Mapping Engineering Constraints from Orbit to the Surface Or How to Certify a Landing Site
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Mapping EngineeringConstraints from Orbit to
the SurfaceOr
How to Certify aLanding Site
Matt GolombekJet Propulsion Laboratory
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How to Certify a Landing Site on Mars?• Selecting landing site critical decision
• If the spacecraft doesn’t land safely there is nothing to show for the effort (and money)– Mission success rests on safe site (including all science)
– Fate of a spacecraft (hundreds millions of dollars) • Must learn everything possible about the site • It is one thing to write a science paper about some topic, it is something else entirely to risk an entire mission on the interpretation
• Engineering Constraints - Derive from s/c and EDL• Address Engineering Constraints with Remote Sensing Data – Mapping Engineering Constraints to Atmosphere and Surface - Better do this, better can select safe site
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Outline• PERSPECTIVE• MER EXAMPLES
–Possible Sites–Data Used to Evaluate Sites–How the Data was Used–How Site was Certified–Assessment of Landing Site Predictions
• EXPECTATIONS FOR MSL –Data Sets–Addition of MRO Data–Certification Process
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VL1 MPF
Meridiani
VL2
Gusev
Landing Sites on Mars
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Golombek’s Perspective• Viking - "The blind leading the blind"
– Predictions of the surface were incorrect, but the atmosphere was within specifications
– Most importantly they both landed successfully• Pathfinder - "Take your best shot"
– Little new data since Viking Mission, but much greater appreciation of how VL1 and 2 landing surfaces relate to Viking Orbital data
– Clear Earth analog near mouth of catastrophic outflow channel– Surface and atmospheric predictions were correct
• MER - "Never has so much data been acquired of and so much work done on 4 small spots on Mars"– An unprecedented explosion of information from MGS and Odyssey resulted in the best imaged, best studied 4 spots in the history of Mars exploration
– The major engineering concerns were addressed by data and scientific and engineering analyses suggested the sites were safe
– Data allowed detailed exposition of testable scientific hypotheses at the sites - became template for surface operations
– Surface and atmospheric predictions (wrt safety) were correct
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Preliminary MER Engineering Constraints
• ATMOSPHERE - ELEVATION– Must be <-1.3 km [wrt MOLA geoid] for Parachute– Atmospheric Column Density, Low-Altitude Winds <20 m/s
• LATITUDE 5°N TO 15°S for MER-A and 15°N to 5°S for MER-B– Solar Power, Temperature, Sub-Solar Latitude; 37° Lander
Separation– Ellipse Size and Orientation, Lat. Dep. – Varied w/simulations
• SURFACE SLOPES <6° RMS (<15°)– Mesa Failure Scenario; Radar Spoof; Lander Bounce/Roll; Rover
Deploy; Power; Later <2° at 1 km; <5° at 100 m; <15° at 3-10 m
• ROCKS– <1% Area Covered by Rocks >0.5 m High for Landing– Athena Rover Trafficability - Total Rock Abundance of <20%– Athena Wants Rocks – It is a Rock Mission
• DUST– Must Have Radar Reflective Surface – Descent Altimeter– Load Bearing and Trafficable Surface– Reduce Lifetime, Coat Solar Panels, Rocks & Instruments
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VL1 MPF
Meridiani Isidis
Elysium
VL2
Gusev
Landing Sites on Mars
15°N
15°S
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Data Used to Evaluate Landing Sites
• Viking Images - 230 m/pixel MDIM (Base Map)• MOLA
– Definitive Elevation, geoid, atmospheric pressure wrt geopotential
– Definitive Slopes at 1 km Scale– Pulse Spread - RMS Relief at ~100 m Scale– 100 m Roughness & Slope from Relief 3 km to 300 m Extrapolated via Hurst Exponent (Self Affine)
– Shaded Relief Maps• Thermophysical Properties
– IRTM Thermal Inertia, Fine Component, Rocks, Albedo [~1°]
– TES Thermal Inertia & Albedo [3 km], Surface Temperature
– Dust Cover Index - TES Thermal Inertia and Particle Size
– THEMIS - Thermal Images [100 m], Surface Temperature
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• Rocks– Abundance from IRTM Spectral Differencing; % Rocks >0.1-0.15 m Diameter Covering Surface
– Model Size-Frequency Distributions; Potentially Hazardous Rocks; Comparison to Test Platform Rock Distributions
– Boulders Visible in MOC Images• MOC and THEMIS Imaging Data
– MOC Images at 1.5-6 m/pixel; Nadir MOLA Shots along image
– THEMIS Visible Images at 18 m/pixel• Stereogrammetry & Photoclinometry
– 10 m and 3 m DEMs (Digital Elevation Models); Slopes• Radar Reflectivity and Roughness (RMS Slope)
– X (3.5 cm)- and S (12.6 cm)-Band: Goldstone & Arecibo– Reflectivity– Specular and Diffuse Scattering
Data Used to Evaluate Landing Sites
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GUSEV CRATER
Clear Morphologic Evidence for Water
High Preservation Potential of Environment in Deposited Sediments
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GUSEV
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GusevCrater LakeSedimentsCratered Surface - No Layers Obvious
Etched Terrain
Dark StreaksDusty
2 km
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Meridiani Planum (Hematite) Site
(MER - B)
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TERRA MERIDIANI
Smoothest, Flattest Place in Equatorial Mars
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MERIDIANI
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Meridiani
BrightDunes
DarkSurface Unit
Bright Underlying
Unit
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Golombek et al., 2003
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General Landing Site Predictions•Broad predictions [Golombek et al., 2003]– Safe for Landing– Trafficable for Rover
•Meridiani– Completely Unlike other Landing Sites, Very Few Rocks, very little dust
– Dark Gray Plain of Sand and Granules with Discontinuous Outcrops of Bright Units that Surface from Beneath
•Gusev– Similar to VL Landing Sites, Less Rocky and Moderately Dusty
– Dust Devil Tracks in THEMIS Images (would be exception)
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Predictions
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Broadly Similar to VL SitesDusty, Moderately Rocky
Spirit Landing Site - Gusev Crater
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How Well Did Remote Sensing Data Predict Surface?
• All Predictions Correct– Thermal Inertia, Rock Abundance, Albedo– Elevation, Slope (1 km, 100 m, 5 m), Roughness
– Important Because•Use landing sites as “ground truth” for orbital data
•Essential for selecting & validating landing sites for future missions
•Correctly interpret surfaces, kinds of materials globally present on Mars
•Use Similar Method for MSL Landing SitesGolombek et al., 2005
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THERMOPHYSICALPROPERTIES
Surface Characteristics
•Thermal Inertia -–Resistance of Surface Materials to Change in Temperature–Dependent on Particle Size or Cohesion
–Is the Surface Load Bearing/Competent?–How Much Dust/Rocks?–Surface Characteristics
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TES Thermal Inertia
Putzig et al., 2005
Albedo Dust Cover Index
Ruff and Christensen, 2002
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Putzig et al. 2005TES Global Albedo vs Thermal Inertia
Meridiani-BGusev-C
A - DustB - DarkC - Dusty, Crusty, Rocky 78% Mars
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THERMAL INERTIA•Meridiani - Bulk Thermal Inertia (I) ~200 SI units
– Predicted to be Sand 0.2 mm•Gusev ~300 Si Units•TES/THEMIS Observations Similar to MiniTES
Predicted to be Competent and Load Bearing
Cemented Soils/Duricrust, Sand and Granules
No Thick Deposits of Cohesionless Dust
No Special Risk to Landing or Roving
Golombek et al., 1997
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THEMIS Thermal InertiaOver THEMIS Visible(18 m/pixel)
Landing Site in Low Inertia Plains - 285
Legacy Pan Partway up Ejecta - 290
Bonneville on Crater Rim - 330
Golombek et al., 2005Fergason et al., 2006
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ROCKS
Surface Characteristics
•Thermal Inertia -–Rock Abundance–Size-Frequency Models–Probability Impact
•Boulder Fields -–Rock Abundance
•Comparison to Test Surfaces -–Airbag Capabilities
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Rock Abundance on Mars
0
0.2
0.4
0.6
0.8
1
0 0.1 0.2 0.3Total Rock Coverage
Relative probability of total rock coverage
Cumulative fraction of Mars surface
IRTM Thermal Differencing1° x 1° PixelsMode is 8%N. Plains Are Rocky
Christensen, 1986
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Rock Abundance• Rocks - IRTM Orbit (±5%)
– Gusev 7-8% ellipse, 7% pixel– Meridiani 5% ellipse, Few% pixel
• Measured at Surface– Spirit 4% at Land Site
•>0.1 m Diameter– 5% & 30% Towards Rim Bonneville
– Size-Frequency Distribution Similar to Model D>0.1 m
– Meridiani Outcrops are Rocks– Consistent Few % Surface Coverage
– Now Sampled Full Spectrum of Rock Abundance Surfaces on Mars
• Safe for Landing• Benign for Roving
Golombek et al., 2005
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Bulk I Versus Rock Abundance
100
200
300
400
500
600
700
800
0 0.1 0.2 0.3 0.4 0.5
Bulk
Iner
tia (S
I uni
ts)
Rock Abundance
MPF
VL1
VL2GusHem
Is
EP80BEP78B
For Lines of Constant Fine Component I for Effective I Rock of 2100 (dashed lines) & 1300 (solid lines) - 20% Possible Rock Abundance Change Golombek et al. [2003]
For Bulk Inertia and Derived Effective Inertia of the Rock Population Can Derive Fine Component Thermal Inertia
Golombek et al., 2003
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Gusev Boulder Fields
MOC image ID E0300012Resolution (m) 2.86Incidence Angle 49.31°Emmission Angle 0.32°
100 m
Golombek et al., 2003
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Identified Gusev Boulder Fields
GUSEV ELLIPSE
Boulder FieldsOutside EllipseInside EllipseBoulder Field Size
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Boulder Size-Frequency Distributions
• Boulder Fields Rare– ~0.1% of MOC Image– Low Sun >38°
• Plotted Max Subareas– Ave, Min 2-10 x Lower
• Extreme Distributions– Steep Slope, Exponential Decay
– Similar to Model Dist.• ~1% Surface Covered by
3-10 m Diameter Boulders
• Can’t See Boulders at 3 Landing Sites, 20%– If Can’t See, <20% Rock Abundance
• Formal Probability Analysis– 0.2-2% Chance Impacting Boulder in Boulder Field
0.0001
0.001
0.01
0.1
0.1 1 10
VL1VL2MPFCrater RimOly MonsGraben FloorGraben FloorGusev S2Gusev Q2
Cum
ulat
ive
Fra
ctio
nal A
rea
Diameter (m)
Golombek et al., 2003
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Airbag Drop Test Platform
60° Dipping Platform at Plum BrookLargest Vacuum Chamber in World
Fully Inflated Airbags Around Full Scale LanderBungee Chord Pulls Lander to Impact VelocitiesAirbags Impact First at Edge Between Tetrahedrons & Then Rotates to Face
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ELEVATION• MOLA Topography & Geoid Excellent for Landing Site Evaluation
• Spirit located at 14.5692°S, 175.4729°E at -1940 m• Tracking Results, 14.5718921°S, 175.47848°E; Radial
Elevation 3392.2997±0.001742 km• Geoid of Closest MOLA point -14.56903°S 175.47075°E,
3394.2367 km, minus elevation, 3392.2967 km, Difference of 3 m, within uncertainty
• Opportunity located at 1.9462°S, 354.4734°E at –1385 m• Tracking Results 1.9482823S, 354.47417°E; Radial
Elevation 3394.1482±0.0004683 km• Geoid of Closest MOLA point -1.94539°S, 354.48697°E,
3395.5351 km minus elevation is 3394.14816 km, which is within 0.04 m
• Actually do not know exactly where any particular MOLA elevation shot is to ±300 m, so uncertainties in map tie and ability to read elevation from map overwhelm comparison
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Atmosphere Models
Limb Profiles
Binned Nadir Profiles
Limb Mean Profile
Nadir Mean Profile
Baseline Profile
•Surface T, P and wind time series–VL1, VL2, MPL)
•Remote soundings of T profiles–TES
·Almost 3 Mars years·~10 km vertical resolution·Inaccurate near the surface
–Viking IRTM–Radio Occultations–Mariner 9 IRIS
Kass et al., 2003
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Meridiani Planum~ 1pm LTSTEast-West cross sectionvertical wind
Strong convection narrow upwellings broad downwellings hexagonal pattern
Extends ~ 5 km vertically
Modest horizontal winds ~4 m/s average random directions
Peak upward velocity~ 6.5 m/s
Peak downward velocity~3.5 m/s
Rafkin et al., 2003
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Mesoscale Wind Model Results
3-D dynamical atmospheric modelsModel meteorological phenomena at the 2 to 200 km scaleTrack pressure, temperature, and wind vectors
Kass et al., 2003
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Atmospheric Profile & Winds• Atmospheric Model VL1 (adj. elev.), TES T
Profiles & MGCM Weather (D. Kass)• Density Derived from Deceleration Profile & Aeroshell Properties
• Derived Temperature Profile– Within 5K Spirit, warm below 15 km, cool above– Within 15K Opportunity
• Profile within 1 standard deviation (low) bounds of atmospheric model– Overestimated mean density by 8% uncertainties below 5 km
• Winds Appear within Expectations based on Mesoscale Models– Gusev Greater Horizontal Winds– Both Experienced Updrafts
Golombek et al., 2005
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TES Albedo Versus Thermal Inertia
Adjusted Meridiani Ellipse to Minimize Cold Nighttime Temperatures
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SLOPES
Surface Characteristics
•1 km Slopes -<2° To Reduce Continuous Role
•100 m Slopes -<5° To Prevent Radar Spoofing
•5 m Slopes -<15° To Reduce Airbag Bounce & Spinup
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MERIDIANIBidirectional
Anderson et al., 2003
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Elysium 1.2 km Slope
Bidirectional Slope
Anderson et al., 2003
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Meridiani 100 m Slope
100 m Slope Derived from Allen Variation/Hurst ExponentHaldemann et al.
MOLA Pulse Spread150 m Scale RoughnessGarvin
Anderson et al., 2003
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1 km and 100 m Statistics
Site Meridiani
Gusev Elysium Isidis VL1 VL2 MPF
1.2 km Bi-Dir.Slope°,Mean±s.d., RMS, n
0.15±0.180.26680
0.20±0.440.49679
0.48±0.550.73934
0.19±0.240.30782
0.27±1.02
0.28±0.28
0.30±1.07
1.2 km A-Dir.Slope°,Mean±s.d., RMS, n
0.24±0.470.53208
0.19±0.290.34277
0.41±0.290.51361
0.14±0.100.17315
0.32±1.01
0.27±0.19
0.25±0.68
Pulse Width, m[G]slopecor Mean±s.d., RMS, n
0.75±0.240.81152
1.42±0.441.51340
1.10±0.41.11366
1.10±0.351.21140
Pulse Width, mnot slopecor[N] Mean±s.d., n
0.8±0.9531
1.5±1.3101
1.9±2.8478
5.1±1.88
2.1±3.73640
1.1±0.4921
2.0±3.62742
Pulse Width, m[N] Mean±s.d., n
0.8±0.8544
1.1±1.0296
1.5±1.75879
1.8±2.87078
1.7±2.9535
1.1±0.4921
2.0±4.11755
Self affine 100 mAllen dev, mRMS slope°
3.41.9
5.83.3
4.02.3
2.61.5
1.81.0
5.02.9
Golombek et al., 2003
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Gusev 10 m DEM
Kirk et al., 2003
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5 m SlopesSite Meridi
aniGusev Elysiu
mIsidis VL1 VL2 MPF
MOC Stereo orPC RMS Adirectional slope°
2-4 4-17 3-5 3-9 5
• Meridiani Smoothest– RMS Slopes Very Low
• Elysium Next Smoothest– RMS Slopes Comparable to MPF
• Isidis Slightly Rougher– Has Rougher Terrains in Ellipse
• Gusev is the Roughest– Has Roughest Terrains in Ellipse
MOC Stereo - 10 m, PC-Photoclinometry generally ~3 m;Corrected to 5 m Kirk et al., 2003
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SLOPE• 1.2 km Scale Slopes Lowest at Meridiani [0.15°& 0.24°; 0.3°] and Lower at Gusev [0.2° and 0.19°; 0.5°] than at VL or MPF 100 m
• 100 m Slope Lowest at Meridiani [1.9°; 0.7°] and Lower at Gusev [3.3°; 1.4°] than at VL1 (comparable to VL2) or MPF
• 5 m RMS Slope (MOC DEM) Lowest at Meridiani and Lower at Gusev than at MPF [2° & 4°]; 1.4° & 2.5°
• Consistent with Extraordinarily Smooth and Flat Surface at Meridiani (smoothest, flattest place investigated) and Reasonably Smooth & Flat Surface at Gusev
• RMS Slopes from Rover Traverse Telemetry
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RADAR
Surface Characteristics
• Is the Surface Radar Reflective? Reflectivity >0.02– Will the Descent Radar Altimeter Function Correctly?
• Does the Surface Have a Reasonable Bulk Density?– Is the Surface Load Bearing? Safe for Landing & Roving
• Surface Roughness– RMS Slope <6°
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Landing Site Radar PropertiesLanding Site
Wavelength Reflectivity1
, 0
rms slope1, rms
Source
Meridiani 3.5 cm 0.050.01 1.30.4 GSSR track: 1.83S, May 3, 2001.
3.5 cm 0.050.01 1.20.4 GSSR track: 1.82S, May 5, 2001.
Gusev 12.6 cm 0.0250.015 1.40.2 GSSR track: 14.59S, Sep. 10,1971
3.5 cm 0.040.02 4.71.6 Average GSSR data unit Hch2.
Isidis 3.5 cm 0.020.01 3.80.7 GSSR track: 5.11N, Jan. 21, 1993.
3.5 cm 0.030.01 3.30.5 GSSR track: 4.86N, Jan. 23, 1993.
3.5 cm 0.030.01 4.01.0 GSSR track: 3.60N, Jun. 17, 2001.
Elysium 3.5 cm 0.050.03 3.01.1 Average GSSR data unit Hr2.1 Quasi-specular scattering reflectivity, 0, as derived from a Hagfors scattering model fit, is the square of the Fresnel normal reflection coefficient, while the Hagfors-derived rms slope, rms, is considered to apply to a length-scale in the range from 10x to 100x the wavelength. 2 Unit Hch is ‘Older channel material’, and unit Hr is ‘Ridged plains material’, as mapped by Greeley and Guest [1997]. Haldemann et al.
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Radar Reflectivity• Engineering Constraint Reflectivity >0.02
• Implies Bulk Density >700kg/m3
• Meridiani (0.05)– ~1500 kg/m3
• Gusev (0.04) ~1200 kg/m3
• Similar to Bulk Densities of Soils Traversed by Pathfinder Rover
• Should Pose No Problems to Landing or RovingGolombek et al., 1997
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Radar RMS Slope
• RMS Slopes Low at Meridiani; Higher at Gusev• Compare Favorably w/Rover Traverse 1.4° & 2.5° at 5 m• RMS Slopes No Rougher than VL1 & MPF, both 3° at 3 m
– Gusev smoother at 12.6 cm• No Unusual Diffuse Scattering• Radar Consistent with MOC DEMs
– Meridiani Smoothest, Followed by and Gusev• Safe for Landing & Roving
Site Meridiani
Gusev Elysium
Isidis VL1 VL2 MPF
MOC Stereo/PC 5 m RMS slope°
2-4 4-17 3-5 3-9 5
3.5 cm Radar RMS slope°12.6 cm Radar
1.3±0.4
4.7±1.6
1.4±0.2
3.0±1.1
3.3±0.5
4.7±1.8
2.0±0.3
4.5±1.8
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Meridiani RMS Slope versus Baseline
Kirk et al., 2003
* MOLA 1.2 Bi *
*
* Allan 100 m
* Radar RMS
**
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Gusev RMS Slope versus Baseline
* MOLA 1.2 Bi
* Allan 100 m
* Radar RMS
*
***
Kirk et al., 2003
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Example Hazard Map: Gusev
Etched TerrainHeavily Cratered TerrainCratered PlainsGolombek et al., 2003
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Digital Terrains Derived from MOC images
Terrains developed by Randy Kirk
Cratered Plains Heavily Cratered Terrain
Etched Terrain
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Landing Simulation Model• 3 Stage Monte Carlo Simulation
–Most Sophisticated Landing Simulation Known–500-2000 Trails/Site
• 6 DOF Entry to Parachute–Entry, Ballistic Descent, Atmosphere Variations
• 18 DOF Parachute to First Bounce–Multibody Sim, Parachute, Winds, Retrorockets
• 3 DOF Bouncing to Roll Stop–Hazard Terrain Unit (DEM), Rocks–Extrapolated from DEM to Ellipse via Hazard Map
• 3 Most Important Factors-Combined–Low-Altitude Horizontal Winds - Add Horizontal Velocity
–Lander Scale Slopes - Airbag Bounce, Spinup–Rocks - Airbag Rip, Abrasion, Stroke Out
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Meridinai - Smooth, Flat Plain
Backshell450 m Away; 1 m HighDust and Rock Free
Dark Surface-Dust Free Granule Lag Surface Ripples Low Albedo ~0.1
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Relatively Dust Free; Albedo 0.195Very Low Relief at 1 km, 100 m, Moderate at 10 m
Spirit Landing Site - Gusev Crater
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Dust Devil TracksAlbedo Difference between Bright (0.26) and Dark Areas (0.19)Pancam Albedo Matches Orbital Albedo
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Mars Pathfinder Landing Site
Relatively Dusty, Albedo 0.22
Relatively High Relief at 1 km, 100 m, 10 m
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Relatively Dusty, Albedo 0.23Low Relief at 1 km, 100 m, 10 m
Viking Lander 2
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Viking Lander 1
Relatively Dusty, Albedo 0.25
Relatively Higher Relief at 1 km, 100 m, 10 m
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Viking Lander 1
Relatively Dusty - Note Drift Material
Relatively Higher Relief at 1 km, 100 m, 10 m
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MER Results• Accurately Predicted Important Safety Characteristics of Both Landing Sites
– Ambiguity in Science of Landing Site• Major Engineering Constraints Addressed by Data and EDL Tested Against Parameters Indicating Sites Safe
• Now Have 5 “Ground Truth” Sites to Compare with Remote Sensing Data – Span Many Important Likely Safe Surfaces *
• Future Efforts to Select Safe Landing Sites are Likely to be Successful
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Putzig et al. 2005 TES Global Albedo vs Thermal Inertia
Meridiani-BGusev-C
A - DustB - DarkC - Dusty, Crusty, Rocky 78% Mars
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Expectations for MSL• Avalanche of New MRO Data• Extensive Data Since MER: Odyssey MEx
• PP is a “Feature” of Site Selection• Extensive Investigation of Sites• Thorough Evaluation of Engineering Constraints - Extensive Testing
• Comprehensive Simulations to Assess Risk and Safety of Sites
• Selection will Balance Science and Safety
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Odyssey and Mars Express Data to Evaluate Landing Sites
• THEMIS Thermal Inertia–Calibrated Global I –Variations 100 m scale
• HRSC Stereo 10 m/pixel–Improved Slopes at 100 m scale–HRSC High Resolution ~2 m/pixel
• Omega Multispectral Data–Composition and Mineralogy
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MRO Data of Landing Sites• HiRISE - 30 cm/pixel, 6 km wide
– Repeat Coverage Stereo - Slopes at m scale– Boulders/Rocks/Outcrops
• CTX - 6 m/pixel, 30 km wide– Repeat Coverage Stereo - Slopes at 10 m scale– Morphology at Intermediate Scale
• CRISM - 20 m/pixel, 11 km wide– Repeat Coverage Stereo - Slopes at 100 m scale– Mineralogy, Compositional Information; 512 bands 0.4-4 m
• All Images Co-Located or Nested– Multiple Resolution Same Location and Lighting– New Data Sets Take Time to Calibrate/Interpret
• MARCI - Global Weather Maps• MCS - Mars Climate Sounder
– Thermal Temperature Sounder-Profiles/5 km– Daily Global Weather
• Challenge is Assimilate New Data and Extract Useful Science and Safety Information on Landing Sites in Timely Manner