Cubesats to face big challenges in deep space
LunaH-Map is one of 10 cubesats that hitched a ride on SLS as secondary payloads. The six-unit (6U) smallsat carried a neutron spectrometer designed to map water ice concentrations at the moon’s south pole.
In the months leading up to the launch, he had been quietly raising concerns about the health of LunaH-Map. The spacecraft was delivered in mid-2021 and installed on the rocket that fall, after which there was no ability to recharge its batteries. As the Artemis 1 launch slipped from early 2022 to late in the year, he worried that the batteries were discharging, keeping the spacecraft from operating immediately after deployment.
At the KSC press site hours before liftoff, he was cautiously optimistic about LunaH-Map. Ground tests of batteries like those on the cubesat showed a low discharge rate, suggesting they should still have plenty of charge left. Even if the batteries were depleted, he said the spacecraft’s solar panels could charge them up enough to get the spacecraft ready for a key maneuver days after launch.
He was right not to be concerned about the cubesat’s batteries. “Our batteries were at 70% state of charge when we got our first piece of telemetry,” he said in a talk about LunaH-Map at the Fall Meeting of the American Geophysical Union (AGU) a month after launch. “It was in line with our very optimistic predictions about where our batteries might be.”
The problem instead was with the cubesat’s propulsion system, an electric thruster called BIT-3 from Busek that uses solid iodine as propellant. The thruster did not operate as expected in the days after launch, causing the spacecraft to miss its primary opportunity to maneuver into orbit around the moon.
Hardgrove said telemetry from LunaH-Map suggested that a valve in the thruster was partially stuck closed. “The sticking is something that we knew about,” he said, suggesting it came from the long wait for the launch. “We didn’t really want to wait around for a year, but we had no choice.”
Engineers think that heating the valve may free it up. If that happens by mid-January, he said, LunaH-Map can maneuver into an alternative trajectory that would allow it to enter orbit around the moon in about a year.
Despite the struggles with the SIMPLEx missions and the Artemis 1 cubesats, smallsats have had some successes beyond Earth orbit. A second JAXA cubesat on Artemis 1, EQUULEUS (for Equilibrium Lunar-Earth point 6U Spacecraft), successfully flew by the moon and tested a water-based propulsion system that placed the spacecraft on a low-energy trajectory to the Earth-moon L-2 Lagrange point. NASA’s BioSentinel cubesat was tumbling after deployment. Still, controllers were able to stabilize the spacecraft and maintain contact with it as it flew by the moon to study the effects of radiation on microorganisms.
LICIACube exceeded expectations. “NASA was expecting to get a couple pictures” from LICIACube, said David Avino, chief executive of Argotec, in an interview in November. “We had 627 pictures taken by our spacecraft.”
He hopes the success of the two cubesat missions will generate more demand for its smallsats for both Earth orbit and deep space missions. “We want to have something that will not be cheap but will be reliable,” he said. “The main keyword is reliability. That means something that will allow our satellites to last up to five years, even in deep space.”
Even before launch, those who worked on the Artemis 1 cubesats knew that many of their satellites might malfunction. In an April 2022 report from a workshop on deep space smallsats, they compared their efforts to the early development of cubesats, when missions had high failure rates as designers struggled with the technical and cost limitations of such spacecraft.