NASA Facts Fire 1 the Reentry Heating Spacecraft

8/7/2019 NASA Facts Fire 1 the Reentry Heating Spacecraft

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PageNASA FACTSAn Educational Services Publication of the

National Aeronautics and Space AdministrationVol. II, No. 11

THE REENTRY FIRE IHEATINGN65 - 21 92 9&-dc.-lSPACECRAFTOczt=- ~ /~ ! ' = I I ! !

NASA's FIRE I Spacecraft successfully reentered the earth's a tmosphere an April 14, 1964, and t ransmit ted much valuable daabout the extremely hot gas ca p of environmental ai r with which future spacecraft will have to contend upo n returning to ear

from space missions. A second launching Is planned .

A spacecraft returning to earth at superorb ita l speed encounters the same phenomenonas natural meteors. Appearing as a fireball,th e phenomenon is the result of the impact ofthe reentry body on the atmosphere an d thereaction of the atmosphere on the reentry body.

At the fringe of the earth's atmosphere theair molecules are very far apart, but when theyare disturbed by the passage of a high speed reentry body the molecules pile up and form adense cloud of excited atoms that envelop thebody and leave a brill iant visible trail behind.T.hus, the spacecraft has created a very unusualenvironment, wh ich is often referred to as a hotgas cap, where temperatures are many timeshigher than can be contained in almost any ofearth's furnaces. The environment moves withthe spacecraft at high speed and envelops thespacecraft as a furnace would envelop a laboratory model spacecraft.

FIRE SPACECRAFT DESIGN PROBLEMSThe first pro.blem in design of the FIRE

spacecraft was to find a way to reproduce thetypical reentry environment of spacecraft re-

turning from the moon . The reentry speewould be about 37,000 feet pe r second, whicmeans penetrating 7 miles of atmosphere eacsecond . The angle of approach would beshallow 15 degrees slope below horizontalThe altitude where the env ironment reactiowould start to become noticeable would baround 400,000 feet which is about 75 milehigh.

The second problem was to design sensorand measurement systems for the spacecraft anprotect them from the severe reentry environment. Temperatures would be measured boton-board the spacecraft and in t he surroundinhot gas cap. Spectrograph ic measurements tdetermine the species of excited atoms of air ithe gas ca p would be attempted . Envi ronmental air pressure would be measured. Antenna power losses due to the surrounding hogas sheath would be measured . Other performance sensors such as t imer sequences, orientation gyros and internal pressures and temperatures would have to be incorpora ted . An d , thentire spacecra ft would have to be designed arounthe sensors and measurement systems in a wa


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Page 2,to insure proper performance and provide ample

' protection.The third problem was to find a way to g e

the measured data away from the spacecraft andback to the earth stations along the test range.The severe reentry environment would preventdirect radio transmission of the real time databecause of th e black-out effects of the hot gascap . Recovery of the spacecraft and storeddata after splash impact in the Atlantic Oceanwould not be feasible because of excessive additional costs.

Final design of the FIRE I spacecraft grewout of these requirements and from the solutionof these problems.

Looking down a t th e Project Fire booster and payload a tCape Kennedy. Th e heat shield protects, and here concealsf rom view, th e payload (velocity package and reen t ry body) .Th e shroud will be je t t isoned in flight, after the payload ha s

risen safely above the bulk of the atmosphere.

NASA FACTS Vol. II, No . 11LAUNCH VEHICLE

The function of the Fire launch vehicle is toboost the spacecraft into a high ballistic coasting trajectory allowing plenty of room above theearth for the final thrust back into the atmosphere, reaching the high velocity before reentry.The payload does not go into orbit. The dis-tance from launch point at Cape Kennedy to"splash point" in the South Atlantic ocean isover 5,200 miles. The highest alt itude is 520miles which it reaches in a little less than 16minutes after launch. The f l ight sequence isshown in the illustration "Trajectory and FlightSequence. "

The launch vehicle is the li quid fueledAtlas 0, 66 feet tall, with a thrust equ iva lent tothe power of more than 200 of the most powerfu l diesel locomotives .

SPACECRAFT (VELOCITY PACKAGE)The spacecraft starts out as a two-ton pay

load which consists of tw o major parts-a velocity package (illustrated as it appears inside thetwo-piece heat shroud), and a reentry package.Th e pay load includes the velocity package and t he reentry

package, shawn here as enclosed in th e heat shroud .

CLAMSHELLHEAT SHROUD(JETTISONEDAFTER ATLASCUTOFF)

~ ~ i 1 t \ / VE LOC ITY PACK AGE SHELL

VELOCITY PACKAGEADAPTER(MECHANI CALLYSECURES ATLAS TOy.p. UNTIL ATLASIS JETTISO NED)


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NASA FACTS Vol. II, No. 11The velocity package contains a large solid

fuel rocket, the Antares, and a highly sophisticated guidance and control system used fo rstabilizing and aiming the spacecraft fo r thefinal thrust back into the atmosphere.

The reentry package contains a complexarrangement of experimental instruments, batteries, an d telemetry transmitters.

FLIGHT SEQUENCEThe function of the Atlas launch vehicle is

to boost the spacecraft an d guide it into thecorrect coasting ballistic trajectory where theAntares rocket can accelerate the reentry packag e to maximum velocity before starting thereentry experiment. The reentry package mustreach a velocity of 37,000 feet per second(about 25,000 MPH) by the time it descends to400,000 feet altitude where it must be headed15 below horizontal.

The "f l ight sequence" is portrayed in theaccompanying diagram starting with l ift-off (1)and booster engine separation (2).

About six minutes after lift-off, the Atlassustainer engine shuts off (3), and the two-pieceshroud that protects the reentry package fromatmospheric friction drops away (4), followed

Page 3by vernier cut-off (5) and spacecraft separation(6). For the next 20 minutes the spacecrafcoasts, while the inertial guidance system of thevelocity package and a set of gas jets keep iaimed (7) in the proper position fo r reentry.

About 26 minutes after launch, the spacecraft, still holding the proper attitude, goesthrough its final maneuvers. The entire spacecraft is spun-up (8) to stabilize the reentry package at 180 RPM.

Next, the velocity package separates (9and th e Antares rocket ignites (10) and carriesthe reentry package through burnout (11) andseparation (12). To do this, the Antares rockeconsumes its 2,550 pounds of solid fuel in abou33 seconds, increasing the velocity of the spacecraft by 17,000 feet per second.

Finally, the reentry package separates itselfrom the Antares rocket which is slowed down bytumble rockets (13) so as not to collide with thereentry package during the experimental period

The reentry package quickly encountersenough atmosphere to heat up. The heatingrate is very high, reaching a peak a few secondsbefore maximum dynamic air pressure brakes thespeed at a maximum deceleration load of abou78 g's. The "heat pulse" lasts fo r about one

Trajectory ond flight sequence.

@SPIN -UP 1574sec/4601mi.t l P ' rrJ-A::.~ ~ ~ ~ SPACECRAFT SEPARATION 308.3sec/486mi.Q)ORIENTATION 319 .3sec/535mi .

~ SUSTAINER ENGINE CUTOFF4 SHROUD SEPARATION

5 VERNI ER CUTOFF

VELOCITY PACKAGE SHELL JETTISON 1577sec/4613mi.@X259 MOTOR IGNITION 1580.2sec/4624mi.@ THRUST=ZERO AT 1640.2sec/4958mi .X259 BURNOUT All. 452,458 ft. REENTRY PACKAGE~ .. . SEPARATION Vel. 25,426mph

~ ~ ce:;rnNOTE

CONDITIONS REQUIRED FOR FIRE 1NASA EXPERIMENTS(@TUMBLE ROCKET IGNITION 1646.2sec/4995mi. ',\ "

(D BOOSTER ENGINE CUTOFFLIFTOFF

ALTITUDE 400,OOOFTVELOCITY 25,227 mphREENTRY ANGLE 15(REF HORIZONTAL)\\ ~

"SPLASH" 1972sec/5234 mi. ~


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Page 4

FOREBODY

NASA FACTS Vol. II, No. 11

AFTERBODY (66 0 CONE)r AFTERBODY OPTICAL WINDOW

C-BAND ANTENNAI r X COOLER ASSEMBLY~ / REENTRY PACKAGE~ SEPARATION, SYSTEM(PUSHESREENTRYPACKAGE

AWAY FROMVELOCITYPACKAGE)

c:j N D ANTENNAReentry package (cross section).

minute. Getting exact measurements duringhis heat pulse is the primary objective of theexperiment.

It is fitting now to examine the reentrypackage in some detail to see how this and theother objectives of the experiment are achieved.

REENTRY PACKAGEThe reentry package, with its spherical

front surface and conical afterbody, is about26 1/2 inches in diameter by 21 inches long, andweighs about 220 pounds. Its shape is similaro that of the Apollo spacecraft which must passthrough a similar environment when it returnsfrom a moon trip.

The reentry package is tightly packed withinstruments: thermocouples, radiometers, signalconditioners , sequence timers, tape recorder,batteries, two radio transmitters, a tracking bea-con, and a refrigerator to maintain normal temperatures fo r the electronic components includedin this equipment.

HEAT SENSORSThe front of th e reentry package is of

" layer cake" construction, composed of sixlayers.

The first, third, and fifth layers are solidberyllium, instrumented with thermocouples (elec-trical thermometers). Each beryll ium layer withits thermocouples constitutes a calorimeter-anapparatus that measures the amoun t of heatabsorbed from the fiery hot ga s cap out in front.

The first calorimeter takes measurements atthe start of the heat pulse until the temperaturerises so fast that the beryllium me l ts away.Then a Jayer of phenolic asbestos protects thesecond calorimeter fo r a fe w seconds so that itsmeasurements will be taken near the peak of theheat pulse. The third calorimeter is like w iseprotected for a few seconds and then takesmeasurements near the end of the pulse beforethe heating rate returns to normal.

These three data periods, each of a fewseconds duration, help to define the heat pulse.


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-- ~ - - ' - ~NASA FACTS Vol. II, No. 11 Page

4) . .. .o .'...: " ' . !AFTER DATA yBODY PACKAGE CALORIMETERS AND HEAT SHIELDS

Reentry package befare assembly, shawing calarimeters an d heat shields .

The protective layers of phenolic asbestosare also instrumented to record the temperaturedifferences an d there are other thermocoupleson the afterbody and inside the reentry package.All told, the reentry package contains 258thermocouples.

HEATING EFFECTS OF THE GAS GAPThe reentry package has a blunt face. A

it speeds into the atmosphere it heats up quicklas the gaseous air directly in front is compressedThe compressed ai r is known as a gas cap an d thcenter of the gas ca p is known as the stag

This exploded view of the reentry packoge shows th e three main assemblies and instrumentation.

FMMULTIPLEXER

TIME CODEGENERATOR

REAL SPECTRALTIME TOTALTRANS- RADIOMETER

DELAY MITTERTRANSMITTER

THERMOCOUPLES

OUTER BERYLLIUMHEAT SHIELD

- ---- - -- --- ---


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Page 6nation point. At th e reentry speed o f 38,000fps. the gas cap becomes brilliantly incandescent,s:eaching a stagnation temperature of about20,000 degrees F. Much of the heating of thef ront face is due to convective heat transferfrom the hot gas cap to th e beryll ium calorimeter. Additional heat is transferred into thecalorimeter by direct radiat ion from the incandescent gas cap. The calorimeter thereforemeasures the total heating it receives from bothsources. Other instru ments, th e radiometers,determine how much o f the heating it receivesis du e to radiation.

STAGNATIONREGION

Stagnat ion region in gas cap.

MEASURING THE HOT GAS CAPOne important question that Project Fire is

to clear up is this: What part of theotal heat transferred to the spacecraft is at

radiation from the hot gasap and what part is convective heating? To

answer this question, the reentry package isequipped with special instruments called radiometers that directly measure the radiant heat.

he difference between the radiant heat andhe total heat will be th e amount attributable toconvective heating.

The radiometers are located inside the re-entry package an d " look" out through smallglass windows of fused quartz. One looks atthe gas cap stagnation area, another looks atthe hot ga s near the shoulder of the reentrypackage, and a third looks out th e side wherethe gas forms a sheath.

All three radiometers measure the amounto f radiant heat energy they see at their respective look angles. In addition, the stagnationpoint radiometer contains a spectrometer which

~ --NASA FACTS Vol. II, No. 11breaks apart the wavelengths of l ight energybetween 2000 and 6000 angstrom s fo r detailedstudy of the molecular species to be found inth e hot ga s cap.

TELEMETRYThe reentry package contains two radio

telemetry systems to insure reception of themeasurement data by stations on the earth'ssurface. One telemeter broadcasts th e eventsas they occur in " rea l t ime" and the otherbroadcasts in delayed time. The latter is ac-complished by using a tape recorder whichstores 45 seconds worth of data before playback on the broadcast channel. This meansthat when the reentry package is in the "blackout" period caused by th e hot gas cap, themeasurement data is stored on tape for rebroadcast. After emergence from black out, the realtime telemeter is also switched to the tape sothat both channels will relay the play back of theheating data. There is t ime before splash fo rthis recording to be played 5 or 6 times to makeit possible for each of the receiving stations toget at least one good copy.

GROUND TRACKING ANDDATA ACQUISITION

To be certain of receiving the vital recording of data from the experiment during reentry,the spacecraft is tracked all of the way from thelaunch pad to the peak of its trajectory and backdown to the reentry point. The tracking is accomplished chiefly by use of an on board C-band radar transponder, which transmits a recognition signal to each ground based radar stationinvolved. The tracking network extends fromCape Kennedy, along the West Indies, to Ascension Island.

Radar tracking of the spacecraft allows eachof the telemetry stations in the reentry area tobeam their receivers in th e precise directionnecessary to "hear" the spacecraft broadcast theplayback data.

The radar tracking also helps a number ofstations to aim optical instruments in the precisedirection necessary to obtain photographic coverage of the reentry events. Ballistic camerasat Ascension get lapse-time pictures of the flre-


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NASA FACTS Vol. II, No. 11"ball against the known star background. Thein formation is used to calculate exact posit ion ofthe spacecraft a number of tim es durin g the re -entry phase. Specia l movie cameras obtainevents pictures whic h indicate the separationtimes of the several heat shie lds. Streak cam -eras giv ea composite picture of the severa l fiery pathsmadebythe spacecraft ,spent booster andany debris th at could be present.

Most im portantof the opticalgroundbasedinstruments is the tele spe ctr ograph located atAscens ion Island . It consis ts of a 36-inch re-flecting telescope having a spectroscope andcamera attached on a servo-electr ic mount allweighing about 22 tons. As a back-up for th espectral radiometer on board the spacecraft , th etelespectrograph photographs the spectrum ofli ght from the hot gas cap for identific atio n ofit s mole cular spec ie s .

- - - - - - -Page7HOW THE FIRE I SPACECRAFT PERFORMED

The Fire I spacecraft was launched at4:4 2p.m. EST on April 14, 1964 f rom Pad 12 atCape Kennedy, F la . The Atlas booster per-formance was excellent. The spacecraft, in -cluding velocity package, separated smoothlyand re oriented it self pro perl y. The Antaresmoto r provided addit io nal thrust to reach a ve-lo city of 37,890 feet per second at the start ofthe reentry phase. The re entr y anglewas 14.5 below hori zontal.

The reen try package performance wasvery good. Timer functions and heat sh ie ld eiections worked properly.

Measurement th erm ocouple s, quartz windows and radiometers perfo rmed as expected.All data were recorded on the dela y tape re-corder. Minor malfunctions that occurred wereloss of some of the gyro s and a periodic fade-

Opti ca l spectr ograph onAsce ns ion Is la nd . The in st rument is equip pedwith a 36in choptic al telescopecoupled to a very sensi -

ti ve spectro graphto observe andanalyze chemicalconsti tue nts in the hotgaseous re gion surro undin g th e spacecraftduring reentr y .

It is manuallyoperated and is st eere d incor re ct posi tion by radar to locate th e spacecr af t.

--- ------


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Page 8out of the delay-time transmitter which resultedin a partial loss of data at the receiving stations.Also, the burned ou t velocity package apparently passed th e reentry package sufficiently closeduring peak heating to cause a severe wobbleIn the reentry package.

A substantial amount, 60%, of useful datawas obtained. When evaluated by scientistsan d engineers, the new facts about the reentryheating environment will represent a significantadvance in reentry technology and spacecraftdes ign.

Cape Kennedy, Flor ida-Projec t Fire reentry spacecraf t packag e being mated to the Antares rocket motor . An Atlas-Dlaunch vehicle will place th e pay load in a ballistic path. TheAntares mator adds the speed ne e de d to drive the reentrypay load back in to the a tmosphere a t 25,000 MP H . Primepurpose fo r th e mission is to obtain direct measuremen t s ofreent ry hea t ing , similar to a reent ry af te r a l unar journey.

NASA FACTS fo rmat Is des igned fo r bullet in-board displayuncut or fo r 8 x lO Y, l oose leaf no tebook Inser t ion whencut along dot ted l ines an d folded along solid lines . Fo rnotebook r ing In ser t ion , punch a t solid dots in th e margins.

NASA FACTS Vol. II, No. 11

DEFINITIONS(From NASA's Short Glossary of Space Terms)

Ablat ion: the removal of surface material from a body by vaporization, melting or other process .

Angstrom: a unit of length, used chiefly in expressing shortwavelengths . Ten billion angstroms equal one meter.

Ballistic t rajectory: the trajectory followed by a body beingacted upon only by gravitational forces an d resistance of themedium through which it posses.

Infrared: by " infrared radiation" scientists refer to electromagnetic radiation in the wavelength interval from the red endof the visible spectrum on the lower limit to microwaves usedin radar on the upper limit.

Ion: on atom or mole cu lar ly bound group of atoms having onelectr ic charge , a free electron, or other charged su batom icparticle .

Plasma: on electrically conductive gas composed of neutral particles, ionized particles, and free electrons but which token asa whole is electronically neutral.

Reentry: th e event occuring when a spacecraft or other objectcomeS bock in to the sensible atmosphere after being rocketedto altitudes above the sensible atmosphe re; the ac t ion involvedin this event.

Spectrum: 1 . In phys ics, any series of energies arranged according to wavelength (o r frequency); spe c ifically, the series ofimages produced when a beam of radiant energy, such assunlight, is d ispersed by a prism or a reflecting grating . 2.Short for "e lectromagnetic spectrum " or for an y port of itused for a specific purpose a s the " radio spectrum" (1 0 kilocycles to 300,000 megacycles).

Stage-and-a-half : a liquid-rocket propulsion unit of which onlyport falls away from the rocket vehicle during flight, as in thecase of booster rockets falling away to leave the sustoinerengine to co nsume remaining fuel.

Telemetry: the science of measuring a quantity or quantities,transmitting the measured value to a distant station, and thereinterpreting, in d icating, or recording the quantities measured.

Ultraviolet radiat ion: electromagnetic radiation sh orter inwavelength than visible radiation bu t longer than X-rays;roughly, rad ia tion in the wavelength interval between 10 and4000 angstroms .

NASA FACTS Is an educat ional publicat ion of NASA's Educational Programs a nd Services Office. It will be mailedto addressees who request it from: NASA, Educational Publications Distribution, AFEE-l, Washington, D.C., 20546.

U. S. GOVERNMENT PRINTING OFFICE : 1965 OF-766-185

for sale by the Superintendent of Docume nts, U.S. Government Printing OfficeWashington, D.C. , 20402 - Price 15 cents per copy

NASA Facts Fire 1 the Reentry Heating Spacecraft

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