NASA Facts Explorer XIX, The Air Density Satellite NASA Facts, Vol. II-2

8/6/2019 NASA Facts Explorer XIX, The Air Density Satellite NASA Facts, Vol. II-2

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NASA FACT SAn Educational Services Publication of the

National Aeronautics and Space AdministrationEXPLORER XIX

THE AIR DENSITY SATELLITE

N 64 27069w.--

The 12-foot diameter Explorer XIX is inflation tested . At upper le f t of sphere are solar ce llsthat convert sunlight to electricity for powering the satellite 's radio transmitter .

THE EARTH'S ATMOSPHERE

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Explorer XIX is one of a series of satellitesdesigned to increase knowledge about air densities at altitudes above a hundrec;l miles. Suchinformation is important not only fo r the advancement of science but also in predicting theinfluence of the thin air at these altitudes onspacecraft motion .

The earth is surrounded by a vast oceaof air called the atmosphere. The air is a mixture of oxygen, nitrogen, water vapor, heliumhydrogen, and other gases.

Scientists once believed that the atmosphere stopped at about 100,000 feet above


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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 is no closerthan 40,000 miles to earth ' s surface.

About 99 percent of the air in the atmosphere 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 of air in the upper atmosphere. Asan example, on e calculation derived from satellite data is that the air at earth's surface is40 trillion times denser than at an altitude of400 miles.

UPPER ATMOSPHERE DENSITY VARIESThe 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 is a period of about 1 1 yearsduring which solar activity, as evidenced by thefrequency and magnitude of sunspots, solarflares, and other eruptions, starts at a maximum,declines to a minimum, and then again rises toa maximum.


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NASA FACTS VOL . 11-2 Page 3

Technicians make final ch eck of Explorer XIX payload wh i ch is 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 an y altitude.

DESCRIPTION OF EXPLORER XIXExplorer XIX is essentially a 12-foot diam

eter inAated sphere weighing about 17 pounds.Because it is so large and so l ight in weight, itis markedly affected even by the sparse ai ratoms and molecules of the upper atmosphere.Scientists calculate air density in the satelli!e'spath by comparing the spacecraft ' s orbit with atheoretical orbit based upon the absence of air.

Explorer XIX is constructed of a four-plylaminate, consisting of alternating layers ofl/2-mil-thick polyester plastic film and l/2-mi l-thickaluminum foil. The aluminum foil forms theoutside surface; and the plastic, the inside surface . (A mil is one-thousandth of an inch.)

White circl.es (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 is required fo r operation of the spacecraft's electronic equipment.

Mounted inside of th e satellite is a smallradio that transmits a tracking signal. Its poweris 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 sil icon, amaterial that emits electrons when struck bylight. The electrons are channeled into w iresand, thus harnessed, become an electric current.

EXPERIMENT DESCRIPTIONA principal purpose of the Explorer XIX

experiment is to extend measurements of ai rdensity in the upper atmosphere to t he polarregions. Prior experiments have furnishedmeasurements of the atmosphere over otherareas of earth . The various measurements


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. ~ - - - . ~ - - ' - _ . - - - ~ - ~ ~ ~ - - - - - ~ - -Page 4permit comparison of densities and temperaturesof the upper atmosphere over different latitudesof earth.

Another goal is to learn more about thecontributions of energetic particles and ultraviolet l ight to heating and, consequently, densityof the upper atmosphere. Energetic particlesare electrified constituents of atoms such as protons 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 is part of a familycalled the electromagnetic spectrum . Amongthe ether members of this family are X-rays,radio waves, and visible light. Most of theultraviolet radiation streaming to earth is absorbed by earth ' s atmosphere. For a longtime, scientists believed that ultraviolet rayswere chiefly responsible fo r heating of the upperatmosphere .

NASA FACTS VOL. 11-2In recent years, however, many scientists

have theorized that energetic particles ma y alsoplaya major role in heating of the upper atmosphere. 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 similarto Explorer XIX. It burned up during re-entryon April 9, 1964.

The polar areas were chosen fo r study oftemperature variations due to 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 magnetic field tend to become nearly vertical, insteadof horizontal, at the poles. As a result, theflight of energetic particles to earth is not barred

Folding of a 12-foot diameter Ai r Density Explorer satellite . After folding, technicians willpack it in a metal cylinder 9 inches in diameter and 19 inches long to be launched intoEarth or b it by a Scout launch vehicle .


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NASA FACTS VOL. 11-2

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Scout launch vehicle rocke ts Explorer XIX from Point A rguello ,California .

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 sprinklingiron filings around a bar magnet. Note howthe iron filings, which follow the magnet's linesof force, curve inward at both ends, or 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 11 6minutes.

At launch, Explorer XIX was folded andpacked inside a metal cylinder 8V2 inches indiameter and 19 inches long. In orbit, com-pressed nitrogen gas pushed the sphere from itscontainer and inflated it to a 12-foot diameter.

The orbit of Explorer XIX swings as fa rnorth as Thule, Greenland, and as fa r south asthe Antarctic continent, enabling the satellite tocover most of the globe. Explorer XIX is beingtracked by NASA radio tracking stations and bythe sensitive telescopic cameras of the worldwide Baker-Nunn network, which is operated bythe Smithsonian Astrophysical Observatory.

IQSYINTERNATIONAL QUIET SUN YEAR

On January 1, 1964, scientis ts of mony nat ionsinaugurated a two-year cooperat ive s tudy of the su ncalled IQ5Y fo r International Quiet Su n Years. Th eprogram is a sequel to th e IGY, or Internat ional Geo-physical Years , a study of the ear th and space con-ducted by world scientists in 1957 and 1958.

The somewhat incongruous term "quiet sun" has it sorigin in observat ions made during many years whichindicated, as noted previously, that the tempo of solaractivity follows a cycle of roughly 11 years , beginninga t peak solar activity, d ropp ing to a low, and risingagain to a maximum .

IQSY is being conducted during th e t ime of min-imum solar activity when th e su n is relat ively free ofsolar flares, sunspots, and o ther eruptions. During


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Page 6IGY, the su n was in the mast act ive t ime of it s cycleof activity.

A major goal of IQSY is to compare it s observat ions with those of IGY. Such comparisons and otherIQSY s tudies a re expected to yield increased unders tanding of how the su n behaves and how it governsnatural events on and near earth.

Th e major NASA effort support ing U.S. participation in IQSY will be th e launching of a series of Pioneerspacecraft on long-duration missions during which theywill cover millions of miles of interplanetary space .

NASA FACTS VOL. 11-2

, Th e spacecraft monitors solar radiat ion and magnetic fields a t widely separated points in space. Theirexperiments are designed to provide basic data on th ein terplanetary environment and measu re solar effectsupon th e environment .

Data from NASA scientific satelli tes an d soundingrockets are already contribut ing informat ion relatingto the IQSY. Among such satelli tes ' ;re Explorer XIX(described In this NASA FACTS) an d Explorer XVIII, th efirst of a 5erles af In terp lane tary Explorer Satel l i tes .(See NASA FACTS-Interplanetary Explorer Satellites . )

Deflated and folded Explorer XIX is carefully fitted insidE! the metal container in which it willride into orbit .

NASA FACTS format is designed fo r bulletin-board displayuncut, or fo r 8 x lOY. looseleaf notebook insertion whencut along dotted lines and folded along solid lines. Fo rnotebook ring insertion, punch a t solid dots in th e margins.

NASA FACTS is an educational publicatian af NASA's Divisianaf Educational Programs an d Services. It will be mai led toaddressees who request it from: NASA, Educational Publicat ions Distribution Center , AFEE-l, Washington, D.C., 20S46.

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