Renewing Solar Science the Solar Maximum Repair Mission

8/8/2019 Renewing Solar Science the Solar Maximum Repair Mission

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REPAR MISSION

- National Aeronautics andSpace AdministrationGoddard Space Flight Center


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H gh above the clouds and filtering atmosphere, ideallylocated to watch the sun, an elaboratesolar observatory movesidly through space, operating at a mere fraction of its full capability.Once the source of a wealth of information about energetic eventson the sun, the satellite is a victim not of age but of a technicalproblem. Of the seven advanced scientific instruments on board,only three continue to function. The others require very precisepointing and stability, which the spacecraft no longer can provide.Such is the plight of the Solar Maximum Mission,commonly knownasSolar Max. Just nine monthsafter launch in February 1980, fusesin the attitude control system failed and the satellite lost its abilityto point with fine precision at the sun. To the dismay of solar sci-entists around the world, a spectacular mission abruptly faltered.Although a few instrumentscontinuedto send valuabledata despitethe loss of fine pointing, most of the instrumentswere useless andthose still operating lost the benefitsof partnership n a coordinatedobserving program. The mission was declared a success, becauseits operation, though abbreviated, fulfilled the success criteriaestablished before aunch. However, its reduction romthe expectedtwo years to nine months meant a significant loss to solar science.Although its performance now is severely curtailed, Solar Max willnot remain idle indefinitely. The first satellite of a new breed, SolarMax is designed to be serviced in space by a Space Shuttle crew.In 1984, the Shuttlewill make a repair visit to the satellite.The faultyattitude control system module will be replaced, and two of thescientific instrumentswill be serviced.This repairvisit should reviveSolar Max for at least several more years of coordinated observa-tions of the sun.The Solar Maximum Repair Mission will demonstrate the satelliteservicing capabilities of the Space Shuttle for the first time. It willalso revive the most ambitious and successful solar flare researchprogram ever attempted. The purpose of the Solar Max RepairMission is to restore the operational capability of the only majorsolar observatory currently in space. Because no comparable newobservatory is planned, this renewal of solar science is imperativefor improved understanding of the sun and its effects on Earth's


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- THESOLAR MAXIMUM MISSIONLeft: Awhite lightphotographof the sun taken on April 10,1980,showstwo sunspot regions (to the right) well studiedby Solar Max. Forsomereason, the uppergroup of sunspots did not produceflares, but thelowergroup producedthem in profusion.Passageof these two activeregionsacross the sun causedthe first big decrease inthe solar' constant, measured by the Active Cavity RadiometeronSolar Max.Right: Layersof the suncan be identifiedby their characteristic tempera-tures and electromagneticemissions. Extremetemperaturedifferencesresult inseveralmysteriousphenomena. For example, relativelycoolprominencesexistwithin the 150times hottercorona, like icecubeswithin afurnace.BelowPortionsofthe electromagneticspectrumcoveredby SolarMaximum Mission instruments.

Ultraviolet Hard X-Ray ImagingSpectrometer Spectrometer

Ultraviolett1,000,000,aM) emperature (K)

T e Solar Maximum Mission was named and sched-uled to coincidewith the peak period of activity in the current Prediction of solar Rare activity is difficult and unreliable becausethe flare process is not yet understood in detail. The aim of Solar


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minutes, buttheir effecton thesun may lingerfor hours. Their effect Solar Max is designed to meet the confflctingdemands for spatial


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ORIGINAL PAGEGDLOR PHOTOGRAPH

STUDYING= SOLAR FLAT''

Chromosphere~c~vapwationsJ

mongastrophysicists,solar flares are a controver-A ial subject.A numberof theoretical explanationsandcandidatemodelsexist, butbettermeasurements are requiredbeforethe flare control and data acquisition through the new Tracking and DataRelaySatelliteSystem (TDRSS), will enhancethe science returnofSolarMax.


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Leff: Flaresmay betriggeredwhen two loops ofmagneticfields collideand interact. High-energy .charged particles speed through theseloopsand,' "excite" the flare plasmatoemit various kindsatradiation.

Right: A white light photograph of the sun takenfromthe MarshallSpaceFlight Center0bse~atorYon May 21,1980, shows severalsunspotgroups inactive regions.A majorflarewas associatedwith thesmall sunspotgroup near thecenter of the solar 1disc. Imageson the next pagereveal how differentSolar Max instrumentssaw the same flare region.Below: Usually,aflare beginswith asudden flash ofhardX-ray andultraviolet radiation, followedby aslower riseof soft X-raysand a gradual fadingof thesoft X-rayand ultraviolet glow.A Red- HardX-raysGreen- Soft X-raysBlue - Ultraviolet~re:~lare impulsive ~heimalrState Phase GradualPhase DecayPhase

1collide and electrons are acceleratedto energiesof 10 o 100 hou-sand electron volts (keV).The feet of flare loops rest in sunspot regionsof opposite magnetic

the solar cycle has progressed four years, the repair mission willoccur during a quieter, waning phase, though still punctuated bystrong flare activity. Scientists now have an unforeseen chance to


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- 7resultant X-ravs are rich in diaclnostic informationabout flare plasma. I/Because theaintensityof x-ray emissions from highly ionifed ele-ments is temperature dependent, X-rays can be read as ttw-~-~om- May 21, 1980 SeveralSolarMax instruments can view the sameeters that indicate the temperature of the emitting plasma. X-ray flare region at once for a comprehensive look at events occurring there.data may also provide information about turbulence within a flare. Coordinatedobservations from ground-based nstruments provideadditional information.All of these images recorda major flare observedSolar flares produce X-rays at both ends of an energy spectrum: on M~~21,980,more energetic "hard" X-rays (less than 1 Angstrom wavelength)and lessenergetic "soft" ones (1 100 Angstrom wavelength). Burstsof hard X-rays signal the onset of a flare. Typically lasting from 10to 100 seconds, hard X-ray bursts seem to emanate from the foot-points of flare loops. They indicate the deceleration of very highenergy electrons (16-30 keV), accelerated elsewhere in the flare,depositing energy sufficient to raise the plasma temperature by Right: Viewed through a hydrogen-alpha filter, theflare appearsverymillions of degrees. brightagainst the solar background.This image of the chromosphereatabout 6000' was taken at the MarshallSpace Flight Center observatory.Soft X-rays arise from plasma in the temperature range of 1-50million degrees. They seem to originate primarily between foot- Below: This image represents the magnetic field at thepoints,well up in the flare loops. During aflare, soft X-ray brightness surface Of thesun, as measured by the SpaceFlight Center Vector Magnetograph.The field points awayincreases in intensity for 5 to 10 minutes, then decays gradually. from the solar surface in redareas and toward the surfaceSoft X-rays indicate the presence of electrons in the energy range in blue areas. Black line seaments indicate the orientationof 0.1 to 10 keV. of the magnetic field in theplane of the solar surface,perpendicular to the line-of-sight.Three Solar Max instruments watch the sun in X-rays: the Hard X-GaussRay Imaging Spectrometer, the Hard X-Ray Burst Spectrometer, 652and the X-Ray Polychromator.Together they have measured flare 800400temperatures with unprecedented precision and collected data on 200the state of the plasma before, during, and after flares. As a result 100of successive observations in fractions of seconds, scientists are 50now able to read a detailed X-ray history of flare events. Flareplasma appears to be very complex in composition and to change 0significantly in temperature over very brief time intervals. -14-49The X-ray instruments have revealed many surprises. An unsus- -100pected class of flare events, coronal flares, is one such discovery. -200Confined to the corona, with no observable change in the lower 1layer (chromosphere) where flares typically arise, coronal flares -1390appear several hours after a major flare. This impressive phenom-enon warrants further investigation. For the first time, a giant X-rayarch was observed to linger for hours over the site of a decayedflare. Coordinated radio telescope observations from the groundlinkedthis arch to a major postflare radio noise storm. The relation-


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- ORIQINAI; RAGECOtaA PHOTOGRAPHSeen in the light of ionizedmagnesium by the

' rlltravioletSpectrometer/Polarimeter, the struc-ture of the flare becomesvisible. The brightyellow ribbons ndicate he opposite footpointsof

anarcade of flaring loops in the chromosphere.The white contoursshow areas of hard X-rayemission (16-30keV) observed simultaneouslybythe HardX-Ray lmagingSpectrometer.This wasL the first direct evidencethat hard X-rays comefrom the footpoints rather than the tops of loopsduring the impulsive phase, or onset, of a flare.In this image of the impulsivephase of theflare,made bythe HardX-Ray lmaging Spectrometer,thecolor scale indicatessoft X-ray (3.5-8 keV)intensity.The least intense emission isgreen andthe most intense is blue.Thetwo white patchesmarkthe locationof high-energyX-rays (16-30keV), believedto be thetwo footpoints of a mag-netic loop.

Red - mpulsive Phasehard X-rays"-ange - hermal Phasesoft X-rays

10 15 20

The X-Ray Polychromator producessimultaneousmaps of anactive regionat sevendifferentX-raywavelengths. These four imagesshow the region ust after the peak of the flare. Each image (from left toright) representsemissionfrom plasma ata differenttemperature: ionizedoxygen (3 milliondegrees),ionized magnesium (4 % milliondegrees), ionizedsilicon (8 milliondegrees), and ionized iron (30 milliondegrees). tLeft: This timeplot shows thetwodistinct phasesof the May 21stflare event. HardX-rays originate from electrons acceleratedduringtheexplosive release of energy in the impulsive phase.Soft X-raysare produced asthe plasma is heatedbythe high-energyparticlesin thethermal phase.The intensityof X-ray emissiondropsastheplasmacools down to its originaltemperature.


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particles (above 1 million electron volts or 1 MeV). Since gammaray radiation travels at the speedgf light from the sun to the Earthin ust 8 minutes, it arrives well ah%d9 most flare debris and alertsus to the possible onslaught of high-ki&&'&olar particles. Gammaradiation from the sun also carries clues to very high energy pro-cesses in other stars.A Gamma RaySpectrometer aboard Solar Maxalready has observedmore gamma ray events than the total previously recorded and hasseen features never viewed before. This instrument detected high-energy neutrons near Earth for the first time following a tremendoussolar flare on June 21, 1980. A particularly exciting event occurredon June 3, 1982, when the satellite detected intense neutron radia-tion for some 20 minutes after a major flare. These Solar Maxobservations confirmed the theoretical prediction that flares arecapable of producing extraordinarily high-energy particles. Morethan a dozen new spectral features, predicted but never beforeobserved, havebeendetected in a few of the strongest flares. Thesefeatures appear when very high energy particles disrupt atomicnuclei near the sun's surface. The gamma ray "signature" givesnew insight into rare and unusually powerful solar flare activity.Valuable information about flare effects can be gleaned from thesun's normally invisible halo or corona. By artificially eclipsing thesun and by viewing it from above the atmosphere against the blackbackground of space, one can observe the corona in visible light(4000-7000 Angstroms). The reward is to witness coronal massejections - huge high-speed disruptions of the sun's outermostatmosphere. The Solar Max Coronagraph/Polarimeter has viewedscores of these massive ejections of solar material moving throughthe corona after flares. Variations in the density of ejected coronalplasma also have been observed, but the exact correspondencebetweencoronal structures and flares has not yet been determined.Flare Maps Where on the sun do flares occur? Where withina flare are the sources of emissions? These basic questions Aboutthe location of flares are difficult to answer because the structure ofthe sun's atmosphere is complex and variable. The sun consists oflayers of gas, each having its own temperature and density. Thelayers are knitted together by a tangled, pervasive magnetic field.When a flare occurs, the characteristics of the plasma and, presum-

This graph of data obtained by1980 June 2125 -140MeV theGamma Ray SpectrometerOn June 21, 1980,records thefirst detection of extremelv hiahInergy neutrons near the ~a>t iafter a major flare.Theseneutrons flowed ~ a s the satellit1for 17minutes. he energy scacorresponds o the neutron

N ~ t r a nrr,.gy ,MY, arrival times: the first neutronselectron volts [MeV) while later

theone-minute mpulsivephasof the flare.I

-1000 -500 0 500 1000Seconds offer 1 18 20 16 UT


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Let: The Hard X-Ray Imaging Spectrometerprovidesadifferentview of the filling of a magnetic loop with hot.X-ray emitting plasma, representedhere in the lightershades of yellow. This sequence of imagesof a flare onApril 12,1980, shows (a) the brightonset of the flare;(b) brighteningof another point about one minute laterand evidenceof a connectingmagnetic loop; (c)approx-imately two minutes later, X-ray emissionthroughout thewhole loop, with a brightness comparable to that at theoriginal flare site.

\ Two white light images taken by the Coronagraph/Polarimeteron emissionduring a largesolar flare on June 3. 1982,which bathedAugust 18.1980, show an ejection of matter into the corona.The event Solar Max in neutrons or more than 20 minutes. The horizontalwasassociated with an eruptive prominencebelow.The first frame streak near the center indicatesgamma radiation from neutronsshows material moving into the corona; in the second, taken a half hour captured in the sun, and the lower streak representsneutronslater, the coronaappears as an expanding ring around the material. arrivingat the spacecraft.

6 Nov.1980 NOV 5 I- 6 TO 380 LevX-RAYS- LTRAVIOLET COV) The almost perfectcorrelationbetweenthese two curvesprovesthat electronsacceleratedto highenergies in the primaryenergyreleaseof a flare losetheir energyby collisionwith the upper chro-

mosphere, where ultravioletemission can be formed. The X-rayplot is from the HardX-Ray BurstSpectrometer; the ultravioletplotis from the UltravioletSpectro-


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The Subtle sun The solar radiant energy flux, over all wave-lengths, that reaches Earth is called the "solar constant" becauseits value (as measured with previous ~nstruments) oes not seemto changemarkedly.This energy interacts with the terrestrialatmos-phere, oceans: and?~d!%asses to drive atmospheric circulationand ~ e a t h e [ . $ y s t f i ~ . ~ ~ ~ ~ ~ # . ~ m . ~ tf solar energy is a criticallyimportantfacfdr in the delicate balanceof our biosphere. Changesof only a few percent are thought to affect global ice coverage, sealevel, and mean temperature.The approximate value of the solar constant is 1368 watts persquare meter, though it is difficult to measureaccuratelyfrom under-neath Earth's atmosphere. Access to space and the developmentof advanced instruments, however, provide an opportunity to meas-ure total solar radiation directly and precisely.Solar Max carries an Active Cavity Radiometer lrradiance Monitorthat is hindered only a little by the satellite's attitude control prob-lems. The monitor can detect changes in the solar energy flux assmall as one-thousandth of one percent; indeed, it has detected along-termdimming of the sun by one tenth of one percent during itsfirst twoyears of continuous operation. Over shorter periodsof daysto weeks, larger variations in total solar energy output have beencorrelated with magnetically active regions; for example, dark sun-spot patches temporarily reduce the radiant energy output by up totwo tenths of one percent.The instrumentalso discerned minute, periodic variations in radiantoutput at five minute intervals, as if the sun were "breathing." Thesignificance of these oscillations in the solar constant is not yet fullyunderstood,but they seem to arise fromwaves that movedeep into,and even through, the sun. Thus, these brightness luctuationsofferinsight into phenomenaand structures in the solar interior.Only by long-term monitoring can scientists detect variations in thesun's total energy output linked to the solar activity cycle. Bothsolarphysicists and terrestrial climatologists are interested n the c~ang -ing value of the solar constant.The as yet unansweredquestion iswhether small but persistent trends have a subtle effect on Earth'sweather and climate. Continued monitoring, over many years andmany solar cycles, is necessarybefore convincing correlations canbe made.

Right: TheActive Cavity Radiometer lrradiance Monitor is the first instru-ment able to make measurementsprecise enough to detect subtlechanges in total solar radiance.Since Solar Max was placed in orbit, themonitor has recordeda persistentdecrease in the "solar constant," hevalue of the sun's radiant energy receivedat the Earth.To date,thistrend amounts to a decrease of approximatelyone-tenthof one percent.Below:Many observatories around the world participated n the SolarMaximumYear research program.Renewalof the Solar MaximumMissionoffers another opportunity for coordinatedflare observations byinstrumentson the ground and on the satellite.

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rthe around as well as instrumentson balloons. rockets. and satel-liteLoperatedtogether with the orbitingobservatory to batch des-ignatedareas on the sun.Suchanambitious and concentratedsolar flare researcheffort wasunprecedented.The scientists continue to meet in workshops todiscuss solar flare theory and observations. This continued teameffort and peer review promotes a unified rather than fragmentarystudy of solar flares. The workshops offer a public forum for pro-ponents of competing flare models, and they stimulate rapid andclose communicationamong solar scientists.At the focus of this cooperativeresearcheffort, Solar Max becameavaluablescientific resource. Itsfull potentialwas just beginningtobe exploitedwhen the satellite was crippled. Restorationof SolarMax operationswill revive the coordinatedsolar flare researchpro-gram and keep intactthe links between solar scientists aroundtheworld. rSun-Earth Links A renewed Solar Maximum Mission isimportantto the searchfor solar-terrestrialconnections.Explosionsonthe sun havean impacton Earth;flares changethe intensityandcompositionof solar radiationandmatter that bombardour planet.Resultantmagneticstorms in Earth'sspace environment occasion-allydisruptcommunications,endangerorbiting spacecraft, damagepower stations and pipelines, and alter the chemistry and physicsof the atmosphere. Evidencesuggests that solar activity influencesterrestrial weather and climate, but the physical links are not yetidentified.Renewalof Solar Max offers three majorbenefits o solar-terrestrialstudies. Better understanding of the flare process should enablebetterpredictionof flareeventsandthedisruptiveradiationthat mayaffectspacecraft orvulnerableelectronicequipmenton the ground.AnextendedSolar Max Missionalsoenables longer-termmeasure-mentsof totalsolaroutput; accumulation of thesedata isnecessaryfor correlatingchanges in Earth'sweather andclimatewithchangesin solar radiation. Finally, coordinated observations of Earth'satmospherewill revealhowozoneandother constituentgases.varywith solar activity.The Sun as a Star The sun isour neareststar, the only onescientists can examine at sufficiently close range to resolve its


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Left: Solar Maximum Mission research is an essentialpartof theeffort to understandthe sun's influenceonthe Earth's magnetosphereand atmosphere.Below: Auroras arevisible evidenceof the far-reachingeffectsof solar flares. Auroralactivity increases mark-edly as solar particlesbombard the Earth's upperatmosphereafter a flare outburst.Below, right: Seen from space, theaurora rings theEarth'spolar regionswith a tremendous dischargeofenergy.This image was made by an instrumentaboardthe Dynamics Explorersatelliteon another missionmanaged by GoddardSpace Flight Center.


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SOLARMAXIMUMREPAIRMISSIONI the pastwhen anorbitingspacecraftor scientificinstrument suffered massive failures, thescientific community onEarthwas almost helpless.Typically, the opportunitytoextend humanknowledgewas lost, alongwith a considerable investment of talentand material resources. The riskof equipment failureshadows anyresearch project in space. The best insurance has always beenredundahcy, the expensive incorporationof backup components ininstruments sent into space.Now the Shuttle era introduces new options for ensuring the suc-cess of scientific missions. As access to space becomes moreconvenient wRh the Shuttle, it is now possible to send repair crewsand spare parts on service calls to ailing satellites. It makes sensetodesignmodularsatelliteswith replaceablepartsfor on-orbit repairservice. The Solar Maximum Repair Mission is thefirst demonstra-tion of this new capability.During the mission, the Shuttle crew will rendezvous with the sat-ellite, capture t, and mount it in thecargo bayfor repairs. Thefaultyattitude control system module will be replaced with a spare, andtwo of the sevenscientific nstrumentswill beserviced. After check-out, the repairedSolar Maxsatellitewill beremovedfrom theShuttleand returned to orbit. The faulty parts will be returned t~ Earth foranalysis, andfor possible refurbishmentand use on another mission.TheSolar Max Repair Mission will revive the most advanced solarobservatory in the world and its solar flare research effort. Thisrenewal of solar science will yield significant new informatior) thatcannot beobtained byobservatoriesontheground. Onlyan orbitalobservatory canwatch the sun long enough and precisely enoyghtogainafull understandingof solarflareenergybuildupandrelease.Restorationof Solar Max bythe repair mission is estimatedto costonly one-fourth of the replacement cost of this incomparable


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SMM OBSERVATORY

Coarse Sun SensorsThermalEnclosure

ElectronicsEnclosure

ACS

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Trunnion Pin- - - - - Grapple PointTransition ~ d a ~ t e t - 4


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Active Cavity Radiometer lrradiance MonitorDr. Richard C. WillsonJet Propulsion LaboratoryPasadena, CaliforniaCoronagraphIPolarimeterDr. Lewis L. HouseHigh Altitude O bservatoryBoulder, ColoradoGamma Ray SpectrometerDr. Edward L. ChuppUniversity of New HampshireDurham, New HampshireHard X-Ray Burst SpectrometerMr. Ken neth FrostNASA Goddard Space Flight CenterGreenbelt, M arylandHard X-Ray Imaging SpectrometerProf. C. De Jage rThe Astronomical Institute at UtrechtThe NetherlandsUltraviolet Spectrometer/PolarimeterDr. Einar Tandberg-Hansse nNASA Marshall Space Flight CenterHuntsville, AlabamaX-Ray PolychromatorDr. Loren W. ActonLockheed Palo Alto R esearch LaboratoryPalo Alto, Ca lifornia


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Renewing Solar Science the Solar Maximum Repair Mission

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