9-4. Near-term Nuclear Space Missions DANA G. ANDREWS Summary This paper summarizes the current status of proposed NASA Human Exploration Missions (HEMs), presenting detail with respect to schedule and system features. Using the Lunar exploration and Mars exploration missions as design drivers, new vehicle elements have been configured and optimized to meet proposed mission requirements. Both conventional chemical propulsion and alternative vehicle designs incorporating advanced nuclear propulsion systems are included, and the total mass required in Low Earth Orbit (LEO) is compared for each propulsion system. 1 Introduction Successful completion of the Civil Space Leadership Initiatives, and in particular, the Human Exploration of the Solar System as currently being defined by the Office of Exploration (OEXP) will require system capabilities to evolve beyond current capabilities, and humans to learn to live and work in space for periods measured in years instead of days. This will require new and innovative designs for spacecraft and surface elements, and thoughtful approaches to the problems of long-term space power. Space-based nuclear reactors are prime candidates to provide this power because of their low specific mass at the multimegawatt power levels and their ability to operate in all orbits and on planetary surfaces. Accordingly, we have concentrated on nuclear reactors as alternative propulsion and power elements in this paper. The overall objective of this paper is to summarize the human exploration case studies, define reference spacecraft systems and complementary advanced technology alternatives, performance-size the various elements to meet mission requirements, and determine what mix of vehicle types and technology developments results in the most cost effective system capable of completing the candidate mission cases. 2 Mission Characteristics Definition Baseline mission scenarios were established using the case studies in OEXP's Exploration Studies Technical Report, Scenarios Requirements Document, and the FY'89 Focused Case Studies White Paper [1-3] as guidelines. A key issue brought forth in [3], with respect to the baseline scenarios, and addressed in this paper, is the need to assemble very massive spacecraft in LEO using Block I technologies, or alternativey, the need to develop Nuclear Thermal Rockets (NTRs) and Nuclear Electric Propulsion (NEP) as Block II Technologies. As we shall show later, development of NEP reduces the need for the massive chemical stages assembled in LEO, making it an enabling technology for several of the case studies and cost effective for the others. Dana G. Andrews, Boeing Aerospace, M/S 8K-53, PO Box 3999, Seattle, Washington 98124, USA. Paper number IAF-ICOSP89-9-4.
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