This paper discusses vehicle configuration options using nuclear thermal rocket (NTR) propulsion application to Mars missions. A reference mission in 2016 using an opposition-class Mars transfer trajectory is assumed. The total mission duration is 435 days. A single 75,000-lb-thrust nuclear engine is used for all major propulsive maneuvers. The studies indicate that three perigee kick burns upon leaving Earth result in the lowest stage weights required in low Earth orbit (LEO). The stay time on Mars is assumed to be 30 days. On the interplanetary return leg en route to Earth, a gravity assist by Venus is employed.
The reference mission assumes that the nuclear engine delivers a specific impulse of 925 s with an engine thrust-to-weight ratio of 4. The total stage thrust-to-weight ratio was 0.06. To determine which engine parameters were most critical to good mission performance, calculations were performed over arange of specific impulses and thrust-to-weight ratios. One of the major conclusions resulting from this study is that engine specific impulse is the single most important engine parameter in reducing overall stage weight, provided the engine thrust-to-weight ratio is above approximately 4. Lower engine thrust-to-weight ratios were found to incur severe performance penalties
