WASHINGTON — NASA has ended the mission of a cubesat intended to enter orbit across the moon but which was unable to achieve this due to problems with its propulsion system.
NASA’s Jet Propulsion Laboratory announced May 12 the top of the Lunar Flashlight mission, five months after its launch. The spacecraft was unable to enter its planned polar orbit across the moon because its propulsion system couldn’t produce the required thrust.
Engineers spent several months attempting to troubleshoot the issue, identified shortly after its December 2022 launch. They suspected that debris of some kind was blocking propellant lines, reducing the quantity 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 shutting valves. That technique, tried on one among the spacecraft’s 4 thrusters, had shown some success, “inconsistently producing some increased levels of thrust.”
Nevertheless, those efforts weren’t enough to maintain the spacecraft within the vicinity of the moon, leading JPL to bring the mission to an end. Mission planners had, by that time, ruled out placing the spacecraft right into a near-rectilinear halo orbit across the moon, but hoped to have the ability to position it right into a distant Earth orbit that allowed for monthly flybys of the moon.
How the debris got into the propulsion system just isn’t 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’s commercializing that propulsion system, noted the constraints imposed by the 6U cubesat design limited engineers’ ability to place filters into the system.
“Due to the scale constraints, we couldn’t put filters in all places. So, we relied heavily on precision cleansing, inspections and contamination controls. But there was a process slip in some unspecified time in the future,” he said. The info from the cubesat, he noted, was consistent with ground tests of thrusters with debris of their propellant lines.
Lunar Flashlight was the primary spacecraft to transcend Earth orbit to make use of a non-toxic “green” propellant called Advanced Spacecraft Energetic Non-Toxic, or ASCENT, developed on 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 brand new flight computer called Sphinx that may 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 so they’re essential for NASA to check and learn,” Christopher Baker, program executive for small spacecraft technology in NASA’s Space Technology Mission Directorate, said in an announcement announcing the top of the mission. “Lunar Flashlight was highly successful from the standpoint of being a testbed for brand spanking new systems that had never flown in space before.”
Lunar Flashlight also had a science mission, using a laser reflectometer instrument to search for water ice in permanently shadowed craters on the south pole of the moon. While the spacecraft won’t have the ability to gather any science, it did test the instrument and confirmed it was working as expected.
“It’s disappointing for the science team, and for the entire Lunar Flashlight team, that we won’t have the ability to make use of our laser reflectometer to make measurements on the moon,” Barbara Cohen, principal investigator for the mission on the Goddard Space Flight Center, said within the statement. She added, though, that the mission “collected numerous in-flight performance data” on the instrument that may very well be used on designs for similar instruments on future missions.
Lunar Flashlight was originally manifested on Artemis 1, the primary launch of the Space Launch System rocket, together with 12 other cubesats. Nevertheless, a switch within the design of the propulsion system caused the spacecraft to mission a deadline of the autumn of 2021 to be integrated on the SLS. NASA as an alternative flew it as a secondary payload on the Falcon 9 launch of the HAKUTO-R M1 lander from Japanese company ispace, which lifted off lower than a month after Artemis 1.
Several of the ten 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 attempting to resolve an issue with its electric propulsion system. He said then that if they might not free a stuck valve in that system by the top of May, they might likely wind down operations.
JPL said that Lunar Flashlight will make a flyby of Earth May 17 at an altitude of 65,000 kilometers after which head into deep space. Since other systems on the spacecraft proceed to operate despite the propulsion problem, “NASA is weighing options for the long run of the spacecraft.”