Mass performance characteristics of assembly and departure orbits for piloted Mars missions

This paper discusses a systematic investigation of the mass performance resulting from the use of various Earth orbits for assembling and launching piloted missions to Mars. The premise for this study is that all the spacecraft mass associated with a piloted Mars mission (i.e. hardware and propellant) will be initially launched into a low altitude circular orbit. The spacecraft could then depart directly for Mars from this orbit or the interplanetary vehicle could be assembled in an intermediate orbit at higher altitude prior to departure. Use of a 'nuclear safe orbit' for the assembly and departure of nuclear thermal or nuclear electric rocket stages is one example of an intermediate orbit. A figure of merit for the mass performance associated with using these intermediate orbits is a comparison of the initial mass required in a low altitude circular orbit for each of the following cases: a spacecraft using the intermediate orbit and a spacecraft departing directly, assuming an identical payload mass for both spacecraft. The investigation is structured to cover all possible intermediate parking orbits. Results indicate that based solely on the mass performance figure of merit, direct departures from low altitude circular orbits are the best option. This analysis does indicate that if other constraints require higher orbits, there are families of orbits that provide the same performance for different orbit geometries.