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NASA NTRS2021

Trajectory Design and Maneuver Performance of the OSIRIS-REx Low-Altitude Reconnaissance of Bennu

With more than a year of asteroid proximity operations, the OSIRIS-REx team was able to identify one primary and one backup site for sample collection. The next step was to finalize on-board, localized image libraries and site-specific terrain information prior to attempting sample acquisition. Collecting this information required additional, low-altitude asteroid flyby reconnaissance activities. These activities, referred to as ‘sorties’, involved special maneuver and trajectory designs, unique from any other OSIRIS-REx maneuver activity. In order to minimize time between flybys and decrease the total number of maneuvers required, this trajectory design departed from and returned to a frozen Sun-terminator plane orbit within the span of a few hours. This work discusses the trajectory design and performance of the four flybys that were used to collect key topographic science observations of the primary and backup sample sites, which helped lead to a successful sample collection.

Andrew Levine↗
NASA NTRSDate not supplied

Salty Bennu: Halite and Sylvite in Fines Returned by OSIRIS-REx

Salt phases such as halite (NaCl) and sylvite (KCl) are important hosts of halogens (e.g., Br and I) and volatile alkali metals (i.e., Na, K) and are very rare in extra-terrestrial materials. Halite and sylvite have been discovered in carbonaceous chondrite clasts in ordinary chondrite meteorite falls Zag H3-6 regolith breccia (Zag), Monahans (1998) breccia (Monahans), and Sidi El Habib H5 chondrite, as well as on the surface of particles from asteroid Itokawa. Yet, it is uncertain whether the evaporites are indigenous or exogenous to their respective parent bodies, and their origin is debated. Analysis of the extinct 129I/129Xe decay system and 40Ar/39Ar show that halite in Zag may have formed within the first 8 Myr of the solar system, possibly from aqueous fluids during local and episodic low-temperature alteration on the parent body. Halite and sylvite in Zag are characterized by light δ37Cl values of −1.7 ‰. Halite in Zag could have been transported from the outer solar system, perhaps a P- or D-class asteroid, as indicated by O, H, N, and C isotopes. An alternative is a cometary or interstellar ice origin due to their deuterium-rich and 16O-poor composition.

N E Timms↗