o MPD-arcjet thruster specific impulse = 2500 sec, efficiency = 45%, and specific power = 10 KWj/KG (or thrust/weight about 0.08). o Single ended Brayton cycle turbogenerator energy converter system, arbitrarily selected because of its better definition. o Total thrust power =4.0 MWj. It is noted that recent Boeing study indicates that total spacecraft mass is nearly identical for either the thermionic or Brayton converter design. Thus, total COTV hardware and propellant mass figures are representative of either design. Additionally, final disposal of the COTV's nuclear reactor to solar system escape (SSE) is costly in COTV propellant tank weight; alternate disposal techniques, such as solar orbit or even storage in orbit with subsequent disassembly and selective component return to Earth, may prove to be a better choice. Finally, the selection of 2500 sec specific impulse is thought to be conservative and based on the uncertainties of thruster performance. Recent Boeing studies indicate that a figure of about 5000 sec, if attainable, is closer to optimum. In summary, a round trip nuclear-electric tug for 3 month LEO- GEO transfer of a 500,000 lb. payload has a total vehicle and propellant mass about equal to the payload mass. Due to the need for Earth biosphere protection, disposal of the tug's radioactive components after useful life appears to be a serious problem. OPERATIONS The nuclear-electric tug is operationally expensive, both because of the 120 day round trip transfer time required for the basic mission and due to the long operational period associated with final disposal of the vehicle at the end of its service life. For its basic, orbit transfer mission, SPS operational capabilities, including ground tracking, communication, monitor, and control, would be used. The major tradeoff is between long operating time versus COTV/propellant life, size, mass, and cost. The 90 day up trip time is considered about a minimum commensurate with reasonable vehicle design. A major unique requirement for the nuclear-electric COTV consists of long term, separate, deep space operational support for vehicle disposal to solar system escape or to solar orbit. This assumes that vehicle disassembly and recovery of the reactor for alternate, radioactive waste disposal does not prove to be feasible, and requires that a significant portion of the system life must be reserved for the disposal mission. COSTS A comprehensive cost analysis, including all nonrecurring as well as recurring programmatic costs, has not been made of the nuclear- electric COTV. JPL has made a rough, recurring cost estimate of $50M
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