nasa facts the explorer satellites

8/7/2019 NASA Facts the Explorer Satellites

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NASA FACTS format is des igned fo r bulle t in-board displayuncut, or fo r 8 x lOJ1 "loose 'eaf notebook insert ion whencut along dotted lines and fo lded a long solid lines. Fo rnotebook ring insertion, punch a t solid dots in th e margins.

Page 2Explorer XV, in a smaller orbit, with an apogee

of 10,950 miles and a perigee of 195 miles,circles the earth in 5 and one-quarter hours. Thissatellite entered into orbit with a problem; it wasspinning too fast. A deliberate "spin-up," imparted to keep it aimed accurately during thejourney to orbital altitude (like the spin of a riflebullet which has a similar purpose) should haveslowed it down and did not. The mechanism forthis slowing process is a set of small weights, designed to spring out from the sides, with an effectsimilar to that achieved by a spinning ice skater

NASA FACTS will be mailed only to addressees who requestit from: Office of Educational Programs and Services, NASA,400 Maryland Avenue, S.W., Washing ton 25 , D.C.

NASA FACTS (E-l0-62)when he extends his arms to slow down. Theweight system did not funct ion, with th e resultthat Explorer XV went into orbit spinning at least10 times too fast .

This has created problems with the interpretation of results from tw o of th e seven experiments,but the transmissions are adequate for accomplishment of Explorer XV's miss ion, which is toinvestigate radiat ion belts created by high altitude nuclear testing by both the U.S. and Russia.

(This artificial radiation, the scientists pointout, is not, strictly speaking, "space weather,"

The Explorer XIV space weather satellite is oriented in orbit to permit gathering data both within and outside of the magnetosphere . Successive positions relative to the sun are shown, counterclockwise . ._ _" "ORBIT OF EXPLORER XIV / / / /

4. ABOUT 1 YEARAFTER LAUNCH-- ---- "- ,

\_..;..--1 ~ / -- l '/./

ORBITAL PATHE A R T H ~ IMAGNETOSPHERE I

~ I

, ./ ////

/I/

/ I/ It C ~ \ ;'\ , __ / / 3. 6 MONTHS AFTER

1. LAUNCHEDOCT. 2, 1962

LAUNCH

----,.-/I ~ I .---\ /\. --..... ----

2. 4 MONTHS AFTERLAUNCH


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NASA FACTS (E-10-62)since the belts are results of man's experiments,bu t the conditions are similar to those which areexplored by other space weather satellites.)

ENERGETIC PARTICLESThe Explorer Satellites' sensitive electronic

instruments seek more knowledge fo r man aboutelectrons and protons, the sub-atomic particlesthat are the minute building blocks of all matter.

These so-called energetic particles play leading roles in the phenomena of "space weather"which must be better understood i f man and hisinstruments are to journey safely into space.

Many of these particles possess very highenergies and travel at nearly the speed of l ight.They are responsible fo r some of the spectacularand intriguing space phenomena that we observeon earth: Disturbances in the reflective sky layer

Page 3known as the ionosphere which disrupt com-munications throughout the world; creation of thestarting Iy beautiful display of.. auroras, observedlast year as far south as Washington, D.C.Possibly they have a role in modifying the earth'sweather.

Infinitesimal as they are, the particles canharm man an d da mage instruments he uses toexplore space . An understanding of their lifehistories can advance such national objectives asmanned space fl ight, and th e use of space forforeseeable practical benefits as communications,weather forecasting and navigation.

Just as we seek to learn the scientific causesof hurricanes an d tornadoes - h ow they are cre-ated, how they live and how they d i e -we seekto fathom the mysteries of storms in space.

The Van Allen belts, here illustrated , ar e within and are part of the magnetosphe re . (See d iagram on pa g e 2 for out-line of the magnetosphere .) Scientists postulate that the Van Allen belts an d the whole magnetosphere of which theyar e a part, constitute a reservior in which solar flare energy can be stored in the form of trapped particles , for a con-siderable time, until some subsequent solar event disturbs the magnetic field an d d islodges particles from the Van Allenbelts as apples are shaken from a tree . When the particles ar e dislodged, they descend through the horns of the VanAllen zone (see above) , transferring their kinetic energy to the atmosphere by ion izing coll isions. Th is is probably thecause of the aurora .


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Vanguard " ' gave on e of the first measurements, fromspace, of the earth ' s magnetic field .

Where Explorer XV takes readings relativelyclose to the earth, studying th e artificial radiation belts created by man made high altitudenuclear explosions, the principal mission of Explorer XIV is to determine the particle populationand energies in the magnetosphere and th e regions of interplanetary space beyond. Weknow the sun is the principal vil lain, or hero, asthe case may be. The phenomena themselvescomprise one of the biggest mysteries in thehistory of mankind.

THE MAGNETOSPHEREThe magnetosphere begins several hundred

miles out in space and extends fo r thousands ofmiles. This in itself is a mystery. In this region are the natural Van Allen radiation beltsdiscovered by Explorer I in 1958.

NASA FACTS (E-l 0-62)We have swiftly gained knowledge of this

region thw.ugh the satellites which fol lowed thepioneeri ng work of Explorer I. But l ike all greatdiscover ies, each new satellite posed more unanswered scientific questions.

Explorer I told us that there were energeticpartic les trapped above the earth and that theearth 's magnetic field probably acts as a storagebin for these bits of matter that spiral aroundthe earth's magnetic force lines . But it remainsfo r other satellites to look fo r the answers to theintriguing riddles of how many particles of acertain energy range are in a particular area ofspace. I t undoubtedly wil l take several years,before we come anywhere near an understandingof the processes involved.

As an example: It was thought from earlysatellite experiments that the Van Allen radiationconsisted of two distinct bel ts -one primarily ofelectrons and the other of protons . As withmany scientif ic theories, this was shattered byhard investigative facts. Explorer XII determined that there was no such distinction; ratherthat the magnetosphere is one big trapping region with particles in various areas having different characteristics.

Instruments on spacecraft that preceded Ex-plore r XII could possibly have detected thisdiscrepancy had they been f inely tuned fo r sucha definite investigation. But changing solaractivity may be th e basic cause of the discrepancy . Perhaps the particle population andenergies change with the variations of the sun'sown "weather," again an unknown.

Almost the same holds true fo r magnetic fieldmeasurements by satellites, which are enablingus to learn more about the earth ' s interi or byprobing with instruments that have left this planetthan by earth-bound activity. Vanguard III gaveone of the first measurements of the earth's magnetic field from space. Pioneer V and ExplorerX detected the area in space where the earth'smagnetic field leveled off and the interplanetarymagnetic field assumed command. And Explorer


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NASA FACTS (E-10-62)XII more accurately pin-pointed the precise areaand also provided the dividend of indication thatthere may be a turbulent transition region betweenthe earth and the interplanetary fields.

Another piece in the space phenomena puzzleIS concerned with a theory that has intriguedscientists since 1830. It was then postulatedthat there was a ring current, * separate fromthe earth at some unknown position in space.At first, data from Explorer VI indicated that thiscurrent had been detected. However, furtheranalysis made this dubious. But, this thread ofevidence whetted scientific appetites. Succeeding satellites, Pioneer V, Explorer X, Explorer XIIinvestigated this area, but with litt le success, according to data analyzed to date . Explorer XIVmay shed l ight on this space mystery.

These unknowns may be part ial ly solved butno one expects a complete answer, except

Ring current: A current of charged particles flowing in a ring aroundthe earth, ar other bady .

Pioneer V (and other satellites) found a spectrum of en-ergy from the speed of light on down .

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When a solar d isturbance occurs, a huge tongue of magnetic field lines is formed, an d these lines, in effect, constitute a"m agnetic bottle."

SUN

PROPAGATION OF SOLAR DISTURBANCESFROM SUN TO EARTH

SOLAR PROTONS--'


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Page 6through th e cumulative efforts of future spacecraft designed specif ically to monitor the sun,the ionosphere, and how energetic par t ic lesparticular ly th e dangerous solar protons - t r a verse the 93 million miles from the sun to earth .

One such satellite to be launched next yearwill explore interplanetary space between earthand the moon, recording these proton events.Assessing the destructive capability of these particles is mandatory fo r support of the mannedlunar explorat ion program.

Stil l another series of satellites, OrbitingSolar Observatories, or OSO (NASA FACTSB-62), will continue to monitor the sun to learnthe processes involved in sending out these dangerous radiations. From this program alonecould come a system for predicting when the sunis l ikely to emit radiations dangerous to man.

NASA FACTS (E-l0-62)As weather forecasts today indicate safe flyingweather, so could such a solar flare forecastingsystem indicate safe space "f lying weather . "

Instruments on Explorer XIV will not measureprecisely the artif icial radiation belts caused bythe United States and Russian high altitudenuclear detonations because they were designedand built prior to its creation. However, Explorer XIV should give world scientists a morecomplete picture of the changes induced by thelessened solar activity predicted fo r this year, orby effects of the nuclear explosion, in the naturalradiation zones .

Importantly , Ex plorer XIV carries a solar cellexper i ment to determine the effect of both thenatural and artificial radiation on satellite powersources . These cells convert about 15 percentof the sun ' s energy into usable electricity.

Explorer VI suggested the possibility of a ring current of magnetism.


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Explorer X helped to pinpoint the area where the earth's magnetic field levels off and the interplanetary magneticfield tokes command.

Explorer XV, using the spare flight unit ofExplorer XIV, but with different instrumentationfor measuring the particular artificial radiationbelt particles, seeks to determine how the beltis decaying with t ime, assess the effects of thebelt on future satellites, and give the scientificcommunity addit ional basic information on theartificially created environment.

It is known that man and instruments cansafely traverse both the art if icial and naturalradiation regions i f there is adequate shielding.However, because of the effect of the radiation,the l ifetime of Explorer XIV may vary from amonth to a year. The spacecraft's highly ellip-

tical orbit will keep it farther out in space mostof the t ime, away from the degrading effects ofthe radiation. Explorer XV, which is specificallydesigned to remain in the artificial radiationzone, has solar cells coated with 60-mil-thickglass. (A mi l is .001 inch.) In contrast, Ex-plorer XIV, l ike Explorer X", moving quicklythrough the zones, has a 6-mil-thick coating .

Although solution of the mystery of the char-acteristics of space radiation will take many moreyears and many more satellites, before scientistshave precise understanding of the phenomena,a general picture has emerged.

It is now believed that when an eruption occurs


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ARTIFICIALRADIATION

NASA FACTS (E-) 0-62)

- - - - - -VAN ALLEN

Explorer XV was sent into an orbit ranging from a perigee of 10,950 mi les, to tran smit data f rom the art ific ialradiation belt.

on the sun, a huge tongue of magnetic field lines, *with their roots remaining on th e sun, reachesout into space -somet i mes towards earth, butalso in many other directions.

According to one hypothesis, the Explorer XIVspacecraft should provide more understanding ofthese l ines which, in effect, form a magnetic"bott le." Cosmic rays from outer space-a lsopossessing very high energies-apparent ly areexcluded from the bottle, with the " wind" orplasma, erupting from the sun being confined tothe area within.

Magnetic field l ines . Imaginary l ines start ing an a positive pole andending at a negative pole .

This plasma , the fourth state of mat te r neither sol id, Ii qu i d nor gas - is composed oflow energy charged particles . Known rules ofphysics, sugges t that the plasma , in turn, sets upanother magnetic field that moves along with it .It is believed that higher energy particles spiralaround the bottle , just as magnetosphere particles sp i ra l around the earth, and are carriedalong by the magnet ic field lines.

But i t remains unclear, and is subject to scientific debate, whether these particles start outwith high energies or whether they acquire mostof this energy by being accelerated to highvelocities when they are pushed along by the


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NASA FACTS (E-l0-62)magnetic field. One thing is known: Whenthese particles reached such spacecraft as Ex-plorer XII, Explorer X and Pioneer V, there wasa spectrum of energy from the speed of l ight ondown.

It is believed that this solar tongue continuesto expand, as an onrushing t ide, and eventuallyenvelops the earth ' s magnetosphere, distortingit. Some scientists th ink that the magnetosphereis compressed toward the earth on the sunlit side,but on th e opposite side of the earth assumescone-like shape which extends out to manythousands of miles .

Explorer XIV, taking over where Explorer XIIleft off, reports data leading to a better undertanding of these phenomena . In addition,geoprobes wi II have to be sent out even greaterdistances in space to provide more conclusive

Page 9evidence of the extent of these boundaries, i f ineffect, they can be proved.

Much of th e success of Explorer XIV dependson the tricky task of correctly aligning the space-craft with respect to the sun when placed intoorbit . Th i s critica l positioning in space perhapscon be visualized by thinking of the earthrevolving around the sun each 365 days.

Next, imagine the magnetosphere envelopingthe earth in a shape l ike an ice cream cone -the ice cream top compressed close to the earth'ssurface on the sunlit side, and tape ri ng off cone-like on the side away from the sun . (See diagram, page 2.)

Then visualize the highly ellipt ical orbit of thespacecraft, inclined about 75 degrees from thesun when first injected into orbit. The angletoward the sun becomes higher each month. As

Explorer XII is shown with technicians, illustrating its size . Explorers XIV an d XV ar e the same size .


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- - - - - - .- _.- --- - .---- - - --Page 10 NASA FACTS (E-10-62)

Note the similarity of Explorer XIV in this illustration to Explorer XII on page 9 . Beginning with Explorer XII thesatellites in this series have used flight units of the same type, with differing instrumentation .

the angle to the sun increases, the satel l i te-orbiting the earth as the earth orbits the s u n -probes various areas of the magnetosphere.After six months, the satell ite is completely en-veloped by it, but at other times it is in interplanetary space beyond, constantly plotting theboundaries and quantities of the particles.

The Goddard Space Flight Center, Greenbelt,Md., has been assigned project managementresponsibility fo r the Explorers.

For Explorer XIV, the project consists essen-t ially of the following: A cosmic ra y experiment,an ion-electron detector experiment and a solar

MARINER IINew data and refined calculations relating to th e tra

jectory of Mariner II, th e spacecraft launched towards th evicinity of Venus, resulted in a new est imate fo r alti tudeof "fly-by" as compared with the figure given in NASAFACTS 0-62. Earlier calculations ha d indicated fly-by a tabout 10,000 miles.

Th e new measurements added up to a "probable missdistance" of 20,900 miles plus or minus 3,000 miles, indicating approach might be to a point as near as 17,900miles from the surface of Venus, or as fa r away as 23,900miles. This predicted range was considered satisfactory;the spacecraft 's instruments were designed to functionat any distance up to 35,000 miles.


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NASA FACTS (E-1 0-62) Page 11PAYLOAD

SOLID PROPELLANTENGINE

LIQUIDENGINE

FIRST STAGE(THOR BOOSTER)

EXPLORER XIV-DELTA VEHICLEThe Delta launch vehicle consists of a booster plus two upper stages as illustrated in this cutaway.

cell by NASA's Goddard Space Flight Center; aproton analyzer experiment by NASA's AmesResearch Center; a trapped particle radiationexperiment by the State University of NewHampshire. A Goddard photocell optical sensingsystem furnishes information on the satellite'sorientation in space.

For Explorer XV, the University of Californiaat San Diego prepared an experiment to measureelectron flux. A sim i lar experiment was furnished by the Bell Telephone laboratories (BTL)and Goddard. University of California and BTLalso contributed experiments to determine thedistribution in pitch angle of the electrons. TheUniversity of New Hampshire provided a magnetometer. Goddard has an ion-electron experiment, and an opticol aspect sensor to determinethe satellite's orientation to the sun . BTL supplied a solar cell damage experiment.

THE DELTA LAUNCH VEHICLEThe launch vehicle for Explorer XIV was a

Delta, a three-stage rocket developed by NASAwhich has performed flawlessly in the last twelveof its thirteen launch attempts. Delta is ninestories high and weighs 57 tons.

The vehicle's first stage is a 60-foot modification of the Air Force-developed Thor (SM-75)and generates 170,000 pounds of thrust duringthe 2 and one-half minutes its 50 tons of propellan t burn.

The second stage is 17 feet tall and weighsa little more than tw o and one-half tons. It ispowered by a l iquid engine which develops7,500 pounds of thrust and burns slightly lessthan 2 minutes.

Delta's one-half ton, solid-propellant thirdstage is 5 feet high and uses an ABl 248 en-


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- - - ~ - - . - - ~ ~ ~ - - - - Page 12 NASA FACTS (E-1 0-62)gine with a thrust of 3 ,000 pounds. Its burningti 'me is 40 seconds .

For a min ute and a half after I ift-off, Deltais gu ided by its Thor autopilot.After burn-out ofthe Thor booster , the radio guidance systemmakes refined ve locity and steering correctionsas needed . Shortly after first stage burn-outseparation , and afte r ignition of the second stage,the fairing-covering th e third stage and thepayload -is jett isoned.

Second sta-ge burning ends about 4 an d onehalf minutes after lift-off. The vehicle, withsecond and third stages still attached is now atan altitude of about 1 25 miles . At this pointa 6 minute coasting period occurs. During thisperiod , guidance is provided by a 42-poundflight contro .1 system contained in the secondstage. The satell ite and the third stage are spinstab ilized by small rockets mounted on a " spintable " between the second and third stages.

At the end of the coast period-about 10minutes afte r launch-the second stage separatesand third stage ign it ion occurs. Soon the required o ,' bital ve locity of about 19,000 milesper hour is reached a nd the satellite, trailed byth e third stage, is injected into orbit.

A De lta veh ic le launched Explorer XIV on October 2,1962 . Explorer XV 's launch on October 27 was simi lar .

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