A Powder Delivery System (PoDS) for Mars in situ Science

Many instruments proposed for in situ Mars science investigations work best with fine-grained samples of rocks or soils. Such instruments include the mineral analyzer CheMin [1] and any instrument that requires samples having high surface areas (e.g., mass spectrometers, organic analyzers, etc). The Powder Delivery System (PoDS) is designed to deliver powders of selected grain sizes from a sample acquisition device such as an arm-deployed robotic driller or corer to an instrument suite located on the body of a rover/lander. PoDS is capable of size-selective sampling of crushed rocks, soil or drill powder for delivery to instruments that require specific grain sizes (e.g. 5-50 mg of less than150 micron powder for CheMin). Sample material is transported as an aerosol of particles and gas by vacuum advection. In the laboratory a venturi pump driven by compressed air provides the impulse. On Mars, the ambient atmosphere is a source of CO2 that can be captured and compressed by adsorption pumping during diurnal temperature cycling [2]. The lower atmospheric pressure on the surface of Mars (7 torr) will affect fundamental parameters of gas-particle interaction such as Reynolds, Stocks and Knudsen numbers [3]. However, calculations show that the PoDS will operate under both Martian and terrestrial atmospheric conditions. Cyclone separators with appropriate particle size selection ranges remove particles from the aerosol stream. The vortex flow inside the cyclone causes grains larger than a specific size to be collected, while smaller grains remain entrained in the gas. Cyclones are very efficient inertial and centrifugal particle separators with cut sizes (d50) as low as 4 microns. Depending on the particle size ranges desired, a series of cyclones with descending cut sizes may be used, the simplest case being a single cyclone for particle deposition without mass separation. Transmission / membrane filters of appropriate pore sizes may also be used to collect powder from the aerosol stream. Results of a number of tests of the prototype PoDS will be presented. [1] Blake D. F., Sarrazin P., Bish D. L., Feldman S., Chipera S. J, Vaniman D.T., and Collins S., 2004, Definitive Mineralogical Analysis of Mars Analog Rocks Using the CheMin XRD/XRF Instrument, LPSC XXXV abstr. #1794 (CD-ROM). [2] Finn J. E., McKay C. P. and Sridhar R. K., 1999, Martian Atmosphere Utilization by Temperature-Swing Adsorption, University of Arizona, Publication No.961597, http://stl.ame.arizona.edu/publications/961597.pdf [3] Hinds W. C., 1999, Aerosol Technology - Properties, Behavior, and Measurement of Airborne Particles, Second edition, John Wiley & Sons, Inc., pp 15-67, 111-136.