Speaker
Description
We define a mission concept to perform a cratering and deflection experiment at Apophis with an independent impactor spacecraft that leverages the formidable capabilities of OSIRIS-APEX as an observer. This is relevant to both planetary defense and science.
A 65kg spacecraft impacting Apophis at 7km/s will make a crater between 20-50m [1,2], and result in an excavation of 2-8m deep. This is deeper than previously explored in rubble piles and into the depths where studies have suggested increased strength at the asteroids Bennu and Ryugu [1,3]. For the estimated mass of Apophis the resulting Delta-V would be ~0.01mm/s. While incredibly small, it is ~2.5x larger than the formal 1-sigma tracking uncertainties for OSIRIS-REx at Bennu and OSIRIS-APEX at Apophis would be similarly capable [4]. While estimates exist for the response of rubble piles to cratering impacts of this magnitude, additional experiments, like this one, are needed for objects the size of Apophis, which has implications for planetary defense strategies.
Performing this experiment after OSIRIS-APEX achieves its primary science goals means that the mass and spin state of Apophis would be known, where a mass measurement to 1% accuracy is planned [5]. This will permit a very accurate measurement of the momentum transfer due to the cratering impact.
There are many technical pathways to achieve this mission [6]. Since OSIRIS-APEX would be employed for the measurement of the target mass, imparted Delta-V and cratering outcomes, the only required vehicle is an impactor that has sufficient combination of speed and mass to produce the required 0.01mm/s Delta-V. There are several low C3 (<5 km2/s2), ballistic transfer opportunities in 2029 and 2030 that impact Apophis after the OSIRIS-APEX science campaign. The relatively low-mass and low-launch energy means the mission can use a small-to-medium lift launch vehicle, keeping costs low.
Some of the possible pathways include resonant trajectories that permit concept of operations that include a trial run, or a two-spacecraft concept with impacts on consecutive years. Similarly, other scenarios could utilize the JANUS spacecraft, where one spacecraft impacts while the other provides flyby reconnaissance of the event.
One important note is that this kinetic impact and cratering experiment would not change the risk of an Apophis impact. The targeted Delta-V and the time of impact are bracketed by the values studied in the hazard assessment of the Apophis Specific Action Team Report, where impacts with 100x this Delta-V were included at similar epochs [7]. They found that such perturbations to Apophis’s orbit were “assuredly safe” and there was no chance of impact out to the 2116 Earth encounter. We can thus see this experiment as an extraordinary opportunity to contribute to our understanding of the response of potentially hazardous asteroids to a deflection test with no risk, following the NASA DART-ESA Hera deflection test and leveraging the knowledge gained by missions visiting Apophis in the previous months, like ESA RAMSES and NASA OSIRIS-APEX.
References:
[1] M. Arakawa, et al., Science, vol. 368, pp. 67-71, 2020.
[2] E. B. Bierhaus, et al., Icarus, vol. 406, 2023.
[3] Daly, R. T., et al., Icarus, vol. 384, Art. no. 115058, 2022.
[4] D. Farnocchia, et al., Icarus, vol. 369, 2021.
[5] D. N. DellaGiustina, et al., The Planetary Science Journal, 2023.
[6] Klein, V., Walsh K. J., and Kayser E. IAC 2024 Paper #87838. 2024. https://iafastro.directory/iac/paper/id/87838/summary/
[7] J. L. Dotson, in Apophis T-6: Knowledge Opportunities for the Science of Planetary Defense, Leiden, 2023.