surface plus additional expendables to sustain one crew person at a reasonable standard of living. Assuming the equipment arrives as cargo and the expendables as supplies on the manned vehicle, a 30 crew base would require 300 tons of cargo and approximately five manned flights as necessary overhead. For the lunar base reference scenario outlined previously, the total mass in LEO to provide this overhead would be 1630 tons (750 tons for manned flights and 880 tons for cargo flights). This assumes chemical rockets using lunar oxygen and reusable lunar landers. Using NEP for the cargo portion of the scenario would reduce the mass in LEO by 325 tons, while using the NTR for the cargo portion would do slightly better, reducing the mass by 370 tons. Assuming a new heavy-lift launch vehicle would be available by the turn of the century, and could deliver pay loads to LEO for $1 million a ton, it appears to be uneconomical to develop either nuclear option strictly for lunar development. For the reference Martian development scenario, the total mass in LEO would be 6150 tons (5350 tons for manned flights and 800 tons for cargo flights). This assumes aerobraking in the Martian atmosphere, use of in situ propellants at the Phobos gateway station, and reusable MCSVs and MCLs. Using NTRs for both the cargo and manned flights reduces the total mass in LEO to 5170 tons (4480 tons for manned flights and 690 tons for cargo flights). The assumptions for the NTR are the same as in the reference case. Using the NEP for both cargo and manned flights would reduce the total mass in LEO to 3250 tons (2700 tons for manned flights and 550 tons for cargo). In the case of the NEP, there is no need to aerobrake the transit vehicle in the Martian atmosphere, which simplifies packaging, but the MCSVs and MCLs still aerobrake to land and the other assumptions still hold. The launch cost savings available with the nuclear alternatives are significant for the Martian development scenario. The NTR would save $980 million which could almost pay for the NTR development, while the NEP would save $2.9 billion in launch costs, enough to pay for the NEP development plus the recurring costs. The beauty of developing the NEP is that once it's paid for, it would become the deep space propulsion vehicle for next half century. Its potential for interplanetary exploration is almost limitless. Therefore, we recommend the nuclear-electric option be continued and even expanded as a potential powerplant for all phases the Mars exploration. The potential savings appear worth the additional development risk. ACKNOWLEDGEMENTS This paper was derived from work supported in part by Contract NAS9-18040, Life Support Technology Definition Study for Long-Duration Planetary Missions. REFERENCES [1] NASA Office of Exploration (1988) Exploration Studies Technical Report, Volumes I & II (Washington, D.C.). [2] NASA Office of Exploration (1988) Doc No. Z-MASS-SRD-001, Scenario Requirements Document Version 1.0 (Washington, D.C.). [3] Craig, M.K. (1988) Focused Case Studies White Paper, Mission Analysis, System Engineering & Integration, November 15 (Johnson Space Center).
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