The Lunar Farside: A Science and Exploration Imperative · 2019. 2. 5. · High-Level Trade Space...
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1 Lunar Science for Landed Missions Workshop,10-12 January 2018 The Lunar Farside : A Science and Exploration Imperative Lunar Science for Landed Mission Workshop NASA Ames Research Center, 10 - 12 January 2018 Jack Burns and Raul Monsalve University of Colorado Boulder Abhirup Datta Indian Institute of Technology, Indore A NASA-funded SSERVI Team
Transcript of The Lunar Farside: A Science and Exploration Imperative · 2019. 2. 5. · High-Level Trade Space...
1Lunar Science for LandedMissionsWorkshop,10-12 January 2018
TheLunarFarside:AScience
andExplorationImperative
LunarScienceforLandedMissionWorkshopNASAAmesResearchCenter,10-12January2018
JackBurnsandRaulMonsalveUniversityofColoradoBoulder
AbhirupDattaIndianInstituteofTechnology,Indore
ANASA-fundedSSERVITeam
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WhytheLunarFarside?
• Awholenew,unexploredworldinEarth’sbackyard!Nearly4× landareaoftheUnitedStates.
• Opportunitytodemonstratehuman-roboticexplorationstrategiesneededtoexploretheMoon,asteroids,&Mars.
• Farside includestheSouthPole-Aitkenbasin– largest,deepest,&oldestimpactbasinintheinnersolarsystem.
• Farside alwaysfacesawayfromEarthandistheonlypristineradio-quietsitetopursueobservationsoftheearlyUniverse’sCosmicDawn.at?~10-80MHz.
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WhyEmplaceRadioTelescopesontheFarside?
• Earth’sIonosphere(e.g.,Vedantham etal.2014;Dattaetal.2016;Rogersetal.2015;Sokolowskietal.2015)
o Refraction,absorption,&emission.o Spatial&temporalvariationsrelatedtoforcingactionbysolarUV&X-rays
=>1/forflickernoiseactsasanothersystematicorbias.o Effectsscaleasν-2 sotheygetmuchworseapproaching10MHz.
• RadioFrequencyInterference(RFI)o RFIparticularlyproblematicforFMband(88-110MHz).o ReflectionofftheMoon,spacedebris,aircraft,&ionizedmeteortrailsare
anissueeverywhereonEarth(e.g.,Tingayetal.2013;Vedanthametal.2013).
o EveninLEO(108K)orlunarnearside(106 K),RFIbrightnessTB ishigh.NeedtosuppressRFIbyatleast-80dBtoobservecosmologicalsignal.
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AstrophysicsCommunitySurveysAdvocatefor
LowRadioFrequencyCosmologyontheFarside
Publications:o Burnsetal.2013,Adv. SpaceRes.,52,306.o Lazio,MacDowall,Burnsetal.,2011,Adv.Space
Res.,48,1942
•Astrophysics Decadal “New Worlds, NewHorizons”: “A great mystery now confrontsus: When and how did the first galaxies formout of cold clumps of hydrogen gas and startto shine—whenwas our Cosmic Dawn?”
•NASA Astrophysics Division Roadmap(2013): HowDoes our UniverseWork?•Small Mission: “Mapping the Universe’shydrogen clouds using 21-cm radio wavelengthsvia a lunar orbiter observing from the farside ofthe Moon”.•Visionary Era: “Cosmic Dawn Mapper (21-cmlunar surface radio telescope array) … Detailedmap of structure formation in the Dark Ages via21-cm observations”.
SurfaceTelerobotics Deployment
Astronaut-assisted Deployment
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High-LevelTradeSpaceforLunarRadioTelescopes
Environment PowerDeployment
CommunicationsLocation
Instruments
RFI
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InstrumentsHydrogenCosmologyGlobalSignalTelescope
CosmicDawnMapper
• 10-100MHz• Polarimeter• GroundPlane• Operation temperature=-250Cto+150C
• Power<200W• Datastorage(<1GBper24hr)• Datatransmission(<1GBperday)
• At10MHz,1° resolutionrequires~2kmbaselines
• Filledaperture:1element/3600sq.m• Circlelayout:1element/6meters
• 105 squaremeterscollectingarearequires>1000dipoles
• 1000dipoles*2pol*20MHzbandwidthà~40GB/s
• Power~2.5kW
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CanaLowFrequencyAntennabeSitedina
PolarCrater?
Receiver
Batteries
Antenna
Solarpanels CommunicationAntenna
1-m
HitbySunlight(Periodicallyorcontinuously)
NoSunlightEverCrateratLunarNorth/SouthPole
UndergroundforhigherandmorestabletemperaturesSideview
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RadioFrequencyInterference(RFI)withina
craterattheLunarPole
NO NPQR SR
ℎ
U = ℎ2
X
1
NO
+1
NP
�
SimulatingRFIinapolarcrater,withtheedgeofthecraterasaknife-edge.Thetransmitter(TX)isonEarth,andthereceiver(RX)isinthecrater,atadistanceNP fromtheedge.TheRFIattenuationatRX iscomputedusing:
\ = 0, _`U < 0
\ = 6 +9U + 1.27Uf, _`0 < U < 2.4
\ = 13 +20 log U , _`U > 2.4
Attenuation
Problems:• Insufficient attenuation• Crater rimblockssky&corrupts
antennabeam.
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GlobalFarside RadioFrequencyInterference
Fromsimulation byDattaetal.(2018).Atlatitudeof-80° andfrequencyof1MHz,-80dBisachievedat≈45° fromthelunarlimb
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RFIConstraintsonTelescopeLocation
=>Northeasternquadrant ofSchrödingerimpactbasinissufficientlyquiet.
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• Data are required for the electricalconductivity & permittivity of the regolith,to model the response of low-frequencyantennas.
• On dayside, UV & X-rays positively-chargesurface with 1–5 V whereas nightside hasnegative surface potential with ≳-500 V.Charged dust grains are levitated (Fig. 1).
• Changes in surface potential by 10x occurduring solar energetic particle event
=> Need to stay grounded to plasma.• Elevated dust (Fig. 1) can cause visibilityproblems, especially for teleoperation.
• Strong electric fields occur in terminator &shadowed regions. Gradients causenegatively charged particles to accelerateaway from the surface (Fig. 2). Effect onelectronics mitigated by placing electronicsunderground (<1 m), & within Faradaycages.
Figure1. Top: ObservationsofelevateddustbySurveyor(Colwell2007).Bottom:Lunarsurfaceispositivechargedondayside&negativelychargedonnightside (Farrelletal.2007).
Figure2.Localizedelectricfieldeffects(Farrelletal.2007).
TheLunarEnvironment
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Longitude-averagetemperaturemodel(Source:LRODiviner)
Day
TheLunarEnvironmentSurfaceTemperature(K)
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Power,Communications,andtheDeep
SpaceGateway
PowerRequirement:0.2– 2.5kW• Assumingaboveaccountsforinstrumentandthermalcontrolelectronics.
• Battery+solarpanels(outsidecraterifnecessary).
• RTG(radioactive).• PowerbeamedfromDeepSpaceGateway.
Communications
• UseDeepSpaceGatewayascommunicationrelayforfirstgenerationinstruments.
DataDownlinkRequirement:<1GBper24hr to40GB/sec
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Summaryand Conclusions
• LunarFarside is theonlylocationintheinnersolarsystemquietenoughtoconductobservationsofCosmicDawndownto~10MHz.
• Possibleinstruments:SingleantennaforGlobal21-cmSignalandArrayofDipolestomeasurethespatialstructureintheearlyUniverse.
• Polar cratersdonotprovideenoughattenuationofRFIforsitingalowfrequencyradiotelescope.
• But,locations<80° latitudeand45° fromthelunarlimbonthefarside aresuitablesites.ThisincludesaNEquadrantofSchrödinger.
• Lunarenvironment:• Elevateddustandchangesinsurfacepotentialarepossibleissues.Needtostaygroundedtolocalplasma.Sitingelectronicsbelowgroundand/orinFaradaycagesareprobablyneeded.
• Day/nighttemperaturevariationsareanissue,butforelevations<70° temperaturesvaryfrom0℃ to-150℃.
• Power,communication,anddeploymentofaninitiallowradiofrequencyobservatorycanbefacilitatedbytheDeepSpaceGateway.
