a10-6g environment. Distance (r) Is measuredbetween the centers of mass of the laboratoryand of Earth. While the laboratory is still onEarth, the distance between their centers is6,370 kilometers (equal to the approximateradius of Earth, re). To achieve 10-6g, the,..00ratory has to be moved to a distance of1,000 Earth radii. In the equation, r thenbecomes 1,000 r. or rin 6.37x106km.

Cavendish determined that the value of G is0.0000000000667 newton m2/kg2 or6.67 x 10-11 Nm2/kg2. With G added to theequation, the Universal Law of Gravitationbecomes:

F = Ginim2

Creating Microgravity

Drop Towers and Tubes

In a practical sense, microgravity can beachieved with a number of technologies,each depending upon the act of free fall.Drop towers and drop tubes are high-techversions of the elevator analogy presentedin a previous section. The large version ofthese facilities is essentially a hole in theground.

Drop towers accommodate large experimentpackages, generally using a drop shield tocontain the package and isolate the experi-ment from aerodynamic drag during free fallin the open environment.

n

4NASA's Lewis Research Center in Cleveland,Ohio has a 145-meter drop tower facility thatbegins on the surface and descends intoEarth like a mine shaft. The test section ofthe facility is 6.1 meters in diameter and 132meters deep. Beneath the test section is acatch basin filled with polystyrene beads. The132-meter drop creates a microgravity envi-ronment for a period of 5.2 seconds.

To begin a drop experiment, the experimentapparatus is placed in either a cylindrical orrectangular test vehicle that can carry experi-ment loads of up to 450 kilograms. Thevehicle is suspended from a cap that enclosesthe upper end of the facility. Air is pumpedout of the facility until vacuum of 10-2 torr isachieved. (Atmospheric pressure is 760 torr.)By doing so, the acceleration effects causedby aerodynamic drag on the vehicle arereduced to less than 10-5 g. During the drop,cameras within the vehicle record the actionand data is telemetered to recorders.

Optical Pyrometer

MassSpectrometer

MechanicalRoughing

Purrp

Silicon Detector

TimeCalibration

Detector

Indium Antimoo!ticDetector

MechanicalRoughing

PurrpInert Gas Supply

DetachableCatchSystem

Tuto-MolecularVacuum Pump,

Figure 2. 100-Meter Drop Tube at the NASAMarshall Space Flight Center.

A smaller facility for microgravity research islocated at the NASA Marshall Space FlightCenter in Huntsville, Alabama. It is a 100-meter -high, 25.4-centimeter-diameter evacu-

Experiment InPredrop Poe Nion

DecelerationSpites

Hoist

CheckoutArea

Noe *elicitContainers

Sand Storage

Figure 3. 30-Meter Drop Tower at the NASA LewisResearch Center.

ated drop tube that can achieve microgravityfor perhds of as long as 4.5 seconds. Theupper end of the tube is fitted with a stainlesssteel bell jar. For solidification experiments,an electron bombardment or an electromag-netic levitator furnace is mounted inside thejar to melt the test samples. After the samplemelts, drops are formed and fall through thetube to a detachable catch fixture at thebottom of the tube. (Figure 2.)

Additional drop facilities of different sizes andfor different purposes are located at the NASAField Centers and in other countries. A 490-

meter -deep vertical mine shaft in Japan hasbeen converted to a drop facility that canachieve a 10-5g environment for up to 11.7seconds.

Aircraft

Airplanes can achieve low-gravity for peri-ods of about 25 seconds or longer. TheNASA Johnson Space Center in Houston, Texasoperates a KC-135 aircraft for astronauttraining and conducting experiments. Theplane is a commercial-sized transport jet(Boeing 707) with most of its passenger

seats removed. The walls are padded forprotection of the people inside. Althoughairplanes cannot achieve microgravity condi-tions of as high quality as those produced indrop towers and drop tubes (since they arenever completely in free fall and their drag forcesare quite high), they do offer an importantadvantage over drop facilitiesexperimenterscan ride along with their experiments.

10.5

I 9.0

a

7.5

1 x10'3g (5-15 sec)14-....

Lif2-2.5 g 1x10'2g 2-2.5166.0 rwMax. (15-25 sec) "...Ill* llax71

Figure 4. Parabolic Flight Characteristics.

A typical flight lasts 2 to 3 hours and carriesexperiments and crewmembers to a begin-ning altitude about 7 km above sea level.The plane climbs rapidly at a 45-degreeangle (pull up), traces a parabola (push-over), and then descends at a 45-degreeangle (pull out). (Figure 4) During the pullup and pull out segments, crew and experi-ments experience between 2g and2.59. During the parabola, at ,0altitudes ranging from 7.3 to10.4 kilometers, net accel- _SA_

flight, 40 parabolictrajectories are flown.The gut-wrenchingsensations producedon the flight haveearned the planethe nickname of"vomit comet."

Launch

NASA alsooperates aLearjet for low-gravity researchout of theNASA LewisResearchCenter. Flyingon a trajectorysimilar to theone followed bythe KC-135, theLearjet providesa low-accelera-tion environ-ment of 5x102gto 75x102 g forup to ?0 sec-onds.

Rockets

5

Experiment

MeasurementModule

Experiment

Experiment

Telemetry

Housing

Nose Cone andRecovery System

ExperimentServiceModule

Umbilical AdaptorRing

Experiment

Experiment

Rate Control System

Solid PropellantRacket Motor

Figure 6. Small Rocket forMicrogravity Experiments.

3mall rockets provide a third technology forcreating microgravity. A sounding rocketfollows a suborbital trajectory and can pro-duce several minutes of free fall. The periodof free fall exists during its coast, after burnout, and before entering the atmosphere.Acceleration levels are usually at or below10-5g. NASA has employed many differentsounding rockets for microgravity experi-ments. The most comprehensive series of

launches used SPAR (Space Process-ing Application Rocket) rockets for

embolic Tralectory

fluid physics, capillarity, liquiddiffusion, containerless pro -

cessing, and electrolysisD"S"bm \ experiments from 1975 to

1981. The SPAR couldlift 300 kg payloads intofree-fall parabolictrajectories lasting fourto six minutes.(Figures 5, 6)

MknaravIty

eration drops as low as10-3 g. On a typical

PaikAd lisparakai

i socalacaltonToluhaary

Ra:ovary',

Figure 5. Rocket Parabolic Flight Profile.

12

6Orbiting Spacecraft

Although airplanes, drop facilities, and smallrockets can be used to establish a micro-gravity environment, all of these laboratoriesshare a common problem. After a fewseconds or minutes of low-g, Earth gets inthe way and the free fall stops. In spite ofthis limitation, much can be learned aboutfluid dynamics and mixing, liquid-gas sur-face interactions, and crystallization andmacromolecular structure. But to conductlonger term experiments (days, weeks,months, and years), it is necessary travelinto space and orbit Earth. Having moretime available for experiments means thatslower processes and more subtle effectscan be investigated.

To see how it is possible to establish micro-gravity conditions for long periods of time, itis first necessary to understand what keepsa spacecraft in orbit. Ask any group ofstudents or adults what keeps satellites andSpace Shuttles in orbit and you will probablyget a variety of answers. Two commonanswers are: "The rocket engines keep firingto hold it up." and "There is no gravity inspace."

Although the first answer is theoreticallypossible, the path followed by the spacecraftwould technically not be an orbit. Otherthan the altitude involved and the specificmeans of exerting an upward force, therewould be little difference between a space-craft with its engines constantly firing and anairplane flying around the world. In the caseof the satellite, it would just not be possibleto provide it with enough fuel to maintain itsaltitude for more than a few minutes.

The second answer is also wrong. In aprevious section, we discussed that IsaacNewton proved that the circular paths of theplanets through space was due to gravity'spresence, not its absence.

Newton expanded on his conclusions aboutgravity and hypothesized how an artificialsatellite could be made to orbit Earth. Heenvisioned a very tall mountain extendingabove Earth's atmosphere so that frictionwith the air would not be a factor. He thenimagined a cannon at the top of that moun-tain firing cannonballs parallel to the ground.As each cannonball was fired, it was actedupon by two forces. One force, the explo-sion of the black powder, propelled thecannonball straight outward. If no otherforce were to act on the cannon ball, theshot would travel in a straight line and at aconstant velocity. But Newton knew that asecond force would act on the cannonball:

Figure 7. Illustration from Isaac Newton,Principia, VII, Book III, p551.

the presence of gravity would cause thepath of the cannonball to bend into an arcending at Earth's surface. (Figure 7)

Newton demonstrated how additional can-nonballs would travel farther from the moun-tain if the cannon were loaded with moreblack powder each time it was tired. Witheach shot, the path would lengthen andsoon, the cannonballs would disappear overthe horizon. Eventually, if a cannonballwere fired with enough energy, it would fallentirely around Earth and come back to itsstarting point. The cannonball would beginto orbit Earth. Provided no force other thangravity interfered with the cannonball's

7

"Microgravity Room"

One of the common questions asked byvisitors to the NASA Johnson Space Center inHouston, Texas is, "Where is the room wherea button is pushed and gravity goes away sothat astronauts float?" No such room existsbecause gravity can never be made to goaway. The misconception comes from thetelevision pictures that NASA takes of astro-nauts training in the KC-135 and from under-water training pictures. Astronauts scheduledto wear spacesuits for extravehicular activities

train in the Weightless Environment TrainingFacility (WET F). The WET F is a swimming poollarge enough to hold a Space Shuttle payload baymock-up and mock-ups of satellites and experi-ments. Since the astronauts' spacesuits are filledwith air, heavy weights are added to the suits toachieve neutral buoyancy in the water. Thefacility provkies an excellent simulation of what itis like to work in space with two exceptions: inthe pool it is possible to swim with hand and legmotions, and if a hand tool is dropped, it falls tothe bottom.

motion, it would continue circling Earth inthat orbit.

This is how the Space Shuttle stays in orbit.It is launched in a trajectory that arcs aboveEarth so that the orbiter is traveling at theright speed to keep it falling while maintain-ing a constant altitude above the surface.For example, if the Shuttle climbs to a 320 -kilometer -high orbit, it must travel at a speedof about 27,740 kilometers per hour toachieve a stable orbit. At that speed andaltitude, the Shuttle's falling path will beparallel to the curvature of Earth. Becausethe Space Shuttle is free-falling aroundEarth and upper atmospheric friction isextremely low, a microgravity environment isestablished.

Orbiting spacecraft provideideal laboratories for micro-gravity research. As on air-planes, scientists can fly withthe experiments that are onthe spacecraft. Because theexperiments are tended, theydo not have to be fully auto-matic in operation. A 'alfunc-tion in an experiment on-ducted with a drop tower orsmall rocket means a lois ofdata or complete failure. Inorbiting spacecraft, crewmem-bers can make repairs so that

there is little or no loss of data. They canalso make on-orbit modifications in experi-ments to gather more diverse data.

Perhaps the greatest advantage of orbitingspacecraft for microgravity research is theamount of time during which microgravityconditions can be achieved. Experimentslasting for more than a week are possiblewith the Space Shuttle. When NASA'splanned international Space Station Free-dom is assembled and ready for use, thetime available for experiments will stretch tomonths. Space Station Freedom will pro-vide a manned microgravity laboratoryfacility unrivaled by any on Earth.(Figure 8)

-- AIM lremorFigure 8. Space Station Freedom.

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8

Microgravity PrimerGravity is a dominant factor in many chemi-cal and physical processes on Earth.

Heat applied to the bottom of a soup potis conducted by the metal of the pot tothe soup inside. The heated soupexpands and becomes less dense thanthe soup above. It rises because cool,dense soup is pulled down by gravity,and the warm, less dense, soup rises tothe top. A circulation pattern is pro-duced that mixes the entire soup. Thisis called buoyancy-driven convection.

Liquids of unequal density which do notinteract chemically, like vinegar and oil,mix only temporarily when shakenvigorously together. Their differentdensities cause them to separate intotwo distinct layers. This is called sedi-mentation.

Crystals and metal alloys contain de-fects and have properties which aredirectly and indirectly attributed to grav-ity-related effects. Convective flowssuch as those described above arepresent in the molten form of the mate-rial from which the solids are formed.As a result, some of the atoms andmolecules making up the crystallinestructure may be displaced from theirintended positions. Dislocations, extraor missing half planes of atoms in thecrystal structure, are one example ofmicroscopic defects which create subtle,but important, distortions in the opticaland electrical properties of the crystal.

Many basic processes are strongly influ-enced by gravity. For the scientific re-searcher, buoyancy-driven convection andsedimentation are significant phenomenabecause they have such a profound directeffect on the processes involved. They canalso mask other phenomena that may beequally important but too subtle to be easilyobserved. If gravity's effects were elimi-nated, how would liquids of unequal densi-ties mix? Could new alloys be formed?Could large crystals with precisely controlledcrystalline and chemical perfection begrown? What would happen to the flame ofa candle? There are many theories andexperiments which predict the answers tothese questions, but the only way to answerand fully understand these questions and ahost of others is to effectively eliminategravity as a factor. Drop towers, airplanes,sounding rockets, and the Space Shuttlemake this possible, as will Space StationFreedom in a few years.

What are the subtle phenomena that gravitymasks? What research will scientists pur-sue in microgravity?

The Fluid State

To most of us, the word "fluid" brings tomind images of water and other liquids. Butto a scientist, the word fluid means muchmore. A fluid is any liquid or gaseous mate-rial that flows and, in gravity, assumes theshape of the container it is in. Gases fill thewhole container; liquids on Earth fill only thelower part of the container equal to thevolume of the liquid.

Scientists are interested in fluids for a vari-ety of reasons. Fluids are an important partof life processes, from the blood in our veinsand arteries to the oxygen in the air. Theproperties of fluids make plumbing, automo-biles, and even fluorescent lighting possible.Fluid mechanics describes many processes

15

that occur within the human body and alsoexplains the flow of sap through plants. Thepreparation of materials often involves afluid state that ultimately has a strong impacton the characteristics of the final product.

Figure 9. A liquid is manipulated by soundwaves in the Drop Dynamics Module experi-ment on Spacelab 3. By using sound wavesto position the drop, possible container wallcontamination is eliminated.

Scientists gain increased insight into theproperties and behavior of fluids by studyingtheir movement or flow, the processes thatoccur within fluids, and the transformationbetween the different states of a fluid (liquidand gas) and the solid state. Studying thesephenomena in microgravity allows the scien-tists to examine processes and conditionsimpossible to study when influenced byEarth's gravity. The knowledge gained canbe used to improve fluid handling, materialsprocessing, and many other areas in whichfluids play a role. This knowledge can beapplied not only on Earth, but also in space.

Fluid Dynamics and TransportPhenomena

Fluid dynamics and transport phenomenaare central to a wide range of physical,chemical and biological processes, many ofwhich are technologically important in bothEarth- and space-based applications. In thiscontext, the term transport phenomena

9

refers to the different mechanisms by whichenergy and matter (e.g., atoms, molecules,particles, etc.) move. Gravity often intro-duces complexities which severely limit thefundamental understanding of a large num-ber of these different transport mechanisms.

For example, buoyancy-driven flows, whicharise from density differences in the fluid,often prevent the study of other importanttransport phenomena such as diffusion andsurface tension-driven flows. Surface ten-sion-driven flows are caused by differencesin the temperature and/or chemical compo-sition at the fluid surface. The fluid flowsfrom areas where the surface tension is lowto areas where it is high. Low gravity condi-tions can reduce by orders of magnitude theeffects of buoyancy, sedimentation, andhydrostatic pressure, enabling observationsand measurements which are difficult orimpossible to obtain in a terrestrial labora-tory. (Hydrostatic pressure is that pressurewhich is exerted on a portion of a column offluid as a result of the weight of the fluidabove it.)

Figure 10. During an experiment on Spacelab 3,a rotating liquid drop assumes a "dog bone"shape.

The systematic study of fluids under micro-gravity conditions holds the promise ofrefining existing theory or allowing the for-mulation of new theories to describe fluid

1 (3

10dynamics and transport phenomena. Suchresearch promises to improve the under-standing of those aspects of fluid dynamicsand transport phenomena whose fundamen-tal behavior is limited or affected by theinfluence of gravity. Several research areascontain promising opportunities for signifi-cant advancements through low-gravityexperiments. These research areas include:capillary phenomena, multiphase flows andheat transfer, diffusive transport, magneto/electrohydrodynamics, colloids, and solid-fluid interface dynamics. These terms willbe defined in their respective sections.

Capillary Phenomena. Capillarity describesthe relative attraction of a fluid for a solidsurface compared with its self-attraction. Atypical example of capillary action is the riseof sap in plants. Research in capillary phe-nomena is a particularly fertile area for low-gravity experiments because of the in-creased importance of capillary forces asthe effects of gravity are reduced. Suchcircumstances are always encountered inmultiphase fluid systems where there is aliquid-liquid, liquid-vapor, or liquid-solidinterface. Surface tension-driven flows alsobecome increasingly important as the ef-fects of gravity are reduced and can dra-matically affect other phenomena suchas the interactions and coalescence ofdrops and bubbles.

Multiphase Flow and Heat Transfer. Capil-lary forces also play a significant role inmultiphase flow and heat transfer, particu-larly under reduced-gravity conditions. It isimportant to be able to accurately predict therate at which heat will be transported be-tween two-phase mixtures and solid sur-facesfor example, as a liquid and gas flowthrough a pipe. Of course, it is equallyimportant to be able to predict the heatexchange between the two different fluidphases. Furthermore, when the rate oftransferring heat to or from the multiphase

fluid system reaches a sufficient level, theliquids or gases present may change phase.That is, the liquid may boil (heat entering theliquid), the liquid may freeze (heat leavingthe liquid), or the gas may condense (heatleaving the gas). While the phase changeprocesses of melting and solidification underreduced-gravity conditions have been stud-ied extensivelydue to their importance inmaterials processingsimilar progress hasnot been made in understanding the pro-cess of boiling and condensation. Althoughthese processes are broadly affected bygravity, improvements in the fundamentalunderstanding of such effects have beenhindered by the lack of experimental data.

Diffusive Transport. Diffusion is a mecha-nism by which atoms and molecules movethrough solids, liquids, and gases. Theconstituent atoms and molecules spreadthrough the medium (in this case, liquidsand gases) due primarily to differences inconcentration, though a difference in tem-perature can be an important secondaryeffect in microgravity. Much of the importantresearch in this area involves studies whereseveral types of diffusion occur simulta-neously. The significant reduction in

Figure 11. Space Shuttle Atlantis crewmembersJohn E. Blaha and Shannon W. Lucid prepare liquidsin a middeck experiment on polymer membraneprocessing.

17

buoyancy-driven convection that occurs in afree-fall orbit may provide more accuratemeasurements and insights into thesecomplicated transport processes.

Magneto/Electrohydrodynamics. Theresearch areas of magnetohydrodynamicsand electrohydrodynamics involve the studyof the effects of magnetic and electric fieldson mass transport (atoms, molecules, andparticles) in fluids. Low velocity fluid flows,such as those found in poor electrical con-ductors in a magnetic field, are particularlyinteresting. The most promising low-gravityresearch in magneto/electrohydrodynamicsdeals with the study of effects normallyobscured by buoyancy-driven convection.Under normal gravity conditions, buoyancy-driven convection can be caused by the fluidbecoming heated due to its electrical resis-tance as it interacts with electric and mag-netic fields. The heating of a materialcaused by the flow of electric currentthrough it is known as Joule heating. Stud-ies in space may improve techniques formanipulating multiphase systems such asthose containing fluid globules and separa-tion processes such as electrophoresis,which uses applied electric fields to sepa-rate biological materials.

Colloids. Colloids are suspensions of finelydivided solids or liquids in gaseous or liquidfluids. Colloidal dispersions of liquids ingases are commonly called aerosols.Smoke is an example of fine solid particlesdispersed in gases. Gels are colloidalmixtures of liquids and solids where thesolids have linked together to form a con-tinuous network. Research interest in thecolloids area includes the study of formationand growth phenomena clueing phase transi-tions--e.g., when liquids change to solids.Research in microgravity may allow mea-surement of large scale aggregation orclustering phenomena without the complica-tion of the different sedimentation rates due

11

to size and particle distortion caused bysettling and fluid flows that occur undernormal gravity.

Solid-Fluid Interface Dynamics. A betterunderstanding of solid-fluid interface dynam-ics, how the boundary between a solid and afluid acquires and maintains its shape, cancontribute to improved materials processingapplications. The morphological (shape)stability of an advancing solid-fluid interfaceis a key problem in such materials process-ing activities as the growth of homogeneoussingle crystals. Experiments in low-gravity,with significant reductions in buoyancy-driven convection, could allow mass trans-port in the fluid phase by diffusion only.Such conditions are particularly attractive fortesting existing theories for processes andfor providing unique data to advance theo-ries for chemical systems where the inter-face interactions strongly depend on direc-tion and shape.

Combustion Science

There is ample practical motivation foradvancing combustion science. It plays akey role in energy transformation, air pollu-tion, surface-based transportation, space-craft and aircraft propulsion, global environ-mental heating, materials processing, andhazardous waste disposal through incinera-tion. These and many other applications ofcombustion science have great importancein national economic, social, political, andmilitary issues. While the combustion pro-cess is clearly beneficial, it is also extremelydangerous when not controlled. Enormousnumbers of lives and valuable property aredestroyed each year by fires and explo-sions. Two accidents involving U.S. space-craft in the Apollo program were attributed togaps in the available knowledge of combus-tion fundamentals under special circum-stances. Planning for a permanent humanpresence in space demands the develop-

12ment of fundamental combustion science inreduced gravity to either eliminate space-craft fires as a practical possibility or todevelop powerful strategies to detect andextinguish incipient spacecraft fires. Ad-vances in understanding the combustionprocess will also benefit fire safety in air-craft, industry, and the home.

The recently developed capability to performexperiments in microgravity may prove to bea vital tool in completing our understandingof combustion processes. From a funda-mental viewpoint, the most prominent fea-ture that distinguishes combustion pro-cesses from processes involving fluid flow isthe large temperature variations whichinvariably exist in a reacting flow. Theselarge temperature variations are caused byhighly-localized, highly-exothermic heatrelease from the chemical reactions charac-teristic of combustion processes. For ex-ample, the temperature of a reactive mixturecan increase from the unreacted, ambientstate of about 25° C (around room tempera-ture) to the totally reacted state of over2750° C. These large temperature differ-ences lead to correspondingly large densitydifferences and hence, to the potentialexistence of strong buoyancy-driven fluidflows. These flows can modify, mask, oreven dominate the convective-diffusivetransport processes that mix and heat thefuel and oxidant reactants before chemicalreactions can be initiated. For combustionin two-phase flows, the presence of gravityintroduces additional complications. Hereparticles and droplets can settle, causingstratification in the mixture. The effects ofsurface tension on the shape and motion ofthe surface of a. large body of liquid fuel canalso be modified due to the presence ofbuoyancy-driven flows.

Gravity can introduce a degree of asymme-try in an otherwise symmetrical phenom-enon. For example, combustion of a gas-

eous jet injected horizontally quickly losesits symmetry along its long axis as the hotflame plume gradually tilts 'upward.' Thefluid transport processes in these situationsare inherently multi-dimensional and highly

complex.

Important as it is, buoyancy is frequentlyneglected in the mathematical analysis ofcombustion phenomena either for math-ematical simplicity or to facilitate identifica-tion of the characteristics of those controllingprocesses which do not depend on gravity.Such implications, however, can renderdirect comparison between theory andexperiment either difficult or meaningless. Italso weakens the feedback process be-tween theoretical and experimental develop-ments which is so essential in the advance-ment of science.

Materials Science

The current materials science program ischaracterized by a balance of fundamentalresearch and applications-oriented investi-gations. The goal of the materials scienceprogram is to utilize the unique characteris-tics of the space environment to further ourunderstanding of the processes by whichmaterials are produced, and to further ourunderstanding of their properties, some ofwhich may be produced only in the spaceenvironment. The program attempts toadvance the fundamental understanding ofthe physics associated with phase changes.This includes solidification, crystal growth,condensation from the vapor, etc. Materialsscience also seeks explanations for previ-ous space-based research results for whichno clear explanations exist. Researchactivities are supported which investigatematerials processing techniques unique tothe microgravity environment, or which,when studied in microgravity, may yieldunique information with terrestrial applica-tions.

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tat'

Crystal of mercuric iodide grown by gas vapordeposition during a Spacelab experiment.

Microgravity Materials ScienceBackground

The orbital space environment offers theresearcher two unique features which areattainable on Earth to only a very limitedextent. These are 'free fall' with the atten-dant reduced gravity environment and ahigh quality vacuum of vast extent. Subor-bital conditions of free fall are limited to lessthan 10 seconds in drop towers, less than25 seconds during aircraft maneuvers, andless than 15 minutes during rocket flights.The quality of the microgravity environmentof these various ground-based optionsranges from 10-2g to 10-5g. With the SpaceShuttle, this duration has been extended todays and weekswith Space Station andfree flyers, to months and years.

In a reduced gravity environment, relativemotion is slowed in direct proportion to thereduction in net acceleration. At 10-6g,particles suspended in a fluid will sediment amillion times more slowly than they do onEarth. Thermal and solutal convection ismuch less vigorous in microgravity than it ison Earth, and in some cases seems tobecome a secondary transport mechanism.

13Both thermal and solutal convection areexamples of buoyancy-driven convection. Inthe first case, the difference in density iscaused by a difference in temperature; inthe second case, the density difference iscaused by the changing chemical composi-tion of the liquid. As indicated previously,buoyancy-induced convection can be sup-pressed in a low-gravity environment. Formany materials science investigations, thisexperimental condition is extremely interest-ing because it allows us to study purelydiffusive behavior in systems for whichconditions of constant density are difficult orimpossible to create or for which experi-ments in 'convection-free' capillaries lead toambiguous results.

To date, much of the space-based researchhas focused on this unique condition withrespect to processing materials which areparticularly susceptible to compositionalnonuniformities resulting from convective orsedimentation effects. The process bywhich compositionally nonuniform materialis produced is referred to as segregation.Some of the first microgravity experiments inmetallurgy were attempts to form fine dis-persions of metal particles in another metalwhen the two liquid metals are immiscible.Unexpected separation of the two metalsseen in several low gravity experiments inthis area has given us new insight into themechanisms behind dispersion formation(fine droplets of one metal dispersed inanother metal), but a complete model in-cluding the role of critical wetting, dropletmigration, and particle pushing has yet to beformulated.

There is no dispute that gravity-driven con-vective flows in crystal growth processesaffect mass transport. This has been dem-onstrated for crystals growing from the meltas well as from the vapor. The distributionof components in a multicomponent systemhas a marked influence on the resultant

20

14properties of a material (for example, thedistribution of selenium atoms in the impor-tant electronic material, GaAs). Conse-quently, space processing of materials hasalways carried with it the hope of reducingconvective flows during crystal growth tosuch a degree that crystallization wouldproceed in a purely diffusive environment formass transport, to result in crystals withuniform composition. However, the expec-tation of space-processed, perfectly homo-geneous materials with improved propertieshas yet to be realized. Future experimentson crystal growth will be directed at a widevariety of electronic materials such as GaAs,triglycine sulfate, Hg 12, HgCdTe (from thevapor), CdTe, HgZnTe, PbBr2 and PbSnTe.In addition, the research of our internationalcollaborators will include InGaAs, InSb,SiAsTe, Si, GalnSb, InP, and Ge.

In order to understand crystal growth pro-cesses in microgravity, it is essential thatmany aspects of these phase transforma-tions (e.g., liquid to solid, vapor to solid) beunderstood. This includes a thoroughknowledge of the behavior of fluids (gasesand liquids), a fundamental understanding ofthe crystallization process, and a sufficientdata base of thermophysical information(e.g., thermal conductivities, diffusion coeffi-cients, etc.) with which various theories canbe tested. It may be necessary to measuresome of these quantities in microgravity, asground-based data may be either subject toerror or even impossible to generate.

The flight research focussing on fundamen-tal problems in solidification reflects thisbroad scope of activity, ranging from studiesof morphological stability in transparentorganic systems (which serve as excellentexperimental models of metallic systems) tostudies of metals solidifying without theconfinement of a container.

Microgravity Materials Science Research

The field of materials science is extremelybroad. It encompasses essentially all mate-rials, concerns itself with the synthesis,production, and further processing of thesematerials, and deals with matter both on anatomistic level and on a bulk levtl. Althoughmaterials science addresses a n iiriad ofproblems, there are fundamental scientificissues common to all of its subdisciplines.These include evolution of the microscopicstructure of the materials, transport phenom-ena, and the determination of relevantthermophysical properties. Interface mor-phology and stability, and macro- and micro-segregation (the distribution of a componenton the microscopic and macroscopic scales)represent ongoing challenges.

Historically, the materials science commu-nity has segmented itself on the basis ofmaterials (composites, steels, polymers), onthe basis of specific processes (casting,solidification, welding), and on the basis offundamental physical phenomena (propertymeasurements, diffusion studies, study ofmorphological stability).

Materials. The materials of interest to themicrogravity materials science disciplinehave traditionally been categorized aselectronic, metallic, glass, and ceramic.However, recent space experiments havebroadened this traditional categorization toinclude polymeric materials as well. Addi-tional classes of materials which may benefitgreatly from being studied in a low gravityenvironment are: advanced composites,electronic and opto-electronic crystals, highperformance metal alloys, and superconduc-tors (high temperature and low temperature,metallic, ceramic, and organic). For theirscientific and technological significance,there is also strong interest in composites,fibers, foams, and films, whatever their

constitution, when the requirement for ex-periments in low gravity can be clearlydefined.

Processes. Because the manifestation ofgravitational effects is greatest in the pres-ence of a fluid, the following processes areof considerable im-portance: solidifica-tion, crystallizationfrom solution, andcondensation fromthe vapor. Theseprocesses have beenthe subject of numer-ous low-gravity inves-tigations for manyyears. Scientificallyinteresting, and po-tentially importanttechnologically, arethe processes of welding and electrodeposi-tion. Unique welding experiments in Skylaband recent low-gravity electrodepositionexperiments in sounding rockets haveproduced unexplained results. The ultra-high vacuum and nearly infinite pumpingrate of space offer researchers the possibil-ity of pursuing ultra-high vacuum process-ing of materials and, perhaps, ultra-purifica-tion.

Vapor Crystal

15gaseous fluid from which a material is eithersolidifying, crystallizing, or condensing. Ona microscale, the arrangement of atoms ormolecules in a solid occurs at a boundarybetween the 'frozen' solid and the convect-ing fluid. The interaction between theseconvective flows and the resultant solid

formation needsmuch greater under-standing. A criticalissue facing space-based materialsscience research isthe response ofexperiments to moreor less randomacceleration environ-ments within amanned spacecraft.Are compositionalinhomogeneities and

other major defects results of such randomaccelerations? What is the tolerable accel-eration level for a given experiment? Arethere ways of increasing experimentaltolerance to a given level of acceleration?The answers to these questions will not onlyenhance our understanding of fundamentalphenomena but also provide the foundationsupon which useful space-based laboratoriesfor materials science can be designed.

Growth System

Seed warmed; Seed cooled; Source depleted;atoms go from crystal growth growth complete.seed to source. begins.

Of primary importance is the utility of thespace environment in helping aninvestigator understand the processof interest. Can a low-gravity envi-ronment be used to our advantagein elucidating important scientificinformation concerning these pro-cesses? Are there processes thatare truly unique to the microgravityenvironment?

Phenomena. On a macroscale,convective motion, induced byresidual accelerations or othereffects, persists in the liquid or

Solution Crystal Growth Process

Ir

'I 1

e red. .41t

Seed crystalprotected fromsolution; crystal-lites dissolving.

Crystal growthfrom solutioninitiated.

Growth com-pleted; seedprotected.

16

Shot TowersThe idea of using "free fall" or micro-gravity for research and materialsprocessing is not a new one. Ameri-can colonists used free fall to pro-duce lead shot for their weapons.This process, patented by Britishmerchant William Watts in 1782,involved pouring molten lead througha sieve at the top of a 15- to 30-meter -tall tower. As the lead fell, thedrops became nearly perfect solidspheres that were quenched uponlanding in a pool of water at the footof the tower. Free fall produced shotsuperior to that produced by othermethods. Scientists now exploreboth the phenomenon of microgravityand the use of inicrogravity for mate-rials research.

Since the pioneering diffusion experimentsconducted on Spacelab D-1 concerning self-diffusion in tin, there has been a heightenedawareness of the need to measure theappropriate thermophysical parameters ofthe material under investigation. It hardlysuffices, in many instances, to conduct anexperiment in a diffusion-controlled environ-ment, if the analysis of the experiment usesground-based thermophysical data whichmay be in error. To avoid ambiguity in theinterpretation of space experiments, it maybe necessary to generate data on selectedmaterials parameters from actual low-gravityexperiments. This area of research is: par-ticularly important to the entire materialsscience field.

Biotechnology

The biotechnology program is comprised ofthree areas of research: protein crystalgrowth, mammalian cell culture, and funda-mentals of biotechnology.

Protein Crystal Growth

The protein crystal growth program is di-rected to: (1) contribute to the advance inknowledge of biological molecular structuresthrough the utilization of the space environ-ment to help overcome a principal obstaclein the determination of molecular struc-turesthe growth of crystals suitable foranalysis by X-ray diffraction; and (2) ad-vance the understanding of the fundamentalmechanisms by which large biological mol-ecules form crystals. The program seeks todevelop these objectives through a coordi-nated effort of space- and ground-basedresearch, whereby ground-based researchattempts to use and explain the results offlight research, and flight research incorpo-rates the knowledge gained from ground-based research and prior flight experienceto develop refined techniques and objectivesfor subsequent experiments.

Space-grown canavalin protein crystals.

Mammalian Cell Culture

The mammalian cell culture program seeksto develop an understanding sufficient toassess the scientific value of mammaliancells and tissues cultured under low-gravityconditions, where mechanical stresses ongrowing tissues and cells can be held to

23

very low levels. Preliminary evidence fromthe culture of a variety of suspended cells inrotating vessels has shown indications ofincreased viability and tissue differentiation.These results suggest that better control ofthe stresses exerted on cells or tissues canplay an important role in the culture of invitro tumor models, normal tissues, andother challenging problems.

Fundamentals of Biotechnology

This area of research is concerned with theidentification and understanding of biotech-nological processes and biophysical phe-nomena which can be advantageouslystudied in the space environment. Potentialresearch areas include molecular and cellu-lar aggregation, the behavior of electrically-driven flows, and capillary and surfacephenomena, as applied uniquely to biologi-cal systems.

Background of Protein Crystal GrowthFlight Experiments

The first protein crystal growth experimentsin space were conducted on the Spacelab-1mission in 1983 where crystals of hen eggwhite lysozyme and beta-galactosidasewere grown. In the mid-1980's, a hand-helddevice for protein crystal growth experi-ments was developed and flown on fourShuttle missions as a precursor to the VaporDiffusion Apparatus (VDA) - Refrigerator/Incubator Module experiments later flown inthe Shuttle middeck. Despite having en-countered a number of minor technicaldifficulties on several flights, the project hasenjoyed significant success. These includethe growth of crystals to sizes and degreesof perfection beyond any ground-basedefforts, and the formation of crystals inscientifically useful forms which had notbeen previously encountered in similarground-based experiments. Though thephysics of protein crystal growth are under-

17stood in broad terms, there is currently noagreement on a detailed mechanistic expla-nation for these phenomena.

Microgravity andSpace Flight

Until the mid-20th century, gravity was anunavoidable aspect of research and technol-ogy. During the latter half of the century,although drop towers could be used toreduce the effects of gravity, the extremelyshort periods of time they provided (<6seconds) severely restricted the type ofresearch that could be performed.

Initial research centered around solvingspace flight problems created by micrograv-ity. How do you get the proper amount offuel to a rocket engine in space or water toan astronaut on a spacewalk? The briefperiods of microgravity available in droptowers at the NASA Lewis Research Centerand NASA Marshall Space Flight Centerwere sufficient to answer these basic ques-tions and to develop the pressurized sys-tems and other new technologies needed tocope with this new environment. But, theystill were not sufficient to investigate thehost of other questions that were raised byhaving gravity as an experimental variable.

The first long-term opportunities to explorethe microgravity environment and conductresearch relatively free of the effects ofgravity came during the latter stages ofNASA's first great era of discovery. TheApollo program presented scientists with thechance to test ideas for using the spaceenvironment for research in materials, fluid,and life sciences. The current NASA micro-gravity program had its beginning in theexperiments conducted in the later flights ofApollo, the Apollo-Soyuz Test Project, andonboard Skylab, America's first space sta-tion.

2,-;

1

18Preliminary microgravity experiments con-ducted during the 1970's were severelyconstrained, either by the relatively lowpower levels and volume available on theApollo spacecraft, or by the low number offlight opportunities provided by Skylab.These experiments, as simple as they were,often stimulated new insights in the roles offluid and heat flows in materials processing.Much of our understanding of the physicsunderlying semiconductor crystal growth, forexample, can be traced back to researchinitiated with Skylab.

jeTy,

4:Y1114t ik,`,

1;1

Skylab.

Since the early 1980's, NASA has sentcrews and payloads into orbit on board theSpace Shuttle. The Space Shuttle hasgiven microgravity scientists an opportunityto bring their experiments to low-earth orbiton a more regular basis. The Shuttle intro-duced significant new capabilities for micro-gravity research: larger, scientifically trainedcrews; a major increase in payload, volume,mass, and available power; and the return toEarth of all instruments, samples, and data.The Spacelab module, developed for theShuttle by the European Space Agency,

gives scientists a laboratory with enoughpower and volume to conduct a limitedrange of sophisticated microgravity experi-ments in space.

Use of the Shuttle for microgravity researchbegan in 1982, on its third flight, and contin-ues today on many missions. In fact, mostShuttle missions carry microgravity experi-ments as secondary payloads.

Spacelab-1, November 1983

The Spacelab-1 mission was launched inNovember 19C3. Over ten days, the sevencrewmembers carried out a broad variety ofspace science experiments, including re-search in microgravity sciences, astrophys-ics, space plasma physics, and Earth obser-vations.

Although the primary purpose of the missionwas to test the operations of the complexSpacelab and its subsystems, the 71 micro-gravity experiments, conducted using instru-ments from the European Space Agency,produced many interesting and provocativeresults. One investigator used the travellingheater method to grow a crystal of galliumantimonide doped with tellurium (a com-pound useful for making electronic devices).Due to the absence of gravity-driven con-vection, the space-grown crystal had a farmore uniform distribution of tellurium thancould be achieved on Earth. A secondinvestigator used molten tin to study diffu-sion in low gravityresearch that can im-prove our understanding of the behavior ofmolten metals. A German investigator grewprotein crystals that were significantly betterthan those grown from the same startingmaterials on the g. 'nd. These crystalswere analyzed using X-rays to determinethe structure of the protein that was grown.

r111141....

Spacelab 1 in payload bay of Shuttle OrbiterColumbia.

Spacelab-3, April 1985

Another Shuttle mission using theSpacelab module was Spacelab-3, whichflew in April 1985. SL-3 was the firstmission to include U.S.-developedmicrogravity research instruments in theSpacelab. One of these instrumentssupported an experiment to study thegrowth of crystals of mercury iodideamaterial of significant interest for use as asensitive detector of X-rays and gammarays. The experiment produced a crystalof mercury iodide grown at a rate muchhigher than that achievable on the ground.Despite the high rate of growth and rela-tively short growth time available, theresulting crystal was as good as the bestcrystal grown in the Earth-based labora-tory. Another U.S. experiment consistedof a series of tests on fluid behavior usinga spherical test cell. The microgravityenvironment allowed the researcher to usethe test cell to mimic the behavior of theatmosphere over a large part of Earth'ssurface. Results from this experimenthave been used to improve numericalmodels of our atmosphere.

19

Spacelab D-1, October 1985

In October 1985, six months after the flightof SL-3, NASA launched a Spacelab mis-sion sponsored by the Federal Republic ofGermany, designated Spacelab-D1. Thismission included a significant number ofsophisticated microgravity materials andfluid science experiments. American andGerman scientists conducted experiments tosynthesize high quality semiconductorcrystals useful in infrared detectors andlasers. These crystals had improved prop-erties and were more uniform in compositionthan their Earth-grown counterparts. Re-searchers also successfully measuredcritical properties of molten alloys. OnEarth, convection-induced disturbancesmake such measurements impossible.

Spacelab long module in Orbiter payload bay.

Spacelab Life Sciences-1, June 1991

The Spacelab Life Sciences-1 mission,flown in June 1991, was the first Spacelabmission dedicated to life sciences research.Mission experiments were aimed at trying toanswer many important questions regardingthe functioning of the human body in micro-gravity and its readaptation to the normalenvironment on Earth. Ten major investiga-tions probed autonomic cardiovascular

2G

20controls, cardiovascular adaptation to micro-gravity, vestibular functions, pulmonaryfunction, protein metabolism, mineral loss,and fluid-electrolyte regulation.

International Microgravity Laboratory-1,January 1992

More than 220 scientists from the UnitedStates and 14 other countries contributed tothe experiments flown on the first Interna-tional Microgravity Laboratory in January1992. Forty experiments in life and rnateri-als sciences were conducted by the crewwhich included payload specialists fromCanada and the European Space Agency.Life sciences experiments probed the spacemotion sickness problem that many astro-nauts feel in microgravity, plant growth, and

r.

G

IML-1 crewmembers Roberta L. Bondar andNorman E. Thagard operate microgravityexperiments inside of Spacelab.

cell separation. Materials science experi-ments concentrated on crystallization, cast-ing and solidification technology, and criticalpoint observations.

United States MicrogravityLaboratory 1, June 1992

In 1987, the NASA Microgravity MaterialsScience Assessment Task Force called for aseries of United States Microgravity Labora-tory missions ". . . in order to develop acomprehensive program which would ac-commodate both U.S. research needs andSpace Station development." The specificobjectives of USML-1 were 1) to conductscientific and technological investigations inmaterials, fluids, combustion, and biologicalprocesses; 2) to establish U.S. preeminencein microgravity research; 3) to form a basisfor evolution into future Spacelab and SpaceStation missions; and 4) to explore potentialapplications of space for commercial prod-ucts and processes.

The first United States Microgravity Labora-tory (USML-1) was the longest Shuttle flightto date-14 days. Over thirty investigationscomprised the payload, covering five basicareas: fluid dynamics, crystal growth, com-bustion science, biological science, andtechnology demonstrations.

The mission was an unqualified operationalsuccess in all of the areas listed above, withthe crew conducting what became known as a"dress rehearsal" for Space Station Freedom.For example, a flexible glovebox, which pro-vided an extra level of safety, was attached tothe Crystal Growth Furnace. The furnace wasthen opened, previously processed sampleswere removed and an additional sample wasinserted. This enabled another three experi-ments to be conducted. (Two other unproc-essed samples were already in the furnace.)

27

Small candles were burned in an enclosed,safe environment. The results were similar(though much longer lived) to what can beseen by conducting the experiment in freefall, here on Earth. (See Activity #8, CandleDrop, in the Activities section of thisteacher's guide.) The candles burned forabout 45-60 seconds in the microgravity ofcontinuous free fall aboard the SpaceShuttle Columbia.

Surface tension controlled the shape of fluidsurfaces in ways that confirmed theoreticalpredictions. Preliminary results indicate thatthe dynamics of rotating drops of silicone oilalso conformed to theoretical predictions.Results of this kind are significant in thatthey illustrate an important part of the scien-tific method: hypotheses are formed, andexperiments are conducted to test them.

The crew of scientist astronauts in thespacelab played an important role in maxi-mizing the science return from this mission.They were able to look first hand at how wellcrystal growth solutions were mixed. Thestart-up process for growing protein crystalswas examined and modified by the crew.Samples were reconfigured by hand topermit solutions to be completely injectedinto the experiment chamber. These arejust a few examples of how the scientists inspace worked with the scientists on theground to get the most from each experi-ment.

The flight of the first United StatesMicrogravity Laboratory marked the begin-ning of a new era in microgravity research.

Secondary Objectives

In addition to Spacelab flights, NASA fre-quently flies microgravity experiments in theSpace Shuttle middeck, in the cargo bay, andin the Get-Away-Special (GAS) canisters.Since 1988, NASA has built on the results of

21

the first Spacelab mission by growing crystalsof many different kinds of proteins on theShuttle middeck, including several sets ofspace-grown protein crystals that are sub-stantially better than Earth-grown crystals ofthe same materials. Medical and agriculturalresearchers hope to use information from theseprotein crystals to improve their understand-ing of how the proteins function.

Research conducted in the Shuttle middeckhas also led to the first space product: tinyspheres of latex that are significantly moreuniform in size than those produced on theground. These precision latex spheres are souniform that they are sold by the NationalInstitute of Standards and Technology (NIST)as a reference standard for calibrating devicessuch as electron microscopes and particlecounters.

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22

Activity List

Activities

Activity 1 Free Fall DemonstratorActivity 2 Falling WaterActivity 3 Gravity and AccelerationActivity 4 Inertial Balance, Part 1Activity 5 Inertial Balance, Part 2Activity 6 Gravity-Driven Fluid FlowActivity 7 Candle FlamesActivity 8 Candle DropActivity 9 Contact AngleActivity 10 Fiber PullingActivity 11 Crystal GrowthActivity 12 Microscopic Observation of Crystal Growth

A Note on Measurement

These activities use metric units of measure. In a few exceptions, notably within the"materials needed" lists, English units have been listed. In the United States, metric-sizedparts, such as screws, wood stock, and pipe are not as accessible as their Englishequivalents. Therefore, English units have been used to facilitate obtaining requiredmaterials.

2O

OBJECTIVE:

To demonstrate that free fall eliminates thelocal effects of gravity

BACKGROUND:

Microgravity conditions can be created in anumber of ways. Amusement park custom-ers feel a second or two of low-gravity oncertain high-performance rides. Springboarddivers experience low-gravity from the mo-ment they leave the board until they hit thewater. NASA achieves several seconds ofmicrogravity with drop towers and drop tubes.Longer periods, from 25 seconds to a minute,can be achieved in airplanes following para-bolic trajectories. Microgravity conditionslasting several minutes are possible usingunmanned sounding rockets. The longestperiods of microgravity are achieved withorbiting spacecraft.

The free fall demonstrator in thisactivity is an ideal device for classroomdemonstrations on the effect of low-gravity.When stationary, the lead fishing weightstretches the rubber band so that the weighthangs near the bottom of the frame. Whenthe frame is dropped, the whole apparatusgoes into free fall, so the weight (the force ofgravity) of the sinker becomes nearly zero.The stretched rubber bands then have noforce to counteract their tension, so they pullthe sinker, with the pin, up toward the bal-loon, causing it to pop. (In fact, initially thesinker's acceleration toward the bal;oon will

30

23

Activity 1

Free FallDemonstrator

be at 9.8 m/s2. Before the frame wasdropped, tension in the rubber bands com-pensated for gravity on the sinker, so theforce from that tension will accelerate thesinker at the same rate that gravity would.) If

a second frame, with string instead of rubberbands supporting the weight, is used forcomparison, the pin will not puncture theballoon as the device falls.

The demonstration works best whenstudents are asked to predict what will hap-pen when the frame is dropped. Will theballoon pop? If so, when will it pop? If yourschool has videotape equipment, you maywish to videotape the demonstration and usethe slow motion controls on the playbackmachine to determine more precisely whenthe balloon popped.

24

MATERIALS NEEDED:2 pieces of wood 16x2x1 in.2 pieces of wood 10x2x1 in.4 wood screws (#8 or #10 by 2 in.)Glue2 screw eyes4-6 rubber bands1 3-oz fishing sinker or 3 1-oz. fishing

sinkers (taped together)Long sewing pin or needleSmall round balloonsShort piece of string.Drill, 1/2 in. bit, and bit for piloting holes

for wood screwsScrewdriverPillow or chair cushion(Optional Make a second frame with

string supporting the sinker.)

PROCEDURE:

Step 1. Assemble the supporting frame asshown in the diagram. Be sure to drillpilot holes for the screws and gluethe frame pieces before screwingthem together.

Step 2. Drill a 1/2 inch-diameter hole throughthe center of the top of the frame. Besure the hole is free of splinters.

Step 3. Screw the two screw eyes into theunderside of the top of the frame asshown in the diagram. (Before doingso, check to see that the metal gap atthe eye is wide enough to slip arubber band over it. If not, use pliersto spread the gap slightly.)

Step 4. Loop three rubber bands togetherand then loop one end through themetal loop of the fishing sinker(s).

Step 5. Follow the same procedure with theother three rubber bands. The fishingweight should hang downward like aswing, near the bottom of the frame.If the weight hangs near the top, therubber bands are too strong. Re-place them with thinner rubber bands.

Step 6. Attach the pin or needle, with thepoint upward, to the metal loop of thefishing weight. It may be possible toslip it through the rubber band loopsto hold it in place. If not, use a smallamount of tape or glue to hold it.

Step 7. Inflate the balloon, and tie off thenozzle with a short length of string.Thread the string through the holeand pull the balloon nozzle through.If the balloon nozzle does not remainin the hole, use the string to tie itthere.

Step 8. Place a pillow or cushion on the floor.Raise the demonstrator at least 6 feetoff the floor. Do not permit the weightto swing. Drop the entire unit ontothe cushion. The balloon will popalmost immediately after release.

3

OBJECTIVE:

To demonstrate that free fall eliminates thelocal effects of gravity

BACKGROUND:

Weight is a property that is produced bygravitational force. An object at rest onEarth will weigh only one-sixth as much onthe Moon because of the lower gravitationalforce there. That same object will weighalmost three times as much on Jupiterbecause of the giant planet's greater gravi-tational attraction. The apparent weight ofthe object can also change on Earth simplyby changing its acceleration. If the object isplaced on a fast elevator acceleratingupward, its apparent weight would increase.However, if that same elevator were accel-erating downward, the object's apparentweight would decrease. Finally, if thatelevator were accelerating downward at thesame rate as a freely falling object, theobject's apparent weight would diminish tonear zero.

Free fall is the way scientists createmicrogravity for their research. Varioustechniques, including drop towers, air-planes, sounding rockets, and orbitingspacecraft, achieve different degrees ofperfection in matching the actual accelera-tion of a free-falling object.

25

Activity 2

Falling Water

In this demonstration, a water-filledcup is inverted and dropped. Before re-lease, the forces on the cup and water(their weight, caused by Earth's gravity) arecounteracted by the cookie sheet. Onrelease, if no horizontal forces are exertedon the cup when the sheet is removed, theonly forces acting (neglecting air) are thoseof gravity. Since Galileo demonstrated thatall objects accelerate similarly in Earth'sgravity, the cup and water move together.Consequently, the water remains in the cupthroughout the entire fall.

To make this demonstration pos-sible, two additional scientific principles areinvolved. The cup is first filled with water.A cookie sheet is placed over the cup'smouth, and the sheet and the cup are

32

26

MATERIALS NEEDED:Plastic drinking cupCookie sheet (with at least one edge

without a rim)Soda pop can (empty)Sharp nailCatch basin (large pail, waste basket)WaterChair or step-ladder (optional)Towels

inverted together. Air pressure and surfacetension forces keep the water from seepingout of the cup. Next, the cookie sheet ispulled away quickly, like the old trick ofremoving a table cioth from under a set ofdishes. The inertia of the cup and waterresists the movement of the cookie sheetso that both are momentarily suspended inair. The inverted cup and the water insidefall together.

PROCEDURE:

Step 1. Place the catch basin in the centerof an open area in the classroom.

Step 2. Fill the cup with water.Step 3. Place the cookie sheet over the

opening of the cup. Hold the cuptight to the cookie sheet whileinverting the sheet and cup.

Step 4. Hold the cookie sheet and cup highabove the catch basin. You maywish to stand on a sturdy table orclimb on a step-ladder to raise thecup higher.

Step 5. While holding the cookie sheetlevel, slowly slide the cup to theedge of the cookie sheet.

Step 6. Observe what happens.Step 7. Refill the cup with water and invert

it on the cookie sheet.

Step 8. Quickly pull the cookie sheetstraight out from under the cup.

Step 9. Observe the fall of the cup andwater.

Step 10. If your school has videotapeequipment, you may wish to tapethe activity and replay the fall usingslow motion or pause controls tostudy the action at various points ofthe fall.

FOR FURTHER RESEARCH:

1. As an alternate or a supportive activity,punch a small hole near the bottom of anempty soda pop can. Fill the can withwater and seal the hole with your thumb.Position the can over a catch basin andremove your thumb. Observe the waterstream. Toss the can through the air toa second catch basin. Try not to makethe can tumble or spin in flight. Observewhat happens to the water stream. Theflight of the can is a good demonstrationof the parabolic trajectory followed byNASA's KC-135. (Note: Recycle the canwhen you are through.)

2. Why should you avoid tumbling or spin-ning the can?

3. Drop the can while standing on a chair,desk, or ladder. Compare the resultswith 1.

OBJECTIVE:

To use a plasma sheet to observe accelera-tion forces that are experienced on board aspace vehicle

BACKGROUND:

The accelerations experienced on board aspace vehicle during flight are vector quan-tities resulting from forces acting on thevehicle and the equipment. These accel-erations have many sources, such asresidual gravity, orbiter rotation, vibrationfrom equipment, and crew activity. Theequivalent acceleration vector at any onespot in the orbiter is a combination of manydifferent sources and is thus a very com-plex vector quantity changing over time.The magnitude and direction of the vector ishighly dependent on the activities occurringat any time. The accelerations also dependon what has happened in the recent pastdue to the structural response (e.g., flexingand relaxing) of the vehicle to some activi-ties, such as thruster firing, etc.

On the other hand, the gravity expe-rienced on Earth is a relatively stable accel-eration vector quantity because of thedominating large acceleration towardEarth's center. Some activities, such asearthquakes and subsurface magma move-ments and altitude changes, may perturblocal gravitational acceleration.

Gravity and artificial accelerationsmay be investigated and demonstrated

27

Activity 3

Gravity andAcceleration

visually by using a common toy available inmany toy, novelty, and museum stores.The toy consists of a clear, flat, plastic boxwith two liquids of different densities inside.By changing the orientation of the box,droplets of one liquid will pour through theother to the bottom. For the purposes ofthis activity, the toy will be referred to as aplasma sheet.

PROCEDURE:

Step 1. Lay the plasma sheet on its flat sideon the stage of an overhead pro-jector. Project the action inside thesheet on a screen for the entireclass to observe. The coloredliquids will settle into a dispersedpattern across the sheet.

Step 2. Raise one end of the sheet slightlyto add a new component to theacceleration vector, and support it

3,;

28

MATERIALS NEEDED:Plasma sheet toyRecord turntableFile cardsOverhead projectorSlide projectorProjection screen

by placing a one-centimeter-thickpile of file cards under the raisedend. Observe the movement of thefluids inside.

Step 3. Raise the end of the plasma sheetfurther and support it with anotherstack of cards. Again, observe themovements of the fluids.

Step 4. Aim the slide projector at thescreen. Project a white beam oflight at the screen. Stand theplasma sheet on its end in front ofthe projected beam to cast shad-ows. Observe the action of thefalling liquids.

Step 5. Lay the plasma sheet on its flat sideso that the colored liquid will accu-mulate in the center. Hold thesheet horizontally in your handand, using your arm as a pendu-lum, swing the sheet from side toside several times. Observe whathappens to the liquid.

Step 6. Lay the plasma sheet on its flat sideon a phonograph record turntable.Start the turntable moving. Ob-serve what happens to the liquid.

HorizontalOrientation

Gravity

0

Light Fluid

Heavy Fluid

Rotational Acceleration DemonstrationPlasma Sheet

Acceleration(when rotating)

RecordPlayer

Turntable

Acceleration(when rotating)

Resultant GravityAcceleration

Vector

Step 7. Experiment with elevating the outeredge of the plasma sheet on theturntable until the accelerationvector produces a distribution ofliquid similar to the dispersionobserved in step 1.

QUESTIONS:

1. What implications do the plasma sheetdemonstrations have for scientific re-searchers interested in investigatingmicrogravity phenomena? How willSpace Shuttle orbiter thruster firings andcrew movements affect sensitive experi-ments?

2. How might acceleration vectors bereduced on the Space Shuttle? Wouldthere be any advantage to the quality ofmicrogravity research by conducting thatresearch on Space Station Freedom?

FOR FURTHER RESEARCH:

1. Investigate how scientists measureacceleration vectors in their research.

2. Challenge the students to design asimple and rugged accelerometer thatcould be used to measure accelerationsexperienced in a package sent throughthe U.S. Mail.

OBJECTIVE:

To demonstrate how mass can be mea-sured in microgravity

BACKGROUND:

The microgravity environment of an orbitingSpace Shuttle or space station presentsmany research challenges for scientists.One of these challenges is the measure-ment of the mass of experiment samplesand subjects. In life sciences research, forexernple, nutrition studies of astronauts inorbit may require daily monitoring of anastronaut's mass. In materials scienceresearch, it may be desirable to determinehow the mass of a growing crystal changesdaily. To meet these needs, an accuratemeasurement of mass is vital.

On Earth, mass measurement issimple. The samples and subjects aremeasured on a scale or beam balance.Calibrated springs in scales are com-pressed to derive the needed measure-ment. Beam balances measure an un-known mass by comparison to a knownmass (kilogram weights). In both of thesemethods, the measurement is dependentupon the force produced by Earth's gravita-tional pull.

In space, neither method worksbecause of the free fall condition of orbit.However, a third method for mass mea-surement is possible using the principle ofinertia. Inertia is the property of matter that

29

Activity 4

Inertial BalancePart 1

causes it to resist acceleration. Theamount of resistance to acceleration isdirectly proportional to the object's mass.

To measure mass in space, scien-tists use an inertial balance. An inertialbalance is a spring device that vibrates thesubject or sample being measured. Thefrequency of the vibration will vary with themass of the object and the stiffness of thespring (in this diagram, the yard stick). Fora given spring, an object with greater masswill vibrate more slowly than an object withless mass. The object to be measured isplaced in the inertial balance, and a springmechanism starts the vibration. The timeneeded to complete a given number ofcycles is measured, and the mass of theobject is calculated.

PROCEDURE:

Step 1. Using the drill and bit to make thenecessary holes, bolt two blocks ofwood to the opposite sides of oneend of the steel yard stick.

36

30

MATERIALS NEEDED:

Metal yardstick*2 C-clamps*Plastz 35mm film canisterPillow foam (cut in plug shape to fit

canister)Masking tapeWood blocks2 bolts and nutsDrill and bitCoins or other objects to be measuredGraph paper, ruler, and pencilPennies and nickelsStopwatch*Available from hardware store

Step 2. Tape an empty plastic film canisterto the opposite end of the yard-stick. Insert the foam plug.

Step 3. Anchor the wood block end of theinertial balance to a table top withC-clamps. The other end of theyard stick should be free to swingfrom side to side.

Step 4. Calibrate the inertial balance byplacing objects of known mass(pennies) in the sample bucket(canister with foam plug). Beginwith just the bucket. Push the endof the yard stick to one side andrelease it. Using a stopwatch orclock with a second hand, timehow long it takes for the stick tocomplete 25 cycles.

Step 5. Plot the time on a graph above thevalue of 0. (See sample graph.)

Step 6. Place a single penny in the bucket.Use the foam to anchor the pennyso that it does not move inside thebucket. Any movement of thesample mass will result in an error(oscillations of the mass can causea damping effect). Measure thetime needed to complete 25 cycles.

Plot the number over the value of 1on the graph.

Step 7. Repeat the procedure for differentnumbers of pennies up to 10.

Step 8. Draw a curve on the graph throughthe plotted points.

Step y. Place a nicicel (object of unknownmass) in the bucket and measurethe time required for 25 cycles.Find the horizontal line that repre-sents the number of vibrations forthe nickel. Follow the line until itintersects the graph plot. Follow avertical line from that point on theplot to the penny scale at thebottom of the graph. This will givethe mass of the nickel in "penny"units.

Note: This activity makes use of pennies as astandard of measurement. If you haveaccess to a metric beam balance, you cancalibrate t'ie inertial balance into metricmass measurements using the weights asthe standards.

19

18

17

16

15

14

13

12

11

Sample Graph

A NickelThe mass of two pennies and themass of a nickel differed by only0.1 gram when measured on atraditional metric beam balance.

0 1 2 3 4 5 6 7 8 9 10

Number of Pennies

QUESTIONS:

1. Does the length of the ruler make adifference in the results?

2. What are some of the possible sourcesof error in measuring the cycles?

3. Why is it important to use foam to anchorthe pennies in the bucket?

OBJECTIVE:

To feel how inertia effects acceleration

BACKGROUND:

The inertial balance in Part 1 of this activityoperates by virtue of the fundamentalproperty of all matter that causes it to resistchanges in motion. In the case of theinertial balance, the resistance to motion isreferred to as rotational inertia. This isbecause the yardstick pivots at the point onthe table where it is anchored and thebucket swings through an arc. Unlike linearmotion, the placement of mass in rotationalmovements is important. Rotational inertiaincreases with increasing distance from theaxis of rotation.

The inertial balance in Part 1 uses ametal yardstick as a spring. The bucket forholding samples is located at the endopposite the axis of rotation. Moving thebucket closer to the axis will make a stifferspring that increases the sensitivity of thedevice.

The relationship of the placement ofmass to distance from the axis of rotation iseasily demonstrated with a set of inertiarods. The rods are identical in appearanceand mass and even have identical centersof mass. Yet, one rod is easy to rotate andthe other is difficult. The secret of the rodsis the location of the mass inside of them.In one rod, the mass is close to the axis ofrotation, and in the other, the mass is

31

Activity 5

Inertial BalancePart 2

concentrated at the ends of the rod. Stu-dents will be able to feel the difference inrotational inertia between the two rods asthey try to rotate them.

PROCEDURE:

Step 1. Using a saw, cut the PVC tube inhalf. Smooth out the ends, andcheck to see that the caps fit theends.

Step 2. Squeeze a generous amount ofsilicone rubber sealant into the endof one of the tubes. Slide thenipple into the tube. Using thedowel rod, push the nipple to themiddle of the tube. Add sealant tothe other end of the tube and insertthe second nipple. Position bothnipples so that they are touchingeach other and straddling thecenter of the tube. Set the tubeaside to dry.

30

32

MATERIALS NEEDED:PVC 3/4 in. water pipe

(about 1.5 to 2 m long)4 iron pipe nipples

(sized to fit inside PVC pipe)4 PVC caps to fit water pipeSilicone rubber sealantScale or beam balanceSawVery fine sand paper1/2 in. dowel rod

Step 3. Squeeze some sealant into theends of the second tube. Push theremaining pipe nipples into theends of the tubes until the ends ofthe nipples are flush with the tubeends. Be sure there is enoughcompound to cement the nipples inplace. Set the tube aside to dry.

Step 4. When the sealant of both tubes isdry, check to see that the nipplesare firmly cemented in place. If

not, add additional sealant tocomplete the cementing. Weighboth rods. If one rod is lighter thanthe other, add small amounts ofsealant to both ends of the rod.Re-weigh. Add more sealant ifnecessary.

Step 5. Spread some sealant on the insideof the PVC caps. Slide them ontothe ends of the tubes to cementthem in place.

Step 6. Use fine sand paper to clean therods.

Massconcentratedat end

Massconcentratedin center

Massconcentrated

6f5 at end

QUESTIONS:

1. How does the placement of mass in thetwo rods affect the ease with which theyare rotated from side to side? Why?

2. If an equal side to side rotational force(known as torque) was exerted on themiddle of each rod, which one wouldaccelerate faster?

MICROGRAVIN

sms_

33

Activity 6

OBJECTIVE:

To observe the gravity-driven fluid flow thatis caused by differences in solution density

BACKGROUND:

Many crystals grow in solutions of differentcompounds. For example, crystals of saltgrow in concentrated solutions of saltdissolved in water. Crystals of proteins andother molecules grown in experiments onthe Space Shuttle are also grown in similartypes of solutions.

Gravity has been shown to cause thefluid around a growing crystal to flow up-ward. "Up" is defined here as being oppo-site the direction of gravity. This flow offluid around the growing crystal is sus-pected to be detrimental to some types ofcrystal growth. Such flow may disrupt thearrangement of atoms or molecules on thesurface of the growing crystal, makingfurther growth non-uniform.

Understanding and controlling solu-tion flows is vital to studies of crystalgrowth. The flow appears to be caused bydifferences in the density of solutionswhich, in the presence of gravity, createfluid motion around the growing crystal.The solution nearest the crystal surfacedeposits its chemical material onto thecrystal surface, thereby reducing the mo-lecular weight of the solution. The lightersolution tends to float upward, thus creatingfluid motion. This experiment recreates the

Gravity-DrivenFluid Flow

phenomenon of gravity-driven fluid motionand makes it visible.

PROCEDURE:

Step 1. Fill the large glass container withvery salty water.

Step 2. Fill the small vial with unsaltedwater and add two or three dropsof food coloring to make it a darkcolor.

Step 3. Attach a thread to the upper end ofthe vial, and lower it carefully butquickly into the salt water in thelarge container. Let the vial sit onthe bottom undisturbed.

Step 4. Observe the results.Step 5. Repeat the experiment using col-

ored salt water in the small vial andunsalted water in the large con-tainer.

Step 6. Observe the results.

40

34

MATERIALS NEEDED:Large (500 ml) glass beaker or tall

drinking glassSmall (5 to 10 ml) glass vialThreadFood coloringSaltSpoon or stirring rod

QUESTIONS:

1. Based on your observations, whichsolution is denser (salt water or un-salted, dyed water)?

2. What do you think would happen if saltwater were in both the small vial and thelarge container? What would happen ifunsalted water were in both the smallvial and the large containe?

3. What results would you expect if theexperiment had been performed in amicrogravity environment?

4. How does this experiment simulate whathappens to a crystal growing in solution?

FOR FURTHER RESEARCH:

1. Repeat the experiment, but replace thewater in the small vial with hot, unsaltedwater. Replace the salt water in thelarge container with cold, unsalted water.

2. Repeat the experiment with differentamounts of salt.

3. Try replacing the salt in the experimentwith sugar and/or baking soda.

4. Attempt to control the observed flows bycombining the effects of temperature andsalinity in each container.

5. Try to observe the fluid flows withoutusing food coloring. You will have toobserve carefully to see the effects.

OBJECTIVE:

To illustrate the effects of gravity on theburning rate of candles

BACKGROUND:

A candle flame is often used to illustrate thecomplicated physio-chemical processes ofcombustion. The flame surface itself repre-sents the location where fuel vapor andoxygen mix at high temperature and withthe release of heat. Heat from the flamemelts the wax (typically a Ca to C35 hydro-carbon) at the base of the exposed wick.The liquid wax rises by capillary action upthe wick, bringing it into closer proximity tothe hot flame. This close proximity causesthe liquid wax to vaporize. The wax vaporsthen migrate toward the flame surface,breaking down into smaller hydrocarbonsenroute. Oxygen from the surroundingatmosphere also migrates toward the flamesurface by diffusion and convection. Thesurvival and location of the flame surface isdetermined by the balance of these pro-cesses.

In normal gravity, buoyancy-drivenconvection develops due to the hot, lessdense combustion products. This actionhas several effects: (a) the hot reactionproducts are carried away due to theirbuoyancy, and fresh oxygen is carriedtoward the flame zone; (b) solid particles ofsoot form in the region between the flameand the wick and are convected upward,

(-

35

Activity 7

Candle Flames

where they burn off, yielding the brightyellow tip of the flame; (c) to overcome theloss of heat due to buoyancy, the flameanchors itself close to the wick; (d) thecombination of these effects causes theflame to be shaped like a tear drop.

In the absence of buoyancy-drivenconvection, as in microgravity, the supply ofoxygen and f:Jel vapor to the flame is con-trolled by the much slower process ofmolecular diffusion. Where there is no "up"or "down," the flame tends toward spheric-ity. Heat lost to the top of the candlecauses the base of the flame to bequenched, and only a portion of the sphereis seen. The diminished supply of oxygenand fuel causes the flame temperature to

36

be lowered to the point that little or no sootforms. It also causes the flame to anchorfar from the wick, so that the burning rate(the amount of wax consumed per unittime) is reduced.

MATERIALS NEEDED:Birthday candles (several)MatchesBalance beam scale (0.1 gm or greater

sensitivity)Clock with second-hand or stopwatchWire cutter/pliersWireSmall pan to collect dripping wax

PROCEDURE:

Step 1. Form candle holders from the wireas shown in the diagram. Deter-mine and record the weight of eachcandle and its holder.

Step 2. Light the "upright" candle andpermit it to burn for one minute. Asit burns, record the colors, size,and shape of the candle flame.

Step 3. Weigh the candle and holder andcalculate how much mass was lost.

Step 4. Place the inverted candle on asmall pan to collect dripping wax.(Note: The candle should be in-verted to an angle of about 70degrees from the horizontal. If thecandle is too steep, dripping waxwill extinguish the flame.)

Step 5. Light the candle and permit it toburn for one minute. As it burns,record the colors, size, and shapeof the candle flame.

Step 6. Weigh the candle and holder andcalculate how much mass was lost.

QUESTIONS:

1. Which candle burned faster? Why?2. How were the colors and flame shapes

and sizes different?3. Why did one candle drip and the other

not?4. Which candle was easier to blow out?5. What do you think would happen if you

burned a candle horizontally?

FOR FURTHER RESEARCH:

1. Burn a horizontally-held candle. As itburns, record the colors, size, and shapeof the candle flame. Weigh the candleand calculate how much mass was lostafter one minute.

2. Repeat the above experiments with thecandles inside a large jar. Let thecandles burn to completion. Record thetime it takes each candle to burn. Deter-mine how and why the burning ratechange.:

3. Burn two candies which are close to-gether. Record the burning rate andweigh the candles. Is it faster or slowerthan each candle alone? Why?

4. Obtain a copy of Michael Faraday'sbook, The Chemical History of a Candle,and do the experiments described. (Seereference list.)

43

4

37

H2O, CO2(Unburned

Carbon)

Luminous

Light Zone

Yellow (Carbon1200°C luminesces

and burns)

Dark RedBrown1000°C

White1400°C

Orange800 °C

Blue

02

MainReaction

Zone

Primary(initial)

ReactionZone,

(Carbon particles)

H2OCO2OH

Ca

DeadSpace600°C

Candle Flame Reaction Zones,Emissions, and Temperature*

*Candle flame diagrams adapted from "The Science ofFlames poster," National Energy Foundation, Salt LakeCity, UT.

38

OBJECTIVE:

To observe candle flame properties infree fall

BACKGROUND:

Drop tower and Space Shuttle experi-ments have provided scientists valuableinsights on the dynamics and chemistry ofcombustion. In both research environments,a flammable material is ignited by a hot wire,and the combustion process is recorded bymovie cameras and other data collectiondevices.

The sequence of pictures beginning atthe bottom of this page illustrates a combus-tion experiment conducted at the NASALewis Research Center 150 Meter DropTower. These pictures of a candle flamewere recorded during a 5-second droptower test. An electrically-heated wire wasused to ignite the candle and then with-drawn one second into the drop. As the

1 second

Activity 8

Candle Drop

2 seconds 3 seconds

Combustion Drop TestNASA Lewis Research Center

4

Hot Wire Ignition in Microgravity

4 seconds 5 seconds

pictures illustrate, the flame stabilizesquickly, and its shape appears to be con-stant throughout the remainder of the drop.

Microgravity tests performed on theSpace Shuttle furthered this research bydetermining the survivability of a candleflame. If the oxygen does not diffuse rap-idly enough to the flame front, the flametemperature will diminish. Consequently,the heat feedback to and vaporization ofthe candle wax will be reduced. If the flametemperature and these other processes fallbelow critical values, the candle flame willbe extinguished. Candles on board the firstUnited States Microgravity Laboratory,launched in June 1992, burned from 45seconds to longer than 60 seconds.

MATERIALS NEEDED:

Clear plastic jar and lid (2 liter volume)*Wood blockScrewsBirthday-size candlesMatchesDrill and bitVideo camera and monitor (optional)* Empty large plastic peanut butter jar

can be used.

PROCEDURE:

Step 1. Cut a small wood block to fit insidethe lid of the jar. Attach the block tothe jar lid with screws from the top.

Step 2. Drill a hole in the center of the blockto serve as a candle-holder.

Step 3. Insert a candle into the hole. Darkenthe room. With the lid on the bottom,light the candle and quickly screw theplastic jar over the candle.

39

Step 4. Observe the shape, brightness, andcolor of the candle flame. If theoxygen inside the jar is depletedbefore the observations are com-pleted, remove the jar and flush outthe foul air. Relight the candle andseal the jar again.

Step 5. Raise the jar towards the ceiling ofthe room. Drop the jar with the litcandle to the floor. Position a studentnear the floor to catch the jar.

Step 6. As the candle drops, observe theshape, brightness, and color of thecandle flame. Because the actiontakes place very quickly, performseveral drops to complete the obser-vation process.

QUESTIONS:

1. Did the candle flame change shape duringthe drop? If so, what new form did theflame take and why?

2. Did the brightness of the candle flamechange? If it did change, why?

3. Did the candle flame go out? If the flamedid go out, when did it go out and why?

4. Were the observations consistent fromdrop to drop?

4G

FOR FURTHER RESEARCH:

1. If videotape equipment is available,videotape the candle flame during thedrop. Use the pause control during theplayback to examine the flame shape.

2. If a balcony is available, drop the jar froma greater distance than is possible in aclassroom. Does the candle continue toburn through the entire drop? For longerdrops, it is recommended that a catchbasin be used to catch the jar. Fill up alarge box or a plastic trash can withstyrofoam packing material or looselycrumpled newspaper.

40

/RIASA

MICROGRAM

OBJECTIVE:

To measure the contact angle of a fluid

BACKGROUND:

In the absence of the stabilizing effect ofgravity, fluids partly filling a container inspace are acted on primarily by surfaceforces and can behave in striking, unfamil-iar ways. Scientists must understand thisbehavior to manage fluids in space effec-tively.

Liquids always meet clean, smooth,solid surfaces in a definite angle, called thecontact angle. This angle can be measuredby observing the attraction of fluid intosharp corners by surface forces. Even inEarth's gravity, the measurement techniquecan be observed. If a corner is vertical andsharp enough, surface forces win out overthe downward pull of gravity, and the fluidmoves upward into the corner. If the anglebetween the two glass planes is slowlydecreased, the fluid the glass is standing injumps up suddenly when the critical valueof the corner angle is reached. In theabsence of gravity's effects, the jump wouldbe very striking, with a large amount of fluidpulled into the corner.

Activity 9

Contact Angle

PROCEDURE:

Step 1. Place a small amount of distilledwater in a dish. (Note: It is impor-tant that the dish and the slides areclean.)

Step 2. Place two clean microscope slidesinto the water so that their endstouch the bottom of the dish andthe long slides touch each other atan angle of at least 30 degrees.(Optional step: You may find iteasier to manipulate the slides if atape hinge is used to hold theslides together.)

Step 3. Slowly close the angle between thetwo slides.

Step 4. Stop closing the angle when thewater rises between the slides.Use the protractor to measure thecontact angle (angle the waterrises up between the slides). Alsomeasure the angle between thetwo slides.

4"

MATERIALS NEEDED:

Distilled waterMicroscope slidesShallow dishProtractorCellophane tape

QUESTIONS:1. What is the mathematical relationship

between the contact angle and the anglebetween the two slides?

Contact angle = 90 -1/2 wedge angle2. Why is it important to understand the

behavior of fluids in microgravity?

TapeHinge

Water

40

41

FOR FURTHER RESEARCH:1. Add some food coloring to the water to

make it easier to see. Does the additionof coloring change the contact angle?

2. Measure the contact angle for otherliquids. Add a drop of liquid soap oralcohol to the water to see if it alterswaters contact angle.

3. Try opening the wedge of the two slidesafter the water has risen. Does thewater come back down easily to itsoriginal position?

42

OA?4 0

MICIVOR4V17Y )IVOR.;71I

OBJECTIVE:

To illustrate the effects of gravity and sur-face tension on fiber pulling

BACKGROUND:

Fiber pulling is an important process inthe manufacture of synthetic fabrics such asnylon and polyester and more recently, in themanufacture of optical fibers for communica-tion networks. Chances are, when you usethe telephone for long distance calls, yourvoice is carried by light waves over opticalfibers.

Fibers can be drawn successfully onlywhen the fluid is sufficiently viscous or"sticky." Two effects limit the process: gravitytends to cause the fiber to stretch and breakunder its own weight, and surface tensioncauses the fluid to have as little surface areaas possible for a given volume. A long slen-der column of liquid responds to this lattereffect by breaking up into a series of smalldroplets. A sphere has less surface areathan a cylinder of the same volume. Thiseffect is known as the "Rayleigh instability"after the work of Lord Rayleigh who explainedthis behavior mathematically in the late1800's. A high viscosity slows the fluidmotion and allows the fiber to stiffen as itcools before these effects cause the strand tobreak apart.

Some of the new exotic glass systemsunder consideration for improved opticalfibers are much less viscous in the melt thanthe quartz used to make the fibers presently

Activity 10

Fiber Pulling

'n use: this low viscosity makes them difficultto draw into fibers. The destructive effects ofgravity could be reduced by forming fibers inspace. However, the Rayleigh instability isstill a factor in microgravity. Can a reductionin gravity's effects extend the range of vis-cosities over which fibers can be successfullydrawn? This question must be answeredbefore we invest heavily in developing expen-sive experiment apparatus to test high tem-perature melts in microgravity. Fortunately,there are a number of liquids that, at roomtemperature, have fluid properties similar tothose of molten glass. This allows us to usecommon fluids to model the behavior ofmolten materials in microgravity.

PROCEDURE: (for several demonstrations)

Step 1. While wearing eye and hand protec-tion, use the propane torch or Bunsenburner to melt a blob of glass at oneend of a stirring rod. Touch a secondrod to the melted blob and pull a thinstrand downward. Measure how longthe fiber gets before it breaks. Cau-tion: When broken, the fiber frag-ments are sharp. Dispose ofsafely.

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MATERIALS NEEDED:Propane torch or Bunsen burnerSmall-diameter glass stirring rods (soft glass)Disposable syringes (10 ml) without needlesVarious fluids (water, honey, corn syrup,

mineral oil, and light cooking oil)Small ball bearings or BBsSmall graduated cylinders or test tubes (at

least 5 times the diameter of the ballbearing)

Stopwatch or clock with second-handEye protectionProtective glovesMetric ruler

Step 2. Squirt a small stream of water from thesyringe. Observe how the streambreaks up into small droplets after ashort distance. This breakup iscaused by the Rayleigh instability ofthe liquid stream. Measure the lengthof the stream to the point where thebreak-up occurs. Do the same forother liquids and compare the results.

Step 3. Touch the end of a cold stirring rod tothe surface of a small quantity ofwater. Try to draw a fiber.

Step 4. Repeat #3 with more viscous fluids,such as honey.

Step 5. Compare the ability to pull strands ofthe various fluids with the molten glassand with the measurements made instep 2.

Step 6. Pour about 5 centimeters of water intoa small test tube. Drop the ball bear-ing into the tube. Record the time ittakes for the ball bearing to reach thebottom. (This is a measure of theviscosity of the fluid.)

Step 7. Repeat #6 for each of the fluids.Record the fall times through eachfluid.

QUESTIONS:

1. Which of the fluids has the closest behaviorto molten glass? Which fluid has the leastsimilar behavior to molten glass? (Rankthe fluids.)

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2. How do the different fluids compare inviscosity (ball bearing fall times)? Whatproperty of the fluid is the most importantfor modeling the behavior of the glassmelt?

3. What is the relationship between fiberlength and viscosity of the fluid?

FOR FURTHER RESEARCH:

1.

2.

With a syringe, squirt a thin continuousstream of each of the test fluids downwardinto a pan or bucket. Carefully observethe behavior of the stream as it falls.Does it break up? How does it break up?Can you distinguish whether the breakupis due to gravity effects or to the Rayleighinstability? How does the strand breakwhen the syringe runs out of fluid? (Formore viscous fluids, it may be necessaryto do this experiment in the stairwell withstudents stationed at different levels toobserve the breakup.)Have the students calculate the curvedsurface area (ignore the area of the endcaps) of cylinders with length to diameterratios of 1, 2, 3, and 4 of equal volume.Now, calculate the surface area of asphere with the same volume. Sincenature wants to minimize the surface areaof a given volume of free liquid, what canyou conclude by comparing these variousratios of surface area to volume ratios?(Note: This calculation is only an approxi-mation of what actually happens. Thecylinder (without the end caps) will haveless surface area than a sphere of thesame volume until its length exceeds 2.25times its diameter from the above calcula-tion. Rayleigh's theory calculates theincrease in surface area resulting from adisturbance in the form of a periodicsurface wave. He showed that for a fixedvolume, the surface area would increase ifthe wavelength was less than it times thediameter, but would decrease for longerwaves. Therefore, a long slender columnof liquid will become unstable and willbreak into droplets separated by it timesthe diameter of the column.)

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OBJECTIVE:

To observe crystal growth phenomena in a1 -g environment

BACKGROUND:

A number of crystals having practical appli-cations, such as L-arginine phosphate(LAP) and triglycine sulfate (TGS), may begrown from solutions. In a one-gravityenvironment, buoyancy-driven convectionmay be responsible for the formation ofliquid inclusions and other defects whichcan degrade the performance of devicesmade from these materials. The virtualabsence of convection in a microgravityenvironment may result in far fewer inclu-sions than in crystals grown on Earth. Forthis reason, solution crystal growth is anactive area of microgravity research.

Crystal growing experiments consistof a controlled growth environment on Earthand an experimental growth environment inmicrogravity on a spacecraft. In this activ-ity, students will become familiar with crys-tal growing in 1-g. One or more crystals ofalum (aluminum potassium sulfate orAIK(SO4)212H20 will be grown from seedcrystals suspended in a crystal growthsolution. With the use of collimated light,shadowgraph views of the growing crystalswill reveal buoyancy-driven convectiveplumes in the growth solution. (Refer toactivity 6 for additional background informa-tion.)

Activity 11

Crystal Growth

PROCEDURE:

Step 1. Create a seed crystal of alum bydissolving some alum in a smallquantity of water in a beaker.Permit the water to evaporate overseveral days. Small crystals willform along the sides and bottom ofthe beaker.

Step 2. Remove one of the small crystals ofalum and attach it to a short lengthof monofilament fishing line with adab of silicone cement.

Step 3. Prepare the crystal growth solutionby dissolving powdered or crystal-line alum in a beaker of warm

5

MATERIALS NEEDED:

Aluminum Potassium SulfateAlK(SO4)212H20*

Square acrylic box**Distilled waterStirring rodMonofiliment fishing lineSilicone cementBeakerSlide projectorProjection screenEye protectionHot plateThermometerBalance*Refer to the chart on the next page for

the amount of alum needed for thecapacity of the growth chamber(bottle) you use.

**Clear acrylic boxes, about 10x10x13cm are available from craft stores.Select a box that has no opticaldistortions.

water. The amount of alum thatcan be dissolved in the waterdepends upon the amount of thewater used and its temperature.Refer to the table (Alum Solubilityin Water) for the quantity required.

Step 4. When no more alum can be dis-solved in the water, transfer thesolution to the growth chamberacrylic box.

Step 5. Punch a small hole through thecenter of the lid of the box. Threadthe seed crystal line through thehole and secure it in place with asmall amount of tape. Place theseed crystal in the box and placethe lid on the box at a 45 degreeangle. This will expose the surfaceof the solution to the outside air topromote evaporation. It may benecessary to adjust the length of

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the line so that the seed crystal isseveral centimeters above thebottom of the bottle.

Step 6. Set the box aside in a place whereit can be observed for several dayswithout being disturbed. If thecrystal should disappear, dissolvemore alum into the solution andsuspend a new seed crystal.

Step 7. Record the growth rate of thecrystal by comparing it to a metricruler. The crystal may also beremoved and its mass measuredon a balance.

Step 8. Periodically observe the fluid flowassociated with the crystal's growthby directing the light beam of aslide projector through the box to aprojection screen. Observeplumes around the shadow of thecrystal. Convection currents in thegrowth solution distort the lightpassing through the growth solu-tion.

QUESTIONS:

1. What is the geometric shape of the alumcrystal?

2. What can cause more than one crystal toform around a seed?

3. What do shadowgraph plumes aroundthe growing crystal indicate? Do youthink that plumes would form aroundcrystals growing in microgravity?

4. Does the growth rate of the crystal re-main constant? Why or why not?

5. What would cause a seed crystal todisappear? Could a crystal decrease insize? Why?

6. What are some of the possible applica-tions for space-grown crystals?

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FOR FURTHER RESEARCH:

1. Grow additional alum crystals without thecap placed over the box. In one experi-ment, permit the growth solution toevaporate at room temperature. Inanother, place the growth chamber in awarm area or even on a hot plate set atthe lowest possible setting. Are thereany differences in the crystals producedcompared to the first one grown? Howdoes the growth rate compare in each ofthe experiments?

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30

25

20

15

10

Alum Solubility in WaterAIK(Sql )2.12132 0

2. Experiment with growing crystals of otherchemicals such as table salt, coppersulfate, chrome alum, Rochelle salt, etc.Caution: Become familiar with potentialhazards of any of the chemicals youchoose and take appropriate safetyprecautions.

3. Review scientific literature for resultsfrom microgravity crystal growing experi-ments.

20 25 30 35 40 45 50

Temperature (degrees Celsius)

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Shadowgraph image of a growth plumerising from a growing crystal.

OBJECTIVE:

To observe crystal nucleation and growthrate during directional solidification

BACKGROUND:

Directional solidification refers to a processby which a liquid is transformed (by freez-ing) into a solid through the application of atemperature gradient in which heat is re-moved from one direction. A container ofliquid will turn to a solid in the direction thetemperature is lowered. If this liquid has asolute present, typically, some of the solutewill be rejected into the liquid ahead of theliquid/solid interface. However, this rejec-tion does not always occur, and in somecases, the solute is incorporated into thesolid. This phenomenon has many impor-tant consequences for the solid. As aresult, solute rejection is studied extensivelyin solidification experiments.

The rejected material tends to buildup at the interface to form a mass boundarylayer. This experiment demonstrates whathappens when the growth rate is too fastand solute in the boundary layer is trapped.

Fluid flow in the melt can also affectthe buildup of the mass boundary layer. OnEarth, fluids that expand become lessdense. This causes a vertical flow of liquidwhich will interfere with the mass boundarylayer. In space, by avoiding this fluid flow,a more uniform mass boundary layer will be

5

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Activity 12

MicroscopicObservation ofCrystal Growth

achieved. This, in turn, will improve theuniformity with which the solute is incorpo-rated into the growing crystal.

PROCEDURE:

Observations of Mannite*

Step 1. Place a small amount of mannite ona microscope slide and place theslide on a hot plate. Raise thetemperature of the hot plate untilthe mannite melts. Be careful notto touch the hotplate or heatedslide. Handle the slide withforcepts.

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MATERIALS NEEDED:

Bismarck Brown Y**Mannite (d-Mannitol)

HOCH2(CHOH)4CH2OH*Salol (Phenyl Salicylate)

Cr3H1003**MicroprojectorStudent microscopes (alternate to

microprojector)Glass microscope slides with cover

glassCeramic bread and butter plateRefrigeratorHot plateDesktop coffee cup warmerForcepsDissecting needleSpatulaEye protectionGlovesMarker pen for writing on slides

Step 2. After melting, cover the mannitewith a cover glass and place theslide on a ceramic bread-and-butter plate that has been chilled ina refrigerator. Permit the liquidmannite to crystallize.

Step 3. Observe the sample with a micro-projector. Note the size, shape,number, and boundaries of thecrystals.

Step 4. Prepare a second slide, but place itimmediately on the microprojectorstage. Permit the mannite to coolslowly. Again, observe the size,shape, and boundaries of thecrystals. Mark and save the twoslides for comparison using studentmicroscopes. Forty power is

ufficient for comparison. Have thestudents make sketches of thecrystals on the two slides and labelthem by cooling rate.

Observations of Salol

Step 5. Repeat the procedure for mannite(steps 1-4) with the salol, but donot use glass cover slips. Use adesktop coffee cup warmer to meltthe salol. It may be necessary toadd a seed crystal to the liquid oneach slide to start the crystalliza-tion. Use a spatula to carry theseed to the salol. If the seedmelts, wait a moment and try againwhen the liquid is a bit cooler. (Ifthe microprojector you use doesnot have heat filters, the heat fromthe lamp may remelt the salolbefore crystallization is completed.The chemical thymol (C1oH140)may be substituted for the salol.Avoid breathing its vapors. Do notsubstitute thymol for salol if studentmicroscopes are used.)

Step 6. Prepare a new salol slide and placeit on the microprojector stage.Drop a tiny seed crystal into themelt and observe the solid-liquidinterface.

Step 7. Remelt the salol on the slide andsprinkle a tiny amount of BismarckBrown on the melt. Drop a seedcrystal into the melt and observethe motion of the Bismarck Browngranules. The granules will makethe movements of the liquid visible.Pay close attention to the granulesnear the growing edges and pointsof the salol crystals. How is theliquid moving?

NOTES ON CHEMICALS USED:

Bismarck Brown YBismarck Brown is a stain used todye bone specimens for microscopeslides. Because Bismarck Brown isa stain, avoid getting it on yourfingers. Bismarck Brown is watersolulable.

Mannite (d-Mannitol)HOCH2(CHOH)4CH2OHMannite has a melting point ofapproximately 168° C. It may beharmful if inhaled or swallowed.Wear eye protection and gloveswhen handling this chemical. Con-duct the experiment in a well venti-lated area.

Salol (Phenyl Salicylate)C13H1003

It has a melting point of 43° C. Itmay irritate eyes. Wear eye protec-tion.

QUESTIONS:

1. What happens to crystals when they begingrowing from multiple nuclei?

2. Are there any differences in crystals thatform from a melt that has cooled rapidlyand from one that has cooled slowly?What are those differences?

3. What happens to the resulting crystalswhen impurities exist in the melt?

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4. What caused the circulation patterns ofthe liquid around the growing crystalfaces? Do you think these circulationpatterns affect the atomic arrangementsof the crystals?

5. How do you think the growth of thecrystals would be affected by growingthem in microgravity?

FOR FURTHER RESEARCH:

1. Design a crystal growing experiment thatcould be flown in space. The experi-ment should be self-contained and theonly astronaut involvement that of turn-ing on and off a switch.

2. Design a crystal growing experiment forspace flight that requires astronautobservations and interpretations.

3. Research previous crystal growing ex-periments in space and some of thepotential benefits researchers expectfrom space-grown crystals.

Because of the higher temperaturesinvolved, the mannite slides should beprepared by the teacher. !f you wish,you may process the mannite slides athome in an oven. By doing so, you willeliminate the need for a hotplate. Markthe two prepared slides by cooling rate.Obtain the smallest quantities availablefrom chemical supply houses.

Sample Microscope SketchesMannite Crystallization

Slow Cooling 5 Fast Cooling

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GlossaryAcceleration - The rate at which an object'svelocity changes with time.

Buoyancy-Driven Convection - Convec-tion created by the difference in densitybetween two or more fluids in a gravitationalfield.

Convection - Energy and/or mass transferin a fluid by means of bulk motion of thefluid.

Diffusion - Intermixing of atoms and/ormolecules in solids, liquids, and gases dueto a difference in composition.

Drop Tower Research facility that createsa microgravity environment by permittingexperiments to free fall through an enclosedvertical tube.

Exothermic - Releasing heat.

Fluid - Anything that flows (liquid or gas).

Free Fall - Falling in a gravitational fieldwhere the acceleration is the same as thatdue to gravity alone.

G Universal Gravitational Constant(6.67X10-11 Nm2/kg2)

g The acceleration Earth's gravitationalfield exerts on objects at Earth's surface.(approximately 9.8 meters per secondsquared)

Gravitation - The attraction of objects dueto their masses.

Inertia - A property of matter that causes itto resist changes in velocity.

Law of Universal Gravitation - A lawstating t; clt every mass in the universeattracts every other mass with a force pro-portional to the product of their masses andinversely proportional to the square of thedistances between their centers.

Microgravity (pg) An environment thatimparts to an object a net acceleration thatis small compared with that produced byEarth at its surface.

Parabolic Flight Path - The flight pathfollowed by airplanes in creating a micro-gravity environment (the shape of a pa-rabola).

Skylab - NASA's first orbital laboratory thatwas operated in 1973 and 1974.

Space Station Freedom NASA's interna-tional space station planned for operation bythe end of the 1990's.

Spacelab - A scientific laboratory developedby the European Space Agency that iscarried into Earth orbit in the Space Shuttle'spayload bay.

Microgravity References

(1981), Combustion Experiments in aZero-gravity Laboratory, American Insti-tute of Aeronautics and Astronautics,New York.

(1988), "Mastering Microgravity,"Space World, v7n295, p4.

(1989), Chemistry: "Making Bigger,Better Crystals," Science News,v136n22, p349.

(1989), "Making Plastics in Galileo'sShadow," Science News, v136n18,p286.

, (1992), "Can You Carry Your CoffeeInto Orbit?," USRA Quarterly, Winter-Spring 1992.

Chandler, D., (1991), "Weightlessness andMicrogravity," Physics Teacher, v29n5,pp312-313.

Cornia, R., (1991), "The Science of Flames,"The Science Teacher, v58n8, pp43-45.

Faraday, M., (1988), The Chemical Historyof a Candle, Chicago Review Press.

Frazer, L., (1991), "Can People Survive inSpace?," Ad Astra, v3n8, pp14-18.

Froehlich, W., (1982), Spacelab, EP-165,National Aeronautics and Space Admin-istration, Washington.

Halliday, D. & Resnick, R., (1988), Funda-mentals of Physics, John Wiley & Sons,New York.

Howard, B., (1991), "The Light Stuff," Omni,v14n2, pp50-54.

51

Lyons, J., (1985), Fire, Scientific AmericanPublishers, Inc., Chapter 2.

NASA, (1976 - ), Spinoff , National Aeronau-tics and Space Administration, Washing-ton (annual publication).

NASA, (1988), Science in Orbit TheShuttle and Spacelab Experience: 1981-1986, NASA Marshall Space FlightCenter, Huntsville, AL.

Naumann, R. & Herring, H., (1980), Materi-als Processing In Space: Early Experi-ments, Scientific and Technical Informa-tion Branch, National Aeronautics andSpace Administration, Washington.

Noland, D., (1990), "Zero-G Blues," Dis-cover, vil n5, pp74-80.

NASA, (1991,, "International MicrogravityLaboratory-1, MW 010/12-91," FlightCrew Operations Directorate, NASAJohnson Space Center, Houston, TX.

NASA, (1992), "Mission Highlights STS-42,"MHL 010/2-92, Flight Crew OperationsDirectorate, NASA Johnson SpaceCenter, Houston, TX.

NASA, (1991), "United States MicrogravityLaboratory-1, MW 013/6-92," Flight CrewOperations Directorate, NASA JohnsonSpace Center, Houston, TX.

NASA, (1992), "Mission Highlights STS-50,"MHL 013/7-92, Flight Crew OperationsDirectorate, NASA Johnson SpaceCenter, Houston, TX.

Pool, R., (1989), "Zero Gravity ProducesWeighty Improvements," Science,v246n4930, p580.

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NASA Educational Resources

NASA Space link: An Electronic Information System

NASA Space link is a computer information service that individuals may access to receive

news about current NASA programs, activities, and other space-related information, historicaldata, current news, lesson plans, classroom activities, and even entire publications. Althoughit is primarily intended as a resource for teachers, the network is available to anyone with a

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Users need a computer, modem, communications software, and a long-distance telephoneline to access Space link. The Space link computer access number is (205) 895-0028. Thedata word format is 8 bits, no parity, and 1 stop bit. For more information, contact:

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NASA Space link is also available through the Internet, a worldwide computer network con-

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Microgravity - Teachers Guide With Activities - Secondary Level

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2. The procedures for the activities have sufficient information and are easily understood.

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