NASA ends Lunar Flashlight mission because of thruster problems

WASHINGTON — NASA has ended the mission of a cubesat intended to go into orbit around the moon but which was unable to do so because of problems with its propulsion system.

NASA's Jet Propulsion Laboratory announced May 12 the end of the Lunar Flashlight mission, five months after its launch. The spacecraft was unable to go into its planned polar orbit around the moon because its propulsion system could not produce the required thrust.

Engineers spent several months trying to troubleshoot the problem, identified shortly after its December 2022 launch. They suspected that debris of some kind was blocking propellant lines, reducing the amount of propellant reaching the thrusters.

NASA said May 5 that they were making one final effort to clear the obstructions by increasing fuel pump pressures "far beyond" operational limits while opening and closing valves. That technique, tried on one of the spacecraft's four thrusters, had shown some success, "inconsistently producing some increased levels of thrust."

However, those efforts weren't enough to keep the spacecraft in the vicinity of the moon, leading JPL to bring the mission to an end. Mission planners had, by that point, ruled out placing the spacecraft into a near-rectilinear halo orbit around the moon, but hoped to be able to place it into a distant Earth orbit that allowed for monthly flybys of the moon.

How the debris got into the propulsion system is not clear. In a recent interview, Daniel Cavender, who was the project manager for the cubesat's propulsion system at NASA and is now director of Rubicon Space Systems, a division of Plasma Processes LLC that is commercializing that propulsion system, noted the constraints imposed by the 6U cubesat design limited engineers’ ability to put filters into the system.

"Because of the size constraints, we could not put filters everywhere. So, we relied heavily on precision cleaning, inspections and contamination controls. But there was a process slip at some point," he said. The data from the cubesat, he noted, was consistent with ground tests of thrusters with debris in their propellant lines.

Lunar Flashlight was the first spacecraft to go beyond Earth orbit to use a non-toxic "green" propellant called Advanced Spacecraft Energetic Non-Toxic, or ASCENT, developed at the Air Force Research Laboratory. Cavender noted that the thrusters worked well until the debris problem starved them of propellant, calling it a "significant validation in space."

NASA emphasized other technologies that Lunar Flashlight successfully tested. They included a new flight computer called Sphinx that can operate at low power levels and survive the radiation environment of deep space, and an upgraded radio called Iris.

"Technology demonstrations are, by their nature, higher risk and high reward, and they’re essential for NASA to test and learn," Christopher Baker, program executive for small spacecraft technology in NASA's Space Technology Mission Directorate, said in a statement announcing the end of the mission. "Lunar Flashlight was highly successful from the standpoint of being a testbed for new systems that had never flown in space before."

Lunar Flashlight also had a science mission, using a laser reflectometer instrument to look for water ice in permanently shadowed craters at the south pole of the moon. While the spacecraft won't be able to collect any science, it did test the instrument and confirmed it was working as expected.

"It's disappointing for the science team, and for the whole Lunar Flashlight team, that we won't be able to use our laser reflectometer to make measurements at the moon," Barbara Cohen, principal investigator for the mission at the Goddard Space Flight Center, said in the statement. She added, though, that the mission "collected a lot of in-flight performance data" on the instrument that could be used on designs for similar instruments on future missions.

Lunar Flashlight was originally manifested on Artemis 1, the first launch of the Space Launch System rocket, along with 12 other cubesats. However, a switch in the design of the propulsion system caused the spacecraft to mission a deadline of the fall of 2021 to be integrated on the SLS. NASA instead flew it as a secondary payload on the Falcon 9 launch of the HAKUTO-R M1 lander from Japanese company ispace, which lifted off less than a month after Artemis 1.

Several of the 10 cubesats launched on Artemis 1 also suffered technical problems that prevented them from carrying out their missions. At a May 1 workshop, Craig Hardgrove, principal investigator for the LunaH-Map cubesat, said his team was still trying to resolve a problem with its electric propulsion system. He said then that if they could not free a stuck valve in that system by the end of May, they would likely wind down operations.

JPL said that Lunar Flashlight will make a flyby of Earth May 17 at an altitude of 65,000 kilometers and then head into deep space. Since other systems on the spacecraft continue to operate despite the propulsion problem, "NASA is weighing options for the future of the spacecraft."

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews.He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor's degree with honors in geophysics and planetary science... More by Jeff Foust