OPTIMIZATION OF MANY-BURN ORBITAL TRANSFERS

Optimization of medium and low-thrust orbital transfers is important f or future upper stages. Previous research has generally either conside red a fairly small number of burns with medium thrust or has assumed c ontinuous thrusting for low-thrust transfers. The acceleration level c onsidered in this paper is too high to use orbit averaging and too low (in most cases) to use only a few burns. The optimization scheme used is an optimal control solution for each burn, and a parameter optimiz ation for the ensemble of burns. The solution for each burn is availab le in open-loop and closed-loop form, so that the method also provides a guidance scheme for Eying the transfers. The optimization includes oblateness terms, complicating many-burn transfers with plane change. Results compare favorably to several published cases. This paper also includes additional transfer cases and parametric results. These resul ts are easy to obtain in comparison with many-bum (non averaged) multi -point boundary value problem solutions, which require the determinati on of a number of sensitive parameters. Cases examined include transfe r to high-Earth orbit, transfer to geostationary orbit, transfer to th e Global Positioning System (GPS) orbit, escape from orbit, and transf er to the lunar sphere of influence.