Irene Klotz The mission, which is costing NASA $981 million, including the launch, is the first to the Trojan asteroids.
Irene Klotz
A United Launch Alliance Atlas V lifted off from Cape Canaveral Space Force Station on Oct. 16, sending the Lucy spacecraft on an exquisite trajectory that will pass by a main belt asteroid and seven Jupiter Trojan asteroids. Credit: ULA
Rare is the NASA mission whose name is not an acronym. Rarer still is a deep-space mission with a multidestination itinerary. But what makes NASA’s recently launched Lucy mission unique is where the robotic explorer is headed and how it will get there.
The spacecraft, built by Lockheed Martin, is designed to answer fundamental questions about how the Solar System came to exist in its present configuration, with four rocky planets circling relatively close to the Sun and four gas giants relegated to the backyard.
Scientists theorize that the Solar System’s geometry shifted rather radically shortly after the planets formed some 4.6 billion years ago, with Jupiter and her big sisters shifting inward and then heading out.
Evidence for the great migration may lie in two caches of small bodies located in stable orbits where the gravity of the Sun and the gravity of Jupiter are in balance—ruts in space known as Lagrange points. The trapped bodies are called the Jupiter Trojan asteroids.
Telescope observations show the 10,000 known Trojans are an integrated family. Members have different colors and spectral signatures, which hint of varied origins and/or histories. Scientists speculate that the bodies formed in different parts of the outer Solar System before being mixed together in the gravitational tumult caused by the giant planets’ migrations. When the proverbial dust settled, two groups of small bodies ended up locked in orbits about 60 deg. ahead of and 60 deg. trailing Jupiter.
The Lucy spacecraft, which launched aboard a United Launch Alliance Atlas V rocket on Oct. 16, named after the 3.2-million-year-old skeletal remains of a prehuman ancestor discovered in Ethiopia in 1974, which paleoanthropologists named Lucy. Similar to how the skeleton provided insights into human evolution, the Lucy spacecraft is expected to broaden our understanding of the origin of the planets and the evolution of the Solar System.
Reaching the Trojan asteroids is no easy feat, especially for a spacecraft visiting both swarms. “When I first saw that orbit, I looked at this like, ‘You gotta be kidding me,’” says Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate. “It just seems absolutely crazy.”
“I spent 40 years worshipping at the feet of the celestial mechanics gods,” adds Lucy Principal Investigator Hal Levison, with the Southwest Research Institute. “They are actually paying us back.”
Levison and his team started off searching for a pair of Trojan asteroids, one red and one gray, which were very similar to each other. “We wanted to compare the colors directly,” Levison says.
The project grew as one target, then another, appeared on the celestial road map. Currently, Lucy is on track to fly by seven Trojan asteroids during its 12-year primary mission. As a bonus, on its way out to the orbit of Jupiter, some five times farther from the Sun than Earth, the spacecraft will encounter a main belt asteroid beyond Mars.
“We’re pretty lucky to be able to get the diversity [of targets] that we have,” Levison says. “This is an amazing trajectory.”
An hour after its 5:34 a.m. EDT launch from Cape Canaveral Space Force Station on Oct. 16, Lucy separated from the rocket’s Centaur stage to begin its trek toward interplanetary space. In a year, it is planned to loop around Earth, coming as close to the planet as 186 mi.—closer than the orbit of the International Space Station—to pick up speed and cycle out deeper into the Solar System.
Two years later, Lucy is slated to return for a second gravitational boost from Earth that will set it on course to reach the swarm of Trojan asteroids orbiting ahead of Jupiter. Between August 2027 and November 2028, Lucy is to pass by four Trojan asteroids, the first of which, Eurybates, has a tiny moon named Queta.
The Lucy spacecraft, built by Lockheed Martin, was prepared for encapsulation in its payload fairing at Astrotech Space Operations in Titusville, Florida. Credit: Glenn Benson/NASA
Lucy is expected to return to the vicinity of Earth in 2030 for another boost out to Jupiter’s orbit. By the time it arrives again in 2033, the second swarm of Trojans will be in range, with Lucy due to fly by three more asteroids.
To operate at approximately 530 million mi. from the Sun, the 3,300-lb. spacecraft is outfitted with two circular 24-ft.-dia. solar arrays, which were deployed about 90 min. after launch. Ground control teams, however, did not receive confirmation that both arrays had fully unfurled and latched into place.
“Analysis currently shows the second solar array is partially unfurled,” NASA said on Oct. 19, adding that the affected array is generating nearly the same level of power as the fully deployed wing.
“This power level is enough to keep the spacecraft healthy and functioning,” NASA said.
Additional troubleshooting was planned for late October. Deployment of the spacecraft’s instrument pointing platform, slated for Oct. 18, was postponed. Flight directors also determined that Lucy’s first trajectory correction maneuver, slated for 30 days after launch, was not needed. The first steering burn is now expected in mid-December.
The Lucy instrument suite includes:
The mission, which is costing NASA $981 million, including the launch, is the first to the Trojan asteroids. If successful, the spacecraft will have visited more bodies in the Solar System than any previous probe.
