The 2nd NASA/ARO/ASCE Workshop on
Granular Materials in Lunar and Martian Exploration

As a follow up to the very successful First Workshop held at the Kennedy Space Center (Feb. 2--3, 2005), the 2nd NASA/ARO/ASCE Workshop on Granular Materials in Lunar and Martian Exploration will be held as an integral part of the 10th ASCE Aerospace Division International Conference on Engineering, Construction and Operations in Challenging Environments (Earth & Space 2006) to be held in League City/Houston, TX, U.S.A. (near NASA Johnson Space Center) during March 5-8, 2006. You are welcome and invited to participate in the workshop.

If you are also interested in making a presentation at the workshop, you are invited to submit an abstract. For more information on the abstracts/papers submission, please visit the Abstracts/Papers/Special Session submission page. Conference proceedings will be published and made available at the Conference.

Purpose and Scope of the Workshop

For humans to explore the Moon and Mars, most mission scenarios require that we shall make use of in-situ resources. This requires us to understand the properties and mechanics of the extraterrestrial regoliths, to predict the behaviors of granular geomaterials in lunar and Martian environments, and to design technology capable of reliably controlling the various complex fluid flow regimes of these materials. Dealing with granular materials in an extraterrestrial environment, where we have limited experience and limited experimental access to the materials themselves, presents a unique challenge to the human exploration of the solar system. This workshop will bring together scientists, engineers, and mission managers to identify the key challenges and the necessary research directions that must be pursued to answer them.

An example of in situ resource utilization (ISRU) is to make propellant for the return journey from Mars to Earth using carbon and oxygen from the Martian atmosphere and hydrogen from water ice excavated beneath the Martian surface. This would make a human-tended Mars mission more economically feasible since it avoids the excessive cost in lofting the propellant from the Earth's surface and transporting it to Mars. Most of the relevant in-situ resources of the Moon and Mars are found in the regolith (the loose layer of sand and rocks covering the surface). Developing technology to work with these geomaterials is therefore of paramount importance to human exploration of the solar system.

Other related challenges are the need to excavate beneath the lunar and Martian surfaces for scientific objectives, and the need to control the high-speed blast of sand and microscopic grit when a rocket lands on the surface in the vicinity of other mission-critical hardware. The program is also considering ways to use the regolith in the construction of habitats and for radiation shielding.

Designing technology to work with the Martian or lunar regolith is challenging for several reasons. First, we have limited knowledge of the mechanics of the Martian regolith (more so than the lunar regolith) over the range of locations and seasonal conditions that are important to exploration, especially at the scale of depth beneath the surface required for ISRU. Robotic exploration of Mars is advancing our knowledge of the regolith, but effective planning of the robotic program requires that we know what are the specific questions to be answered and how we may design spacecraft to effectively answer them.

Second, predicting soil mechanics is difficult because there is no fundamental understanding of the physics - no physical law with the pedigree of the Navier-Stokes equation to predict how any granular material will behave. Geotechnical descriptions of terrestrial soils have traditionally treated them as a plastic continua using material parameters fitted to match the experimental behavior of the soil. This method provides predictive capability, but extrapolating the method to lunar and Martian conditions (atmospheric and subsurface gas inventory and pressures, ice inventory and micromechanical structure, and heterogeneous variability in a region of unknown geologic history) injects significant uncertainty into the fidelity of the predictions. Furthermore there are practical problems even in terrestrial civil engineering such as those related to scale-up, which make robust predictions difficult without practical experience in the relevant applications and environments.

Third, the mechanics of granular materials present a spectrum of unique technological challenges due to their self-organizing, fragile, and non-homogeneous flow behaviors. Various manifestations of these phenomena have long been known to industry and agriculture, including the frequent collapse of grain silos, the jamming of hoppers or other equipment, human death by burial in an unexpected slumping of material, and the inability to smoothly mix granular materials together. Many of these problems have come into investigative focus only during the past several decades, largely due to advances in computing power which have made it possible for the first time to simulate the internal state of granular materials to discover why they behave as they do. These internal state behaviors include jamming and arching, non-uniform convection and flow patterns, directional stress propagation, vibration-induced pattern formation, the heterogeneity of the stress field including the formation of percolating force-chain networks, auto-segregation or auto-stratification, and self-organized criticality. As a result, scientists and engineers from a wide variety of interrelated disciplines are actively using new theoretical, experimental and modeling techniques to understand these aspects of granular and soil physics and to apply their new advances into improved granular material technology. These disciplines include civil engineering (especially geotechnical), mechanical engineering, mining and excavation, soft condensed matter physics (and statistical mechanics), chemistry and chemical engineering, geology, planetary science, terrestrial soil science, and cold regions / permafrost science, among others.

This workshop will bring together a group of researchers from this spectrum of disciplines to identify the challenges and necessary research in granular and regolith mechanics to make lunar and Martian exploration successful.

Key Questions to be Addressed

1. 1. What kind of modeling techniques are necessary to describe lunar soil, both for geotechnical applications and for ISRU processing (granular flow) applications.
2. 2. What kind of constitutive or contact or materials models need to be developed to adequately describe the behaviors of lunar soil?
3. 3. How do we go about developing these lunar soil models and constitutives?
4. 4. How do we address the wide separation of scaling between laboratory experiments and large engineering applications on the Moon without easy experimental access to lunar soil or the lunar environment?
5. 5. How do we address the wide separation of scaling between discrete element modeling and finite element modeling of engineering applications?
6. 6. What measurements (both in terrestrial laboratories and in situ on the Moon or Mars) and what instruments are necessary both to support modeling and to get direct engineering data?
7. 7. How do we design lunar and Martian in situ instruments to be small, light, and multi-sited?
8. 8. What techniques are most effective for lunar (and eventually Martian) excavation and for ISRU processing of granular materials?
9. 9. What emerging insights from (more fundamental) granular physics should be addressed in a program of extraterrestrial soil modeling?
10. 10. Are there any additional granular material challenges, applications, or lunar/Martian environmental issues that were not identified in the first workshop?

Conveners/Contacts:

Allen Wilkinson, NASA John G. Glenn Research Center, Cleveland, OH
E-Mail: aw@grc.nasa.gov

Philip Metzger, NASA John F. Kennedy Space Center, FL
E-mail: Philip.T.Metzger@nasa.gov

Ramesh B. Malla, University of Connecticut, Storrs, CT
E-mail: MallaR@engr.uconn.edu

Richard A. Schultz, University of Nevada, Reno, NV
E-Mail: schultz@mines.unr.edu