Orbit Determination and Positioning for Multi-Objective Mars Exploration Mission Using Same-Beam VLBI Tracking

Precise Mars orbiter orbit determination, high-precision lander positioning and planetary interior parameter inversion are core technical requirements for future Mars exploration. The Tianwen-3 Mars sample-return mission requires coordinated orbiter–lander operations, imposing stricter demands on deep-space radio measurements. The Martian tidal Love number k2 describes Mars’ interior structure and tidal response; its accurate estimation constrains the core-mantle configuration and thermal evolution. This study is a simulation-based observability analysis rather than an empirical determination of the Martian tidal parameters. It establishes a joint framework for orbit determination, lander positioning and tidal parameter estimation by integrating ground range-rate and orbiter–lander same-beam VLBI (Very Long Baseline Interferometry) observations. The high-fidelity dynamical models are adopted to build observation models, accounting for the Martian gravity field with degree and order 120, third-body perturbations, solar radiation pressure, relativistic effects and solid tides. Weighted batch least-squares is used to jointly estimate orbiter states, lander coordinates and k2, and the influence of observation arc length on solution accuracy is analyzed. Simulation residuals match preset noise levels. Adding VLBI data reduces the orbiter’s 3D position error by 7.3–33.9%, with an average reduction of approximately 16.8% and full-arc error below 1.6 m. Longer arcs improve lander positioning, reducing 3D error from 88.418 m (7-day) to 33.349 m (45-day). The retrieved k2 0.152866 ± 0.0487 agrees with the reference value of 0.152. However, the current two-station same-beam setup and arc length yield weak empirical constraints on k2, requiring longer observation spans or improved geometries to recover the Martian tidal parameters from real data. Same-beam VLBI provides complementary geometric constraints unavailable from range-rate alone, supporting multi-spacecraft orbit solutions and Martian interior inversion for Tianwen-3.