Geotechnical Review of Existing Mars Soil Simulants for Surface Mobility

Heather A. Oravec, Ph.D. – The University of Akron, Akron, OH Vivake M. Asnani – NASA Glenn Research Center, Cleveland, OH Colin M. Creager – NASA Glenn Research Center, Cleveland, OH Scott J. Moreland, Ph.D. – Jet Propulsion Laboratory, Pasadena, CA

1 Photo credit: NASA Presentation Outline

• Introduction

• Current Terrain/Soil Knowledge Base

• Mars Terrain and Soil

• Mars Simulants

• Direct Mars Soil/Simulant Comparison

• Results and Discussion

• Summary and Conclusions

2 Photo credit: NASA Introduction

Background: • Many rovers have successfully traversed the surface of Mars • Spirit, Opportunity, Sojourner • Successful landing of Perseverance rover (Feb 18th, 2021) • Wheel design based on performance of previous rovers • “Large”, 6 wheeled rover with rocker-bogie suspension system • Sample Return Mission planned for the second half of this decade • Novel wheel and tire assembly design • “Small”, 4-wheeled rover Photo credit: NASA • Prior knowledge of the terrain along the proposed drive paths

Motivation: To provide a thorough review of Mars regolith simulants and determine those with mechanical properties appropriate for vehicle mobility studies

Scope: • Currently available lunar and Mars simulants • Mars wind drift regions • Sourcing and processing considerations 3 Credit: NASA Credit: NASA Credit: NASA Current Terrain/Soil Knowledge Base

Mariner 4, 6, 7

Flybys

Mars Dawn Odyssey

Mariner Viking 1, 2 Sojourner 9 Credit: NASA

Viking MAVEN Perseverance Spirit 1, 2 In- Mars Orbiters Sight Landers Pathfinder Rovers

Mars Mars Recon Global Phoenix Curiosity Opportunity Orbiter Surveyor

4 Ripples on smooth outcrop/regolith Mars Terrain and Soil Terrain: • Rough outcrop • Smooth outcrop • Fractured bedrock • Aeolian ripples and dunes • Smooth regolith Credit: NASA JPL Soil: • Drift materials Smooth outcrop, no ripples Credit: NASA JPL • Smooth, relatively unfractured surface • Very fine grained with low cohesion • Low in strength • Crusty-to-cloddy materials • Most prominent in terms of acreage • Fine-grained material, behaves like a moderately dense soil with some cohesion • Layered in nature and adhered to edges of rock • Blocky or duricrust materials • Stronger and higher cohesion than drift or crust materials • Not easily eroded by Mars winds • Rock materials • Diameters ranging from 3.5 to 45 cm • Varied from breccia to vesicular in nature 5 Mars Terrain and Soil, cont.

Typical mechanical properties of Mars terrain from past missions. Note that these are engineering estimates and not the result of direct measurements. Credit: NASA JPL

Smooth outcrop, no ripples Credit: NASA JPL

6 Mars Simulants

Property replicated Current Simulants

Chemical/Mineralogical JEZ-1, JMSS-1, MGS-1, MMS-1 and -2, Y-Mars M90 simulant at Physical/geotechnical ES-X; KMS-1; MMS Mojave Mars Simulant; 15x (top) and 60x UC Mars1; M90 (bottom) Spectral JSC Mars-1 and -1A magnification Magnetic Salten Skov 1

Terrain analogues: • Hawaii’s volcanic lava rock fields • Pu’u Nene’s cinder cone (similar spectral properties) • California’s Mojave Desert (physical analogue to Martian Highlands) • Australia’s rocky plains

7 Mars Simulants, cont. Mars simulant Source Comments JSC Mars-1 Developed by JSC and sourced from Pu-u Nene cinder cone in Hawaii • Designed to match spectral properties, but is used as a general-purpose Mars Simulant • Has since been replaced by JSC Mars-1A (Orbitec) • Neither is currently available outside of NASA ES-X • Engineering Soil Simulants 1 through 4 developed by the European Space • ES-1 replicates the fine dust portion of Mars soils Agency • ES-2 replicates the aeolian soils of the ripples • ES-1 through -3 are procured from Sibelco UK Ltd • A coarse sand like Mars soil found near the base of ridges • ES-2 is not available in bulk • Compact silty sand with gravel (“highway soil”) JMSS-1 Chinese designed multi-purpose simulant made of basaltic lava rock sourced • Designed to match chemical and mineralogical properties of Mars basaltic rock from Inner Mongolia MGS-1 Mars Global Simulant made from easily obtainable materials • Designed to match chemical and mineralogical properties from Rocknest windblown deposits at Gale Crater

MMS Mojave Mars Simulant, developed at JPL in California and derived from • Better hygroscopic analogue material than JSC Mars-1 Saddleback basaltic boulders in the Mojave Desert • Currently not available outside of JPL/NASA UC Mars1 University of Canterbury, sourced from the Banks Peninsula on the South Island • Representative of the Mars soil near the Columbia Hills region of Gusev Crater of New Zealand • 30 kg can be produced per hour MER Yard Exists at JPL • Used for testing of the Spirit and Opportunity rovers • Poorly sorted, crushed volcanic rock containing up to 6% silt Mars Yard Exists at JPL, sourced from decomposed granite dust and cinders mixed with • Poorly sorted soil with up to 2% silt washed sand • Stored outdoors and constantly evolving • 25 tons of MMS sand was mixed with this material in the 2000s M90 Obtained from Soil Direct • Used by JPL in Mars 2020 rover wheel development and testing • Similar to wind drift soils GRC-3 Mixture of commercially available sands from Best Sands Company in Chardon, • Designed for lunar excavation studies, but has been used in a loose condition for Mars tire traction testing at OH with silt mines from a quarry in Colorado NASA GRC • The silt from Colorado is no longer available, so GRC-3b has been developed to replace GRC-3 8 Mars Simulants, cont.

9 Mars Simulants, cont.

Current limitations: Path forward: • No two simulants are alike • Directly compare existing simulants • No standard simulant has been developed or • Determine likeness to Martian soil for vehicle accepted for mobility testing mobility studies • Lack of available geotechnical data to compare • Consider the following parameters for mobility to their mechanical performance studies: • Most simulants require significant processing to obtain an appropriate grain size distribution Particle Particle Size Internal Sourcing/ Bulk Density Cohesion • Require significant schedule and cost for bulk Shape Dist. Friction Angle Processing quantities necessary for full-scale vehicle testing Lower friction Round to sub Informs Lower cohesion is Poorly graded angles are Widely available angular compaction conservative conservative

Wide range implies Round particles Loose in nature can exist as loose Less thrust Less traction Available in bulk can flow or dense soil

Not enough known Weaker (aeolian) Challenging for about Mars Worse trafficability Cheap soil mobility density

Quick production

10 Net traction test on Mars 2020 wheel at GRC Direct Mars Soil/Simulant Comparison

11 Direct Mars Soil/Simulant Comparison, cont.

Comparison methodology:

• Determine parameters for the terrain most challenging in terms of mobility and set values representative of Mars wind drift regions

• Set a point system and rank according to: • Good analogue • Good analogue, with limitations • No data available

• Weight each parameter in terms contribution to soil strength for mobility • Angle of internal friction • Cohesion • Particle shape • Particle size • Bulk density

• Combine the ranked points and weighting to calculate a fidelity value • The higher the value the more representative of Mars wind drift soil

12 Results and Discussion

Fidelity value ranked in order of Observations: most representative to least • Angle of internal friction, the highest weighted category, had the lowest number of simulants which representative wind-drift soil could be considered “good analogues with limitations” • None of the simulants had friction angles within the range of 15-25° • Those with the lowest friction angle were considered good with limitations

• All simulants met the cohesion requirements, those with the lowest values were ranked the highest

• M90 ranked the highest, followed by ES-1 and ES-2 (equally ranked) • ES-2 was specifically designed as a wind drift soil • ES-2 requires significant processing so ES-1 may be preferred • M90 is readily available and was used from Mars 2020 testing

As with any simulant, caution should be used as they are rarely “one- size-fits-all” and their specific properties may represent one area of Mars better than another.

13 Summary and Conclusions

• Existing Mars simulants were investigated and compared to geotechnical properties of Mars soil obtained from previous missions

• Soil properties contributing to vehicle mobility were selected for Mars wind drift soils

• Simulants were ranked according to how well they matched these properties

• A fidelity value was assigned based on a weighted point system

• M90 was identified as the most representative Mars wind drift simulant

• M90 is also readily available in bulk quantities for a reasonable cost

• ES-1 and -2 were the next highest fidelity, but ES-2 required much processing

• There are still gaps in existing Mars terrain data and simulant data that need to be resolved and will be the focus of future work in order to complete this study 14 Acknowledgements

• This work was performed under NASA contract NNC13BA10B

• The authors would like to thank Scott Cutlip, Kyle Johnson, and Erin Rezich of the NASA Glenn Research Center for their contributions to the bevameter tests performed on GRC-3 and M90 simulants

• The authors would also like to thank Gregory Peters of JPL for his review of and guidance on this paper

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