Primer vector theory is used to investigate a specific class of minimum-fuel
spacecraft trajectory problems in which high- and low-thrust propulsion
systems are utilized sequentially. The problem considered assumes a spacecraft
initially on-station in an established orbit about the Earth. It is desired
to intercept a pre-determined position in space in a timely manner for collision
avoidance or platform surveillance, using an optimal high-thrust program.
The spacecraft then returns to the original orbit station using optimal
low-thrust propulsion. Fixed-time minimum- fuel solutions are obtained
using the Clohessy-Wiltshire linearized dynamic model. In the time-open
case, the optimal final time is unbounded. For this case a composite performance
index involving both fuel consumption and the final time is minimized to
obtain optimal finite-time solutions.