In 2005, NASA’s Project Prometheus continued comprehensive efforts to develop advanced technologies for space use. One key to these efforts was the development of electric propulsion technologies that would enable new missions, particularly when combined with power generated by a space nuclear reactor (ref. 1). This year, spacecraft requirements were finalized, ion thrusters were tested, and power-processing and control units were chosen for the 200-kW design.
The mission attributes that would be enabled by these technologies include more sophisticated active/passive remote sensing, greater launch window flexibility, spacecraft maneuverability at the destination planet or moon, and greatly increased science data rates. The first proposed mission application, the Jupiter Icy Moons Orbiter mission, focused on a 200-kW Prometheus 1 Spaceship utilizing electric propulsion, as shown in the illustration.
Spacecraft concept proposed for the Jupiter Icy Moons Orbiter.
The proposed mission had two principle objectives:
Specific requirements for the Prometheus 1 Spaceship were finalized in July 2005. The requirements were based on Prometheus 1 design team tradeoff analyses, including mission studies to optimize the propulsion parameters. The key driving requirements resulted in the following implementation: six 30-kW ion thrusters (2000-kg xenon throughput), each with a nominal thrust of 0.65 N at 7000-sec specific impulse; six 20-kW Hall thrusters, each with a nominal thrust of 1.0 N (in combination with two ion thrusters, each with a nominal thrust of 0.65 N); a power processor that is more than 96.5-percent efficient and that can operate in radiation levels greater than 5 Mrad; and a single 12,000-kg-capacity, carbon-overwrapped supercritical xenon tank.
The main challenge for the ion thrusters was the qualification of the engine and components in the electric propulsion system for the >2000-kg xenon throughput requirements of the mission (~10 times the state of the art). The basic wear test methodology was to perform component and full-scale tests followed by post-test evaluation. Resulting data were to be used to develop and refine analytical models that could more accurately project for the Prometheus 1 lifetime. Two of these early wear tests were completed this year: precursor ion thruster 2000-hr wear tests using the High Power Electric Propulsion (HiPEP) and Nuclear Electric Xenon Ion System (NEXIS) thrusters (refs. 2 to 8).
Work began on designing direct-drive power processing and control (PP&C) units that would provide the required conditioned power to the thrusters for the 200-kW-class nuclear electric propulsion system. These units would operate from a three-phase ac1 power bus operating at 400 V and would process 30 kW each at 5000 Vdc to operate the ion thruster. Tradeoff studies demonstrated that this was a viable approach that had several advantages over state-of-the-art dc-to-dc2 converter technology, including simplicity, higher efficiency, and inherent radiation resistance. The beam and accelerator supplies were to be integrated with the discharge, neutralizer, and heater supplies to complete the breadboard PP&C unit (ref. 9).
On the basis of these recent efforts, Hall thruster technology for both the large and small Hall thruster elements was deemed sufficiently mature to proceed directly to the preliminary design phase as soon as a small radiation compatibility effort was completed (ref. 10). Although the Prometheus 1 program has since been cancelled, the technology advances made in this work will be of great benefit to NASA in future exploration missions using electric propulsion.
Last updated: October 7, 2006
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