JuRa: the Juventas Radar on Hera to fathom Didymoon

The ESA HERA mission approved by the last ESA council Space19+ will be launched in 2024 to deeply investigate the Didymos binary system and especially its moonlet. In 2022, DART/NASA will impact the moonlet to quantify the mechanical response of the body, mainly from ground-based observation [1]. Five years later, HERA/ESA is a unique opportunity to observe in detail the bodies, the crater and the ejecta in order to better constrain mechanical models providing a global characterization of the binary system: shape, density, dynamic properties, thermal properties and composition [2]. The Hera mothercraft will carry two CubeSat’s, Juventas and Milani.

The small spacecraft Juventas will investigate the asteroids’ internal structure. Information about the internal structure is crucial for science, planetary defense and exploration since our current knowledge relies entirely on inferences from remote sensing observations of the surface and theoretical modeling [3]. The Juventas Radar -JuRa- will fathom Didymoon and provide the first direct observations of the deep interior of an asteroid. JuRa is a monostatic radar, BPSK coded at 60MHz carrier frequency and 20MHz bandwidth, inherited from CONSERT/Rosetta [4], [5] and redesigned in the frame of the AIDA/AIM phase A/B [2], [6]. The instrument design is under validation for a flight model delivery in fall of 2022.

JuRa maps the backscatter coefficient (sigma zero - s₀) of the surface or subsurface, which quantifies the returned power per surface or volume unit. It is related to the degree of heterogeneity at the scale of the wavelength and to the dielectric contrast of heterogeneities, giving access to both, the sub-meter texture of the constituent material and larger scale structures.

• The first objective of JuRA is to characterize the moonlet’s interior, to identify internal geological structure such as layers, voids and sub-aggregates, to bring out the aggregate structure and to characterize its constituent blocks in terms of size distribution and heterogeneity at from submetric to global scale.
• The second objective is to estimate the average permittivity and to monitor its spatial variation in order to retrieve information on its composition and porosity. Radar bypasses the near surface alteration by space-weathering and thermal-cycling as observed with optical remote sensing. The observation of the structure and composition of the moonlet will provide constraints on the mechanical model of the impact process.
• The same characterization applied to the main asteroid of the binary system is among the secondary objectives, to detect differences in texture and composition. When compared to the observation of the moonlet, it will constraint the model of binary system formation to discriminate between progressive versus catastrophic process and more generally on the stability conditions of the system.

In this talk, we will review the JuRa science objectives at the instrument development status. We will show the results of the engineering model end-to-end tests and the corresponding instrument performances. Then we will present the proposed operation strategy.

Acknowledgments

• Hera is the ESA contribution to the AIDA collaboration.
• Juventas and JuRa are developed under ESA contract supported by national agencies.
• JuRa is built by Emtronix (LU), UGA/IPAG (FR), TU Dresden (DE), Astronika (PL) and FZ(CZ). Juventas is built by Gomspace (LU). Juventas navigation plan is developed by GMV (RO)
• This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 870377 (project NEO-MAPP).

References

[1] A. F. Cheng et al., « Asteroid Impact & Deflection Assessment mission: Kinetic impactor », Planetary and Space Science, vol. 121, p. 27‑35, févr. 2016, doi: 10.1016/j.pss.2015.12.004.

[2] P. Michel et al., « Science case for the Asteroid Impact Mission (AIM): A component of the Asteroid Impact & Deflection Assessment (AIDA) mission », Advances in Space Research, vol. 57, n^o 12, p. 2529‑2547, juin 2016, doi: 10.1016/j.asr.2016.03.031.

[3] A. Herique et al., « Direct observations of asteroid interior and regolith structure: Science measurement requirements », Advances in Space Research, vol. 62, n^o 8, p. 2141‑2162, oct. 2018, doi: 10.1016/j.asr.2017.10.020.

[4] W. Kofman et al., « The Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT): A Short Description of the Instrument and of the Commissioning Stages », Space Science Reviews, vol. 128, n^o 1‑4, p. 413‑432, mai 2007, doi: 10.1007/s11214-006-9034-9.

[5] W. Kofman et al., « Properties of the 67P/Churyumov-Gerasimenko interior revealed by CONSERT radar », Science, vol. 349, n^o 6247, p. aab0639, juill. 2015, doi: 10.1126/science.aab0639.

[6] A. Herique et al., « A radar package for asteroid subsurface investigations: Implications of implementing and integration into the MASCOT nanoscale landing platform from science requirements to baseline design », Acta Astronautica, mars 2018, doi: 10.1016/j.actaastro.2018.03.058.