Geodetic Investigations of the Europa Clipper Mission

One of the objectives of the Gravity and Radio Science (G/RS) instrument on NASA’s EuropaClipper mission is to improve our knowledge of Europa’s ephemerides, to trace the moon’sthermal-orbital evolution. Here, we present a complementary methodology to use the Radarfor Europa Assessment and Sounding: Ocean to Near-surface (REASON) instrument to enhancethese measurements by tracking echoes from Europa at greater distances, beyond its primaryrole of subsurface sounding during close flybys. We investigate the possibility of occasionalREASON measurements during the non-nadir phase at altitudes beyond 40,000 km to extendthe ephemerides dataset. Through radar simulations of REASON’s echoes, we evaluate anddemonstrate this approach by determining the maximum altitude for surface return detection,achieved by coherently processing hundreds to thousands of pulses within the signal’s round-triptime. The received signal’s power can be further enhanced by maximizing pulse length, targetingEuropa’s most reflective (leading sub-Jovian) hemisphere, and summing many compressedpulses. We also explore a phase shift approach for velocity measurements, which uses existingranging pulses. Using Europa Clipper’s most recent trajectory design, we identify flybys thatalign with the best working scenarios for this approach. Our performance estimates for rangeand velocity resolution demonstrate that this approach could obtain measurements relevant toEuropa’s ephemerides. This method offers key insights into Europa’s orbital evolution and,ultimately, its long-term habitability.