RASP-based sample acquisition of analogue Martian permafrost samples: Implications for NASA's Phoenix scout mission

Sample acquisition studies of ice–dirt mixtures under simulated Martian conditions approximating the 2007/8 Phoenix Scout mission are reported. The experiments were performed using a prototype rapid acquisition sampling package (RASP) that is similar to the one mounted on the 2007/8 Phoenix scout robotic arm. This mission will acquire a sample from permafrost-like regolith that is estimated at strengths near 45 MPa to measure the volatile composition including H2O. Sublimation loss during sample acquisition and transfer will have a significant effect on the determination of water content, a major Phoenix mission goal. Laboratory sample acquisition was performed under Martian ambient pressures (5 Torr) in which water is unstable and ice quickly sublimates. Basalt samples consisting of various size, and shapes subjected to various temperature ranges were used as the aggregate material of the water saturated permafrost analogues expected to be found at the Phoenix landing site. In our laboratory experiments roughly 5–6% of the initial water–ice was sublimed due to energy imparted by the tool to the sample during sample acquisition. This loss is in addition to any others from passive sublimation as the samples are transferred to the instruments for analysis. We determined that the energy necessary to excavate the permafrost samples with the RASP to be on the order of 0.05 W h/cm3. Finally, we discuss the potential to use a RASP on future in situ Martian missions.