Lucy Solar Array Problem Could Complicate Mission to the Trojan Asteroids

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NASA’s Lucy spacecraft started its journey to the Trojan asteroids with a successful launch yesterday, but today the agency said one of the two solar arrays, critical to mission success, may not be properly latched. Still, the arrays are producing power and charging the battery, so the long term consequences are yet to be determined. More information could come out tomorrow at an already scheduled meeting on NASA’s space science missions.

Lucy will visit seven of the Trojan asteroids that share Jupiter’s orbit around the Sun plus another in the main asteroid belt over its 12-year mission.

The spacecraft lifted off from Cape Canaveral Space Force Station, FL at 5:34 am ET Saturday on a United Launch Alliance (ULA) Atlas V rocket. The rocket performed flawlessly, maintaining its 100 percent success record.

Lucy is traveling far from the Sun — 853 million kilometers (530 million miles) — but nonetheless is relying on solar arrays to generate power to operate spacecraft systems and scientific instruments. Usually spacecraft on missions deep into the solar system use nuclear Radioisotope Power Systems (RPS) that generate power from the natural decay of plutonium-238 since energy from the Sun is insufficient at those distances.

To generate the amount of power needed, Lucy has two 7.3-meter (24-foot) diameter circular “Ultra Flex” solar arrays that generate 500 watts. That is not very much, about what it takes to operate a washing machine according to NASA, but enough for Lucy to accomplish its tasks.

The arrays took 22 minutes to deploy once Lucy separated from the Atlas V and embarked on its journey yesterday.

Lockheed Martin built the Lucy spacecraft. Northrop Grumman provided the solar arrays.

Today, Thomas Zurbuchen, head of NASA’s Science Mission Directorate, tweeted that although both arrays deployed, one may not be fully latched.

In a statement on the Lucy blog, the agency said the spacecraft nonetheless is “operating well and is stable.”

Following a successful launch on Oct. 16, 2021, analysis of NASA’s Lucy spacecraft systems show the spacecraft is operating well and is stable. Lucy’s two solar arrays have deployed, and both are producing power and the battery is charging. While one of the arrays has latched, indications are that the second array may not be fully latched. All other subsystems are normal. In the current spacecraft attitude, Lucy can continue to operate with no threat to its health and safety. The team is analyzing spacecraft data to understand the situation and determine next steps to achieve full deployment of the solar array.

No further details were provided. Zurbuchen already planned a Town Hall meeting Monday afternoon for the NASA science community to provide an update on all of NASA’s science missions. More information might become available then.

Lucy is not an acronym like many NASA spacecraft. Instead it is named after the fossilized human ancestor found in 1974 in Ethiopia and given that name by the anthropologists that found her, Donald Johanson and Pamela Alderman, and were listening to the Beatles song Lucy in the Sky With Diamonds while celebrating the discovery. NASA’s project scientists used the name because the Trojan asteroids are remnants — fossils — of the formation of the solar system.  Principal Investigator Harold Levison of the Southwest Research Institute (SwRI) said “These asteroids really are like diamonds in the sky in terms of their scientific value for understanding how the giant planets formed and the solar system evolved.”

The asteroids are in the same orbit around the Sun as Jupiter, but are not near the planet. Instead they are 60 degrees ahead of and behind Jupiter at the Sun-Jupiter L4 and L5 Lagrange points. The closest Lucy will be to Jupiter itself is when it is at Earth.

Lucy’s complicated trajectory will bring it back to Earth three times to get gravity assists to reach the two Lagrange points where the gravity of the Sun and Jupiter create an equilibrium that locks the asteroids into those locations.

Lucy will return to Earth’s vicinity in 2022 and 2024 to get gravity assists.  In April 2024 it will fly past a main belt asteroid (between Mars and Jupiter) that is named after Johanson. Then it will head to the L4 “swarm” of Trojans and fly past Eurybates and its moonlet Queta in August 2027, Polymele in September 2027, Leucus in April 2028, and Orus in November 2028. Then it swings by Earth again in 2030 for another gravity assist to get to the L5 swarm and visit Patroclus and Menoetius, a near-equal binary system, in March 2033.

At that point its primary mission is done, although it will remain in its orbit passing through the Trojan swarms for thousands or millions of years.

Lucy is the 13th mission in NASA’s Discovery series and is managed at NASA’s Goddard Space Flight Center. Project Manager Donya Douglas-Bradshaw said at a pre-launch press conference that the total cost of the mission is $981 million.

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