Despite the mission’s technological wins, Lunar Flashlight’s miniaturized propulsion system struggled to provide sufficient thrust to put the CubeSat on course for the planned near-rectilinear halo orbit that would have given the spacecraft weekly flybys of the Moon’s South Pole.
The team suspects that debris obstructed the fuel lines, causing the diminished and inconsistent thrust. The miniaturized propulsion system included an additively manufactured fuel feed system that likely developed the debris – such as metal powder or shavings – and obstructed fuel flow to the thrusters, limiting their performance. Although the team devised a creative method for using just one thruster to maneuver the spacecraft, Lunar Flashlight needed more consistent thrust to reach its planned orbit.
The operations team calculated a new orbit that could be reached using the spacecraft’s small amount of potential remaining thrust. The plan called for putting the CubeSat on a path that would place it in orbit around Earth rather than the Moon, with monthly flybys of the lunar South Pole. While this would have meant fewer flybys, the spacecraft would have flown closer to the surface.
With the mission running out of time to arrive at the needed orbit, the operations team tried to dislodge any debris from the fuel lines by increasing the fuel pressure well beyond the propulsion system’s designed capacity. Despite limited success, the required trajectory correction maneuvers couldn’t be completed in time.
“The student operations team at Georgia Tech, with assistance from JPL and NASA’s Marshall Space Flight Center, rose to the challenge and came up with an incredible array of inventive techniques to utilize what tiny amount of thrust Lunar Flashlight’s propulsion system could deliver,” said John Baker, Lunar Flashlight project manager at JPL. “We learned a lot and honed new methods and strategies for working with tiny spacecraft.”
After having traveled out past the Moon, Lunar Flashlight is now moving back toward Earth and will fly past our planet with a close approach of about 40,000 miles (65,000 kilometers) on May 17. The CubeSat will then continue into deep space and orbit the Sun. It continues to communicate with mission operators, and NASA is weighing options for the future of the spacecraft.
