electrolysis unit. The variation in trip time among the other concepts is merely the result of weight variations and is not significant. Since none of these concepts uses over 20 percent of the available satellite power, shorter trip times are possible for each, with weight penalties dependent on each concept. Figure VI-D-1-14 illustrates the trend of trip time with power requirements. For the numbers presented in table VI-D-1-6, the same caveat as expressed for the chemical stage applies: these values must be regarded as highly preliminary and subject to large changes as the ground rules and assumptions change. Three major assumptions for these dependent electric COTV concepts that do influence the COTV sizing are as follows: 0 no satellite penalty for supplying power to COTV ° satellite performs own altitude control ° no allowance made for occultation thrusting 1.3.4 TECHNOLOGY ISSUES Except for the issue common to all dependent electric COTV's of power distribution from the satellite, there do not appear to be any significant technology issues for the electrolysis concept. It shares, with the chemical as well as the other electric stages, the problem of size, construction, operation, and economic viability discussed earlier. The resistojet is a simple electric thruster with demonstrated high reliability. The major technology issue associated with the resistojet is the unknown impacts of the several order-of-magnitude scale-up from existing thrusters to the size required for the COTV. A similar uncertainty regarding scale-up exists for the arcjet thruster, together with concerns regarding the weight and cost of a thruster some 20 to 50 times larger than the largest existing thruster. Electrode erosion has been a life-limiting factor for arcjet, and the attempt to build high performance, lightweight, long-life thrusters will be a significant technology challenge.
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