Didymos Gravity Science Investigations through Ground-based and Inter-Satellite Links Doppler Tracking

Abstract

<p>The Asteroid Impact and Deflection Assessment (AIDA) is an international collaboration supported by ESA and NASA to assess the feasibility of the kinetic impactor technique to deflect an asteroid, combining data obtained from NASA’s DART and ESA’s Hera missions. Together the missions represent the first humankind’s investigations of a planetary defense technique. In 2022, DART will impact Dimorphos, the secondary of the binary near-Earth asteroid (65803) Didymos.  After 4 years, Hera will follow-up with a detailed post-impact survey of Didymos, to fully characterize and validate this planetary defense technique. In addition, Hera will deploy two CubeSats around Didymos once the Early Characterization Phase has completed, to augment the observations of the mother spacecraft. Juventas, the first Cubesat, will complete a low-frequency radar survey of the secondary, to unveil its interior. Milani, the second Cubesat, will perform a global mapping of Didymos and Dimorphos, with a focus on their compositional difference and their surface properties. One of the main objectives of Hera is to determine the binary system’s mass, gravity field, and dynamical state using radio tracking data in combination with imaging data. The gravity science experiment includes classical ground-based radiometric measurements between Hera and ground stations on Earth by means of a standard two-way X-band link, onboard images of Didymos, and spacecraft-to-spacecraft inter-satellite (ISL) radiometric tracking between Hera and the Cubesats. The satellite-to-satellite link is a crucial add-on to the gravity estimation of low-gravity bodies by exploiting the Cubesats’ proximity to the binary, as the range-rate measurements carried out by the inter-satellite link contain information on the dynamics of the system, i.e., masses and gravity field of Didymos primary and secondary.</p><p>We will describe the updated mission scenario for the Hera radio science experiment to be jointly carried out by the three mission elements, i.e., Hera, Juventas and Milani. To conclude, our updated analysis and latest results, as well as the achievable accuracy for the estimation of the mass and gravity field of Didymos and Dimorphos, are presented.</p>

The ESA Hera Mission: Detailed Characterization of the DART Impact Outcome and of the Binary Asteroid (65803) Didymos

“…In order to derive a realistic model of the systemʼs evolution, both of these effects require an excellent knowledge of the masses of the bodies involved. This knowledge will be acquired via the RSE with Hera, involving the main spacecraft and the CubeSats (Tortora et al 2019(Tortora et al , 2020Zannoni et al 2020;Tortora et al 2021). However, to determine the YORP and BYORP effects, a key observable is the one coming from spacecraft angular measurements, where the novel WBDDOR system will be a key enabling technology boosting the determination accuracy.…”

“…However, while ground-based S/C radio tracking is a well-established technique for relatively large and massive bodies, the use of space-to-space intersatellite links capable of determining the Doppler shift due to the relative line-of-sight velocity between the two bodies would be much more appropriate at small bodies, but this technology has not been explored much. Our previous studies (Tortora et al 2019(Tortora et al , 2020(Tortora et al , 2021Zannoni et al 2020) have shown that the satelliteto-satellite tracking option would ideally complement groundbased radio tracking, providing the best results for both the mass and gravity field determination and S/C positioning. Hera will, for the first time, use a miniaturized and lightweight ISL system, capable of being integrated on nanosatellites weighing a few kilograms.…”