nasa facts orbiting solar observatory

8/7/2019 NASA Facts Orbiting Solar Observatory

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Page 1NASAAn Educational Services Publication of the

National Aeronautics and Space AdministrationNASA FACTS VO L III, NO.7

ORBITING SOLAR OBSERVATORY

Th e Orbiting Solar Observatory (050 I) spacecraft. The 440-pound observatory t ravels in a near-circular orbit aroundear th and completes each trip in 96 minutes. What appear to be t iny window panes in the upper sect ion of the craft

are solar cells which convert sunlight to electrici ty to power th e spacecraft.

Since man began to think and record hisknowledge fo r the benefit of others, he haslearned a great deal about the sun. But, despitehis efforts to obtain accurate information aboutthe sun and its radiant effects upon our earth,

man has been greatly hampered in his observa-tions by the filtering effects of the blanket of ai rwhich protects him from the direct rays of thesun. We have had to rely, until recent years,on the telescopic observations from below the

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Page 2THE SUN

Did you know that radiat ion from th e sun causesal l earth weathe r -snow, rain, hail, w i n d - a s well ashea t and light?

Did you know al l of ear th ' s water power , coal ,petroleum and othe r combust ible fuels find thei rbeginnings in radiat ion from th e sun 's surface?

Did yo u know that in just 1 second of t ime thesun emits more energy than al l of the people of earthcombined have used or consumed in the ent i re historyof the world?

Did you know tha t if it weren ' t fo r th e thickblanket of invisible air that surrounds our planet tha tsome of th e sun's more lethal radiat ion would kill us inan instant?

sometimes opaque blanket of air surroundingearth in our efforts to understand the solarsystem.

As a matter of fact, until the National Aeronautics an d Space Administration launched itsfirst Orbiting Solar Observatory (050), March7, 1962, the technique of studying the sunhadn' t changed much since Gali leo made hisfirst observations some 350 years ago in 1610.

Prior to the development of these orbitingobservatories, a fe w measurements, beyond theatmosphere, of solar radiations that are absorbed in the earth's atmosphere had beenobtained-not to o satisfactorily-with the use ofsounding rockets an d early space probes of theVanguard, Pioneer and Explorer series.

During th e 77 days of almost perfect operation which followed 0 5 0 I's launching fromCape Kennedy, the solar observatory transmittednearly 1,000 hours' data from its lofty vantageof view 350 miles above the earth. In the firstthree months of its operation, the spacecraft obtained more than three times as much information as had been previously obtained in man'shistory about solar emission of X-rays, an d morethan 4,000 t imes th e informat ion previouslyknown about the sun's spectrum . It observedmore than 140 solar flares, mapped the sky ingamma radiation an d examined energy particlesin the low-altitude Van Allen Belt region. Sig-

flcantly, it also found wide discrepancies be -een solar activity above the earth's atmosphere

as compared with observations made on earth.

NASA FACTS VOL. III, NO. 7Scientists estimate that it would have taken12,000 sounding rockets, operating perfectly,to acquire the same amount of inforrnation andat more than 100 times the cost.

A second observatory, 0 5 0 II, in continuance of the NASA program, was launched intoorbit from Cape Kennedy, Florida, on February 3, 1965.

The scientific data obtained by 0 5 0 I and1/ experiments were telemetered to earth by twoindependent tape recorders and transmitters toinsure receIving accuracy. During 90 minutesof each of OSO's 96-minute orbits , informationabout the sun gathered by its optics, scanningthe sun's surface once every tw o seconds, is fedinto a tape recorder. D,uring five of the remainin g six minutes, one of th e five NASA groundstations monitoring OSO's travels directs the0 5 0 recorder to transmit the data . The datais transmitted at a rate 18 times faster than thatat. which it was recorded. A ~ 0 5 0 transmits itsinformation, it simultaneously wipes its tapeclear, so when the broadcasting ceases, it can(during th e remaining 60-seconds) get set torecord more data. NASA ground stations canalso order OSO's transmitter on or off, an d turnon or turn off the experiment equipment aboard050 .

Delta louncloes 0 5 0 II .


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NASA FACTS VOL. III, NO. 7Al l tracking and telemetry stations con

cerned with OSO's globe-girdl ing travels arepart of NASA's Space Tracking and Data Acquisition Network. The primary stations usedin the 050 program are located at Fort Myers,Florida; Blossom Point Maryland; Quito, Ecuador;Lima, Peru; Santiago, Chile; and Woomera,Australia .

THE SUNThe sun, 93 million miles from earth, is a

raging ball of matter and energy approximately864,000 miles in diameter (100 times that ofearth), and has a mass 332,000 times greaterthan that of earth. Its chemical compositionapparently is similar to that of earth although itis so hot- i ts estimated core temperature is 35million degrees Fahrenheit-that it remains completely gaseous. Scientists have computed itsdensity at about one-fourth that of earth.

The surface of this seething furnace iswracked by solar storms of a violence almost incomprehensible to man. Giant flares that couldinstantly engulf earth sometimes leap millions ofmiles into space above its surface and solarprominences billow outward a half-mi"ion milesor more. At times, huge dark patches calledsun spots, generally in pairs and mysteriouslywith opposite magnetic polarities, inexplicablyappear to puncture the sun's surface. They re-

Solar-earth phenomena.

Page 3main visible fo r from days to months before disappearing as abruptly as they appeared .

During these great storms, which seem toreach their maximum on an average of everyeleven years, the earth's atmosphere i-s bombarded with massive and erratic doses of ultraviolet, X-ray and gamma rays. Electrica"ycharged particles from these sun eruptionsstream out across space and collide with earth'smagnetic field.

When this happens, radio transmissions aresometimes blanketed-completely blocked or uninte"igible; compass needles become erratic;electric power transmission in l ines ebbs andgrows in intensity; brilliant auroras borealis andaustralis emanate across polar skies.

Sometimes plant life is accelerated andoften greatly increased rainfalls are associatedwith the intense solar radiations. In fact, scientists tell us solar radiation is responsible fo ra" of earth's weather patterns. And it is hopedthat OSOs wi" not only prove this fact but wi"be able to aid science predict weather with morecertainty. For example, scientists believe thatwhen the sun has "outbursts of temper," variations in the X-ray an d ultraviolet emissions(which cannot be measured on earth because ofabsorption in the upper atmosphere) tr iggerweather changes and sometimes violent and unpredictable storms in the lower atmosphere.

In space travel, we know that man wi" beexposed to larger, more frequent emissions oflethal X-ray and solar proton-neutron radiation.This may require additional radiation shieldingof personnel, or even delay of missions. Yetth e earth's protective atmosphere screens ou tmajor portions of the sun's radiation, making itdiff icult and in some cases impossible forground-based observers to evaluate their causean d effect.

Thus, spatial investigation of sun-earth relations by OSOs contribute greatly to our knowledge of the space environment, directly supporting ou r efforts to advance U.S. space capabilities,to develop manned space f l ight, and to makeother significant applications of space technology. These investigations are important to ou r

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Page '4understanding of weather, of atmospheric behavior and climate, of the ionosphere, magnetic

orms, and auroros, and their influence on radiocommunications.

Therefore, there are tw o equally importantobjectives of NASA's Solar Physics Program.One is to advance our understanding of thesun's constitution and behavior. A second ob-

NASA FACTS VOL. III, NO. 7sition, size, mass, density, an d temperature as abase fo r study of other stars (astrophysical phenomena). It is th e only star on which ou rastronomers can directly observe structural features such as sun spots, flares, or prominences.Also, i t is th e only star near enough to permitth e study of its X-ray, gamma ray, and radioemissions.

Photograph of 0 solar prominence taken during a solar eclipse by Mount Wilson-Palomar Observatories . It shows aprominence, boiling into space beyond the sun's surface fo r hundreds of thousonds of miles. Th e white dot t o th e right

of prominence represents the ear th to scale.

jective is to understand th e physical processesby which th e sun influences th e earth's upperatmosphere, ionosphere, magnetosphere, and

erplanetary space beyond earth.Because the sun is the nearest star, it offers

an unparalleled opportunity to study the compo-

Normally the sun appears as a white,luminous disc without any noticeable surface features. However, i f one looks closely at photographs of th e sun, i t seems to possess a ftnegrained cellular structure. Scientists call this"solar granulat ion." They believe that th e


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- - - - - - - - - - - - - - - - - - - - - - - ~ = = = = = ~ - - - - - - - - - - - - - - - - - - - - - - - -NASA FACTS VOL. III, NO . 7granules seen in photographs actually are turbulent motions of huge rising and descendingcolumns of gas 100-150 miles in diameter.Physicists think these granules are linked in somemysterious way to the process which producesthe magnetic fields of the sunspots.

The sun emits radiation across the entireelectromagnetic spectrum. Visible light, radiowaves, X-rays, gamma rays, infrared and ultraviolet light are al l manifestations of electromagnetic radiation emitted by the sun.

Radiation from the sun, emitted in thevisible region, is transmitted through earth's at-

Photograph of th e sun. Note th e black sunspots.

mosphere. This, of course, is fortunate fo r themaintenance of l ife on earth. Unfortunately fo rsolar physicists, however, the visible l ight fromthe sun does no t contain much information aboutthe processes which take place on the sun.

Ultraviolet and X-rays are for th e mostpart absorbed by the atmosphere and vary inintensity with solar activity, but they contain agreat deal of information about solar processes.Because ultraviolet light and X-rays seem to cont ro l - or at least have a great effect on - theproperties of the earth's ionosphere, scientistsneed to know as much about solar emissions ofultraviolet and X-rays as possible.

Page SSolar proton beams, which are ejected by

sun eruptions (solar flares), are probably thegreatest radiation hazard to crews in unshieldedspacecraft. Solar flares seem to occur betweensunspots. So the ability to predict the timesof their occurrence, or alternatively, the timeswhen they will not occur, is of considerablevalue to America's manned space f l ight effort.Only by thorough study of solar flares andsolar activity can such an ability be developed.

Since most of the scientifically significantradiation from th e sun is absorbed by th e at mosphere, the only way i t can really be aptly

Photograph of the su n t aken monochromatical ly (rulingout al l light but one color) in hydrogen light. Note thegranular appearance of th e sun's surface and th e sunspots

looking like black fissures in its surface.

studied is from a spacecraft. That is one of thereasons why the NASA Orbiting Solar Observatories are so important.

Solar physicists have known fo r many yearsthat there are a number of characteristic periodsof solar phenomena. For example, they knowthat solar activity for some reason builds to amaximum of activity and then subsides in aboutan 11-year cycle. Scientists also know that thenumber of sunspots visible on the sun is a goodindicator of the number of flares which can beexpected. Right now our solar system is at the

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- - - - - - - - - - - ~ ~ - ~ ~ = = ~ ~ : . : - ~ ~ - - - - - - - ~ - ~ ~ : ~ - - - - Page' 6minimum activity phase of the sunspot cycle andfew solar flares have been observed.

There has been, as a result, a world-wideeffort under way to study a variety of geophysical phenomena at solar minimum-The International Quiet Sun Year (IQSY) Program.However, solar activity will be at a maximumagain in 1968 to 1969. NASA scientists areworking at top speed to get everything ready inground laboratories and in th e positioning oforbiting solar observatories in an effort to gatheral l possible information during the 1968-1969period.

Enlarged photo of 0 sunspot field t aken in white light.Note th e appa r en t l ines of magne t ic force around the

sunspot.

ORBITING SOLAR OBSERVATORIESOSOs, depending upon the nature of

their missions, may vary in gross weight fromabout 400 pounds to about 600 pounds.050-1 weighs 450 pounds and 050-11, 545pounds. Experiment equipment carried aboard050-11 weighs 215 pounds.

A feature of th e 0 50 spacecraft is itscapability for maintaining high accuracy in itspositioning in outer space over extended periods

time. This provides solar physicists with ana c t means of observing the sun not heretofore

available.

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NASA FACTS VOL. III, NO. 7The spacecraft, like many other satellites,

uses the gyroscopic properties of a spinningbody for stability. Launched by a three-stageDelta Rocket, 050 travels in a 350-mile high,96-minute, earth orbit.

The spacecraft consists of tw o parts: awheel section and a platform or "sail." There-fore, it is known as a sail-and-wheel vehicle.

The heaviest part of 050 is a nine-sideddrum containing experiments, batteries, radioequipment and position-control apparatus.Mounted on a shaft running through the centerof the drum is a semicircular "sai l" covered onone side with solar cells to convert sunlight intoelectric power, and capable of pointing instruments at the sun. While 050 is getting itsfinal push from the launching rocket's thirdstage, both drum and sail spin rapidly. (Thespinning action gyroscopically aids 050 inmaintaining its orbital path.) After it is in orbit,three arms carrying spherical tanks of high-pressure nitrogen swing outward, an d small nitrogenjets go into action to reduce the spin to a steady30 revolutions per minute.

l ight sensors on 0 50 then begin theirsearch fo r the sun. When the sun is located,nitrogen gas, discharged from a tank in th edrum, revolves the drum's ax is until it is perpendicular to the sun ' s direction . Next, a motoron the central shaft starts turning the sail sothat its solar cells can fix steadily onto the sun'srays. 050 gets gyroscopic stability from thespinning drum, while the solar cells on the pointing sail are always in the right position todevelop maximum power.

Mounted on the sail, and pointed accuratelyat the center of the sun by a special set of me-chanical eyes, are two instrument compartmentswhich carry 050 ' s various sun experiments.Typically, an X-ray spectrometer measures thewave length and strength of X-rays coming fromthe sun. A photomultiplier tube lo oks fo rpowerful gamma rays that are believed to comefrom electrons and positrons annihilating eachother in the sun's churning gas . A dust counterwatches the sun to find out whether microscopicdust particles are coming from its direction.


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, NASA FACTS VOL. III, NO.7 Page 7ORBITING SOLAR OBSERVATORY

COARSE EYESIAZIMUTH)PITCH CONTROL EYES

POWER AMPLIFIERS (2)TAPE RECORDERS (2)COAXIAL SWITCH

SOLAR CELL ARRAY

FINE POINTINGEXPER IMENTS

BOX)

STABILIZATION BOOMSPIN UP ___NOZZLE VDESPIN NOZZLE

GAS BOTTLESFOR SPIN RATECONTROL

OS O II PROGRAM SUMMARY-Major Objectives: To measure electromagnetic radia tion in th e ultraviole t , X-ray, andgamma ra y regions of the spectrum, an d to study their emissions; to study white light coronagraph; and to make zodiacallight device scanning experiments . -Life Time: Estimated at si x months -Launch Vehicle: Thor Delta -Circular Orbit: 342-374NM -Inclination: 32.8 degrees -Orbit Time: 96,4 min . -Payload Weight : 540lbs , -Power: 26 watts (solar cell

conversion) -Stabilization: 30rpm (spin rate)

Other instruments mounted in the "wheel"record 'radiation from both sun and sky as thedrum spins, an d a neutron counter catches neutrons bounced up fr om the earth's atmosphereby the impact of cosmic rays. Al l the readingsare recorded on tape during each orbit. When050 passes over a NASA radio receiving sta-tion, it is given a signal that orders 0 5 0 trans-mitters into operation and to send their datadown to earth stations.

The platform or "sai l" of 05 0 contains anarray of solar cells. Solar energy is the solepower source fo r operating electrical equipmenton the spacecraft. This solar cell array in geniously conve rts solar energy into electricalpowe r when, during its earth orbit, the spacecraft is in sunlight. Electric power thus gene-

rated is stored in batteries housed in one of the"wheel 's" compartments and provides a constant voltage supply to the spacecraft at al ltimes. The total surface of the solar arrayamounts to only 3.7 square feet but it contains1,860 solar cells capable of producing a poweroutput of about 26 watts.

Some nine months of scientific sun-viewingwas accomplished by 05 0 II , during which itsstabilization system unerringly kept 0 50 instrumentation pointed at the sun fo r more than2,000 orbits . However, the useful designlifetime of an 05 0 spacecraft is six months because, by that time, the nitrogen gas jetted byth e extended arms to keep 0 5 0 in orbit willhave been expended. As a result the spacecraf t -unguided-Ioses its sun orientation. In


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. P a g ~ 8turn, the solar cells, which must be kept aimed

t the sun in order to generate electricity neededy the experiments and for the control of data

transmission, become ineffective. The space-craft then may continue, blind and mute, inits earth orbit for years bu t its capability togather, store, and transmit scientific informationis ended.

NASA's Orbiting Solar Observatories arecounted among America's most rewarding spaceventures. Scientists in government, industry,and the world's great universities are obtaining

NASA FACTS VOL. /II, NO. 7complete libraries of important and hitherto unobtainable information about the nature of thesolar system. They are learning much aboutthe cause and effects of solar radiation uponall earth life, weather, communications, andother earth processes, as well as what ourspacemen may expect to face in the hostile environment of space. More OSO missions arescheduled by NASA in coming months. Eachhas a number of specific tasks to perform. Allof them are aimed at providing man with abetter understanding of Earth-the third planet Solar System, Milky Way Galaxy, Universe.

LOCK ON SUN IN ELEVATION ACTUATE PITCH JETS (LOCK ON SUNEACH SATELLITE MORN ING SHUT OFFEACH SATELLITE NIGHT)LOCK ON SUN IN AZIMUTH ANDREMOVE NUTATION

DE-SPIN TO 30 R. P. M. ~ \ \ \ \ \ \

~ 3rd STAGE SEPARATIONARMS OUT

~ 3rd STAGE BURNOUTFI RE 3rd STAGE

\ \\ \ \

~

~ SPIN 3rd STAGE AND SATELLITE TO 120 R. P. M -START SATELLITE TIMEROS O Flight sequence

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