Controllers with the CAPSTONE mission are attempting to regain control of the Moon-bound probe, which is currently tumbling, experiencing temperature issues, and unable to use its solar panels to fully recharge its batteries.
In an update issued on Monday, Advanced Space described it as a “dynamic operational situation.” The company is managing the project for NASA, in which the 55-pound (25-kilogram) cubesat will evaluate a unique halo orbit around the Moon in advance of a lunar space station. CAPSTONE, short for Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment, launched on June 28 and is in the midst of a four-month journey to the Moon.
The problem started either during or after the third trajectory correction manoeuvre (TCM-3) on September 8. An unknown issue caused CAPSTONE to enter into a tumble — one beyond the ability of the probe’s onboard reaction wheels to counter, according to NASA.
CAPSTONE needs to perform seven course corrections to reach its intended halo orbit around the Moon. The recent anomaly occurred either during or after the third trajectory manoeuvre on September 8. (Graphic: Advanced Space)
Multiple course corrections are required to move the probe toward its intended lunar orbit, known as a near-rectilinear halo orbit (NRHO), which CAPSTONE is supposed to reach on November 13. CAPSTONE reached apogee — its farthest point from Earth — on August 26, at a distance of 951,908 miles (1.53 million kilometers) from our planet.
After the latest course correction, ground stations were unable to receive meaningful communications from CAPSTONE, prompting Advanced Space to declare an operational emergency. When contact was finally re-established some 24 hours later, “mission controllers found that the spacecraft was tumbling, the onboard computer systems were periodically resetting, and the spacecraft was using more power than it was generating from its solar panels,” NASA explained.
Mercifully, controllers managed to stabilise the spacecraft by employing NASA’s Deep Space Network, an array of giant radio antennas used to support interplanetary spacecraft missions. “Rapid response enabled by the Deep Space Network support and quick thinking by the team at Terran Orbital allowed mission operators to quickly reconfigure the operational state of the spacecraft to stabilise the situation while recovery plans could be further evaluated,” according to an Advanced Space update. A recovery team made up of experts from NASA, Advanced Space, Terran Orbital (the designer and manufacturer of CAPSTONE), and Stellar Exploration (the provider of CAPSTONE’s propulsion system) is currently evaluating next steps. Without the Deep Space Network, the team “would have little or no information on the status of the spacecraft,” according to Advanced Space. That said, the teams are still being hampered by incomplete information.
The good news is that CAPSTONE has been placed in a stable state. It’s still tumbling and in safe mode, but it’s now generating more power than it’s using. The cubesat is currently spinning in such a way that its solar panels are being partially illuminated, resulting in weak transmissions from its low gain antennas. Importantly, the probe successfully completed its third trajectory correction manoeuvre, which means it’s still on course to its special halo orbit around the Moon.
The recovery team will make a decision on how to move forward in the coming days. In addition to diagnosing the cause of the anomaly, the team needs to resolve unspecified temperature issues with several subsystems, including the propulsion system. The team is also preparing to detumble the spacecraft in an effort to regain control over its orientation. There’s good reason to believe this procedure will work, as a similar detumbling operation was performed in July after CAPSTONE separated from the Electron rocket’s upper stage.
Assuming CAPSTONE can be taken out of its tumble, controllers will then orient the solar panels to fully recharge the probe’s batteries, thereby allowing the mission to continue as planned. But as Advanced Space grimly noted: “Many details remain unknown as to the cause of the anomaly and significant risks are continuing to be analysed.” CAPSTONE isn’t out of the woods, but there’s reason for optimism.
CAPSTONE is a precursor mission for the upcoming Artemis program, in which NASA seeks a permanent and sustainable return to the lunar environment. To support Artemis crews, NASA and its international partners are seeking to place a space station, called Gateway, in the gravitationally stable halo orbit. No probe has ever worked in NHRO, hence the importance of the CAPSTONE scouting mission.