SIIOS in Alaska - Testing an `In-Vault' Option for a Europa Lander Seismometer.

The surface environment of Europa within the radiation-heavy jovian system, poses extreme technical challenges for potential landed missions. The need for radiation shielding and protection from the cold requires instruments to be housed within a thermally insulated and radiation protected `vault'. Unfortunately, this is non-ideal for seismometers as instrument-to-surface coupling is an important factor in the quality of returned data. Delivering a seismic package to an icy world would therefore benefit from the development of a cold-tolerant, radiation-hardened sensor that can survive outside of a protective vault. If such an instrument package were not technologically mature enough, or if lander safety considerations prevent deployment on lander legs, an in-vault location is still a viable option. For such a case, a better understanding of the transmission of seismic signals received through the lander legs is necessary for interpretation of the received signals. The performance, mass, and volume of the `Seismometer to investigate ice and ocean structure' (SIIOS) already meet or exceed flight requirements identified in lander studies for the icy moon Europa. We are testing this flight-candidate in several configurations around and within a lander mock-up, assuming a 1x1 meter vault with extended legs. We compare the received signals from a SIIOS device on the ice with those received by an identical sensor directly above it in the `vault'. We also compare the data from these single-point receivers to that received by two short base-line arrays - A 4-point "in-vault" array and another 4-point array arranged at the ice surface at the base of the lander legs. Our field-testing is performed at Gulkana Glacier, Alaska. The summer melt season provides kilometer-scale regions of coexisting ice, water, and silicate material, thereby providing seismic contrasts analogous to the ice-water layers and possible sub-surface lakes expected at Europa. We demonstrate the sensitivity of SIIOS to detect a variety of passive and active sources from both on-ice and lander-mounted locations, and compare the accuracy of ice-water boundary identification and event location from each configuration.