Space Transfer Technologies
The third element of the ASTP is the in Space Transfer Technologies (STT) project. STT is pursuing technologies that provide performance increase over todays chemical space transfer systems. Because approximately 70 percent of the satellite and its upper stage is propellant, performance improvements could significantly reduce this weight. The result would be larger payload capability or cost reductions from stepping down to smaller, lower cost launch vehicles. One such performance technology is solar-thermal propulsion, promising specific impulse approaching 1,000 for an approximately 50 pound-thrust system. The added advantage of the very lightweight, inflatable structure and solar concentrators are being pursued. The first test of this concept is the Shooting Star flight experiment. Electrodynamic tether propulsion also shows promise for propellantless Earth orbit transfer as well as orbiting space science missions at Jupiter. STT plans to test this concept on the propulsive small expendable deployer system (ProSEDS) as a precursor to multiple applications of tether propulsion. ProSEDS will utilize drag thrust to deorbit the Delta upper stage in days instead of the months now required for the stage to deorbit without the tether. The flight demonstration will demonstrate the first opportunity for commercial tether propulsiona deorbit system for stranded satellites that would otherwise become space debris. For deep space missions, STT is demonstrating solar-electric ion propulsion. A flight is schedule for 1998 of the Deep Space1 (DS1) spacecraft with an ion engine as primary propulsion . Ion propulsion offers 3,000 seconds of specific impulse, reducing the mass of the propulsion system and enabling shorter mission times. The DS1 ion engine has now passed 6,000 hours of its 8,000 hour test.
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