NASA FACTS Explorer XIX the Air Density Satellite

8/8/2019 NASA FACTS Explorer XIX the Air Density Satellite

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AAn Educational Services Publication of the

National Aeronautics and Space AdministrationPage

Source of AcquisibonEXPLORER X X I NASA co n t r ac to r~~ran t eeTHE AIR SATELLITE

The 12-foot diameter Explorer XIX is inflation tested. At upper left of sphere are solar cellsthat convert sunlight to electricity for powering the satellite's radio transmitter.

THE EARTH'S ATMOSPHEREExplorer XIX i s one of a series of satellitesdesigned to increase knowledge about a ir den- The earth i s surrounded by a vast oceasities a t altitudes above a hundred miles. Such of air called the atmosphere. The air i s a miinformation is important not only for the ad- ture of oxygen, nitrogen, water vapor, heliumvancement of science but also in predicting the hydrogen, and other gases.influence of the thin air a t these altitudes on Scientists once believed that the atmospacecraft motion. phere stopped at about 100,000 feet abov


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Page 2 NASA FACTS VOL. 11-2

Artist's conception of Explorer XIX in orbit. Cutaway shows locations of radio trackingbeacon and batteries that are attached to inside surface of the sphere. The insulating banddivides the satellite into two metallic sections that serve as transmitting antennas.

earth because conventional aircraft controlswere ineffective beyond that height. Since theadvent of the Space Age, they have learned thatthe atmosphere extends many thousands of milesinto space. Some scientists contend that theatmosphere continues to the outer edge ofearth's magnetic field. This edge i s no closerthan 40,000 miles to earth's surface.

About 99 percent of the air in the atmos-phere is concentrated in the first 20 miles aboveearth. Some scientists suggest that the upperatmosphere begins at the 20-mile altitude.Others set its beginning at higher altitudes.

Satellite measurements have indicated thesparseness o f air in the upper atmosphere. Asan example, one calculation der ived from sat-ellite data is that the air at earth's surface i s

trillion times denser than at an altitude of

UPPER ATMOSPHERE DENSlTW VARlESThe density of air dwindles with increasing

altitude. Upper atmosphere density has beenfound to vary also from day to day and day tonight. The density over one geographic regionmay differ from that above another. There arealso fluctuations during the 27-day period inwhich the sun makes a complete rotation on itsaxis. Abrupt increases in air density havebeen observed to follow solar flares-suddenoutbursts of matter from the sun.

Air density also fluctuates with the solarcycle. The cycle i s a period of about 1 1 yearsduring which solar activity, as evidenced by thefrequency and magnitude of sunspots, sflares, and other eruptions, starts at a maximdeclines to a minimum, and then again rises toa maximum.


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NASA FACTS VOL. 11-2 Page 3

Technicians make final check of Explorer XIX payloa d which i s mountedon fourth stage of Scout launch vehicle.

Scientists theorize that increased solaractivity warms the upper atmosphere and thatas the atmosphere warms, it swells and liftsdenser layers to higher altitudes. As the sunquiets down, the upper atmosphere cools andcontracts, becoming less dense at any altitude.

DESCRIPTION O F EXPLORER XIXExplorer XIX is essentially a 12 -foo t diam-

eter inflated sphere weighing about 17 pounds.Because it i s so large and so light in weight, iti s markedly affected even by the sparse airatoms and molecules of the upper atmosphere.Scientists calculate air density in the satellite'spath by comparing the spacecraft's orbit w ith atheoretical orbi t based upon the absence of air.

Explorer XIX i s constructed of a four-plylaminate, consisting of alternating layers of

-mil-thick polyester plastic film and '/2-mil-thickinum foil. The aluminum foil forms the

ou ts~de urface; an d the plastic, the inside sur-face. (A mil i s one-thousandth of an inch.)

White circles (resembling polka dots)painted on the satellite's outer surface contributeto temperature balance by absorbing less of thesun's heat than the aluminum skin. Temperaturebalance i s required for operation of the space-craft's electronic equipment.

Moun ted inside of the satellite i s a smallradio that transmits a tracking signal. Its poweri s supplied by a rechargeable storage batterywithin the sphere and a bank of solar cells onthe satellite's outer surface. Solar cells convertsunlight to electricity. They contain silicon, amaterial that emits electrons when struck bylight. The electrons are channeled into wiresand, thus harnessed, become an electric current.

EXPERIMENT DESCRIPTIONA principal purpose of the Explorer XIX

experiment i s to extend measurements of airdensity in the upper atmosphere to the polarregions. Prior experiments have furnishedmeasurements of the atmosphere over otherareas of earth. The various measurements


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Page4 NASA FACTS VOL. 11-2permit.comparison of densities and temperatureso f the upper atmosphere over different latitudesof earth.1 Another goal i s t o learn more about thecontributions of energetic particles and ultra-violet light to heating and, consequently, densityof the upper atmosphere. Energetic particlesare electrified constituents of atoms such as pro-tons and electrons. Bands of these particlesthat have been trapped in earth's magnetic fieldand surround the globe are called the Van AllenRadiation Region.

Ultraviolet radiation i s part of a familycalled the electromagnetic spectrum. Amongthe other members of this family are X-rays,radio waves, and visible light. Most of theultraviolet radiation streaming to earth i s ab-sorbed by earth's atmosphere. For a longtime, scientists believed that ult rav iole t rayswere chiefly responsible for heating of the upperatmosphere. ,.

In recent years, however, many scientistshave theorized that energetic particles may alsplay a major role in heating of the upper atmos-phere. To help determine how the atmospherereacts to such particles, scientists are comparingdata on atmospheric density provided by Ex-plorer XIX as it passed over polar regions withinformation from Explorer IX as it orbited overareas closer to the equator. The Explorer IXsatellite, launched February 16, 1961, is similart o Explorer XIX. It burned up during re-entryon April 9, 1964.

The polar areas were chosen for study oftemperature variations due t o particles becauseenergetic particles penetrate the atmosphereover these areas more deeply than they doregions closer to the equator. This stems fromthe fact that the lines of force of earth's mag-netic field tend to become near ly vertical, insteadof horizontal, a t the poles. As a result, theRight of energetic particles to earth i s not barred

Folding of a 12-foot diameter Air Density Explorer satellite. After folding, technicians willpack it in a metal cylinder 9 inches in diameter and 1 9 inches long to be launched intoEarth orbit by a Scout launch vehicle.


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NASA FACTS VOL. 11-2 Page 5as effectively over the poles as over other areas.

The lines of force of earth's magnetic fieldcan be visualized on a small scale by sprinklingiro n fil ings around a bar magnet. Note howthe iro n filings, which fol low the magnet's linesof force, curve inward at both ends, o r poles ofthe bar magnet.

LAUNCH AND ORBITAL INFORMATIONExplorer XIX was orbited by a Scout launch

vehicle which was fired from Point Arguello,California, on December 19, 1963. Initially,the satellite's apogee (highest altitude) wasalmost 1490 miles; its perigee (lowest altitude),about 368 miles; and its period (time for onerevolution about the earth), approximately 116minutes.

At launch, Explorer XIX was folded andpacked inside a metal cylinder 8'/2 inches indiameter and 1 9 inches long. In orbit, com-pressed nitrogen gas pushed the sphere from itscontainer and inflated it to a 12-f oot diameter.

The orbit of Explorer XIX swings as farnorth as Thule, Greenland, an d as far south asthe Antarctic continent, enabling the satellite tocover most of the globe. Explorer XIX i s beingtracked b y NASA radio tracking stations and bythe sensitive telescopic cameras of the world-wide Baker-Nunn network, which i s operated bythe Smithsonian Astrophysical Observatory.

I Q S YI N T E R N A T I O N A L Q U IE T S U N Y EA R

On January 1, 1964, scientists of many nationsinaugurate d a two -yea r cooperative study of the suncalled IQSY for I nte rna tion al Quie t Sun Years. Theprog ram is a sequel to the IGY, or I nter natio nal Geo-physical Years, a study of th e ea rth a nd space con-ducted b y w orld scientists in 1957 an d 1958.

The somew hat incongruous term &$q uietun" has itsorigin i n observations made dur ing m any years whichindicated, as note d previously, th at the tem po of solaractivity follows a cycle of roughly 11 years, beginningat peak solar activi ty, drop ping to a low, and risingagain to a maximum.

IQSY is being conducted during the time of min-imum solar activi ty when the sun is relative ly free of

Scout launch vehicle rockets Explorer XIX from Point Arguello, solar flares, sunspots, and other eruptions. DuringCalifornia.


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Page 6 NASA FACTS VOL. 11-2I C Y , the sun was i n the most active tim e of i ts cycleof activity.

A major goal of lQSY is to compare its observa-tions with those of IGY. Such comparisons and other

; IQSY studies are e xpected Po yield increased under-standing of h ow the sun behaves and how it governsnatural events on and near earth.

The majo r NASA effo rt supp ortin g U.S. part icipa -tion in IQSY will be the launching of a series of Pioneerspacecraft on long-duration missions during which theywill cover millions of miles of interplanetary space.

The spacecraft mon itors solar r adia tion an d mag-netic fields at wide ly separated points in space. Theirexperiments are designed to provide basic data on theinterplanetary environment and measure solar effectsupon the environment.

Data Prom NASA scientific s atellites and soundingrockets are already contributing inform ation relatin gt o the IQSY. Amo ng such satellites are Explore r XIX(described in Phis NASA FACTS) an d Exp lore r XVIIB, #hefirst of a series of InterplanePary Explorer Satellites.(See NASA FACTS-BnterpBanetary Explo rer Satellites.)

Deflated and folded Explorer XIX is care fully fitted inside the metal container in which it willride into orbit.

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NASA FACTS Explorer XIX the Air Density Satellite

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