Spacecraft Position Determination with the Electra UHF Transceiver: A Comparison of One-Way and Two-Way Doppler Observations

In June 2022, the Electra Relay Operations team began conducting radiometric phase and power data collection during relay overflights of the InSight Lander by the ExoMars Trace Gas Orbiter (TGO). This mode of the Electra radio has potential applications for both navigation and radio science, but is relatively untested in flight. Here, we present both one-way (non-coherent) and two-way (coherent) Doppler observations conducted during 32 TGO relay overflights. Then we explore the ability to find the surface position of the lander with each data set and compare this against other methods.Looking forward to Mars Sample Return, the capability to do one-way Doppler tracking would be essential for monitoring the launch performance of the Mars Ascent Vehicle and determining the final trajectory of the Orbiting Sample container. Testing these positioning capabilities now will help us to prepare for that anticipated need.