(EUROPA) DW Allen, M. Jones, L. McCue, CA Woolsey, & W. B

169 Pages·2013·10.81 MB·English

EXPLORATION OF UNDER-ICE REGIONS
WITH OCEAN PROFILING AGENTS (EUROPA)
D. W. Allen, M. Jones, L. McCue, C. A. Woolsey, & W. B. Moore
aCAS
VirginiaCenterforAutonomousSystems
VirginiaPolytechnicInstitute&StateUniversity
Blacksburg,VA24060
www.unmanned.vt.edu
September14,2013
TechnicalReportNo.VaCAS-2013-01
Copyright(cid:13)c 2013

Summary
Europa is an incredibly enticing target for exploration – the nearest reaches of what may be a vast new
“habitable zone” of interior oceans warmed and stirred by tidal forces. Decades of NASA and National
Academy studies including the most recent planetary science decadal survey [1] have affirmed the pre-
eminence of Europa as a destination for astrobiology research. This report provides a comprehensive
technology roadmap and an assessment of current state of the art and future technologies to enable an
under-ice mission to Europa. In this study, the authors provide an overview of key mission objectives, a
profileofEuropa,andamissionoverview. Theauthorsthendelveintoadiscussionofthekeyfundamental
science objectives and design tradeoffs to arrive at a comprehensive science traceability matrix and value
system for design of a multi-vehicle, under-ice mission to Europa. The current state of the art is assessed
and design alternatives discussed. The report culminates in a concept of operations for the mission and a
recommendedmissionarchitectureutilizingthreesurfaceunits,eachdeployingasinglecryobot,witheach
cryobot carrying three biologically inspired, gliding under-ice hydrobots equipped with sensor packages
thatwillcharacterizethephysicalandchemicalstateofEuropa’soceanoveritsentiredepth.
i
Contents
ListOfAbbreviations xi
1 Introduction 1
1.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 ScienceObjectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 MissionObjectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.3 PlanetaryProtection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Europa 6
3 MissionOverview 9
3.1 MissionPhases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.1 LaunchfromEarth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.2 TransittoEuropa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.3 SurfaceOperations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.4 PenetrationoftheIce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.5 ExplorationoftheOcean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2 PreviousandUpcomingMissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.1 Juno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.2 “Clipper” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4 FundamentalScience 15
4.1 Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2 OceanMechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3 Ocean/IceInteraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.4 IceMechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
ii
4.5 OceanFloorMechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.6 Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.7 SurfaceGeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.8 ScienceTraceabilityMatrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5 ValueSystemDesign 23
5.1 TheAnalyticalHierarchyProcess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.1.1 ExampleofAHPtoaBasicSystem . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.2 SystemDescription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.3 DesignCriteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.3.1 HydrobotPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.3.2 HydrobotScience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.3.3 HydrobotCommunication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.3.4 CryobotPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.3.5 CryobotScience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.6 CryobotCommunication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.7 SurfaceUnitPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.8 SurfaceUnitScience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.9 SurfaceUnitCommunication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.3.10 LandingSystemPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.4 CompleteValueSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6 CurrentState-of-the-ArtTechnologiesandDevelopment 37
6.1 UnderwaterGliders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.1.1 PrinciplesofOperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.1.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.1.3 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1.4 PowerSystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1.5 PerformanceAttributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1.6 PerformanceLimitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6.1.7 NewHorizons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
6.2 MeltProbes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
iii
6.2.1 PrinciplesofOperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
6.2.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.2.3 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
6.3 SpacecraftPowerSources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.3.1 NuclearPowerSources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.3.2 Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.3.3 FuelCells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.4 HydrobotSensorPackages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.4.1 Package3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.4.2 Package2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.4.3 Package1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6.4.4 ScienceTraceabilityMatrixofSensorPackages . . . . . . . . . . . . . . . . . . . 65
6.4.5 DataRate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
6.4.6 Sonar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
7 DesignAlternatives 68
7.1 TransitandLanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
7.1.1 LaunchVehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7.1.2 LandingSystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7.2 SurfaceOperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.2.1 ImportanceofRPSinLander . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.2.2 TechnologyNeedsforLander . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
7.2.3 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
7.2.4 Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
7.3 IceOperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
7.3.1 PayloadCapacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
7.3.2 PowerSource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
7.3.3 DescentTime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
7.3.4 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.3.5 Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
7.4 OceanOperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.4.1 HydrobotDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
iv
7.4.2 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7.4.3 Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7.5 EvaluationofDesignAlternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7.5.1 TransitandLanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
7.5.2 SurfaceUnit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.5.3 Cryobot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7.5.4 Hydrobot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.5.5 CommunicationMenu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
8 MissionArchitectures 93
8.1 ProposedMissionArchitectures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.2 EvaluationofMissionArchitectures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
9 Roadmap,Timeline,NotionalVehicleDesign,andProposedConceptofOperations 97
9.1 RoadmapandTimeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
9.2 NotionalDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9.2.1 SurfaceUnitwithLandingSystem . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9.2.2 Cryobot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9.2.3 Hydrobot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9.3 ProposedConceptofOperations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
10 Conclusions 107
11 Acknowledgements 109
A OtherIce-CoveredWorlds 110
B ExplanationofScienceTraceabilityMatrix 112
B.1 Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
B.2 OceanMechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
B.3 Ocean/IceInterface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
B.4 IceMechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
B.5 OceanFloor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
B.6 Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
v
B.7 SurfaceGeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
C ExplanationoftheValueSystem 118
C.1 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
C.2 ExplanationofSystemDescription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
C.3 DesignCriteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
C.3.1 HydrobotPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
C.3.2 HydrobotScience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
C.3.3 HydrobotCommunication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
C.3.4 CryobotPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
C.3.5 CryobotScience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
C.3.6 CryobotCommunication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
C.3.7 SurfaceUnitPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
C.3.8 SurfaceUnitScience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
C.3.9 SurfaceUnitCommunication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
C.3.10 LandingSystemPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Bibliography 146
vi
List of Figures
2.1 Europa’s interior structure (left) consisting of a metallic core, rock mantle, and water/ice
shell[16]. Theequilibriumtemperaturestructureoftheiceshellisshownontheright,for
threedifferentshellthicknesses: 20km(black),40km(red),and60km(blue). . . . . . . 7
2.2 An illustration of possible structures in the ice shell (after [25]). Warm upwellings and
cold downwellings with scales of about 10 km result in lateral temperature variations of
about 10 degrees C. Near the surface, re-freezing of impact- or friction-generated melts
mayleavelensesorsheetsofprecipitatedsalts. Inwarmerregionsthesemayremainliquid
ashyper-salinebrines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 The configuration of the SLS. Image from NASA, available at http://www.nasa.
gov/pdf/623766main_8143_Singer-AD_industry_day-021312_FINAL3.
pdf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Costsandmassesofpastandupcomingmissionstotheouterplanets. . . . . . . . . . . . 13
3.3 Powersandmassesofmissionstoouterplanets. . . . . . . . . . . . . . . . . . . . . . . 13
5.1 LegendfordesigncriteriatreesshowninFigures5.2,5.3,5.4,and5.5. . . . . . . . . . . . 27
5.2 Designcriteriatreeforthehydrobot. ThelegendisshowninFigure5.1. . . . . . . . . . . 27
5.3 Designcriteriatreeforthecryobot. ThelegendisshowninFigure5.1. . . . . . . . . . . . 28
5.4 Designcriteriatreeforthesurfaceunit. ThelegendisshowninFigure5.1. . . . . . . . . . 29
5.5 Designcriteriatreeforthelandingsystem. ThelegendisshowninFigure5.1. . . . . . . . 30
6.1 Freebodydiagramforwings-levelglidingflight[57]. . . . . . . . . . . . . . . . . . . . . 38
6.2 AnnotatedschematicoftheVirginiaTechunderwaterglider[62]. . . . . . . . . . . . . . . 40
6.3 Neutraldisplacementofacylindricalhullinwaterversuslength. (Finenessratio: l/d = 7) 43
6.4 DragpolarforamodeloftheSlocumglider[57]. . . . . . . . . . . . . . . . . . . . . . . 44
6.5 Exampleofvehiclepathoptimizationinasteady,uniformflow[70]. . . . . . . . . . . . . 45
6.6 Comparison of the relation of tail fin span and area with the body length of various ma-
rine mammals (primarily dolphins). The corresponding values for Deepglider [74], Spray
Glider [75], and SLOCUM [68] are included. Original figure from Review of Dolphin
HydrodynamicsandSwimmingPerformancebyFrankEFish[73]. . . . . . . . . . . . . . 47
vii
6.7 Relationship between sweep angle and aspect ratio of the tail fin of marine mammals.
The corresponding values for Seaglider(cid:63)[76] and SLOCUM [68] are included. Original
figure from Review of Dolphin Hydrodynamics and Swimming Performance by Frank E
Fish[73]. (cid:63)Estimatedfromphotograph. . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
6.8 The specific energies and operating frequencies of several smart materials [79]. The di-
agonal lines indicate specific powers, which are the product of the specific energy and
frequency. The region corresponding to dolphin-like specific power is indicated by the
orange line. These specific powers are based on the total mass of the animal, so is likely
lessthanthepropulsivespecificpower[73]. . . . . . . . . . . . . . . . . . . . . . . . . . 48
6.9 A diagram of the structure of the Philberth probe. From Heat Transfer and Performance
AnalysisofaThermalProbeforGlaciersbyHaldorW.C.Aamot.[90] . . . . . . . . . . . 51
6.10 Descent rate for various sizes of cylindrical probes with various powers, represented by
the color contours. This used equation (6.8) with the following parameters: c =2.2 kJ/kg
p
K,t =273K,t=175K,ρ =920kg/m3,L =330kJ/kg. Thisassumesconstantproperties. . 52
F i ν
6.11 Relationship between performance number and efficiency and non-dimensional tempera-
ture. FromTheoryofPerformanceofIsothermalSolid-NoseHotpointsBoringinTemper-
ateIcebyR.L.Shreve(1962)[93]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.12 SpecificPowerofRTGsovertimewithanexponentialfit. Historicaldataper[101];ASRG
dataper[102]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.13 Thisfigureshowsthepracticalspecificenergiesofprimary,reserve,andsecondarybatter-
ies. Dataper[105]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.14 Thisfigureshowsthepracticalenergydensitiesofprimary,reserve,andsecondarybatter-
ies. Dataper[105]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.15 This figure shows the theoretical specific energies of primary, reserve, and secondary bat-
teries. Dataper[105]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.16 Specificenergiesoffuelcellfuels[109]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.1 From 2006 mission architecture study [126]. Radioisotope power is preferable to battery
powerforaEuropanlander. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
7.2 The mass and thermal power cylinders of varying diameter and different heights made of
GPHS modules. Note that GPHS modules are parallelopipeds, so this is approximated as
acylinderwithmassandpowerdensitiesequivalenttoGPHSmodules. . . . . . . . . . . 73
7.3 Descent time and temperature profile for a linear profile in 10 km thick ice. The ice has
constantpropertieslistedinTable7.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.4 Descent time and temperature profile for a two-step linear profile in 10 km thick ice. The
icehasconstantpropertieslistedinTable7.1. . . . . . . . . . . . . . . . . . . . . . . . . 75
7.5 Comparison of the propulsive efficiency of marine mammals and a notional propeller re-
produced from Passive and Active Flow Control By Swimming Fishes and Mammals by
FrankE.FishandGeorgeV.Lauder[135]. . . . . . . . . . . . . . . . . . . . . . . . . . . 78
viii