Determining Mars Mission NTP Thrust Size and Architecture Impact for Mission Options

Abstract

Future exploration missions across the Solar System need technologies that reduce the time of flight, provide efficient payload capability, and reduce the size and the number of launch systems in order to reduce mission risk and cost. NTP (Nuclear Thermal Propulsion) is the proven, high Technology Readiness Level technology, which provides the performance to enable rapid transit and can minimize the number of SLS launches due to the higher ISP (specific impulse). The future of human Mars exploration will see substantial benefit in terms of lower mission mass and faster trip times when NTP is employed. NTP has been proven scientifically and many of the engineering challenges have been addressed in past ground testing of reactor cores for a range of power levels needed for NTP systems. The challenge today is to create an affordable, highly capable in-space propulsion system. Aerojet Rocketdyne (AR) believes that this could be achieved based on using smaller reactors in the NTP designs (e.g., < 500 MWt) that spring-board off the knowledge gained from past research and development and applies new technologies to improve the life and provide eventually reusability. Also, mission architectures that have the local planetary exploration elements pre-deployed ahead of the human crew can have a significant impact on the design of the human NTP spacecraft, NTP power level (thrust size) and eventual NTP system reusability. The desire would be to have the human crewed vehicle as small as technically feasible, optimize the thrust size and optimize the number of engines based on mission need. This could drive the NTP design to have a smaller reactor, present a more affordable development plan, and lower cost operational footprint for future human Mars exploration transportation systems. Approaches to use a small NTP reactor core could provide a development cost benefit with less uranium content and be more easily tested with a smaller facility foot-print. The smaller facility and lower exhaust flow rate provides for less effluent to clean and manage, which, in turn, reduces the development cost due to environmental safety and nuclear material security concerns. Fundamentally a lower power NTP reactor core (< 500 MWt) can reduce the development, procurement, and operational costs making it a more affordable NTP system for a nuclear cryogenic propulsion stage. AR has been working on several NTP system designs that have a wide range of thrust (core) sizes and the scalability for any exploration mission. AR has performed various architecture and design studies from 2011 through 2015 that have identified NTP approaches for using the capability of smaller size NTP systems for robotic and human Solar System missions. AR has used our multidisciplinary design and architecture analysis capability to analyze a split cargo and crew approach where low to medium power (i.e., 100-150 KWe) Solar Electric Propulsion (SEP) pre-position mission cargo (e.g., long duration habitats, transfer stages, and lander systems) and the crew vehicle uses NTP for rapid transfer to Mars. This paper will focus on results of the study for the NTP stage Mars mission architecture element and the examinations of the thrust size and number of NTP engine systems and how they impact a human Mars mission. 1 Fellow, Mission Architecture, PO Box 109680, M/S 712-67, and AIAA Associate Fellow. 2 Program Manager, Advanced Programs, P.O. Box 7922 / MS RFB19, AIAA Member. 3 Sr. Engineer, Mission Architecture, 555 Discovery Dr.