1987 Summer Symposium, 3-4 Aug 87ocr

7/28/2019 1987 Summer Symposium, 3-4 Aug 87ocr

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198fSUMMER SYMPOSIUMON

SCIENTIFIC USES,OFORBITING. EHTERNRL TRNKS

BOULBEf?, COf OR/?00RUGUST 3-4

SPONSORED BY:UCRR FOUNBflTIONCENTER FOR SPRCE @ GEOSCIENCES PUL ICYNRSRMRRTlN MRRIE7TIp CORPORHTtONUSRR


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WORKSHOP ON SCIENTIFIC USEOF ORBITING SHUTTLE EXTERNAL TANKSAugust 3 - 4, 1987

Monday, August 37:30 am8:00 - 8:30 am

8:30 - 9:00 am

9:oo - 9:30 am

9:30 - 9:45 am

9:45 - lo:15 am

lo:15 - lo:30 amlo:30 - 11:30 am

11:30 - 12:30 am12:30 - 1:30 pm

shuttle service* from hotels to NCARregistration

Walter Orr Roberts Board RoomNational Center for Atmospheric Researchwelcome and introductory remarksChairman - Dr. Walter Orr RobertsPresident Emeritus of UCARCurrent Status of the Space Phoeniz ProgramDr. Randolph WarePresident, External Tanks CorporationRoles for Orbiting ETs in the U.S. Civil Space ProgramDr. George MorgenthalerChairman, Department of Aerospace EngineeringUniversity of ColoradoA Gamma Ray Ezternal Tank ApplicationDr. David KochPrincipal Investigator, Gamma Ray Imaging Telescope

Smithsonian Astrophysical ObservatoryBREAKGRIT and ET backgroundDr. Max Nein - Marshall Space Flight CenterBilly Davis - Marshall Space Flight CenterTom Mobley - Martin Marietta CorporationL U N C H served in meeting roomInitial Comments in Discussion .-Ireas

ASTRONOMY AND ASTROIHYSICSDr. Jack Burns - University of New MexicoDr. Bill Priedhorsky - Los Alamos National Labs


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-2-EARTH OBSERVATION AND REMOTE SENSINGDr. Alex Goetz - University of ColoradoDr. John Gille - NCARDr. Bill Emery - University of ColoradoMATERIALS SCIENCESDr. Jean Koster - University of ColoradoDr. Byron Lichtenburg - Payload Systems Inc.LIFE SCIENCESDr. Byron Lichtenburg - Payload Systems Inc.Dr. Marv Luttges - University of Colorado

1:30 - 5:00 pm Work Sessions in Above Discussion Areas5:00 pm shuttle service * to hotels6:30 pm shuttle service* from hotels to banquet7:00 pm BANQUET (C or and Cleaver, 3295 30th, 443-9505)Dinner Speaker: Margret AugustineSpace Biospheres Ventures

Tuesday, August 47:30 am shuttle service from hotels to NCAR8:15 - 8:30 am reconuene meetingDr. Walter Orr Roberts8:30 - 12:00 am Work Sessions in Discussion Areas12:00 - 1:00 pm L U N C H in NCAR Tree Plaza1:00 - 3:00 pm Group Presentations to Plenary Session3:00 pm adjourn workshop

*Clarion, Hotel Boulderado, and Holiday Inn


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TIC-Augustine, MargretC.E.O., Project DirectorSpace Biosphere VenturesP.C. Box 689Oracle, Arizona 85623Baillif, FayeMartin Marietta MichoudP.O. Box 29304 - Dept. 3018New Orleans, LA 70189Bell, Dr. William4415 Hasting DriveBoulder, CO 80303Bender, Dr.PeterUniversity of ColoradoJoint Institute for LaboratoryAstrophysicsCampus Box 440Boulder, ColoradoBorn, Dr. GeorgeUniversity of ColoradoDirectorColorado Center for AstrodynamicsResearchCampus Box 429Boulder, Colorado 80309Brumley, BobDeputy General CounselDepartment of CommerceWashington, D.C. 20230Burns, Dr. JackNational Center for Supercomputer ApplicationsUniv. of Illinois605 E. Springfield AveChampaign , IL 61820Byerly, Dr. Radford, Jr.University of ColoradoDirectorCenter for Space andGeosciences PolicyCampus Box 18480309


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Cash, Professor Webster C.Center for Astrophysics andSpace AstronomyUniversity of ColoradoCampus Box 391Boulder, Colorado 80309Clement, DavidSubcommittee on Space Scienceand Applications2321 Rayburn BuildingWashington, D.C. 20515Dagel, NancyJohnson Engineering3055 Ceter Green Dr.Boulder, CO 80301Davis, Dr. M.H.Program Director, USRAP.O. Box 391Boulder, Colorado 80306-0391Edelson, Dr. Burton I.NASAAssociate Administrator forSpace Science and ApplicationsMail Code AE-3Washington, D.C. 20546Emery, Dr. BillUniversity of ColoradoColorado Center forAstrodynamics ResearchCampus Box 431Boulder, CO 80309Esposito, Dr. LarryUniversity of ColoradoLaboratory for Atmosphericand Space PhysicsCampus Box 392Boulder, CO 80309Gille, Dr. JohnNational Center for Atmospheric

ResearchGlobal Observations UnitRoom ML-363P.O. Box 3000Boulder, CO 80307


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Goeta, Dr. AlexUniversity of ColoradoCenter for the Studyof Earth from SpaceCampus Box #449Gimarc, Major John A.U.S. Air ForceConsolidated Space OperationsCenter2726 PurgatoryColorado Springs, CO 80918Grodzka, Dr. PhilomenaLockheed Missles & Space Co. Inc.Huntsville Engineering4800 Bradford DriveHuntsville, AL 35807Hansen, ElaineUniversity of ColoradoProgram DirectorSolar Mesosphere ExplorerCampus Box 10Hill, Mr. AllanBoeing Aerospace CompanyP.O. Box 3099 - Mail Stop 8K93Seattle, Washington 98124-2499Hinners, Dr. NoelDirector, NASA Goddard SpaceFlight CenterGreenbelt, Maryland 20771Hofgard, Jefferson S.Assistant DirectorCenter for Space andGeosciences PolicyUniversity of ColoradoCampus Box 184Boulder, Colorado 80309Hosenball, S. Neil, Esq.Davis, Graham and Stubbs1001 22nd Street, N.W., Suite 500Washington, D.C. 20037Jenkener, HelmutEuropean Space Agency3700 San Martin DriveBaltimore, MD


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Jones, Mr. Ronald W.Phillips Petroleum Robotics Group229 PL, PRCBartlesville, OK 74004Kellogg, Dr. William W.Symposium Rapporteur445 College AvenueBoulder, CO 80302Koch, Dr. DavidSmithsonian Astrophysical Observatory60 Garden StreetCambridge, MA 02138Koster, Dr. Jean N.University of ColoradoAssociate DirectorCenter for Low Gravity FluidDynamics and Transport PhenomenaCampus Box # 429Lampton, Dr. MichealUniv. of California - Berkeley1082 Sterling AveBerkeley, CA 94708Levin, Dr. George M.NASA HQBuilding 10-BCode MDWashington, D.C. 20546Lichtenberg, ByronPayload Systems, Inc.66 Central StreetWelesley, MA 02181Luttges, Dr. MarvinUniversity of ColoradoDirectorBioserve Space Technology CenterCampus Box 429Boulder, Colorado 80309Mann DavidConfeience CoordinatorCenter for Space andGeosciences PolicyUniversity of ColoradoCampus Box 184Boulder, Colorado 80309


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Maryniak, GreggExec. Vice PresidentSpace Studies InstituteP.O. Box 82Princeton, NJ 08540Mobley, TomMartin Marietta CorporationP.O. Box 29304 - Dept. 3010Michoud Air SpaceNew Orleans, Louisianna 70189Moore, Dr. JessieBall Aerospace SystemsMorganthaler, GeorgeDean, School of EngineeringUniversity of ColoradoCampus Box 422Boulder, Colorado 80309Nein, MaxNASA - Marshall Space Flight CenterMail Code PS 02Building 4200Marshall Space Flight Center, Alabama 35812Padwa, David J.Vice - ChairmanExternal Tanks Corporation1001 MapletonBoulder, CO 80302Priedhorsky, BillMail Stop D436Los Alamos Nat'1 LabsLos Alamos, NM 87545Roberts, Dr. Walter OrrPresident EmeritusUniversity Corporation forAtmospheric ResearchRoom 208P.O. Box 3000Boulder, Colorado 80307Rogers, Thomas F.Chairman, External Tanks Corporation7404 Colshire DriveMcLean, VA 22102Schmadel, KevinProgram Director, USRAP.O. Box 391Boulder, Colorado 80306-0391


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Stone, Dr. WilliamNational Bureau of StandardsBldg. 226 - B162 CBTWashington, D.C. 20234Sterling, DebDirectorExternal RelationsUniversity Corporation forAtmospheric ResearchP.O. Box 3000Boulder, CO 80307Taranik, Dr. James V.Dean, Mackay School of MinesUniv. of Nevada-RenoReno, NV 89557-0047Ware, Dr. Randolph H.President, External Tanks CorpationRandolph Center1877 BroadwayBoulder, CO 80302Williams, FrankDirector of Program Development/AdvancedPrograms DepartmentMartin Marietta CorporationP.O. Box 29304 - Dept. 3010Michoud Air SpaceNew Orleans, Louisianna 70189


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-

to&H CONGRESSZsf Session HOUSE OF REPRESENTATIVES REPORT100-204

NATIONAL AERONAUTICS AND SPACE ADMINISTRATIONAUTHORIZATION ACT, FISCAL YEAR 1988

JULY 7. 19&7.--Committed to the Committee of the Whole House on the State of theUnion and ordered to be printed-

22

- UTZLIZATXON OF ORBITING SHUT~ZE Ekmxxu TmxsThe Committee notes that the Space Shuttle External Tank (ET)is a potentially valuable resource that should be considered for pos-sible space development. Qualified academic research groups couldbe awarded ET resources for spacebased research much like theland grant concept of the pest. Using orbiting ETs, universitiesworking cooperatively with industry might be able to increase sci-enti& research opportunities, expand our Nations space infra-structure and broaden the spectrum of private space enterprise.In response to the Committees request in House AuthorizationReport 99-829, NASA has delivered to the Committee a reportspecifying the technical, operational, cost, and safety requirementsfor RT orbit insertion. The NASA report External Tank Utiliza-tion on Orbit states: The engineering and operating problems in-volved with this objective are basically within the current state-of-

the-art of Shuttle operations, support system and technology. Thereport also specifies the impact on Shuttle payload, propellant re-quirements for station keeping, requirements for accessibility to or-biting ETs, probability of space debris or micrometeoroid damage,and NASAs estimate of the cost of ET modifications and oper-ations. The Committee appreciates the delivery of this detailedreport in response to the Committees specific request.The Committee is pleased to be informed of progress acheived byuniveftity groups and NASA in the past year toward realizing thepotential value of ET resources: (1) The Universty Corporation forAtmospheric Research (UCAR), a Z-year old group of 57 universi-ties and research institutions, is leading the Space Phoenix pro-gram to obtain orbiting ETs and develop them for scientific andcommercial purposes using non-government funds; (2) NASA hascreated a high level committee to work with UCAR on the SpacePhoenix program; (3) UCAR and the Government are making goodprogress toward an agreement concerning transfer of one or moreFYIs to UCAR; (4) NASA is supporting studies of a Gamma Ray Im-aging Telescope (GRIT) which could be installed in an orbiting ET;(5) Zero gravity simulations of GRIT telescope assembly proceduresare being conducted at the Marshall Space Flight Center; (6) Asymposium of space scientists has been convened by universitygroups to consider science experiments that can be conducted inand from space using ETs.


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I I I I I I I I I I I I I I I I I I JULY 27, 1987.

NEWS

Re&irch Advakes dn 3 Continents ..

extend taok like thla ooe rolled out in 1977 at a NASAity in New Orleans could be converted into M orbitinthat would allow more experimentatios~ in WCC.

From Shuttle TanksTONY REICEEARDT

br mpaceflight opportuni-in-Earth orbit if a small C-4+anopany k able to turn the

shuttles giant external fklprivately owned orbit*

gioeem will atteod a cbeed work-shop io Boulder to take a fut3tcrack at ck6nii science requirementa Tar the Iabitaf a3 the Ex-ternal nlok company (En-CO) hat3labeled ib propoeed facility. Tbemeeting ia eponaored by the Uni-versity Corporation for Atmo-spheric Research (WAR)-a coo-sortium of 55 universities thatown8 80 percent of ETCOrdock--NASA sod aevcml otherco-spoosors, including Martin

9. ;Marietta, which build8 the &uttbtbeltaokn. ;Mthoughtbaidmof&agitlgthetankarpar6nstpropoM!dmanypare ago, NASA bad never ex-preemd any partilx llar interest i npumuing it-in part becaume noonebadahownanyckarueeforatank,ntranded125mikaahovetbeEfu&thatwouldquicklybecomeadangerolgpkceoff4pacejlmkun-ka ita orbit were raked and aabi-l&d. Currently, the tank reaches98 percent of orbital velocity beforeheiogdroppedtoburoupovertbaIodiaooceM.

Tbat at&u& has eofteoed, how-ever. IO February a NASA et&group concluded that the engioeer-ing aod operational requirementsto take the eo4oot40og ttulkasafely to orbit and coove.rt them touseful v&me are within the %u-rent l&ate of the artbf the ahuttk.

Aepecifkuaehaabeeofoundaswell. Under a grant from NASA%MarahaU Space Flight Center, Da-vid Koch of the Harvard/Smitbao-q iao Center hr Astrophy&s andMartiiMarkttaare~thsuseofarefurbiitanktomotmtl 3O-foattha3pemtmrcaIbdGIUTS,brGammaRayfmmging_.._ _. _._ .-_ -.. _ _ _..

nkEcope system.Onceinorbit,thetankwouklheemptied by ktting residual fuel8

boil out and then rep-with gas Mronauta would enterthe taok through portboka (uoda-water train ii atudiea at uarsbanhave ahowo that t hii ia poeeibk) toinstalltbeGlUIS&ectorandother science equipment broughtup by tbe httle. Attitude control,communications and other supportequipment would be attached, andtbetankwouldberaiaedtoanalti-tudeof300to4OOkilometem.Tbetotalalatlbddtle$zoominb~divided eveoly between tiy! hard-ware ad the oparatboal expensea

A space sieveNoooeclaiiitsgoingtobeeay.Space debris k one of my biggestworrka, said Koch. At the altitudeplanned br GRITS, there ia a 90percent chaoca that micromeboroidn would penetrate the taokathin m etal with0 a year, ruptumthepressuritadveneelandruintheexperiment. If you kave it upthere brig emu&,m uyr Koch,~~goiogtohavaaakva

much more ambitious madream--selling ib spa&. Ttimate scientists will be km3e room inaide the cBLabitatataprojectedaxxtof$lpecubic foot per day.President Ftandolph WITIC eventua lly wants volve the wbok university nity in civi l spnce activitiesow knowkdgeabk acientMid be supported tba cogoab. wan nkeptical that butNASAwou.klhaabletoaffordto um the L&tat. Unpeopk &on% have tbe moolmervai.Wue admiUed that tpury,toaucceu&mustattmctalotof cxmtomar Em!0 otiicthaycmnkeKpthecoetacbwobymakiogtbafscilityspartanuoeo-cumbered by bureaucraccbdytaibredtobMicexperimen-tJd.-

Tb bbitat is Dot cwith NASA% Space Stawtomen, Ware emphasizkiUtykmor8tikeakrgeware-houooatthee&eofaninciustria~WUOMillour!3UcceSaping to ckpaod on thcella t -: 1Rei&hafdf ir 0 WnrhingtotonrrWd8rOdditOrOtSSpaOEWOtldmqpdn~


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EXTERNAL TANK GAMMA RAY IMAGING TELESCOPE STUDY

Contract A71128

Final Report

For the Period 15 .July 1986 through 27 January 1987

Principal InvestigatorDavid G. Koch

February 1987

Prepared forMartin Marietta Corporation

New Orleans, Louisiana 70189

Smithsonian InstitutionAstrophysical Observatory

Cambridge, Massachusetts 02138

The Smithsonian Asl.rophysical Observatoryis a member of theCenter for Astrophysics


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Final Report .External Tank Gamma Ray Imaging Telescope Study

David G. KochSmithsonian Aettophysical Observatory

60 Garden StreetCambridge, MA 02138Introduction

This is the final report for a contract to study the use of an .External Tank (ET) for aGamma Ray Imaging Telescope System (GRITS).The purpw of this Gamma-Ray Imaging Telescope System is to do pointed stu-

dies with much improved seqsitivity in high energy gamma-ray astrophysics as a con-tinuation of NASAs program following the survey to be done by the Gamma RayObservatory (GRO).

This final report is not intended to document fully all that has been learned to date concern-ing this concept, since work prior to this study has been drawn upon and work subsequent to thisstudy will be cont inuing. Rather, the intent of this report is to formally transmit the contribu-tions of Smithsonian Astrophysiscal Observatory (SAO) to Martin Marietta (MMA). This materialhas been used in the oral presentations that have been made during the study and is to be used inpreparing of the fina l report to Marshall Space Flight Center (MSFC). Well coordinated, coopera-tive paralle l work was carried out simultaneously at SAO, MMA and MSFC. Much o f the back-ground material upon which this study was based came from a previous SAO fina l report,ALarge-Area Gamma-Ray Imaging Telescope System under NASA contract NASW-3743 in 1983.The form of this report is to present both the charts used for formal presentations and, on the fac-ing pages, an explanation of the topics outlined on the charts.


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Processes For Production of High Energy +pRaysGamma rays are produced by a number of high energy processes. These include h igh energypartic le interactions that lead to the production of x0 -mesons which eventually decay into gamma

rays. Matter-antimatter ann ihilation also produces gamma rays. When electrons and positronsannihila te they produce gamma rays with a characteristicenergy of 0.51 MeV. When protons andanti-protons annihilate they produce pions, including x s. The X spectrum has a characteristicslmpe with a pea.k at 68 MeV. In a process which is the inverse of the normal Compton process,energetic electrons collide with low energy photons, such ss optical or UV photons near an intensesource of radiation, and boost the photon energy up into the gamma-ray regime. Another processinvolving energetic electrons takes place when the electrons scatter off of nuclei due to the Coulombforce. The resulting acceleration of the charged particle as its trajectory is changed causes the elec-tron I,O radiate gamma rays. This is called electron Bremsstrahlung, i.e., braking radiation. Afinal process called magneto-Bremsstrahlung also referred to as synchrotron radiation, results fromdeliecting the path of the energetic electrons with a magnetic field. Again it is the acceleration ofthe charge as its trajectory is changed that causes the electron to radiate. Although gamma raysa.re produced in the spontaneous decay of nuclei, resulting in gamma rays of very distinct energy,t.his gamma-ray line emission s typically of only a few MeV energy.


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Processes For Production of High Energy y-Raysl High Energy nuclear interactionsInteractions that-lead to ?r decayl Matter-antimatter annihilation

e- + e+ 3 27 p+p-M++vi-+n0 Inverse Compton effect

Energetbelwtrons impart energy to low energy photonsl Electron BremsstrahlungEnergetic electrons scatter off of nuclei and radiate y-raysl Synchrotron radiationEnergetic electrons in a strong magnetic field radiate y-raysl Nuclear transitionsEnergies up to a few MeV


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Astrophysical SourcesThe gamma-ray emission that has been measured to date can be classified as either diffuse

emission or emission from discrete sources. The diffuse emission can be divided into the extendedemission coming from the galactic plane and a diffuse extra-galactic component. The formerresults from the nuclear collisions of cosmic rays, primarily protons, with interstellar dust and gasand from electron Bremsstrahlung of cosmic-ray electrons with the same interstellar matter. Theinverse Compton process and synchrotron mechanism are far less significant in the interstellarregions. The gamma-ray flux from a particular portion of the galactic plane is a measure of thecosmic-ray and matter depsity in that part of the Galaxy. Since the matter density can be fairlywell determined from infrared and CO measurements, the in-situ cosmic-ray density can be derivedfor remote portions of the Galaxy. The extra-galactic component is extremely difficult to measurebecause it is a very low flux. It presumably has little or no spatial structure, although it mayresult in part from many faint sources. Any instrument background can make it difficult to estab-lish the absolute flux level.

The discrete sources can be grouped into quite a few categories. These include truly compactobjects, such as, neutron stars, pulsars (which are neutron stars producing detectable periodic radi-ation), black holes and and the galactic center (whose true nature is not yet understood). Anotherpseudc+discrete source but not compact are dense molecular clouds. Again, cosmic rays collidingwith a locally high concentration of matter will result in a high production rate of gamma rays.Gamma-ray bursts at an energy of a few MeV were first detected with the Vela satellites and havesince been detected by many other spacecraft at both lower (x-ray) and higher (tens of MeV) ener-gies. Since there first detection in early 10709, the nature of the sources of these bursts remains amystery. They may be some old familiar source manifesting itself in a newly detected way , suchas comets falling onto neutron stars, or may be an entirely new class of object. In either case, thehigher energy regime has not as yet been explored. Of the two dozen point like sources detected todate, only four have been associated with previously known objects, the Crab and Vela pulsars, thequasar 3C273 and the dense cloud in p Oph. Only the two pulsars are hard clad identificationsbased on the pulsed signature of the gamma-ray emission. The other two are based on positionalcoincidence with very likely candidates. The remaining objects have not been identified due to thecurrently large positional uncertainty.On a much grander scale extra-galactic sources of gamma rays have been and should con-tinue to be found. The one identified discrete source is the quasar 3C273. Although it is one of

the nearest quasars, others should be detected as the sensitivity of the observations is improved.Other active galactic nuclei (AGN) such as BL-Lac type objects and Seyfert galaxies may alsoprove to be soqrces of gamma rays. Closer to home, galaxies in our local group should be detect-able with just one order of magnitude improvement in detection sensitivity. In particular theLarge and Small Clouds of Magellan and the Andromeda Nebula (M31) should be producinggamma rays just as they are produced by the Milky Way given similar densities of gas and dustand fluxes of cosmic rays. One can anticipate mapping the gamma-ray intensity in these objects,since these local galaxies are large (8 , 2.5 and 1.7 respectively), even with respect to the resolu-tion of gamma-ray instruments.


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Astrophysical SourcesDiffuse Galactic Emission

a Cosmic ray nuclei collisions with interstellar gas and dustl Electron Bremsstrahlung with interstellar gas and dust

Discrete Sourcesl Compact objectsPulsars, neutron stars, black holes, the galactic centerl Dense molecular cloudsl Burstersl Unidentified gamma-ray sourcesl Extra-galacticAGN: Quasars, BLLac, SeyfertsLocal group of galaxies: LMC, SMC, M31


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Evolution of Gamma-Ray AstronomyThe birth of gamma-ray astronomy can be traced to predictions made in 1958 in a paper by

Prof. Ph ilip Morrison. This lead to a flurry of optimistic attempts to detect gamma rays. Unlikecosmic x-ray sources which were discovered serendipitously and found to be much brighter thanone would have expected based on previous knowledge of normal stars, it is now known that theflux from gamma-ray sources is much fainter than earlier predictions suggett5ed. In fact tp fluxfrom the strongest source above 100 MeV, the Vela pulsar with a llux of 10 photons/cm set, ismore than one mil lion times less than the flux from the strongest x-ray source in the 2-10 keVregime, Sco X-l, which has a flux that varies from 20 to 40 photons/cm2sec.

For purposes of the following discussion, the range in energy will be restricted to 100 MeV to10 GeV. The reason for this is mult iple. At the lower energies protecting against non-primarygamma-ray background is more difficult, such as from radioactive decay products within theinstrument or deca.y of secondary products from the interact ion of cosmic rays, such as from muondecay. At the lower energies, the gamma rays interact primari ly by the Compton interaction.Since it is impractical to measure the direction of recoil of the nucleus involved, there is a largeuncertainty in the incident direction of any one photon. In fact one is left with an annulus ofuncertainty. At energies in excess of 100 MeV, photons interact exclusively by pair production,resulting in a relatively smaller uncertainty in the incident direction. This uncertain dependsapproximately inversely as the energy. Contrary to what one might at first expect, even withfewer events detectable at the higher energies, the centroid of uncertainty improves with increasingenergy. This is because not only does the extended emission from the galactic plane decrease at thehigher energies, but in addit ion, the solid angle conta ining the source events is reduced by includ-ing only the higher energy events. In this way less of the extended background emission needs tobe included, increasing the signal to noise for the source. At the lower energies, on the order of anMeV, much of the interest is not only in determining the incident direction, but also in preciselymeasuring the energy of the gamma. rays, since there exist important emission line features at theseenergies. At the higher energies, there are no nuclear line emissions and one need only to measurethe broad spectral shape. For example, it is important to determine whether the emission is due to7~ decay or a power law due to Bremsstrahlung and to determine if there is a cutoff or break inthe spectrum. Beyond 100 GeV ground based observations are possible. These measurements arebeginning to produce results with perhaps as many as a dozen sources detected, many with timevarying signatures.

The early attempts to detect gamma-rays with high altitude balloon experiments were notonly frustrated with find ing very low upper limits, but also by a relative ly high background ofsecondary gamma ra.ys produced by cosmic rays in the upper atmosphere. The first truly cosmicgamma rays were detected with an instrument on OSO-3. This instrument made of scintillatorsand solid Cherenkov counters had very limited angular resolution, but was able to distinguish agalactic plane component with an enhancement towards the galactic center. Two space probes ofnearly the same characteristics, SAS-2 and Cos-B, were subsequently flown and are the basis forour knowledge of the gamma-ray sky at energies greater than 100 MeV. A more sensitive anddiverse spacecraft, the Gamma Ray Observatory (GRO), is currently under development .

Throughout the evolution of this field of astrophysics, the capability and size of the detectorsflown have more or less followed the evolution of the launch vehicles for space probes. In each era,although the detectors were not at the true limi t of the launch capab ility, an order of magnitudeincrease in size was not. possible at the time. In addi tion, it is unreasonable to expect al l of theavai lable resources to be committed to creating the largest possible gamma-ray detector. Forexample, SAS-2 was launched on a Scout rocket at the same time that the Saturn V was launch ingmen to the moon. Thus, it would be unreasonable to expect to see a major improvement overGRO until sometime well after a nmjor enhancement in launch capability becomes available, if onefollowed the convent ional approach to the evolution of events.


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Evolution of Gamma-Ray Astronomy( 100 MeV < E < 10 GeV )

Device Launch Duration Area,cm2 PurposeBalloon exper* 1960soso-3 Mar 1967SAS-2* Nov 1972Cos-B* Aug 1975GRO* 1990GRITS mid-1990s

10s hours < 1,000 Pioneering16 months 46 Background7 months 640 Survey81 months 576 Galactic survey

2-4 years 6,500 All sky survey5 years 250,000 Pointed studies

* Spark chambers with large field of view.


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Results Up Through Cos-BAs mentioned earlier, the initial measurements of cosmic gamma rays were made with an

instrument on OSO-3. These measurements indicated an extended galact ic component with anenhancement towards the galactic center. An additional diffuse extra-galactic component was alsomeasured. The results from the two small spark chamber detectors, SAS-2 and Cos-B, provided acatalog of two dozen sources, with only four of the sources being identified with previously knownobjects. Since the positional uncertainty for these objects is on the order o f a few degrees, it is vir-tually impossible to associate them with the many candidate x-ray, optical or radio sources thatare within the error boxes, unless there were some distinguishing feature. This was clearly thecases for the identification with the Crab and Vela pulsars. Even the second brightest gamma-raysource in the sky at galactic coordinates 195+5 cannot be unequivocally associated with a knownobject, although one sof t x-ray source does appear in its error box. The major draw back toimproving this situation is that the very low flux of gamma rays requires a very large detector forbuilding up substantial statisti cs to permit improvement in locating the centroid of the source.Inherent improvement in the angular resolution of the detection technique is also of great advan-tage. The success of Cos-B was a result of being able to operate the instrument for almost sevenyears. The Energetic Gamma-Ray Experiment Telescope (EGRET) on GRO is designed to providean increase in area over SAS-2 by a factor of ten as well as provide improved angular resolution.The main goal of the GRO mission is to perform an all sky survey and detect many more sources.Having four different instruments, it will be able to make measurements from of hard x-rays oftens o f keV up to energies in excess of tens o f GeV.

Astronomy and Astrophysics for the 1980'sThe Astronomy Survey Committee of the National Academy of Sciences often referred to as

the Field Committee, on page 165 of their report Astronomy and Astrophysics for the 1980%has identified the direction that needs to be taken for the future.

Subsequent to GRO, an advanced high-energy gamma-ray telescope of ve ry large area,high sensitiv ity, and high angular resolution will be needed for long-term observations ofselected sources and regions of special knterest. This will be necessary to achieve the sta-tistical accuracy in the counting of gamma-ray photons required to resolve spatial andspectral features of the sources and to analyze their variations. The field o f view of thetelescope need not be wide, and an appropriate goal for angular resolution is the order o f1 to 2 arcmin.


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Results Up Through Cos-Bl Galactic Component with unresolved structurel Small diffuse extra-galactic componentl Twenty-five discrete sources

(Only four have been identified.)l Low flux requires very large area detectors


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History of GRITSThe goals identified by the Astronomy Survey Committee, can be achieved with a detector

that has been developed and proven. The original detection concept that is utilized in theGamma-Ray Imaging Telescope System (GRITS) was proposed by Prof. Kenneth Greisen of Cor-nel l University in 19G6. The basic technique utilizes an imag ing gas Cherenkov counter and plasticscintillators. A prototype of the instrument was bui lt having 4.5 m2 sensitive area with sevenfive-inch phototubes at the focus. The gondola itself was 20 feet long and 10 feet iri diameter. Sixballoon flights of this instrument were carried out in the early 1970s. The results from this flightsseries not only proved the concept, but also made the first detection of a discrete cosmic gamma-ray source of greater than 100 MeV, the Crab pulsar. From the additional flights in the series, itwas determined that t,he intensity of the pulsar was varying. This was subsequently seen in thedata from the Cos-B detector.

The concept has remained dormant for two reasons. The power of the instrument is in con-ducting pointed studies over restricted regions of the sky, rather than in attempting to conduct alarge scale survey. Thus, unt il GRO has begun to produce a catalog of many objects the need forsuch an instrument has not existed. Secondly, the means for effecting the instrument on asufficiently large scale did not exist prior to the implementation of the Shuttle and the Space Sta-tion. It was only when it became apparent that the External Tank (ET) could be avai lable on-orbit and that significant on-orbit assembly could be carried out from the Space Station, that thecurrent concept was proposed to the Space Station Task Force in 1982 and funded as an innova-tive use of the Space Station.The present study, which is funded by NASA Headquarters Office of Space Flight, Code M,and is being conducted concurrently by NASA Marshall Space Flight Center, Martin MariettaMichoud Aerospace and the Smithsonian Astrophysical Observatory, builds on both the previousinstrument development and ET appl ication (ETA or Q) studies.


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History of GRITSl Detection technique conceived by Prof. Ken Greisen, 1966l Prototype built at Cornell Univ. in late 1960sl Six balloon flights in early 1970sl Concept proven by first detection of Crab pulsar >lOO MeV, 1973l ET concept proposed, 1982l Space Station Task Force funded detailing of idea, 1983l Code M RTOP study at MSFC-Martin Marietta-SAO, 1986


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Detection TechniqueA schematic of the instrument is shown on the following page. The basic concept of how the

gamma rays are detected is the following: The incident high energy gamma ray penetrates the thinwall of the pressure vessel and within the trigger module sandwich, the gamma ray converts with a20% probability into an energetic electron-positron pair. Directly underneath the convertermater ial a plastic scintillator detects the passage of these two charged particles by producing apulse of ligh t which is detected with photomul tiplier tubes. The relativistic charged pair then gen-erate UV-visible ligh t as they travel through the gas inside the ET. This light production, knownas the Cherenkov process, results from the charged pair traveling through a dielect ric media with avelocity greater than the velocity of light i n the media. The index of refraction of the gas deter-mines the threshold energy for the process, the light production rate and the emission angle of thelight. The light is radiated at a fixed angle with respect to the direction of travel of the chargedparticle. The ligh t from the charged pair is imaged by a mirror, producing two distinc t rings ofligh t at the focus of the mirror. The ligh t arrives 110 nanoseconds after the pair creation tookplace in the converter. The charged pair on the other hand continues on through the mirror andpasses through a time-of-tlight (TOF) scintillator where they register a signal 79 nanoseconds afterthe pair was created. To reject incident charged particles, another plastic scintillator is placeddirectly above the converter and used to veto incident charged particles which would otherwiseproduce a trigger pulse.

The basic electronic signature for a genuine gamma-ray event is a pulse in the trigger scintil-lator with no pulse seen in the veto scintillator within 5 nanoseconds, a second pulse detected inthe time of flight scintillator 79 nanoseconds later and finally, a pulse of light in the focal plane110 nanoseconds after the pulse was detected in the trigger. In addi tion, the ligh t seen in thetrigger scintillator and at the focus must correspond to that produced by two particles and uponanalysis of the data from the event the image recorded must correspond to two rings of ligh t of theappropriate amplitude and diameter.


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Detection Technique0 Convert gamma ray into an electron-positron pairl Detect the conversion with an adjacent plastic scintillatorl Relativistic charged pair generates visible light in gasl Image and detect two cones of light using conventional opticsl Additional scintillator behind mirror detects exiting pairl Charged particle veto scintillator in front of converterl Event trigger based on high speed threefold timedelayedcoincidence


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I I I I I I

ET - GRIT

Time of Flight Scintillator

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Mirror

MICHOUD AEROSPACE


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Instrument CharacteristicsThe basic instrument characteristics are tabula ted here. The active detection area is 250,000

cm2. Although the cross sectional area of the ET is 555,154 cm2, not a ll of this can be used. Themajor support ring at the bottom of the tank (the 2058 rin !I ) extends 39.4 inches in from the sideof the tank leaving an unobscured aperture of 322,494 cm . Allowing for collection of the lightfrom the edges of the scintillators as well as for a central inactive area behind the focal plane,reduces the active area to the 25 m2. A conversion efficiency of 20% has been chosen. It is atabout the cross over value where the increase in mul tiple scattering of events is no longer outweighed by the improvement in counting statistics.

The fie ld of view is 5 unvignetted, that is, the sensitive area is constant within the fie ld ofview. This is possible by having the mirror and time-of-flight scintillator subtend the entire 27.5foot diameter of the ET so that even events that are 2.5 off-axis near the inner edge of the 2058ring are stil l intercepted by the mirror and TOF.

The inherent angular resolution of GRITS is about the same as EGRET, the limitationsbeing the same physical processes aking place in both instruments. Thus the ability to locate thecentroid of events from a point source depends on the energy of the gamma-rays detected (thisdefines the width of the Gausssian distribution) and the statistics. The improvement over EGRETis simply the ability to accumulate the statistical significance much more quickly.The energy threshold is determined by the index of refraction of the Cherenkov gas and thethreshold for detection of the light. The threshold for the Cherenkov process s determined by theLorentz factor, TT, which has been selected equal to 83. For a particle to produce 280% of themaximum light , 72 2.24~~. Assuming the energy is equally divided between the electron andpositron, the threshold for detection of gamma-rays will be 182 MeV.The time resolution for each event is 5 nanoseconds, the width of the trigger pulse from thescintillators and focal plane phototubes. Only 10 nanoseconds of deadtime is necessary for reject-ing each penetrating charged particle incident on the converter and and about 2 microseconds ofdeadtime per gamma-ray event is necessary for capturing the bulk of the light in the NaI con-verter. The major loss of exposure time will be due to passage through the South Atlantic Ano-maly, SAA, and during attitude maneuvering. This is to be kept to 12570 loss.The spectral resolution of the instrument is obtained by measuring the separation angle

between the electron and positron in each event. Pulse height analysis of the light produced in theNaI scintillator used for a converter will determine the amount of scattering that each event shouldencounter. It is expected that this technique should provide energy resolution to within a factor oftwo. As discussed under the the detection technique and its virtues, the requirements of theCherenkov processes, he three-fold time delayed coincidence and the close proximity of the veto tothe converter and trigger make the detection technique essential immune to all non-gamma-rayevents.It is difficult to state an absolute sensitivity for an instrument, since most of the conditionseffecting the sensitivity are not fixed, such as, the observing time, the background in the region of

the source being viewed, the spectrum and energy interval being considered. However, it is possibleto make a,relative comparison to the EGRET instrument for the same conditions described byThompson . Applying the conditions described in Thompsons Table 1 but using a source only5% as bright as the Crab and observing for only 5 days will result in a S/N of 10 with GRITS anda centroid location for the source of 2.7 arcmin for gamma-rays from 500


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Instrument Characteristicsl ,4rea 250,000 cm20 Conversion efficiency 20%l Field of view 5 unvignettedl Point source centroid 4 arcmin at 250 MeV with S/N of 201 arcmin at 1 GeV with S/N of 20l Threshold ~=83 for Cherenkov process182 MeV for gamma ray detectiona Time resolution 5 nanosecondsl Deadtime 10 nanoseconds/charged particle2 microseconds/gamma-ray event


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Virtues of Detection TechniqueThe combination of the constraints imposed by the Cherenkov process and the three-fold

time-delayed coincidence makes the detection technique inherently immune to all non-gamma-rayevents without any loss in the abil ity to detect real gamma-ray events. Thus, few if any non-gamma-ray events are recorded and very little analysis is required of the individual events.

One of the very nice features of this detection technique is its simplicity of design. In particu-lar only scintillators and phototubes are needed for the detection process. Thus it is a straight forward exercise to scale the instrument up from the balloon experiment with 4.5 m2 sensitive area toan ET with 25 m2 of sensitive area. The main elements; a pressure vessel, scintillators and themirror are easily extendible to the larger diameter without increase in complexity . The focal planeconfiguration is essentially independent of the telescope diameter . Unlike a spark chamber, whichhas ever increasing dead time with increasing size, since all the wires need to be scanned on eachtrigger, this instrument is virtual ly deadtimeless. In addi tion, the threshold for the Cherenkovprocess makes the instrument immune to electrons from decayed muons which emerge on the aver-age 2.2 microseconds after a muon stops in the converter. Thus instead of requiring a veto signalof many microseconds, a ten nanosecond veto si nal is sufficient for rejecting cpi s. arged particles.Speci fically, taking the cosmic ray flux to be l/cm set, a collec ting area of 2.5x10 cm2 and a vetoof 10 nanoseconds results in a fractional loss of 0.0025 due to energetic charged particles.

The pair production process imposes an inherent lim it on the determination of the directionof the incident gamma ray. For example, at 500 MeV the two-dimensional rms angle of uncer-tainty of each particle is 0.4 degrees and depends roughly inversely with energy. MultipleCoulomb scattering of the electron-positron pair before their trajectory can be determined increasesthis angular uncertainty. In GRITS, the total uncertainty per gamma-ray event is about 50%greater than the inherent lower limit. Although this uncertainty is large for each individual event,many events are accumulated to establish sufficient statistical significance before a source detectioncan be claimed. The events associated with the source form a Gaussian distribution about thesource position, and the centroid of the Gaussian can be determined to approximately the width ofthe Gausssian divided by the signal to noise of the measurement. At 500 MeV, the individualevent uncertainty is about 40 arcmin and a S/N of 20 would result in a point source location of 2arcmin. Using events of even higher energy will result in even a smaller positional uncertainty.

The energy of each event is also of great interest. Not only is one interested from an astro-physics standpoint in obtaining the energy spectrum of the source under study, but the energy ofeach event needs to be determined for partitioning the events for centroid determination. Theenergy of each event is obtained primarily from the separation of the two rings of Cherenkov light.This separation is caused by a combination of the pair emission angle and the multiple Coulombscattering of the charged particles in the remainder of the converter material traversed, the triggerscintillator and the gas in the ET. The only variable in this is the thickness of the convertermaterial traversed. This can be measured by using scintillator as an active converter rather than ainert lead or tungsten plate. The light output of the scintillator is proportional to the path lengthtraversed by the charged pair emerging from the converter. The uncertainty of the energy meas-urement for each event will be about a factor of two. This should be adequate for determining thespectral shape of a source, such as , the slope of a power law spectrum and any break in the spec-trum due to absorption or the dominance of some other higher energy process.


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Virtues of Detection Technique0 Unequivocal positive identification of gamma rayl Simplicity of designl Extendible to large area without increasing complexityl Immunity to non-gamma-ray-backgroundl Negligible deadtimel Angular resolution within two of theoretical limitl Energy resolution sufficient to determine spectral shape


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Virtues of Using External TankA major element of this detection technique is the Cherenkov radiation process, which

depends of having a pressurized volume. Therefore, there is a need for a large, clean, rig id, insu-lated, light-tight, gas-tight, thin-walled pressure vessel. The ET is ideal for this purpose. If theET did not exist, than one would have to design a structure with essentially the same properties ofthe ET in order to carry out this experiment.In addition to the ET already existing, as part of its function as a fuel tank for propellingthe Shuttle into orbit, it is already taken to 99% of orbital velocity. When it is taken into orbit,it provides an additional bonus to the Shuttle payload capability. The bonus comes from usingthe main engines to carry the Shutt le al l the way to orbit; the OMS engines which are less effic ientare not needed for the OMS-1 burn; and the maneuvering to safely dispose of the tank is not neces-sary .

As mentioned earlier, conventional thinking would limi t one to an instrument size that isconstrained by the Shutt le payload envelope. However, making use of the ET and assembly capa-bility in the Space Station era permit deployment of a much larger telescope. In fact the NationalCommission on Space report Pioneering The Space Frontier, stated on page 84:

...we feel that 80 great a re8ource [a8 the ET] cannot be ignored, and propoee that a newlook be taken. we cannot set limit8 now on what u8e8 could be made of shuttle tank8 inorbit; ingenuity and the profit motive might produce useful ideas.

In this case the profit being sought is the increase and diffusion of knowledge among men.This approach of assembling the telescope on-orbit not only utilizes an existing resource, but

also allows for a radically different approach to the design of the instrument. Previously, instru-ments had to be fully assembled and functioning as an integral unit at the time of launch. Con-siderable expense has been necessary to ruggedize instruments so that they would survive the firsttwo minutes of life, namely, the launch environment. This dictated considerable integralstrengthening of the structure to support the instrument components adding to the cost andweight. However, on-orbit assembly will allow this program to circumvent this requirement, sincethe separate components can be safely packaged to withstand the ini tia l harsh environment andthen assembled with min ima l structural support in the zero-G environment. Substantial cost sav-ings in instrument development can be realized from this new approach to instrument construction.


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Virtues of Using External Tankl Detection technique requires large, clean, rigid, insulated,light-tight, gas-tight, thin-walled, pressure vessell Sixty-five-thousand pound spacecraft delivered on-orbitwithout incurring design, fabrication, qualification or launch costl Unconventional approach for deployment of a large telescopewithin conventional capabilityl Integral strengthing of telescope for launch as an assembledunit would be prohibitive


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Objectives as a Follow-on to GROIn furthering the objectives of high energy gamma-ray astrophysics, the GRO mission will

add immensely to the collection of knowledge in this discipline. However, as has almost alwaysbeen the case, new enigmas will surface in the search for answers to old mysteries. Data fromGRO should result in detect ion of many more sources than have already been cataloged. Thesenew sources, along with the 25 or so already known sources will require in depth follow-on observa-tions of greater detail than can possibly be achieved with the GRO instruments. Thus, the objec-tives of GRITS are to carry out these follow-on observations.

To date only two sources have been identif ied based on their time varying character, namely,the Crab and Vela pulsars. The statistics for measurement of time varying features depend on thesquare root of the product of the collecting area times the integration time. An increase by a fac-tor of ten or more in the effective area will result in an increase in the temporal resolution by acomparable factor. Features an order of magnitude shorter in time can then be observed. The x-ray binary Cyg X-3 was detected at ultra high energies based on its time varying character.

Most of the sources detected by GRO will be at or near the limiting sensitive of the surveysundertaken. For the stronger sources detected, sufficient statistics should be accumulated to reducethe positional uncertainty to a fraction of a degree. For the fainter more abundant sources thepositional uncertainty will be about the size of the Gaussian distribut ion of events about the sourceposition. Even at 1 GeV, the rms emission angle radius by itself is about rh and at 250 MeV it isabout ?4 a . These error radi i are still too large to permit identification with previously knownsources, particularly in the galact ic plane. Therefore, a major objective of GRITS will be to reducethe positional uncertainty of the fainter sources. In addition, until improved angular resolutionand counting statistics can be achieved, it will be impossible to determine if the extended emissionalong the galact ic plane is due to just diffuse emission from the interaction of cosmic rays with gasand dust or also due to many fa int unresolved point sources.

For extended regions of emission, the technique of centroiding can not be used for improvingupon angular resolution. However, the improved statistics achieved with the larger collecting areaaf GRITS can make possible the use of the maximum entropy method (a non-linear deconvolutiontechnique) to provide maps of enhanced spatial resolution in regions of extended emission.

The nature of gamma-ray bursts remains a mystery. The Burst and Transient Source Exper-iment (BATSE) on GRO is design specifically to detect this phenomena. Some of the bursts haveapparently come from the same locat ion on the sky. The energies measured range from the x-rayup to tens of MeV. Thus there is the potential for bursts of even higher energy. The most likelycandidates for repeating will be viewed with a hope of seeing higher energy bursts. GRITS is par-ticular ly well suited for measuring this kind of phenomena, since the detect ion processes used areon the order of a few nanoseconds. Thus extremely high peak fluxes could be measured withoutjamming the instrument.

As mention earlier the galaxies LMC, SMC and M31 in our local group should be detectableas extended discrete high latitude sources of high energy gamma rays assuming the same highenergy processes are taking place in these galaxies. Since they are extended over a few degrees, itshould be possible to see galactic structure within them. Although, even with the sensitivity ofGRITS a Crab like source would not be detectable (it would be about 600 times fainter), if highenergy bursters exist, their pesk flux may be seen. The most intense gamma-ray burst recorded,that on March 5, 1979, appears to have come from a known supernova remnant in LMC.

Final ly, as always seems to be the case, whenever the observational envelope is enlarged byimproving sensitivity, spatial, spectral or temporal resolution, new serendipitous discoveries aremade. Although this is may not be justification in itself for pursuing an endeavor, it is alwaysexciting when new discoveries are made. This surely is looked forward to with GRO, and furtheron with GRITS.


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Objectives as a Follow-on to GROl Pointed observations of discrete sources:

Improved temporal resolution depends on l/Areal Identify unknown sources:

Improved positional uncertainty, 0, depends on l/area*timel Resolve confused regions:

Primarily within &I45 of galactic centerl Look for high energy galactic bursters with high peak fluxl Map nearby galaxies, LMC, SMC, M31:

Also look for bursters and other variabilityl Serendipitous discoveries from enlarging observational envelope


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Subsystem RequirementsThe scientific instrument requires numerous subsystems for support to perform the on-orbit

operations. These are listed here. The primary element of this experiment is the Cherenkov pro-cess which requires the pressurized environment made possible by use of the ET. The criterion isto provide an index of refraction of n- 1.0000726, which is met by specifying the density of theselected gas. Helium is the only gas that is unacceptable, since it can permeate the phototube glassenvelope. The requisite gas pressure is well within the ET operating pressure of 40 pai.

Since this instrument is intended to carry out pointed studies, the attitude of the ET mustbe held inertially to l-2 degrees, so as to maintain the region of interest within the fov. An atti-tude knowledge of 1 arcmin is required to achieve the fina l point source location. In order to carryout a comprehensive observing program, the attitude control system, ACS, must permit pointingto any portion of the sky at any time, within the constraints of momentum management. This isnecessary to permit measurement of secular changes anticipated in many of the sources. Theefficiency of the ACS including the time lost due to the SAA should be at least 75% with a goal of90%.

The power necessary to support the instrument is currently estimated to be on the order of1-2 kilowatts. A substantial portion of this is dissipated in the high voltage for the phototubes.In addi tion, the nanosecond electronics necessary also require substantially more current to operatethan what one is normally accustomed to.

The data storage is baaed on the anticipated event rate. Combin ing the highest extendedemission region, with the brightest point source, Vela, produces an event rate of M,OOO/day. ThePHA data along with time tags, attitude and subcommutated housekeeping will add up to about512 bytes/event. Thus the total data storage needed will be on the order of 8 megabytes/day.This can easily be accommodated with either memory or tape storage. The data transmission ratewill be required to dump this amount of data in one pass, as well as accommodate a real time rateof 20 kbps for diagnostic purposes. The command rate at this time is TBD and will be determinedprimarily be the periodic uplink of target lists and occasional software changes.

The altitude for this mission is not constrained by the scientific objectives. Rather it isdetermined by various mission operation considerations which are to some extent orthogonal. Alow altitude is desirable for minimizing the effects of the SAA and debris impact. A high altitudeis desirable to obtain orbital lifetime particularly during an era of unfavorable solar activity.Finally, Space Station access or repair purposes will probably be the driving requirement. Aneffective mission life of five years of observing will permit substantially achieving the mission goalsas well as being the typical life expectancy of spacecraft these days.


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Subsystem Requirements0 Gas system

TYPPressure

l Pointing: DeadbandKnowledgeEfficiencyCoverageLimit

0 Power for instrumentl Data storagel Data transmissionl Command ratel Altitude

l Lifetime

Index of refraction n=l.O000726H2 N2 O2 co27.6 3.56 4.01 2.60 psial-2 degrees1 arcminute75% minimum>SO% goalall skyNo sun or moon constraint1-2 kilowatts8 megabytes/day20 kbps for diagnostic purposesTBD, primarily for target listsDepends on: orbit life, SAA avoidance,Space Station access and debris impact5 years usable

Documents

1987 Summer Symposium, 3-4 Aug 87ocr