NASA troubleshoots asteroid-bound Lucy spacecraft from millions of miles away

NASA Lucy Mission Solar Array Anomaly

Shortly after Lucy was launched, one of its solar arrays failed to fully deploy, jeopardizing the mission. This artist’s concept animation shows Lucy’s solar array anomaly. credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

right after successful launch of[{” attribute=””>NASA’s Lucy spacecraft on October 16, 2021, a group of engineers huddled around a long conference table in Titusville, Florida. Lucy was just mere hours into its 12-year journey, but a major unexpected challenge had surfaced for the first-ever Trojan asteroids mission.

Data indicated that one of Lucy’s solar arrays — designed to unfurl like a hand fan — hadn’t fully opened and latched. Since the solar arrays power the spacecraft’s systems, the team had to figure out what to do next.

To troubleshoot the problem, teams from NASA and Lucy mission partners quickly came together. Team members from Lockheed Martin’s Mission Support Area outside of Denver, who were in communication with the spacecraft directly, were on the phone.

Although the conversation was quiet, it was intense. At one end of the room, an engineer sat with furrowed brow, folding and unfolding a paper plate in the same way that Lucy’s enormous circular solar arrays operate.

There were so many unanswered 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 needed to accomplish its science mission?

Because Lucy was already speeding on its way through space, the stakes were incredibly high.

NASA’s Lucy Is Heading to Mission[{” attribute=””>Jupiter Trojans – two swarms of unexplored asteroids trapped in Jupiter’s orbit. Lucy made a picture-perfect launch on October 16, 2021, but when the spacecraft began to unfurl its solar arrays, it encountered an anomaly. One of the arrays failed to fully deploy and latch shut, putting the mission at risk. For months, Lucy’s flight operations team worked meticulously to address the issue and put Lucy back on its solar-powered journey to the Jupiter Trojans.

Within hours, NASA pulled together Lucy’s anomaly response team, which included members from science mission lead Southwest Research Institute (SwRI) in Austin, Texas; mission operations lead NASA’s Goddard Space Flight Center in Greenbelt, Maryland; spacecraft builder Lockheed Martin; and Northrop Grumman in San Diego, solar array system designer and builder.

“This is a talented team, firmly committed to the success of Lucy,” said Donya Douglas-Bradshaw, former Lucy project manager from NASA Goddard. “They have the same grit and dedication that got us to a successful launch during a once-in-a-lifetime pandemic.”

United in their pursuit to ensure Lucy would reach its fullest potential, the team began an exhaustive deep dive to determine the cause of the issue and develop the best path forward.

Given that the spacecraft was otherwise perfectly healthy, the team wasn’t rushing into anything.

“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 principal investigator from SwRI. “Fortunately, the spacecraft was where it was supposed to be, functioning nominally, and – most importantly – safe. We had time.”

Lucy Solar Panel Deployment Tests

At 24 feet (7.3 meters) across each, Lucy’s two solar panels underwent initial deployment tests in January 2021. In this photo, a technician at Lockheed Martin Space in Denver, Colorado, inspects one of Lucy’s arrays during its first deployment. These massive solar arrays will power the Lucy spacecraft throughout its entire 4-billion-mile, 12-year journey through space as it heads out to explore Jupiter’s elusive Trojan asteroids. Credit: Lockheed Martin

Staying focused during many long days and nights, the team worked through options. To evaluate Lucy’s solar array configuration in real-time, the team fired thrusters on the spacecraft and gathered 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 issue.

At last, they closed in on the root cause: a lanyard designed to pull Lucy’s massive solar array open was likely snarled on its bobbin-like spool.

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

In one, they would pull harder on the lanyard by running the array’s backup deployment motor at the same time as its primary motor. The power from two motors should allow the jammed lanyard to wind in further and engage the array’s latching mechanism. While both motors were never originally intended to operate at the same time, the team used models to ensure the concept would work.

The second option: use the array as it was – nearly fully deployed and generating more than 90% of its expected power.

Shortly after Lucy was launched, one of its solar arrays failed to fully deploy, jeopardizing the mission. This artist’s concept animation shows Lucy’s solar array anomaly.

“Each path carries some element of risk to achieve basic science objectives,” said Barry Noakes, Lockheed Martin’s Deep Space Exploration chief engineer. “A large part of our effort was identifying proactive actions that minimize risk in any given scenario.”

The team mapped and tested the possible outcomes for both options. They analyzed hours of test footage of the array, built a ground-based replica of the array’s motor assembly, and tested the replica past its limits to better understand the risks of further deployment attempts. They also developed special, high-fidelity software to simulate Lucy in space and any potential ripple effects on the spacecraft that may be attempted to be redeployed.

“The collaboration and teamwork with the mission partners was phenomenal,” said Frank Burns, vice president of Space Components and Strategic Business at Northrop Grumman.

After months of simulation and testing, NASA decided to move forward with the first option — a multi-stage effort to fully redeploy the solar array. On seven occasions in May and June, the team ordered the spacecraft to simultaneously drive the primary and backup solar array deployment motors. The attempt was successful, pulling in the lanyard, further unwinding and tensioning the array.

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

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

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