NEXT-C Lessons Learned on the DART Mission for Future Integration and Test

Abstract

NASA's Evolutionary Xenon Thruster – Commercial (NEXT-C) was demonstrated as part of the Double Asteroid Redirection Test (DART) mission. During DART mission development, NEXT-C was identified as a new technology that was not required for meeting of the primary mission requirements. Therefore, the operation of NEXT-C in flight was for demonstration purposes only. The initial operation of the NEXT-C system was performed on December 18, 2021 following 4 separate days of system conditioning and checkouts. The initial operation demonstrated that the NEXT-C system performed as expected, however, an anomaly was observed in the spacecraft's power system electronics (PSE) which conditions solar array power for spacecraft bus electronics and is not directly connected to NEXT-C. A joint investigation was unable to conclusively arrive at the root cause of the PSE anomaly and all pending NEXT-C operations have been suspended. In the course of the anomaly investigation, gaps in component level testing, as well as integrated spacecraft-level testing, were identified as candidates for potentially uncovering incompatibilities between the NEXT-C system and the DART spacecraft. Some of the deferred test activities were captured as exceptions to the Test-As-You-Fly philosophy and were accepted as risks with accompanying mitigation steps. DART has a NASA Risk Classification Level C (modified), so some risks were accepted given the cost and schedule constraints. Post-anomaly reviews of the NEXT-C / spacecraft integration and test program highlighted expected operating conditions during NEXT-C commissioning that needed either added or more exhaustive testing due to non-deterministic occurrences of high-energy grid-clearing shorts. The outcome of the team's efforts have been captured as lessons learned for future applications which APL expects to pursue for a variety of candidate mission concepts enabled by NEXT-C.