Paul Diaz, SpaceNav; Pol Mesalles Ripoll, SpaceNav; Matthew Duncan, SpaceNav; Mike Lindsay, Astroscale; Toby Harris, Astroscale; Hugh G. Lewis, University of Southampton
Keywords: Data-Driven Lifetime Risk Assessment and Mitigation Planning for Large-Scale Satellite Constellations
Abstract:
The goal of this research is to better understand and inform risk assessment and mitigation approaches for future planned missions. Specifically, this paper focuses on large constellations of satellites which plan to utilize avoidance maneuvers as a means to mitigate collision risk with large, trackable objects. Space debris and operational payloads continue to pose risks of collisions for future planned missions of individual satellites and constellations of satellites, and this is exacerbated by the growing number of planned constellations. Often in spacecraft operations, possible conjunction events require that avoidance maneuvers are planned and performed prior to the event to mitigate the calculated probability of collision. Avoidance maneuvers are typically performed for high collision probability events which exceed an operator-defined risk mitigation maneuver threshold, and following these avoidance maneuvers, the collision probability is sometimes, but not always, assumed to be reduced. Physical properties and the design of a particular spacecraft can limit its ability maneuver quickly, if at all, and fuel constraints might limit the number and magnitude of avoidance maneuvers which may be performed over the lifetime of the mission. In order to operate safely over the mission lifetime, it is critical to understand the rate at which avoidance maneuvers may be expected and the aggregate probability of collision resulting from a planned risk threshold and mitigation strategy. Accurately predicting operational maneuver frequencies and strategies assists in mission planning by identifying the operational burden which can be expected, and is necessary to remediate collision probabilities so that an acceptable level of constellation-wide aggregate risk is achieved.
This study develops a methodology for mission planning requirements with the goal of allowing spacecraft to operate over their planned operational lifetime while confidently meeting a target aggregate probability of collision. Special analysis is included which focuses on constellations of satellites. The methodology exploits predictive Monte Carlo simulation considering a range of risk mitigation maneuver thresholds, risk reduction factors, maneuver execution times to quantify per-satellite residual risk and maneuver frequencies over an arbitrary interval of time. The residual risk is defined as the aggregate probability of collision assessed over the set of all un-remediated and remediated events. Simulated conjunction events and collision probabilities are modeled numerically using known hard body radii values and secondary object catalog data paired with operational covariance data obtained from a historical database of conjunction data messages. Using a set of simulated conjunction events and estimated collision probabilities, survival probability analysis is used to estimate empirical residual risk for a variety of risk mitigation strategies. Through calculations of residual risk, true risk reduction may be better understood.
The expected outcome of this work is to provide a framework and methodology for identifying the per-satellite risk of a maneuverable satellite within a constellation. We show that given a target aggregate probability of collision, larger constellations will require a smaller per-satellite residual risk than that of smaller constellations. While this might pose significant challenges in terms of spacecraft design, orbit selection, and operational feasibility, the intent of our assessment is to provide insight that will aid in managing the safety and sustainability of the space environment. We also show that there are multiple combinations of risk mitigation maneuver thresholds, risk reduction factors, and maneuver execution times which result in similar residual risk values. These results indicate that residual risk is a better metric of risk to the space environment than simply considering the risk mitigation maneuver threshold, and that there a variety of strategies which can be implemented to acheive a per-satellite target residual risk value.
Date of Conference: September 27-20, 2022
Track: Conjunction/RPO