NASA’s Latest Plan to Fix Trojan Spacecraft’s Unlatched Solar Array Shows Signs of Promise

NASA’s Latest Plan to Fix Trojan Spacecraft’s Unlatched Solar Array Shows Signs of Promise
The Lucy spacecraft will be the first to visit the Trojan asteroids. (Illustration: NASA)

For nearly eight months, Lucy has been sailing its way to Jupiter’s Trojan asteroids while NASA engineers on the ground have been working to fix a pesky solar array that refuses to unfurl. The good news is that there now appears to be some progress.

The solar array failed to open shortly after the spacecraft launched in October 2021. Ground controllers with the NASA project sent commands to the Lucy spacecraft on four separate occasions in May and June, and while the solar array is still not fully deployed, it is showing signs of progress, according to the space agency.

Lucy is on an unprecedented mission to explore the Trojan asteroids, two groups of rocky bodies that lead and follow Jupiter as it orbits the Sun. Jupiter’s Trojans have existed for the past four billion years, yet very little is known about the asteroids’ formation and how they got caught in Jupiter’s gravitational tug. Lucy could shed new light on these enigmatic Jovian groupies.

Unfortunately, however, Lucy ran into trouble shortly after being launched. The spacecraft is equipped with a pair of 6.71 m-wide solar arrays on either side of the spacecraft that were tucked away for launch and designed to unfurl in space with the help of a lanyard rigged to the motors. One of Lucy’s circular solar arrays got stuck at 347 degrees instead of the full 360 degrees. The spacecraft hasn’t suffered any performance issues as a result, but having a wonky solar array is not ideal. Although the two solar arrays are still garnering sufficient amounts of power, mission engineers are concerned that the stubborn solar array could get damaged when the spacecraft fires its main engine.

Concerned, NASA has been developing a plan to fix the glitch. The array has a main and backup motor for operating the lanyard and the mission team has been using both simultaneously in the effort to properly position the array. On May 9, mission control commanded Lucy to deploy the array, in which it ran the motors for a series of short intervals to avoid overheating. They then paused to analyse the data before a second attempt on May 12, when they sent the same commands again. A third attempt was made on May 26 and then again on June 2.

Sending commands to a spacecraft that’s over 60 million miles (96 million kilometers) away from Earth can often be a waiting game. Engineers must stand by to receive returning data from the spacecraft to learn if the commands resulted in success or not. So far, the data has shown that, while the solar array is still not fully deployed, it was continuing to open and get more stiff with each attempt. That’s encouraging news and a positive sign.

“While there is no guarantee that additional attempts will latch the array, there is strong evidence that the process is putting the array under more tension, further stabilizing it,” NASA wrote. “Even if the array does not ultimately latch, the additional stiffening may be enough to fly the mission as planned.”

The spacecraft still has about six years to go before reaching its first target, a Main Belt asteroid called Donaldjohanson. From there, Lucy will travel for another 3,000 days to reach its first Trojan asteroid, Eurybates. The spacecraft will rendezvous with three more Trojans before it flies by the final pair, Patroclus and Menoetius in the year 2033.

On June 7, Lucy completed a trajectory correction manoeuvre, the first in a series of manoeuvres to gear the spacecraft up for its upcoming Earth gravity assist on October 16, which will accelerate the spacecraft and direct its trajectory beyond the orbit of Mars.