Stability Analysis of Spacecraft Motion in the Vicinity of Asteroids

Natural and artificial satellites are subject to perturbations when orbiting near-Earth asteroids. These perturbations include non-uniform gravity from the asteroid, third-body disturbances from the Sun, and solar radiation pressure. For small natural (1 cm-15 m) and artificial satellites, solar radiation pressure is the primary perturbation that will cause their orbits to go unstable. For the asteroid Bennu, the future target of the spacecraft OSIRIS-REx, the possibility of natural satellites having stable orbits around the asteroid and characterizing these stable regions is investigated. It has been found that the main orbital phenomena responsible for the stability or instability of these possible natural satellites are Sun-synchronous orbits, the modified Laplace plane, and the Kozai resonance. These findings are applied to other asteroids as well as to artificial satellites. There have been previous studies of stability around asteroids before, but predominantly with spacecraft, dust around main-belt asteroids, or large satellites not perturbed by solar radiation pressure. This is the first study that looks at objects over a large range of natural satellite diameters that could be stable around a near-Earth asteroid. This research will inform future NASA missions to small bodies and the types of natural satellites that could exist and may interfere with the mission planning and design. By understand where these objects could be stable contingency planning can be implemented beforehand to mitigate any issues and delays that can come from not preparing for a possibility of such an object’s existences around a small body. The re-emission of solar radiation pressure through BYORP is also investigated for binary asteroid systems. Specifically, the BYORP force is combined with the Laplace plane such that BYORP expands the orbit of the binary system along the Laplace surface where the secondary increases in inclination. For obliquities from 68.875°-111.125°the binary will eventually extend into the Laplace instability region, where the eccentricity of the orbit will increase. A subset of the instability region leads to eccentricities high enough that the secondary will impact the primary. This result inspired the development of a hypothesis of a contact-binary binary cycle. YORP will increase the spin rate of a contact binary while also driving the spin-pole to an obliquity of 90°. Eventually, the contact binary will fission. The binary will subsequently become double-synchronous, thus allowing the BYORP acceleration to have secular effects on the orbit. The orbit will then expand along the Laplace surface to the Laplace plane instability region eventually leading to an impact and the start of a new cycle with the YORP process. This research topic explores the possibility of a cycle where an asteroid will go between two main states: a single contact-binary asteroid and a binary asteroid system. This cycle could help explain two observations of the near-asteroid population. First, this would help explain why there are many contact-binary asteroids with a large range of high obliquities, where they have a tendency to be driven to obliquities of 90° as opposed to 0°/180°. Second, this cycle would help uphold the observation that 15% of near-Earth asteroids are binaries. This theory creates a cycle as opposed to an asteroid eventually losing its secondary, an asteroid will go through multiple time periods of being a binary asteroid and thus contribute to the significant population of binary asteroids that we observe.