Advanced Electric Propulsion System
Advanced Electric Propulsion System (AEPS) is a solar electric propulsion system for spacecraft that is being designed, developed and tested by NASA and Aerojet Rocketdyne for large-scale science missions and cargo transportation. "The most probable first application of the AEPS" is to propel the PPE module of the planned Lunar Orbital Platform-Gateway to be launched in 2022. Four identical AEPS engines would consume most of the 50 kW generated by solar power.
The Power and Propulsion Element (PPE) for the Lunar Gateway will have a mass of 8-9 metric tons and will be capable of generating 50 kW of solar electric power for its ion thrusters for maneuverability, which can be supported by chemical propulsion.
Solar-electric propulsion has shown to be reliable, efficient and allows a significant mass reduction of spacecraft. High-power solar electric propulsion is a key technology that has been prioritized because of its significant exploration benefits in cis-lunar space and crewed missions to Mars.
The AEPS Hall thruster system was originally developed since 2015 by NASA Glenn Research Center and the Jet Propulsion Laboratory to be used on the now cancelled Asteroid Redirect Mission. Work on the thruster did not stop following the mission cancellation in April 2017 because there is demand of such thrusters for a range of NASA, defense and commercial missions in deep space. Since May 2016, further work on AEPS has been transitioned to Aerojet Rocketdyne via a competitive contract, that is currently designing and testing the engineering-model hardware.
|Max. power consumption||40 kW|
|Maximum specific impulse (Isp)||2,600 s /engine|
|Maximum thrust||589 mN /engine|
|Theoretical total thrust||2.356 N|
|Actual thrust @ 40 kW||1.77 N|
|Distance range from Sun||0.8 to 1.7 AU|
|Input voltage range||95 - 140 V|
|System mass||100 kg x 4 engines|
|Xenon propellant mass
AEPS is based on the 12.5 kW development model thruster called 'Hall Effect Rocket with Magnetic Shielding' (HERMeS). The AEPS solar electric engine makes use of the Hall-effect thruster in which the propellant is ionized and accelerated by an electric field to produce thrust. To generate 12.5 kW at the thruster actually takes a total of 13.3 kW including power needed for the control electronics. Four identical AEPS engines (thruster and control electronics) would theoretically need 4 x 13.3 = 53.2 kW, more than the 50 kW generated by solar panels of the PPE.  It is stated that the AEPS array is intended only to use 40 kW of the 50 kW, so the maximum thrust would be limited to around 1.77 N.
Tests carried out at the University of Michigan in 2017, using 100 kW on a 3 thruster array built with a 3 concentric ring design, yielded a record setting 5.4 N of thrust. This represents a higher level of efficiency than the current AEPS so there may be room for improved thrust in the design.
The engineering model is also undergoing various vibration tests, thruster dynamic and thermal environment tests. AEPS is expected to accumulate about 5,000 hr by the end of the contract and the design aims to achieve a flight model that offers a half-life of at least 23,000 hours and a full life of about 50,000 hours.
The three main components of the AEPS propulsion engine are: a Hall thruster, Power Processor Unit (PPU), and the Xenon Flow Controller (XFC). The thrusters are throttleable over an input power range of 6.67 - 40 kW with input voltages ranging from 95 to 140 V. The estimated xenon propellant mass for the Lunar Gateway would be 5,000 kg. The Preliminary Design Review took place in August 2017. It was concluded that "The Power Processing Unit successfully demonstrated stable operation of the propulsion system and responded appropriately to all of our planned contingency scenarios."
In July 2017, AEPS was tested at Glenn Research Center. The tests used a Power Processing Unit (PPU), which could also be used for other advanced spacecraft propulsion technology. In August 2018, Aerojet Rocketdyne completed the early systems integration test in a vacuum chamber, leading to the design finalization and verification phase.
- Overview of the Development and Mission Application of the Advanced Electric Propulsion System (AEPS). (PDF). Daniel A. Herman, Todd A. Tofil, Walter Santiago, Hani Kamhawi, James E. Polk, John S. Snyder, Richard R. Hofer, Frank Q. Picha, Jerry Jackson and May Allen. NASA; NASA/TM—2018-219761. 35th International Electric Propulsion Conference. Atlanta, Georgia, October 8–12, 2017. Accessed: 27 July 2018.
- NASA issues study contracts for Deep Space Gateway element. Jeff Foust, Space News. 3 November 2017.
- Chris Gebhardt. "NASA finally sets goals, missions for SLS – eyes multi-step plan to Mars". NASA Spaceflight. Retrieved April 9, 2017.
- Jeff Foust (June 14, 2017). "NASA closing out Asteroid Redirect Mission". Space News. Retrieved September 9, 2017.
- Aerojet Rocketdyne Signs Contract to Develop Advanced Electric Propulsion System for NASA. Aerojet Rocketdyne. Press release, 28 April 2016. Accessed: 27 July 2018.
- NASA Works to Improve Solar Electric Propulsion for Deep Space Exploration. NASA News. April 19, 2016. Accessed 27 July 2018.
- "Ion Thruster Prototype Breaks Records in Tests, Could Send Humans to Mars". space.com. Archived from the original on 20 March 2018. Retrieved 27 April 2018.
- 13kW Advanced Electric Propulsion Flight System Development and Qualification. (PDF). Jerry Jackson, May Allen, Roger Myers, Erich Soendker, Benjamin Welander, Artie Tolentino, Chris Sheehan, Joseph Cardin, John Steven Snyder, Richard R. Hofer, Todd Tofil1, Dan Herman, Sam Hablitze and Chyrl Yeatts. The 35th International Electric Propulsion Conference. Atlanta, Georgia, USA. October 8 – 12, 2017.
- Advanced Electric Propulsion System successfully tested at NASA's Glenn Research Center. Jason Rhian, Spaceflight Insider. 8 July 2017.
- "Advanced Electric Propulsion System successfully tested at NASA's Glenn Research Center - SpaceFlight Insider". www.spaceflightinsider.com. Retrieved 2018-07-28.
- Successful testing gives NASA's Advanced Electric Propulsion System a boost. David Szondy, New Atlas. 29 August 2018.
- Aerojet Rocketdyne demonstrates advanced electric propulsion capabilities. Space Daily. 29 August 2018.