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GRSS: An open-source small-body science tool for planetary defense

Presentation #405.02 in the session Asteroids: Planetary Defense (Poster + Lightning Talk)

Published onOct 23, 2023
GRSS: An open-source small-body science tool for planetary defense

Solar system dynamics is a precision science. This has been demonstrated in planetary defense by NASA’s impact monitoring services and the Double Asteroid Redirection Test (DART). With increasingly accurate astrometry becoming available, it is more important than ever to have reliable, publicly accessible tools that can leverage such datasets to study Near-Earth Objects (NEOs). In this work, we present GRSS, the Gauss-Radau Small-body Simulator, an open-source orbit propagator and orbit determination suite.

The GRSS propagator is based on the IAS15 algorithm [1]. The force model includes relativistic effects from the Einstein-Infeld-Hoffman formalization of the N-body problem and zonal harmonic forces from the Sun and the Earth. Nongravitational effects such as Solar Radiation Pressure (SRP), the Yarkovsky effect and cometary outgassing can also be modeled [3]. The ability to account for impulsive maneuvers allows the user to model planetary defense missions such as DART.

The GRSS library is also capable of fitting asteroid orbits using optical and radar astrometry. This is done via a batch least squares filter that processes optical data from the Minor Planet Center (MPC) and radar data from the JPL Small-body radar API. The astrometry is preprocessed to account for star catalog biases and weighted to ensure statistical reliability of the solution.

The development of this package involved rigorous testing and validation using multiple asteroids and compared against open-source propagators such as ASSIST [2] and the small-body orbit determination code used at JPL. 250-year propagations of the (65803) Didymos system barycenter exhibited less than 1-kilometer differences in position, and an orbit fit for Didymos yielded less than 1-sigma differences. GRSS has already been used to study the heliocentric changes in the Didymos system due to the DART impact [4].

Through its user-friendly interface and easily modifiable source code, GRSS will enable a deeper understanding of the dynamics of asteroids, facilitate the characterization of hazardous NEOs, and support the planning of future planetary defense missions. The package is publicly available to the scientific community via the Python Package Index (PyPI) to ensure widespread utilization and foster collaborative efforts in small-body research.


[1] Rein & Spiegel (2015) MNRAS 446, 2, 1424–1437, 10.1093/mnras/stu2164

[2] Holman, Akmal, Farnocchia et al. (2023) PSJ 4, 69, 10.3847/PSJ/acc9a9

[3] Marsden, Sekanina, Yeomans (1973) AJ 78, 2, 211-225, 10.1086/111402

[4] Makadia, Chesley, Eggl et al. (2023) ACM Conference, Abstract #2128

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