NASA has ended a cube-shaped rover mission that was intended to go into lunar orbit but was unable to do so due to problems with its propulsion system.
NASA’s Jet Propulsion Laboratory announced on 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, which was identified shortly after its launch in December 2022. They suspected that debris of some kind was clogging the thrust lines, reducing the amount of fuel reaching the thrusters.
NASA said on May 5 that it was making a last-ditch effort to clear the obstruction by increasing fuel pump pressures “far beyond” operational limits as the valves opened and closed. The technique, which was tried on one of the spacecraft’s four thrusters, has shown some success, “inconsistently resulting in some increased levels of thrust.”
However, these efforts were not enough to keep the spacecraft close to the Moon, prompting JPL to finish the job. Mission planners had, at that point, ruled out putting the spacecraft into a near-rectilinear halo orbit around the Moon, but hoped to be able to put it into a far-Earth orbit that would allow for monthly flybys of the Moon.
It is unclear how the debris entered the propulsion system. In a recent interview, Daniel Cavender, who was the project manager for the Cubesat propulsion system at NASA and is now the systems manager for Rubicon Space, a division of Plasma Processes LLC that markets this propulsion system, pointed out the limitations that the 6U cubesat design has limited the capability of Engineers are putting the filters into the system.
“Because of size limitations, we couldn’t put filters everywhere. So, we relied heavily on careful cleaning, inspections and contamination controls. But there was a slip up in the process at some point. The data from Cubesat was consistent with ground tests of the thrusters with The presence of debris in its driving lines.
The Lunar Flashlight was the first spacecraft to go beyond Earth’s 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 a debris problem starved them of propellant, calling it “an important space probe.”
NASA has confirmed other technologies that Lunar Flashlight has successfully tested. It included a new flight computer called the Sphinx that could operate at lower power levels and survive the radiation environment in deep space, and an upgraded radio called the Iris.
Christopher Baker, executive director of the Small Spacecraft Technology Program in NASA’s Space Technology Mission Directorate, said in a statement announcing the end of the mission. “Lunar Flashlight has been very successful from the point of view of being a testbed for new systems that have not flown in space before.”
The Lunar Flashlight also had a science mission, using a laser reflectometer instrument to search for water ice in permanently shadowed craters at the moon’s south pole. While the spacecraft will not be able to collect any flag, it has tested the instrument and confirmed that it is working as expected.
“It is disappointing to the science team, and to the entire Lunar Flashlight team, that we will not be able to use our laser reflectometer to take measurements on the Moon,” Barbara Cohen, principal investigator for the mission at Goddard Space Flight Center said in the statement. She added, however, that the mission “collected a lot of in-flight performance data” on the instrument that could be used in designs for similar instruments on future missions.
The Moon Flashlight originally appeared on Artemis 1, the first Space Launch System rocket launch, along with 12 other cubes. However, a shift in propulsion system design has led the spacecraft to a mission with a deadline of fall 2021 to be integrated into the SLS. Instead, NASA flew it as a secondary payload at the Falcon 9 launch of Japanese company ispace’s HAKUTO-R M1 lander, which lifted off less than a month after Artemis 1.
Many of the 10 cubes launched on Artemis 1 also experienced technical problems that prevented them from carrying out their missions. At a workshop on May 1, Craig Hardgrove, the principal investigator for the LunaH-Map cubesat, said his team is still trying to solve the problem with the electric propulsion system. He then said that if they could not free a stuck valve in that system by the end of May, they would probably cease operations.
JPL said the Lunar Flashlight will fly over Earth on May 17 at an altitude of 65,000 km and then head into deep space. As other systems on the spacecraft continue to function despite the thrust issue, “NASA is examining options for the future of the spacecraft.”
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