September 25, 2022

Ground teams trying to regain control of scouting satellite for NASA’s Artemis moon program

Artist’s concept of the CAPSTONE spacecraft near the moon. Credit: llustration by NASA/Daniel Rutter

Ground teams will try to stabilize the motion of NASA’s small CAPSTONE scouting satellite and rescue the $30 million mission on the way to the moon, following a problem Sept. 8 that sent the spacecraft into a tumble and caused controllers to temporarily lose contact with the probe, officials said Monday.

The CAPSTONE mission is a technology demonstration and pathfinder to gather data for future NASA crew missions to the moon. The small satellite successfully departed Earth on June 28 aboard a Rocket Lab launch vehicle, starting a four-and-a-half month voyage culminating in a planned maneuver Nov. 13 to enter a halo orbit around the moon.

Rocket Lab’s Electron launcher and Photon space tug dispatched CAPSTONE on a lengthy but fuel-efficient trajectory to carry the spacecraft into deep space, well beyond the moon. CAPSTONE reached a distance of more than 950,000 miles (1.53 million kilometers) from Earth on Aug. 26, before gravity started pulling the probe onto a course to cross paths with the moon for the Nov. 13 orbit insertion burn.

More than halfway through its transit to the moon, CAPSTONE fired its miniature hydrazine propulsion system Sept. 8 for a course correction maneuver. But NASA said the spacecraft suffered a problem during or shortly after the burn, causing the spacecraft to tumble. CAPSTONE’s reaction wheels, fast-spinning devices designed to control craft’s orientation, were unable to counter the tumble motion.

The spacecraft, about the size of a microwave oven, failed to contract mission controllers after the course correction burn, giving ground teams a first sign that the mission was in trouble, according to Advanced Space, a Colorado-based company that owns and operates the CAPSTONE mission under contract to NASA. In a mission update Monday, Advanced Space said CAPSTONE is in a “dynamic operational situation.”

Advanced Space’s mission control team restored communications with CAPSTONE about 24 hours later, and telemetry from the spacecraft showed it was tumbling, its on-board computer was periodically resetting, and was using more power than it was generating from its solar panels, NASA said Monday in a statement.

Engineers from Terran Orbital, which built the CAPSTONE spacecraft, and Stellar Exploration, the propulsion system supplier, are working with Advanced Space and NASA to rescue the mission.

NASA’s worldwide network of deep space tracking and communications antennas was critical to restoring contact with CAPSTONE. The spacecraft is still tumbling, is in safe mode, but appears to be in a stable health status and is generating electricity, NASA said Monday.

But the tumbling motion means sunlight is only partially illuminating the spacecraft’s solar panels. And without accurate pointing, ground teams are only receiving weak transmissions through the spacecraft’s low gain antennas.

“Without the unique capabilities of the Deep Space Network, the mission team would have little or no information on the status of the spacecraft,” Advanced Space said.

The good news is the Sept. 8 course correction maneuver was completed, or nearly complete, when the spacecraft suffered the problem. “This means the spacecraft remains on the intended trajectory and on course to its near rectilinear halo orbit at the moon,” NASA said.

“While work is ongoing to diagnose the cause of the issue, the team is preparing CAPSTONE to attempt a detumble operation to regain attitude control of the spacecraft,” NASA said Monday. “This detumble operation was successfully demonstrated after separation from the launch upper stage in July.”

Regaining attitude control would allow the CAPSTONE spacecraft to orient its solar panels to the sun to fully recharge its batteries after consuming power during the detumble operation, NASA said. CAPSTONE would then point toward the ground to await instructions from mission control.

The recovery effort will begin by “working to improve the thermal situation of several subsystems, including the propulsion subsystem,” Advanced Space said.

“These recovery operations will be further evaluated over the coming days,” NASA said. “Recovery timing will be guided by the data and analysis available to maximize the probability of a successful spacecraft operation.”

CAPSTONE stands for the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment. The 55-pound (25-kilogram) spacecraft is designed to scout a halo-like, elongated orbit around the moon that NASA has chosen for a future mini-space station called the Gateway. The Gateway station, part of NASA’s Artemis lunar program, will serve as an experiment platform and a stopover for astronauts traveling between Earth and the surface of the moon.

No other spacecraft has flown in the unique path around the moon, called a near rectilinear halo orbit, or NRHO. The halo orbit will take CAPSTONE — and eventually the Gateway station — as close as 1,000 miles (1,500 kilometers) from the moon’s North Pole and as far as 43,500 miles (70,000 kilometers) from the South Pole. Each orbit of the moon will last about six-and-a-half days, according to NASA.

Space agency officials said before CAPSTONE’s launch in June that the pathfinder mission will collect important data, but doesn’t have to be successful to allow NASA to move forward with the Gateway program.

Like the Apollo astronauts of the past, future Artemis crew missions to the moon will travel to the halo orbit quicker than CAPSTONE, covering the quarter-million-mile distance in as few as five days.

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Follow Stephen Clark on Twitter: @StephenClark1.

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