How scientists fixed the Lucy probe’s solar array while it was in space

When the problem with Lucy was diagnosed soon after launch, teams from NASA and project partners got together to troubleshoot. It was not easy. Scientists scrambled to understand what could possibly be done to solve it as the spacecraft sped its way through space.

In the next few hours, NASA got together Lucy’s anomaly response team, which comprised of members from the Southwest Research Institute (SwRI), NASA’, spacecraft builder Lockheed Martin and the solar array system designer and builder Northrop Grumman.

Over a period of a few days, the team worked through its options. They fired Lucy’s thrusters and gathered data on how the thrust force made the solar array vibrate to evaluate the array’s configuration in real-time. They then took this data and fed it into a detailed model of the array’s motor assembly to understand how rigid Lucy’s array was. This helped uncover the source of the issue.

They had finally found the source of the problem: a lanyard designed to pull Lucy’s huge solar array open was likely snarled on its spool. But now, they needed to figure out how to fix the issue. It took months of brainstorming and testing before the Lucy teams settled on two potential solutions.

A diagram of Lucy’s orbital map. (Image credit: Southwest Research Institute)

One potential path forward involved pulling harder on the lanyard using the array’s backup deployment motor as well as the primary motor. In theory, the power from both motors should allow the jammed lanyard to wind in further and engage the array’s latching mechanism. Even though both motors were never intended to operate at the same time, the team used models to make sure that the concept would work.

The second option was far simpler. That was to continue using the array the same way it was working given it was nearly fully deployed and generating more than 90 per cent of its expected power. While this may seem like a better option at the outset, it ran the risk of the mission not being able to achieve its baseline objectives.

The team analysed hours of the array’s test footage and constructed a ground-based replica of the array’s motor assembly to test it past its limits to better understand the risks involved. Also, they developed special high-fidelity software to simulate Lucy in space and gauge any potential ripple effects a redeployment attempt could have on the spacecraft.

After going through months of simulations and testing, NASA decided to go forward with the first option. The team commanded the spacecraft to simultaneously run the primary and backup solar array deployment motors on seven occasions in May and June. The efforts were a success and the motors together pulled the lanyard, opening and tensioning the array.

Lucy teams estimate that the probe’s array is between 353 degrees and 357 degrees open (out of the 360 total degrees required for a fully developed array). According to the estimates, the array is stable enough to operate as needed for mission operations. Lucy is now ready to complete its next mission milestone: an Earth-gravity assist in October 2022. The probe will arrive at its first asteroid target in 2025.