Hera Inter-Satellite link Doppler characterization for Didymos Gravity Science experiments

While ground-based spacecraft radio tracking is a well-established technique, the use of miniaturized space-to-space inter-satellite links, capable of determining the Doppler shift due to the relative line-of-sight velocity between two spacecraft, has not been explored frequently in the past. The satellite-to-satellite tracking option allows to increase the accuracy of the results for both planetary bodies’ mass and gravity field determination as well as S/C positioning. In this work, the Hera mission inter-satellite link is described and characterized. Preliminary laboratory test results show that the system meets the end-to-end range-rate requirements for gravity science investigations. Furthermore, this work presents numerical simulations of the Hera gravity science experiments. The orbit determination results demonstrate that the inter-satellite Doppler measurements are crucial for the characterization of the extended gravity field of Didymos, whose spherical harmonics coefficients can be estimated up to the degree 3 with the current concept of operations.