Table 3.2 Duty Cycle and Mass Savings for Servicing of Degraded Solar Panels Electric Propulsion Systems In the near-future, the demand for satellites in Earth orbit will continue to increase. The programs of Earth resources and environmental monitoring will require many new systems in LEO, intermediate high orbits, polar orbits and GEO will need power systems. Many instruments will be on these vehicles and they will require higher power levels than that of current spacecraft: tens to hundreds of kilowatts (kW) versus only several kW typically used by current systems. The advent of these higher power levels will allow the consideration of more-advanced on-board propulsion and power technologies for satellites. These would include electric propulsion and also other power systems to augment the solar arrays of planned vehicles. Future satellite systems will likely demand higher payloads for more extensive and more economical commercial activities. One of the most powerful ways to improve the cost effectiveness of satellites is to use high performance propulsion systems. Current propulsion systems have a relatively-low specific impulse and even small improvements can allow substantial increases in the usable payload. The potential of electric propulsion also depends greatly on the mission length, mission type and total spacecraft mass. The markets for beamed power electric propulsion systems for applications in OTV's, Lunar operations, and interplanetary travel will be considered below. Over the past several decades, NASA and other space agencies have conducted market analyses of the traffic from LEO to GEO and other orbits. The traffic models were assuming many different missions, including a manned presence in GEO. If these models were accurate, there would be a very high demand for an OTV. The current budget projections, however, do not appear optimistic for the OTV market. One potential scenario using electric propulsion for LEO-GEO transfer may be used as an example of an optimistic market for beamed energy transportation. [Palaszewski, 1987] In this analysis, there were 256 missions over a 16 year period. To deliver these payloads from LEO to GEO, a number of OTV's are needed. This “fleet” of electric OTV's used either a 100 kW solar array or 1 MW nuclear reactor. The largest number of xenon ion propulsion vehicles that were needed is 11 for a 1-MW power level and 21 for a 100 kW power level. The round trip times for the 100 kW OTV's (LEO-GEO-LEO trip) is 400 days for the 100 kW OTV's and 200 days for
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