NASA regains control of the CAPSTONE lunar orbiter • The Register

NASA is back in control of its CAPSTONE spacecraft after the lunar orbiter lost power and communications and was shut down in safe mode for weeks while falling through the void.

Earlier last month, shortly after the spacecraft performed a trajectory correction maneuver en route to lunar orbit, ground control found that the CubeSat was now spinning at a rate that its onboard reaction wheels could no longer control. It had lost full three-axis attitude control.

Regarding communications, the bird was silent for 24 hours until some telemetry finally got through to Earth. By this time, engineers knew the spacecraft was spinning through space, had lost or was losing power, and was repeatedly restarting itself. The whirling probe was still well on course for the moon, but needed to be restored to normal operating condition.

An operational emergency was declared on September 8, and teams at aerospace companies Advanced Space (who developed and managed the probe) and Terran Orbital (who built the thing) racked their brains to come up with a solution. Given the weak state of the spacecraft’s signals, the teams used NASA’s Deep Space Network to gather information and communicate with the spacecraft.

Soon the tinkerers, particularly those at Terran Orbital, were able to figure out CAPSTONE – short for Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment – and send a message to get it back in good working order. Next, it was found that the bird then ran in safe mode and spun stably. That gave the team hope that the microwave-sized satellite could be fully recovered.

“The quick response allowed mission operators to quickly reconfigure the spacecraft’s operational state to stabilize the situation while recovery plans could continue to be evaluated,” Advanced Space said mid-last month.

“Based on this exceptional effort and using the limited data available, the operations teams have determined that the spacecraft is in safe mode and appears to have successfully transitioned to a steady state solar panels and resulting in weak transmit signals from the spacecraft’s low-gain antennas. “

Since then, instructions for properly tuning the orbiter were successfully uploaded and executed last week, resulting in the spacecraft pointing its solar panels at the Sun and its radio antennas at Earth, putting ground control back in the driver’s seat. With reliable power and communications, more commands could be sent and data received as needed to complete the mission.

“Initial telemetry and observation data after the recovery attempt indicate a successful recovery of the system, which has now regained three-axis attitude control,” Advanced Space confirmed in a statement ahead of the weekend.

“The updated spacecraft posture has aligned the spacecraft’s solar panels toward the sun and implemented an alignment for the downlink antennas that significantly improves data downlink performance compared to the pre-recovery posture.”

The teams believe the loss of attitude control was due to a partially open valve on one of CAPSTONE’s eight engines. Each time the propulsion system was pressurized, the faulty valve exerted some thrust and unexpectedly jerked the spacecraft out of position. A workaround is in preparation.

“Over the coming days, the status of the spacecraft will be monitored as the team works to evaluate subsequent changes to spacecraft operational procedures to allow upcoming critical events to be conducted in the possible presence of a partially open valve. In parallel, the Mission Team will work to develop potential solutions to this valve-related issue to further de-risk future propulsion operations,” said Advanced Space.

Launched in June, CAPSTONE flies to the moon where it will enter near straight line halo orbit (NRHO). The orbit means the small satellite will follow a slightly more curved orbit around the moon compared to more traditional elliptical lunar orbiters. CAPSTONE is investigating whether NRHOs are stable enough to place the proposed Lunar Gateway, a space station for astronauts, around the moon in the future.

The mission has obviously not gone smoothly so far. Even before the engine anomaly, the bird lost communication with Earth in July due to a bug in its flight software. If all goes according to plan, CAPSTONE is expected to reach the Moon and be deployed into an NHRO on November 13th. ® NASA regains control of the CAPSTONE lunar orbiter • The Register

Rick Schindler

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