Servicing polar platforms using electric propulsion
The future of space development has been examined in the context of the infrastructure necessary support it. It is concluded that the selection of propulsion systems for in-orbit transportation requires the development of general computer codes capable of simulating the use of a wide range of propulsion systems on near-Earth missions. It is also concluded that, even if limited infrastructural development occurs, polar orbiting spacecraft will be an important feature of future space activities. Replacing current single-use polar spacecraft with extended-life serviceable platforms is attractive. However, the very limited manned access polar orbits in the mid-term future suggests that such platforms will only be possible if remote telerobotic/autonomous servicing can be carried out. To this extent polar platforms are considered to provide a useful driver and first testbed for the development of technologies designed to extend human capability in those regimes where direct mediation is not possible. Options for such remote servicing are examined, the concept of performing nodal transfers by enhanced differential nodal drift is introduced and the application of electric propulsion to this discussed. Low-thrust orbital manoeuvres are analyzed in this context and the conditions for optimum nodal transfer defined. Particular service vehicle configurations are then defined against a projected infrastructure and baseline polar platform constellation. A model for the service vehicle is defined and its performance investigated using a number of electric propulsion systems. Simulations of transfer manoeuvres; have been carried out and the effects and relative importance of the various orbit perturbations identified. It is concluded that a service vehicle propelled by a Xenon ion system offers the capability required and two final configurations are identified characterising different servicing mission upload schemes.