Abstract:
The autonomous formation flying of multiple spacecraft to replace a single large
satellite will be an enabling technology for many future missions. In this research, the
current status of formation flying missions and technologies is determined, and the
Darwin nulling interferometry mission, which aims to detect and characterise
extrasolar planets, is selected as the research focus. Darwin requires high precision
formation flying of multiple telescopes near the Sun-Earth L2 point.
A comprehensive account of current research in astrobiology is presented which
provides the motivation for a Darwin-type mission. Astrobiology is integral to the
definition of formation manoeuvres and target identification. The system design
issues associated with developing a higher resolution, Planet Imager mission are also
explored through a preliminary mission design.
Relative dynamics models for satellite formation flying control in Low Earth Orbit
(LEO) and L2 are developed and methods of incorporating the Earth oblateness
perturbation (J2) into the equations of relative motion to improve model fidelity are
investigated. The linearised J2 effect is included in the Hill equations in time
averaged and time varying form. The models are verified against the Satellite Tool Kit
(STK) numerical orbit propagator, and applied to optimal control system design and
evaluation for formation keeping tasks.
The ‘reference orbit’ modelling approach applied in LEO is applied to the
development of a new formation flying model at L2. In this case, linearised equations
of motion of the mirror satellites relative to the hub are derived and performance
evaluated for different initial conditions. These and other higher order models are
compared to STK. The linearised model is applied to controller design for station
keeping and formation manoeuvring tasks suitable for a Darwin-type mission, and the
role of the model in developing controllers for a load levelling guidance system is
explored.
