Can we exploit shared-beam tracking in historical Mars radio science datasets?

Decades of Doppler tracking data from Mars orbiters and landers have enabled the development of increasingly precise models of Mars’s ephemeris, gravity field, and rotational parameters. These data are typically processed independently for each spacecraft, or combined without fully exploiting the potential for common-mode noise cancellation enabled by simultaneous observations when two spacecraft are within the same tracking antenna’s primary beam.

 

Factors such as link coherence, downlink frequency separation, and the available frequency bands all affect the ability to suppress shared noise sources in shared-beam differential observables [1, 2]. Much of the simultaneous-tracking Mars datasets consist of observables recorded during periods of simultaneous tracking of multiple spacecraft from the same antenna under suboptimal conditions. In most cases, this tracking was enabled by the DSN’s Multiple Spacecraft Per Antenna (MSPA) capability, which supports reception of multiple downlinks using closed-loop receivers, while only one uplink is active at a time [3]. Consequently, most overlaps involve low-quality one-way links, with some two-way/three-way or three-way/three-way data.

 

We investigate the extent to which the shared-beam tracking can be exploited for common-mode noise suppression in such suboptimal cases, and how this capability depends on link configuration, frequency separation, and other factors. Our objective is to identify configurations in which shared-beam observable differentiation and related techniques provide a degree of improvement in spacecraft orbit determination and in the estimation of planetary ephemerides, gravity field and rotation parameters. We also aim to assess opportunities for reprocessing historical data and provide recommendations for future missions, including design and scheduling strategies for multi-spacecraft missions that could benefit from shared-beam tracking without requiring a dedicated radio science payload.

 

 

[1] M. Gregnanin, ‘The Rotation and Solid Tides of Mars from Same Beam Interferometry of a Lander Network’, PhD Thesis, Sapienza University of Rome, 2014.

[2] H. Hanada et al., ‘Overview of Differential VLBI Observations of Lunar Orbiters in SELENE (Kaguya) for Precise Orbit Determination and Lunar Gravity Field Study’, Space Sci Rev, vol. 154, 2010

[3] Jet Propulsion Laboratory, 810-005 DSN Telecommunications Link Design Handbook, 2024.