Gravity Imaging Radio Observer (GIRO) for Planetary Science and Mission Opportunities

The Gravity Imaging Radio Observer (GIRO) is a high-performance, battery-powered radio probe 16 designed to be released in the proximity of a target planetary body to study its gravitational 17 variations. Using the host spacecraft’s communications system, the GIRO probes will receive and 18 transmit a coherent carrier signal back to a host spacecraft, providing high-precision range-rate 19 data with accuracy ≤1 μm/s at 60-s count time, which is 10–100 times better than the performance 20 of conventional ground-based radiometric data. GIRO is spin-stabilized, which significantly 21 reduces non-gravitational perturbations, making it ideal for acquiring clean gravitational signals 22 for exploring planetary interiors. Additionally, the use of a specifically designed, carrier-only, 23 analog transponder makes GIRO low-cost. Furthermore, a host spacecraft can release multiple 24 GIROs, reducing risk when exploring hazardous environments. In this paper, we describe the 25 GIRO probe and deployer design and present scenarios where GIRO enables gravity 26 measurements that would be challenging to achieve with conventional approaches