Adam P. Wilmer, Air Force Institute of Technology; Robert A. Bettinger, U.S. Air Force; Bryan D. Little, Air Force Institute of Technology
Keywords: space domain awareness; space situational awareness; cislunar; periodic orbit
Abstract:
The opening decades of the twenty-first century has witnessed a reemergence of international attention towards the realization of space missions into the cislunar environment and beyond, with both nations and private companies investigating the formation of missions to the Moon and Mars. With national plans to create a Lunar Gateway orbiting the Moon, develop a long-term human presence on the Moon, and facilitate preparations for Human missions to Mars via NASAs Artemis program, the United States has a vested interest in exploring trajectory design within multi-body gravitational systems. One such class of trajectories, identified herein as cislunar periodic orbits, could provide a reliable astrodynamical means of supporting missions such as re-supply, personnel transport, and space-based infrastructure development. With increasing missions beyond near-Earth orbit, the use of a subset of these periodic orbits for space domain awareness (SDA) mission architectures may also prove beneficial for the timely identification and tracking of resident space objects, such as space debris, to ensure safe space traffic management.
Performing SDA utilizing classical terrestrial and/or space-based sensors in near-Earth space becomes increasingly difficult when applied to the cislunar orbit regime. Therefore, cislunar periodic orbits are presented as a means to fill this capability gap. When compared with alternative types of orbital trajectories, periodic orbits provide mission-related benefits in terms propellant savings for orbit maintenance. This is the result of these periodic orbits designed to repeatedly traverse a given region of the toroidal volume of cislunar space with a lower propellant expenditure than typical non-periodic cislunar trajectories. Multiple types of periodic orbits will be investigated for their effectiveness in performing an SDA mission with respect to two notional resident spacecraft in a Lyapunov orbit about the Earth-Moon L1 Lagrange point. The initial conditions required for these periodic orbits are found using previous work from Arenstorf, who used a dated non-dimensional mass parameter in his CR3BP analysis, therefore, differential correction is used to normalize these orbits to a modern non-dimensional mass parameter.
The orbits analyzed will be modeled in the circular restricted three-body problem (CR3BP). The propellant required to maintain the same trajectory when transitioning to the Bicircular restricted four-body problem (BCR4BP) is also presented. The implementation of multiple dynamical models is sought in order to compare orbit maintenance costs when transitioning to higher fidelity models such as from the CR3BP to the BCR4BP.
Propellant expenditure is a dominant cost which determines the lifespan of a given spacecraft system. The periodic orbits analyzed in this work have the ability to repeat their orbital trajectory for months with no additional propellant in the CR3BP. However, chaos is introduced in the system with the added perturbation of the Sun’s gravitational force as seen in the BCR4BP. The computation of orbit maintenance costs for each periodic orbit in the BCR4BP will be made to show the low propellant required for these orbits in higher fidelity models. The factors that are analyzed for determining periodic orbit effectiveness are: SDA coverage, propellant costs in the BCR4BP, and period (i.e., revisit time). For SDA coverage, each variety of periodic orbit will host a sensor bearing satellite constellation consisting of 10 satellites evenly space in time across the orbit monitoring 2 notional satellites, identified herein as “Targets”, in an L1 Lyapunov orbit. Notional space-to-space sensors are used to determine limitations of periodic orbit geometry for the SDA mission as a function of sensor range, capability, and gravitational body exclusion angles. Tabulated results of the findings will be presented with recommendations for which periodic orbit is most effective for this cislunar SDA mission architecture.
Date of Conference: September 14-17, 2021
Track: Cislunar SSA