Space Tug Performance Optimization

I keeping with the concept of reusability the space tug extends the realm of application to near Earth space. Missions which could benefit from the assistance of a tug are now being proposed. From the performance analyst's point of view the trajectories required for these missions are somewhat more complex than those required for missions not employing a reusable assisting vehicle. In order to demonstrate some complexities and indicate one method for analyzing space tug trajectories a particular mission was chosen and is discussed here in some detail. The basic mission profile to be considered is that of the tug-assist-to-escape maneuver. The trajectory is initiated from a circular base orbit. From the base orbit the tug accelerates a spacecraft to an intermediate orbit with energy somewhere between that of the base orbit and escape energy. After separation the spacecraft ignites its engine and accelerates to escape energy. The tug stays in the intermediate orbit for some time and then reignites its engine and returns to the base orbit. Similar results for nonthrusting spacecraft have been obtained by Weyer and Teren.