1. The advanced technologies listed i n table 1 assume significant thruster system development beyond the Reference Mission flight test. The following analysis provides performance comparisions for future spacecraft which have payloads requiring 300 kWe of imbedded electrical power,which can be used to power an electric propulsion system during the orbit transfer phase, and u t i l i z e advanced arcjet thruster technology. This type of spacecraft i s considered a prelude to spacecraft which w i l l be considerably larger and have more demanding power requirements than the spacecraft o f today. Typically, their payloads w i l l require megawatts of electrical power. These characteristics are typical o f proposed SDI space platforms. The technology levels chosen for the advanced ammonia and hydrogen arcjets in table 1 are derived from the base 1ine ammonia arcjet technology being tested today, and are capable o f being f l i g h t ready i n the middle to late 1990's. Constaints and Assumptions
2. For the sake of comparison, Centaur G-prime performance is also considered for this mission. The orbit raising capability of the Centaur Gprime is evaluated using Hohman transfers. The ASE mass required for the Centaur G-prime is 4550 kg in addition to the SNPS/payload ASE mass. This chemical upper stage has a specific impulse of 444 s and a dry mass to propellant ratio of 0.16. Results Centaur Gprime The Centaur G-prime, which is a iquid oxygen-liquid hydrogen upper stage, is a high performance version of the Centaur G. Although i t is being developed for payloads up to-approximately-2700 kg,' i t is assumed in this analysis that it, or a chemical propulsion system with the same performance, can lift any mass payload which can be accomodated in the shuttle. Figure 18 shows the payload delivery capability of this advanced chemical propulsion system to various altitudes and inclinations. Payloads of 1000 kg (powered by a 300 kWe reactor) can be lifted up to 18000 km or inclination changes of up to 25 degrees can be accomplished. The transfer times are much less than one day.
3. thus far, inhibiting their consideration has been the d i f f i c u l t y of storing liquid hydrogen i n space and the mass penalty associated with that storage. Tankage mass can be quite substantial and negate a significant portion of the advantage o f the increased operating efficiency. A specific impulse of 1800 s
4. Advanced ammonia and hydrogen arcjet technologies were examined to assess their orbit raising capability for first generation SDI platforms with 300 kWe of imbedded power on board. Both systems were compared to a chemical transfer assuming Centaur G-prime Performance, The chemical system ran short of payload margine at 22,000 km. Both electric systems had substantial payload margines to GEO. The hydrogen system (Is 1800 s, efficiency 58%)had almost twice payloai capacity but at double the trip time compared to the advanced ammonia system (I IlOOs, efficiency 50%). In addition, the hydro& system could execute plane changes of over 60 degrees as compared to 40 degrees for the ammonia system. A single shuttle launch from KSC was assumed for all the advanced systems.