Low-thrust orbit control of LEO small satellites.
In this thesis, we investigate the orbit control strategies of small satellites in Low
Earth Orbits (LEO) where the disturbance effects are significant, in particular
the nonspherical Earth and atmospheric drag effects. These orbits are not suitable
to be controlled by using traditional ground-based control strategies which
generally require high-thrust propulsion systems and other expensive resources,
both onboard and in the ground segment.
In order to react to those disturbances spontaneously and keep a small satellite
at a pre-defined station using its limited resources, autonomous orbit control
technology needs to be enabled. With the current advances in navigation and
propulsion technology, as well as onboard computation systems, the only key issue
that needs further investigations for practical implementation of an autonomous
orbit operation system is the control algorithm.
The orbit control strategies we investigate here are treated separately for each of
the orbital control phases, i.e. orbit deployment and acquisition, orbit transfer
and orbit maintenance. We present various forms of the solutions of the epicycle
motion which allow us to treat each control problem according to the control
requirements, nature of perturbations, control time scales and available resources.
Although applied in different manners, the optimal low-thrust control scheme is a
common aim for all control problems investigated here, as we mainly focus upon
applications for low cost small satellites in LEO.
The verifications of the strategies proposed in this thesis have been demonstrated
not only via computer simulations, but also sucessfully demonstrated on in-orbit
small satellite platforms thanks to an active small satellite programme at Surrey
Space Centre. The success of this study is hoped to provide a valuable basis for
satellite orbit operations which will involve larger number of satellites with more
complex configurations in the future.