Design and Performance of the MaCro Crosslink Radio Science Instrument for M-MATISSE

The M-MATISSE mission, currently in Phase A with ESA as an M7 candidate, is a dual-spacecraft concept designed to investigate the coupled Martian magnetosphere, ionosphere, and thermosphere (MIT coupling) under varying space-weather and lower-atmosphere conditions. Two identical spacecraft, “Henri” and “Marguerite,” will fly complementary orbits with apocenters of 3,000 km and 10,000 km and common pericenters at 250 km, enabling highly diverse radio occultation geometries through an inter-satellite crosslink.This contribution focuses on the M-MATISSE Crosslink Radio Science (MaCro) instrument, a dedicated mutual radio occultation payload optimized for Mars ionospheric and atmospheric profiling. MaCro employs software-defined radios based on the AD9361 transceiver, dual-band omnidirectional antenna assemblies (UHF/S-band), and ultrastable master reference oscillators with Allan deviation on the order of 10⁻¹³ at 100 s. Simultaneous UHF and S-band links allow separation of dispersive ionospheric effects from neutral atmospheric contributions, while flexible SDR filtering and automatic gain control accommodate large signal dynamics during occultation ingress and egress.We present the MaCro instrument architecture and its expected performance, highlighting design challenges specific to crosslink radio occultation instruments. We provide bounds on the achievable frequency and refractivity retrieval accuracy and its sensitivity to the carrier-to-noise ratio, integration time, and clock stability, and discuss the implications for high-resolution profiling of Mars’ ionosphere and neutral atmosphere.