We Finally Know Why a Solar Array on NASA’s Asteroid Probe Failed to Open

We Finally Know Why a Solar Array on NASA’s Asteroid Probe Failed to Open

In space now for more than three months, the Lucy asteroid explorer is operating normally, save for a solar panel that failed to fully unfurl shortly after launch. Experts with the mission say they’ve identified the problem, but whether they’ll be able to fix it remains an open question.

The circular solar array, one of two on the spacecraft, is currently stuck at 347 degrees instead of the full 360 degrees, explained Hal Levison, principal investigator for the Lucy mission at the Southwest Research Institute, during a January 25 meeting of NASA’s Small Bodies Assessment Group. Levison’s team traced the issue to a lanyard that was supposed to pull the array to its fully deployed position but failed to do so.

“Through some unknown process, there was a period where there was no tension on the lanyard as it was deploying,” said Levison, as Space.com reports. “As a result, the lanyard fell off the spool. We think there’s something like 30 inches [76 centimeters] of lanyard remaining to be pulled in.”

This is not a crisis by any means — at least not yet. As NASA explained in a mission update earlier this month, Lucy’s systems are operating normally and the two arrays are producing sufficient amounts of energy, even if one of them is not in an ideal configuration. NASA is currently running tests to determine if another attempt to deploy the array will be safe and effective, or if doing nothing might be the best approach under the circumstances.

Lucy launched on October 16, 2021 from Cape Canaveral in Florida. The $US981 ($1,362) million spacecraft is on a mission to explore Jupiter’s trojan asteroids, which it will do over 12 years. Jupiter’s trojans are packed in two clumps, one in front of and one behind the gas giant in its solar orbit. These asteroids have been locked like this for billions of years, hence their description as the “fossils” of planetary formation. Lucy is currently in an “outbound cruise” mode, according to NASA, and it will stay in a wide Earth orbit for roughly a year before heading over to the Jovian system.

Shortly after launch, however, one of two solar arrays did not fully deploy and lock into place. Lucy’s solar panels are like Chinese fans, forming a circular array that measures 7 metres in diameter. The solar panels, built by Northrop Grumman, need to provide around 500 watts, which is roughly equal to the energy required to operate a washing machine. That’s not a ton of power, but the arrays need to be large enough to capture the required solar energy at distances reaching 800 million km from the Sun.

Levison and his colleagues are now considering two plans: either use Lucy’s motors to pull the misbehaving lanyard, or do nothing. He said there’s still “plenty of time” because “we’re not scheduled to fire the main engines for a while and we’re in cruise,” so “we’re taking our time to carefully go through our options.” At the meeting, Levison confirmed that power is not currently a problem for Lucy, as the arrays are producing from 92% to 93% of the expected power, Space.com reports.

Tests are currently underway to determine if engaging both the primary motor and a backup motor at the same time will exert enough force to finish the deployment and latch the array in place. NASA is currently targeting a latch attempt for this April.

As for doing nothing, that’s not without consequences. Yes, Lucy has plenty of power, but “the issue is the structural integrity of the array during main engine burns,” Levison said. “The forces and torques going through the array and particularly where it’s connected to the spacecraft are different than designed.” So yeah, not an easy decision.

The Lucy mission is proceeding as planned despite this technical annoyance. The team is currently calibrating guidance and the spacecraft’s navigation system to ensure that Lucy can be pointed in the right direction when the time comes. The probe is expected to reach Jupiter’s trojans in 2027.

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