| Electric Propulsion Technology Overview |
As NASA’s Science Mission Directorate progresses its robotic missions from observers to rovers to sample return missions, the demanding goals exceed the capabilities of conventional propulsion technologies and will ultimately require improved spacecraft capabilities such as those obtained from advanced electric propulsion technologies. The In-Space Propulsion Technology Project is maturing advanced electric propulsion technology product lines for near-term flight infusion opportunities, including advanced ion and hall propulsion systems.
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NASA’s Evolutionary Xenon Thruster (NEXT) during environmental testing at NASA’s Jet Propulsion Laboratory. |
In the early 1990s, NASA identified electric propulsion as a key in-space propulsion technology for future deep space missions and began developing and testing various electric propulsion technologies. Intended to reduce fuel mass, decrease travel times and permit larger payloads, electric propulsion technologies may be one of the keys to our continued exploration of Earth’s neighboring worlds. Electric propulsion technologies generate thrust via electrical energy. This energy is used to accelerate an on-board propellant such as xenon gas.
Spacecraft powered by typical electric propulsion systems may eject propellant at up to 20 times the speed of conventional chemical systems, delivering a much higher specific impulse, or in other words more thrust from the weight of fuel consumed. Therefore, electric-based systems require far less propellant mass than a state-of-art, chemical-propellant craft. Another benefit of electric propulsion is that deep-space missions would no longer be constrained by narrow and rare launch window opportunities dictated by planetary alignment. Traditionally, chemical-propelled spacecraft move from planet to planet as they travel, using “gravity-assist” maneuvers in each world’s orbit to increase their own velocity and “sling-shot” toward their final destination.
NASA’s Evolutionary Xenon Thruster (NEXT) Ion Propulsion System nears TRL-6:
The NEXT system consists of a high-performance, 7-kW ion thruster; a high-efficiency, 7-kW power processor unit (PPU); a highly flexible xenon propellant management system (PMS); a lightweight engine gimbal; and key elements of a digital control interface unit (DCIU) including software algorithms. A Long-Duration Test (LDT) was initiated to validate and qualify the NEXT propellant throughput capability to a qualification-level of 450 kg, 1.5 times the mission-derived throughput requirement of 300 kg. The LDT has exceeded 270 kg in December 2007. The NEXT Prototype Model (PM) ion thruster has passed qualification-level environmental tests. The NEXT Engineering Model (EM) PPU has completed a round of functionality tests and is being prepared for environmental tests. The NEXT PMS has completed all environmental tests. Near term activities include a single-string integration test of the PM thruster the EM PPU and the EM PMS and continuation of the EM thruster life validation test. In addition ISPT is implementing tasks, which will address first-user costs for electric propulsion systems, such as reducing life qualification costs.
High Voltage Hall Accelerator (HiVHAC) Thruster - Hall Thruster:
The recent focus of the HiVHAC thruster task has been to develop a 3.6 kW Hall thruster with increased specific impulse, throttle-ability and lifetime to make Hall propulsion systems available for deep space science missions. The primary application focus for the resulting Hall propulsion system would be cost-capped missions, such as Discovery-class missions. This is another way that ISPT is addressing first-user costs of electric propulsion systems. The thruster has been operated in excess of 85 kg of xenon throughput, and is on track to demonstrate the predicted thruster life. At 3.5 kW the thruster has demonstrated a performance of 55% total efficiency and 2780 seconds total impulse, and a predicted lifetime exceeding 15,000 hours. Plans include the continued wear testing of the thruster configuration leading to the design, fabrication and build of an engineering model thruster that can provide predicted thruster performance across the anticipated environmental conditions.
NASA’s Electric Propulsion team includes researchers from Glenn Research Center in Cleveland; the Jet Propulsion Laboratory in Pasadena, California; and leading-edge partners in other government agencies, industry and academia. The Glenn Research Center manages the In-Space Propulsion Technology Project for the Science Mission Directorate in Washington.
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