Nathan Boone, Air Force Institute of Technology; Robert Bettinger,Air Force Institute of Technology
Keywords: debris, space, artificial, lunar, cislunar, kessler syndrome, Artemis, Gateway, Moon
Abstract:
INTRODUCTION
Over the past several years, interest in lunar exploration has begun to increase, with a variety of new space missions operating in the lunar orbital region. These new space operations include international missions to the Moon such as China’s 2018 Chang’e-4 far side lunar lander, Israel’s 2019 Beresheet mission, India’s 2019 Chandrayaan-2 mission, and China’s 2020 Chang’e-5 lunar sample return mission. Furthermore, NASA plans to return humans to the Moon through the Artemis program within the next decade. The Artemis program aims to provide manned landings on the Moon, lunar colonization, and a manned space station in an orbit near the Moon called the Lunar Gateway. Increased interest in manned exploration of the Moon is expected to lead to even greater numbers of spacecraft operating in the lunar region in the coming years.
As more spacecraft operate in the lunar region, the lunar space environment may become more crowded. As lunar orbit becomes more crowded, proper debris management techniques may be required to avoid a potential scenario much like “Kessler Syndrome” where a cascading series of collisions in lunar orbit renders certain lunar orbits unusable. Artificial debris events of this nature in Earth orbits have been heavily studied, but very few studies have examined the risks from artificial debris in orbits beyond Earth or around other celestial bodies. Debris in lunar orbit could be consequential due to small size of the Moon, which provides more opportunities for intersections with debris, and the lack of atmospheric drag around the Moon, which could cause particles to remain in orbit for extended periods of time.
This research aims to determine the effects of a significant artificial debris generating event in lunar orbit. The debris event will be modeled as a catastrophic spacecraft mishap caused by a spacecraft battery explosion. For a variety of pre-explosion initial positions and velocities, the propagation of debris over time will be analyzed and used to determine the collision risks from the debris to another spacecraft operating in lunar orbit. These risks will be quantified using a spacecraft survivability model. Overall, research into lunar debris propagation will improve understanding of relative importance of debris management in lunar orbit and the potential consequences of mishaps within this orbital regime.
METHODOLOGY
The collision risks to spacecraft from artificial debris will be determined through computer simulation of debris motion following a catastrophic spacecraft mishap. The catastrophic mishap will be modeled through a previously developed statistical model that generates the masses and velocities of debris particles released in a simulated catastrophic battery explosion. Debris particle trajectories will be simulated in a lunar-centric reference frame that incorporates the gravitational forces of the Moon, Earth, and Sun. The non-spherical nature of the Moon’s gravitational field will also be considered. Finally, the survivability of a notional lunar spacecraft moving through the debris field will be determined by applying a variation of the Poisson survivability model developed by Ball in “The Fundamentals of Aircraft Combat Survivability Analysis and Design.” In this survivability model, the debris density within a spherical “danger zone” is used to calculate the probability of intersection with a smaller spherical “hazard zone” that bounds a notional spacecraft threatened by debris. The result of this survivability analysis is the probability of hazard, or the probability that a debris particle that would destroy the spacecraft will enter the hazard zone sphere. The survivability of the notional spacecraft will be evaluated for a several scenarios, each involving different initial conditions for both the notional spacecraft and the spacecraft that suffers the catastrophic mishap.
ANTICIPATED RESULTS
Some preliminary results for this research have already been obtained using the Bi-circular Restricted Four Body Problem (BCR4BP) as the trajectory model. These results simulated the motion of debris particles generated in a catastrophic battery explosion onboard a spacecraft initially in a 110 km circular lunar orbit for one day. The resulting survivability of a notional spacecraft also operating in a 110 km lunar orbit was then determined. The probability of hazard for this spacecraft was a maximum of about 0.003% over the one-day simulation, and debris particles passed within 1 km of the spacecraft in most simulations. This level of risk would likely create some concern in a real-world mission, indicating the need for further research into this topic.
This preliminary research will be built upon in the present study by incorporating a lunar-centric reference frame, a more accurate trajectory model that includes the Moon’s non-spherical gravitational field, and longer simulations. Longer simulations are expected to show increased overall risk, since debris particles are likely to remain in lunar orbit for far longer than one day. Over long simulation periods, the instantaneous risk level will likely eventually begin to diminish due to a lower density of debris and debris that decays to the lunar surface due to the Moon’s non-spherical gravity field.
Date of Conference: September 14-17, 2021
Track: Cislunar SSA