Low-Gravity Mimicking Simulants and Evaluation of Simulant Flow

This project will provide a new method for testing flow/no-flow conditions and other gravity-driven flow behavior of Lunar or planetary regolith under reduced gravity, through the use of surrogate regolith simulants which mimic the effects of reduced gravity. New calibration data for numerical flow simulation models will also be obtained. The new low-g simulants will provide readily accessible, inexpensive means to verify that equipment intended to function under reduced gravity conditions, will actually function as intended when deployed in the 'real' application environment. Drop towers or parabolic flights are the only current viable methods available to create reduced gravity environments for testing equipment, without involving actual flights in space; but they have severe restrictions on test duration, volume and expense. Recent simulations, drop tower tests, and centrifuge tests have demonstrated that granular materials tend to act more 'cohesive' at reduced gravity. This change in behavior at reduced gravity, is not due to a change in cohesive strength of the material, rather it is due to a reduction in the gravity driving force inducing material to flow. Under reduced gravity, reduced flow rates and/or flow stoppages are observed in hoppers; and, in rotating drum flows large clumps and large avalanches develop, which are not seen for the same material at one-g. The large fine-fraction, and potentially increased surface energies, of in-situ regolith material already increase the likelihood of flow stoppages, or no-flow conditions, occurring within in-situ resource utilization processing equipment. The additional risk of flow stoppages because of reduced gravity is difficult to test terrestrially. The low-gravity-emulating surrogate regolith simulants developed and verified under this research, and the calibrated numerical simulation models, will offer new, inexpensive, methods to test whether solids will flow or not under reduced gravity.

If commercialization of space, other than LEO, occurs in the next few decades, it will be with lunar operations. Whether those are robotic recovery of scarce minerals, or manned operations, equipment will still need to be designed that will handle, move and process regolith under reduced gravity. Because of the great expense of moving mass to the moon (~$2M per kg in 2009), most testing of equipment will be done terrestrially. The low-g simulants developed under this research will provide an economical means of doing preliminary flow/no-flow condition testing of regolith handling hardware, intended for use on the moon or other low-g environments.

Almost all plans for extended lunar operations include the production of oxygen from lunar regolith, but even shorter missions will involve collection, moving, handling, and often processing of fine cohesive regolith powder. Reduced gravity will increase the sensitivity of handling and processing equipment to the high-cohesion properties of the fine regolith powder, and dramatically increase the likelihood of plugging or no-flow conditions (as occurred with the Phoenix regolith delivery for testing on Mars, for example). This project includes the design of a series of parabolic-flight regolith simulant flow calibration tests, using existing lunar and Martian regolith simulants. Utilization of these flow-calibration tests, to verify that the new low-g simulants do indeed mimic the effects of reduced gravity, will provide NASA designers the confidence needed to utilize these low-g simulants early in the design/testing process, thereby minimizing the number of no-flow surprises later, when real reduced-gravity environments are encountered.

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