Engineers have made strides in efforts to fully unfold a solar panel wing that stranded on NASA’s Lucy asteroid explorer shortly after launch last October, raising optimism that the spacecraft could complete its 12-year mission as planned.
One of Lucy’s two UltraFlex circular solar panels opened to about 96% of its fully deployed state after arriving in space last October after a launch from Cape Canaveral. The other solar panel fully unfolded as the spacecraft embarked on a robotic science mission to fly through swarms of undiscovered asteroids that direct and track Jupiter in its orbit around the sun.
In recent weeks, ground teams at a Lockheed Martin control center in Colorado have uplinked commands for Lucy to spin primary and backup motors to move the stuck solar panel closer to full deployment.
NASA believes a cord used to pull open the solar panel somehow lost tension and fell off a coil during its first deployment last October, preventing the array from opening fully.
Additional attempts to pull open the solar panel have further coiled the cord. The first attempt on May 9 involved running the insert engines in a series of short intervals to avoid overheating. Ground controllers sent out more commands on May 12, further aiding the placement of the solar panels and putting stress on the structure, stabilizing the array.
Engineers made more progress during two additional deployment attempts, May 26 and June 2. “While the array still didn’t lock, the data indicates it continued to deploy and stiffen during the attempt,” NASA said.
Recently, the Lucy ground team sent another command to spin the deployment engines on June 9, which “further stabilized the array,” NASA said. “There are possibilities in the future to repeat the deployment orders if necessary.”
Officials are increasingly optimistic that the Lucy mission can continue without a hitch, even if the solar panel doesn’t click into place. Before recent attempts to fully deploy the array, the spacecraft’s power system was generating more than 90% of its expected 18,000 watts level.
“While there is no guarantee that additional attempts will lock the array, there is strong evidence that the process puts more stress on the array, further stabilizing it,” NASA said in a statement. “Even if the array doesn’t click in the end, the extra bracing could be enough to fly the mission as planned.”
“We see significant strain in the array,” said Hal Levison, Lucy’s principal investigator at the Southwest Research Institute. “These things are made of fabric, and what you get a lot of power from is by putting tension on it. And we’re clearly at a point where we’re straining the array, which makes it likely, even if we thing not get locked, we will be able to fly the mission as is.
One concern engineers have studied is the effect of engine burns on the partially deployed array. The Lucy spacecraft completed its first orbit correction maneuver on June 7 to lead it to a flyby with Earth in October, the first of several gravity aids to hurl the probe into Jupiter’s orbit in the distant solar system.
Lucy has also expanded the platform with its scientific instruments, and the sensors are all working as designed, Levison said.
Lucy will become the farthest spacecraft from the sun to ever rely on solar energy, reaching a maximum distance of 853 million kilometers, almost six times further than Earth’s orbit. When it reaches the Trojan asteroids, Lucy’s solar panels were expected to generate only 500 watts of power.
That power level is enough to power Lucy’s three scientific instruments, which require only about 82 watts during each encounter with an asteroid. Lucy’s flight computer, communications system and other components will also use power generated by the UltraFlex arrays.
The $981 million Lucy mission is the first to explore the Trojan asteroids, which scientists say are leftover building blocks resembling objects that came together to form the solar system’s giant outer planets. The probe will fly past eight Trojan asteroids between 2027 and 2033, plus one object in the main asteroid belt in 2025.
That’s one more asteroid than scientists expected Lucy to visit when it launched last year.
One of the Trojan asteroids on Lucy’s tour, named Polymele, has a companion. Scientists discovered an apparent satellite of Polymele during an occultation observation on the ground in March, when Polymele passed shortly before a star, temporarily blocking the light from Earth.
The occultation observations were intended to help the Lucy science team determine the shape of Polymele, which only appears as a bright spot in telescope images.
“We got a really nice projected shape of Polymele, and then we were very surprised to detect an object about 200 kilometers (120 miles) from Polymele,” Levison said in a presentation to NASA’s Small Bodies Advisory Group last week. “It has a diameter of 5 kilometers and it sits almost exactly in the equatorial plane of Polymele.”
Lucy’s science team has temporarily named the object Shaun, after “Shaun the Sheep” on the show “Wallace and Gromit”.
More data on the object’s exact position and orbit is needed to assign a permanent name to Polymele’s companion, and that probably won’t happen until after Lucy’s flyby in 2027.
Polymele itself has a “flattened spheroid” or gourd-like shape and is about 17 miles long and 8 miles wide. Polymele’s shape suggests it is likely a remnant of the young solar system from more than 4.5 billion years ago, and may have avoided collisions with other objects throughout history.
“It’s hard to imagine that you could get that shape… from an object that evolved through collisions, so now I think Polymele is probably a primordial object, which will make seeing it really fascinating.”
Polymele’s companion isn’t the first asteroid to be added to Lucy’s flight plan since the mission was approved by NASA in 2017. Astronomers announced in 2020 that observations with the Hubble Space Telescope confirmed a small object, less than 1 kilometer in diameter, orbiting asteroid Eurybates, another Lucy target in the Trojan belt.
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