Speaker
Description
In planetary defense exercise scenarios, most discussions of rapid response reconnaissance missions focus on dedicated spacecraft. These are typically new spacecraft, designed and built specifically for the purpose of surveying a newly discovered asteroid that is potentially threatening Earth. A new reconnaissance spacecraft takes approximately three to five years to reach the launch pad, and then still has to travel months or years to reach the asteroid. As an alternative to a new spacecraft, we consider spacecraft already in flight that could potentially be redirected from their original missions to instead survey the hazardous asteroid.
Retasking a spacecraft has the potential to be much more responsive while saving development costs. However, it requires case-by-case analysis of each in-flight spacecraft to determine if it has a sufficiently capable propulsion system with enough propellant and adequate thrust capacity to reach the hazardous asteroid. Additionally, the redirection trajectory must not violate any spacecraft hardware limitations such as minimum or maximum solar range. Even when redirection is possible, additional analysis is required to determine if the payload suite, likely designed for a different use case, can be adapted for planetary defense reconnaissance.
In this work, we examine the feasibility of retasking in-flight NASA spacecraft (OSIRIS-APEX, Lucy, and Psyche) for two exercise scenarios: the Interagency Table Top Exercise #5 held in April, 2024 (NASA PDCO, 2024), and the PDC 2025 hypothetical exercise. In both exercises, we found that it is possible to redirect one or more spacecraft to fast flybys of the exercise asteroids. Figure 1 shows one such solution for redirecting OSIRIS-APEX to a fast flyby of the PDC 2025 hypothetical asteroid. OSIRIS-APEX would be able to reach the asteroid by retargeting the upcoming Earth gravitational assist. In this case, the final arrival time is similar to that of a dedicated, newly built flyby spacecraft. Figure 2 shows the expected performance of its instrument suite in the high-speed flyby, assuming a 50th percentile (by mass) asteroid. The analysis indicates that, despite the instruments being designed for a rendezvous mission, they could potentially detect the asteroid as early as 4 days prior to the encounter and return roughly 1 m resolution from a 100 km flyby distance. In this scenario, OSIRIS-APEX would be useful for adding redundancy to an already planned dedicated flyby spacecraft and by augmenting the in-situ data set to improve the global shape model.
We conclude by discussing the pros and cons of retasking spacecraft, including when the decision to redirect has to be made and how each spacecraft may or may not be suited for retasking.
Figure 1: Candidate trajectory to redirect OSIRIS-APEX to a fast flyby of 2024 PDC25 for the PDC 2025 exercise.
Figure 2: Expected performance of OSIRIS-APEX’s PolyCam for the 50th percentile asteroid for the PDC 2025 exercise.
Acknowledgements:
We would like to thank Kevin Berry and Steve Snyder for their assistance in providing details about Lucy’s and Psyche’s remaining capabilities.