event that the satellites are disposed intact, power from the SPS satellite can be used and propellant tankage, controls and thrusters from the COTV could be placed on the SPS satellite to provide the necessary thrust and control. In this mode it is likely that one would choose to use equipment that was essentially at the end of its useful life and was salvaged from a COTV. The Rockwell International cargo orbit transfer vehicle is referred to in their * study as an electric orbit transfer vehicle (EOTV), Figure 6.2. It has a dry mass of 1,000 MT and carries 670 MT of propellant. This amount of propellant is sufficient to impart a velocity increment of 1.9 km/s to the SPS satellite. Thus, for the higher energy disposal option, additional propellant tankage will be required. The Rockwell International EOTV configuration includes 144 thrusters of which 20 percent are spares. The present specification on these thrusters is a lifetime of 8,000 hours. This is not sufficient to complete a disposal mission that requires more than 333 days of thrusting time. Thus, for some dispsal options, longer lifetime thrusters or additional spares may be necessary. An alternative to the use of the EOTV thrusters is the use of the attitude control and stationkeeping thrusters of the SPS satellite. Sixteen thrusters are located on each corner of the SPS satellite making a total of 64 thrusters. These thrusters provide a total thrust of 832 newtons at a specific impulse of 13,000 s. Combined, these thrusters can -6 2 impart an acceleration of about 23 x 10 m/s to the SPS satellite. At this acceleration it requires 503 days to obtain a velocity increment of 1 km/s. At this rate it would require several years to dispose of an SPS satellite by means of the disposal options presented. However, with augmentation from the EOTV thrusters, this period of time is dramatically reduced. Satellite Power Systems (SPS) Concept Definition Study, Final Report, Vol. I, Executive Summary, Rockwell International Report No. SSD-79-0010-1, March 1979.
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