Solar Electric Propulsion (SEP)

Under the guidance of NASA's Game Changing Development Program, prior to transitioning to the Technology Demonstration Missions Program, the SEP project began developing large, flexible, radiation-resistant solar arrays that can be stowed into small, lightweight, more cost-effective packages for launch to support the Asteroid Redirect Robotic Mission (ARRM). After launch, they unfurl, capturing solar energy to provide the electrical power required to enable high-powered electric propulsion. 

As the ARRM mission was being sunset, the Gateway Architecture was being established and the 12kW thrusters were identified for use on Gateway's Power and Propulsion Element (PPE).  Initially, Aerojet Rocketdyne was tasked with providing two flight thrusters in addition to the two previously-planned qualification thrusters. PPE's prime contractor requested that SEP no longer provide a string (thruster, power processing unit, and Xenon flow controller) but only provide the thruster as the prime preferred to provide the other string components.  In February 2020, the Gateway Program decided to co-manifest the launch of PPE with the Habitation and Logistics Outpost (HALO).  This decision required modifying the number and orientation of the SEP thrusters given the larger mass being delivered to orbit.  Aerojet Rocketdyne is now producing three flight thrusters, two of which will be gimballed by PPE to allow finer tuning of trajectory.  To stay within mass constraints for the co-manfiested vehicle, STMD made the decision in April 2022 to terminate the Plasma Diagnostics Package (PDP) that was to have flown with the SEP thrusters as developmental flight instrumentation.