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Thursday, February 22, 2024

NASA’s Lucy Mission Gets Ready to Fly by the Trojan Asteroids

On July 30, Emily Gramlich boarded a C-17 military transport plane at Buckley Space Force Base. Gramlich, a test engineer at Lockheed Martin, had never been on this sort of aircraft before. C-17s—which look a bit like overfed sky sharks—have a lot more legroom than a commercial plane. But the open-plan square footage was necessary, because the cargo took up a lot of space. Encased in a giant shipping container was a spacecraft, being shuttled from its birthplace in Colorado to Kennedy Space Center in Florida. The spacecraft’s name is Lucy, and it will soon be on a much longer trip: a 12-year journey to eight different asteroids.

Lucy’s liftoff, with a window of opportunity that begins October 16, will take it to the so-called Trojan asteroids, which orbit the Sun in the same ellipse as Jupiter, but either ahead of or behind the giant planet. They have remained gravitationally trapped in Jupiter’s orbit since the solar system’s early days, billions of years ago. They’re like a freeze-frame of the way that distant part of the solar system used to be—and no spacecraft has ever visited them.

It’s fitting, then, that Lucy itself resembles a giant pair of eyeglasses: Two behemoth solar arrays, each roughly circular and 24 feet across, are attached to the much-smaller spacecraft body. The solar panels look like lensed (and creepily intense) eyes, bridged by the part of Lucy that has all the instruments and communications equipment. The mission, led by the Southwest Research Institute in Boulder, was first approved in 2017, and—after a few years of design work—assembly, test, and launch operations started at Lockheed Martin in August 2020.

That work culminated in this trip from Colorado to the launch site in Florida. Every half hour, Gramlich—who’d helped test Lucy back at Lockheed—would unbuckle herself from the seat to record temperature and humidity data, keeping track of the environment inside the shipping container, to see what the spacecraft was exposed to. This box, which from the outside looks like a space-age panic room, is essentially a tiny clean room. Nicknamed the “Cassini container,” it has previously taken eight other spacecraft across the country, including the eponymous one that went to Saturn.

Lucy had definitely been through worse than a boxed-up, half-continent flight at cruising altitude. At the Lockheed Martin facility outside of Denver, engineers had shaken, heated, cooled, and shone simulated sunlight at the craft, to make sure it could handle the extremes of space—and launch. They had tried out the software code, and checked the flow of electricity to its many components. All systems were nominal, as they say. And so all the systems schlepped down to Florida, where Lucy was about to go through a final gauntlet of tests before launch from the southern Space Coast.

“It is a high-stress job, these missions that are taking off to other planets,” says Gramlich. The launch window is narrower than it would be for, say, a satellite heading to Earth orbit. And so having Lucy pass its penultimate exams—and safely make its way to Kennedy—in time for takeoff was a big milestone. “Now, at the launch site, there’s a new level of excitement,” she says.

The Lucy mission gets its moniker from the fossilized partial skeleton of an early human ancestor, Australopithecus afarensis, discovered in 1974, which altered ideas about human origins and evolution. The research team hopes this spacecraft will do for planetary science what that skeleton did for paleoanthropology, by giving us a look at the formation and evolution of our solar system.

In the solar system’s infancy, debris orbited in a squished disk around a young Sun. Chunks and motes of material stuck together, snowballed, and matured into the tidy planets we see today. Asteroids are essentially the discard pile from that process. “They’re the leftover bits from this very early time before there were planets,” says Tom Statler, the Lucy program scientist at NASA.

He likens asteroid study to pyramid research—if the pyramids, in this metaphor, are Jupiter, Saturn, Uranus, and Neptune, and the Trojan asteroids are the material from which they were built. You can only learn so much about how those great structures came to be from the finished triangular product. Find the abandoned construction area, and you can infer a lot more about their genesis. “The objects that eventually became Trojans formed all over the outer solar system and got transported to and trapped where they are now,” says Statler. “The Trojans are some of the leftovers that got swept up and left there.”

And even though our own planet is rocky, and not a gas giant, studying the outer planets will give us information about how it formed. “It’s become clearer and clearer that no planet develops in isolation,” says Statler. “The Earth is the way it is because the solar system is the way it is … To understand the Earth, we need to understand how the other planets formed and developed.”

Lucy will rely on three main instruments: L’LORRI, L’TES, and L’Ralph. The “L” prefix denotes that they are part of the Lucy mission, because they are each based on devices that have flown before. LORRI and Ralph were instruments aboard the New Horizons mission to Pluto and the Kuiper belt. “L’LORRI,” then, means “Lucy Lorri,” says Michael Vincent, assistant director of the Southwest Research Institute’s space operations department. OTES was part of the OSIRIS-REx spacecraft to asteroid Bennu, and it hailed in part from an instrument called TES, which had previously flown on the Mars Global Surveyor spacecraft. “The devil that we knew is what we wanted to stick with,” says Vincent. (Also, one of the scientists on the mission has a French background and was, Vincent jokes, “trying to class up the place.”)

L’LORRI is essentially a fancy camera, sharp enough that it can take clear pictures of 200-foot craters from 600 miles away, mapping them to reveal an asteroid’s history. It can also hunt for rings and satellites, and will help Lucy navigate toward the asteroids. After all, picking out which distant dot to aim for isn’t simple. “These things aren’t big out there, and we’re going lickety split,” says Vincent.

L’TES works kind of like those non-contact thermometers you might know from Covid-19 screenings, but instead of being aimed at a forehead, the instrument points at a spot on an asteroid and takes its temperature by detecting the infrared radiation coming from it. “Over time, you kind of build up an overall picture by sweeping over and over different surfaces,” says Vincent. Their goal is to measure “thermal inertia,” or how fast or slow parts of the asteroid heat up or cool down—an indicator of what materials it’s made of. Sand, for instance, holds heat differently from rock, which you may have noticed if you’ve ever taken a long walk on the beach at sunset.

Finally, there’s L’Ralph, which packs two sub-instruments. One called LEISA analyzes infrared radiation, separating it into different wavelengths that correspond, like fingerprints, to different substances—rocks, ices, organic compounds, and hydrated minerals—and, within those, to the differences between, say, methane and water ice. The other is a five-color camera called MVIC, which can detect light from the ultraviolet down to the near infrared, a span that includes all visible light. The different colors help reveal asteroids’ compositions. Hydrated minerals called phyllosilicates, for instance, will appear in the red, while troilite, an iron sulfide mineral, will show up in the violet.

The Southwest Research Institute’s Carly Howett is the instrument scientist for L’Ralph. Usually, red is her favorite band, because it tends to be brighter than the others, and shows more detail. “If we see activity in the violet band and it lights up, maybe it will be my new favorite,” she says. But no matter what the images show, she’s excited to witness small worlds that no one else has discovered before. “Seeing new things for the first time never gets old,” she says.

But it will take a long time for Lucy to reach these asteroids; there’s a reason the gas giants they’re floating among are called the “outer planets.” Before it even heads out there, the spacecraft will fly by Earth twice and get two Hot-Wheels-racing-track boosts, so-called gravity assists. Gramlich is looking forward to those mission moments, in 2022 and 2024, when when the spacecraft will whip around this planet. Humans like her—in the right place at the right time—will be able to look up and see something they designed, built, tested, and lit a fire under.

Finally, four years after launch, Lucy will cruise by a non-Trojan asteroid—one not coincidentally named Donaldjohanson after one of the Lucy skeleton’s discoverers—and do a sort of dress rehearsal. After testing out its instruments passing by that interstitial destination, the spacecraft will continue traveling for more than two years before it reaches the Trojans. It will spend more than a year spying on five asteroids orbiting “ahead” of Jupiter, which range in size from half a mile to 40 miles wide. All of these surveilings are flybys. “Fingers crossed,” says Cory Prykull, Lucy’s assembly, test, and launch operations lead at Lockheed, “we don’t plan to have any landings.”

After those drive-bys, the mission will take a surprising turn: one toward home. Lucy will shoot all the way back to Earth, swing around our planet, and get another gravity assist that will fling it toward the asteroid flock orbiting “behind” Jupiter. To us, it will seem like a light lilting across the sky, here again and then gone forever, on its way to distant places that humans might never see up close. That trip back to Earth, then back toward the Trojans, takes more than four years.

But while Lucy will head back to the outer planetary parts of the solar system, the spacecraft still has one last job to do. In 2033, when Lucy reaches the “behind Jupiter” asteroids, it will hit up a binary asteroid duo boasting 70- and 65-mile widths. Simply flying by the pair, as Lucy will have done with its other targets, will allow scientists to compare data about these asteroids to information from the “ahead” swarm. After this encounter, Lucy will have finished its primary mission but will remain in a stable orbit, coasting among the Trojans.

Why spend so much time going to so many targets? Aren’t they all … rocks? In this case, the diversity is the point: “There’s no such thing as ‘just another asteroid,’” says Statler.

As the mission progresses, Lucy will use a high-gain antenna to send back images and data from its rendezvous points. But since its last meeting won’t occur till 2033, the final bits of data won’t make their way to Earth until 12 years after launch. “You have to be really patient when you’re studying the outer solar system, that’s for sure,” says Cathy Olkin, the mission’s deputy principal investigator.

Now that Lucy has touched down in Florida, the craft is undergoing final checks. During the first week in August, the Lucy team ran through an “operational readiness test,” which Olkin says means “sitting at the console preparing and pretending—really practicing—for launch. We went through it as if it were happening.”

Then, engineers tested every copper path to make sure the electricity was flowing and that computers and instruments were working as they had before shipping—Gramlich’s specialty. “I love this test,” says Gramlich, “because it gets to turn on all the components at the same time.” It shows the spacecraft’s organs working together to do what they’re supposed to: make some science happen.

Lucy will also get a final communications check, to ensure the craft can talk and listen to Earth. At some point, the team will even shine a bright flashlight at the back of the instruments to make sure stray photons don’t slip through where they’re not supposed to and contaminate the measurements.

Closer to launch, when Lucy is perched at the top of the rocket, Gramlich and her team will test the electrical aspects one last time. The instruments’ covers will then come off, and the spacecraft will get a final inspection. They’ll power Lucy on and prepare for the 3 … 2 … 1.

“When the spacecraft lifts off from the ground,” says Gramlich, “that’s when we on the test team take a breath.”

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