The team fixes millions of kilometers of bugs in the asteroid-bound Lucy spacecraft

Following the successful launch of NASA’s Lucy spacecraft on October 16, 2021, a group of engineers huddled around a long conference table in Titusville, Florida. Lucy was just hours into her 12-year flight, but an unexpected challenge had cropped up for the first-ever Trojan-asteroid mission.

The data showed that one of Lucy’s solar arrays that powered the spacecraft’s systems – which was supposed to unfold like a hand fan – had not fully opened and latched, and the team considered what to do next.

Teams from NASA and Lucy mission partners quickly came together to troubleshoot. On the phone were team members at Lockheed Martin’s Mission Support Area outside of Denver who were in direct contact with the spacecraft.

The conversation was calm but intense. At one end of the room sat an engineer, frowning, folding and unfolding a paper plate in much the same way Lucy’s giant circular solar arrays work.

There were so many questions. What happened? Was the array open at all? Was there a way to fix it? Without a fully deployed array, would Lucy be able to safely perform the maneuvers required for her scientific mission?

With Lucy already making her way through space, the stakes were high.

Within hours, NASA assembled Lucy’s anomaly response team, composed of members of the Science Mission-led Southwest Research Institute (SwRI), in Austin, Texas; mission operations directs NASA’s Goddard Space Flight Center in Greenbelt, Maryland; spacecraft builder Lockheed Martin; and Northrop Grumman of San Diego, designer and builder of solar systems.

“This is a talented team dedicated to the success of Lucy,” said Donya Douglas-Bradshaw, former Lucy Project Manager at NASA Goddard. “They have the same courage and dedication that got us off to a successful start during a once-in-a-lifetime pandemic.”

United in their quest to ensure Lucy would reach her full potential, the team began with a deep dive to determine the root cause of the problem and the best way forward.

Since the spacecraft was otherwise perfectly healthy, the team didn’t rush things.

“We have an incredibly talented team, but it was important to give them time to figure out what happened and how to move forward,” said Hal Levison, Lucy’s lead investigator at SwRI. “Fortunately, where the spacecraft was supposed to be, it was nominally operational and—most importantly—safe. We had time.”

During many long days and nights, the team stayed focused and worked through options. To evaluate Lucy’s solar array configuration in real time, the team fired thrusters at the spacecraft and collected data on how those forces made the solar array vibrate. Next, they fed the data into a detailed model of the array’s motor assembly to infer how rigid Lucy’s array was — which helped uncover the source of the problem.

They finally got to the root cause: A rope meant to open Lucy’s massive solar array was probably knotted on its spool-like spool.

After months of further brainstorming and testing, Lucy’s team decided on two possible paths forward.

In one instance, they would pull more of the line by running the array’s reserve engine at the same time as the primary engine. The power of two motors should allow the jammed lanyard to continue to wrap and engage the array’s locking mechanism. Although both engines were never originally intended to run simultaneously, the team used mockups to ensure the concept worked.

The second option: use the array as is – almost fully provisioned and with more than 90% of the expected performance.

“Every path involved some risk in order to achieve the basic scientific goals,” said Barry Noakes, chief engineer for space exploration at Lockheed Martin. “A large part of our effort was to identify proactive measures that mitigate risk in both scenarios.”

The team designed and tested possible outcomes for both options. They analyzed hours of the array’s test footage, constructed a ground-based replica of the array’s motor assembly, and tested the replica beyond its limits to better understand the risks of further deployment trials. They also developed special high-fidelity software to simulate Lucy in space and assess the possible effects that an attempted transfer could have on the spacecraft.

“The cooperation and teamwork with the mission partners has been phenomenal,” said Frank Bernas, vice president, space components and strategic businesses at Northrop Grumman.

After months of simulation and testing, NASA decided to proceed with the first option – a multi-stage attempt to completely re-deploy the solar array. On seven occasions during May and June, the team commanded the spacecraft to run the primary and backup solar array deployment engines simultaneously. The effort was successful, the rope was pulled in and the array opened further and tensioned.

The mission now estimates that Lucy’s solar array is open between 353 degrees and 357 degrees (out of a total of 360 degrees for a fully deployed array). Although the array is not fully locked, it is under significantly more tension, making it stable enough for the spacecraft to operate as needed for mission operations.

The spacecraft is now ready and able to complete the next major mission milestone – an Earth gravity assist in October 2022. Lucy is scheduled to reach her first asteroid target in 2025.