1. The linear aerospike engine had the ability to vary the mixture ratio during flight. Varying the mixture ratio in a step-like or continuous manner throughout the ascent increased the vehicle payload capability by nearly 2000 Ibs compared to the case in which it was held constant. Also, by varying the mixture ratio profile, the total oxidizer to fuel ratio of the vehicle could be affected. Since this ratio influenced the weight and performance of the vehicle, its true effect could only be determined through an approach that coupled the vehicle sizing with the trajectory optimization. This approach was also usedtodetermine theoptimal liftoff thrust-to-weight ratio which was directly related to the size of the engine. By changing the oxidizer-to-fuel ratio to 6.5 and the liftoff thrust-to-weight ratio to 1.23, the vehicle empty weight could be reduced by 5% compared to the baseline case.
2. Propulsion system requirements for reusable single-stage-to-orbit rocket vehicles