From Ryugu to Bennu, asteroid exploration has been all the rage among astronomers lately. And now, we’re one step closer to exploring some of the most mysterious asteroids in the solar system.
On October 30, NASA announced that they’ve been given the green light to start building Lucy, a spacecraft that will probe Jupiter’s trojan asteroids and is set to launch in October of 2021. On top of giving the go-ahead for construction, NASA has also solidified the mission’s budget, schedule, and its suite of high-powered instruments. The much-anticipated project will study two populations of asteroids caught by Jupiter’s gravity, about which little is known.
A Long Journey
Studying asteroids is a hefty task, and it’s not going to be a quick one, either. The Lucy mission, named after the 3.2 million year-old hominin fossil who helped us understand human evolution, will take almost 12 years to complete. Once it’s finished, though, the craft will have probed seven different asteroids — six trojans and one main-belt asteroid between Mars and Jupiter.
After launching from Cape Canaveral, the craft will orbit twice around Earth before relying on a gravity assist to fling it out into space. In this slingshot-like maneuver, Lucy will approach Earth from behind and dip briefly into its strong gravitational field for a speed boost. This move will help both reduce the mission’s overall travel time and cut down on the amount of heavy fuel it needs to carry.
The first stop on its celestial voyage will be at 52246 Donaldjohanson, a small main-belt asteroid named after the famous paleoanthropologist who discovered Lucy. It will orbit close to the asteroid and use its infrared mapping spectrometer, thermal infrared spectrometer, and high-resolution visible imager to study its surface composition and physical properties.
With one asteroid under its belt, the mission will continue on its journey to the trojans. These famous asteroids circle the Sun in the same orbit as Jupiter, with one massive group flying ahead of the gas giant, and another trailing behind at what’s known as Lagrangian points. Using the same instruments and techniques, Lucy will probe four trojans in the group leading Jupiter and two in its orbital trail.
Uncovering the Past
When it comes to tracking our solar system’s history, Lucy’s data could prove highly valuable. It’s believed that asteroids are ancient fragments leftover from our solar system’s formation, and that they, unlike planets and moons, have roughly the same structure and chemical composition that they did when they first formed. It’s also thought that asteroids could have transported organic molecules, like water, to larger celestial bodies.
By determining the compositions of these relics, Lucy could gain insight into the chemical elements that made up our infant solar system, and help researchers trace its formation and evolution.
NASA’s Mission to Jupiter’s Trojans Given the Green Light for Development
NASA's mission to perform the first reconnaissance of the Trojans, a population of primitive asteroids orbiting in tandem with Jupiter, passed a critical milestone today. NASA has given approval for the implementation and 2021 launch of the Lucy spacecraft.
The confirmation review, formally known as "Key Decision Point C," authorized continuation of the project into the development phase and set its cost and schedule. The confirmation review panel approved the detailed plans, instrument suite, budget and risk factor analysis for the spacecraft.
The next major mission milestone, the Critical Design Review, will examine the detailed Lucy system design. After a successful critical design review, the project team will assemble the spacecraft and its instruments.
“Up until now this mission has entirely been on paper,” said Lucy Principal Investigator Hal Levison of the Southwest Research Institute at Boulder, Colorado. “Now we have the go ahead to actually cut metal and start putting this spacecraft together.”
Lucy, the first space mission to study the Trojans, takes its name from the fossilized human ancestor called “Lucy” by her discoverers whose skeleton provided unique insight into humanity's evolution. Likewise, the Lucy mission will revolutionize our knowledge of planetary origins and the formation of the solar system.
Lucy is planned for launch October 2021. During its 12-year journey, the spacecraft will visit seven different asteroids - a Main Belt asteroid and six Trojans. The spacecraft and a remote-sensing instrument suite will study the geology, surface composition, and bulk physical properties of these bodies at close range.
“Today’s confirmation of Lucy is a key step towards better understanding the role that small bodies played in the formation of the Solar System and life on Earth,” said Adriana Ocampo, Lucy’s program executive at NASA Headquarters in Washington, DC. “We congratulate the entire team for their hard work.”
Southwest Research Institute (SwRI) in Boulder, Colorado is the principal investigator institution and will lead the science investigation. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will provide overall mission management, systems engineering and safety and mission assurance. Lockheed Martin Space Systems in Denver, Colorado, will build the spacecraft. Instruments will be built by Goddard, the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and Arizona State University in Tempe.
Lucy Finds Its Place in the Solar System: Navigating NASA’s First Mission to the Trojan Asteroids
In science fiction, explorers can hop in futuristic spaceships and traverse half the galaxy in the blink of a plot hole. However, this sidelines the navigational acrobatics required in order to guarantee real-life mission success.
In 2021, the feat of navigation that is the Lucy mission will launch. To steer Lucy towards its targets doesn’t simply involve programming a map into a spacecraft and giving it gas money – it will fly by six asteroid targets, each in different orbits, over the course of 12 years.
Lucy’s destination is among Jupiter’s Trojan asteroids, clusters of rocky bodies almost as old as the Sun itself, and visiting these asteroids may help unlock the secrets of the early solar system. Lucy will encounter a Main Belt asteroid in 2025, where it will conduct a practice run of its instruments before encountering the first four Trojan targets from 2027-2028. In 2033, Lucy will end its mission with a study of a binary system of two Trojans orbiting each other.
Getting the spacecraft where it needs to go is a massive challenge. The solar system is in constant motion, and gravitational forces will pull on Lucy at all times, especially from the targets it aims to visit. Previous missions have flown by and even orbited multiple targets, but none so many as will Lucy.
Scientists and engineers involved with trajectory design have the responsibility of figuring out that route, under Flight Dynamics Team Leader Kevin Berry of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. One such engineer is Jacob Englander, the optimization technical lead for the Lucy mission. “There are two ways to navigate a mission like Lucy,” he said. “You can either burn an enormous amount of propellant and zig-zag your way around trying to find more targets, or you can look for an opportunity where they just all happen to line up perfectly.” To visit these aligned targets, the majority of Lucy’s high-speed lane changes will come from gravity assists, with minimal use of fueled tweaks.
Though Lucy is programmed to throw itself out into a celestial alignment that will not occur for decades, it cannot be left to its own devices. Once the spacecraft begins to approach its asteroid targets, optical navigation is the next required step.
“OpNav,” as optical navigation technical lead Coralie Adam refers to it, is the usage of imagery from the on-board cameras to determine Lucy’s position relative to the target. This is a useful measurement used by the navigation team to tweak Lucy’s route and ensure it stays on the nominal flyby path. Adam works in Simi Valley, California, with KinetX, the company NASA selected to conduct Lucy’s deep space navigation.
By using the communications link from the spacecraft to Earth, Adam said, the Lucy team gets information about the spacecraft’s location, direction and velocity. The spacecraft takes pictures and sends them down to Earth, where Adam and other optical navigators use software to determine where the picture was taken based on the location of stars and the target. The orbit determination team uses this data along with data from the communications link to solve for where the spacecraft is and where it is expected to be, relative to the Trojans. The team then designs a trajectory correction maneuver to get Lucy on track. “The first maneuver is tiny,” said navigation technical lead Dale Stanbridge, who is also of KinetX. “But the second one is at 898 meters per second. That’s a characteristic of Lucy: very large delta V maneuvers.” Delta V refers to the change in speed during the maneuver.
Communicating all of these navigation commands with Lucy is a process all on its own. “Lockheed Martin sends the commands to the spacecraft via the Deep Space Network,” Adam said. “What we do is we work with Lockheed and the Southwest Research Institute, where teams are sequencing the instruments and designing how the spacecraft is pointed, to make sure Lucy takes the pictures we want when we want them.”
“The maneuvers to correct Lucy’s trajectory are all going to be really critical because the spacecraft must encounter the Trojan at the intersection of the spacecraft and Trojan orbital planes,” Stanbridge said. “Changing the spacecraft orbital plane requires a lot of energy, so the maneuvers need to be executed at the optimal time to reach to next body while minimizing the fuel cost.”
While Lucy is conducting deep space maneuvers to correct its trajectory toward its targets, communications with the spacecraft are sometimes lost for brief periods. “Blackout periods can be up to 30 minutes for some of our bigger maneuvers,” Stanbridge said. “Other times you could lose communications would be when, for example, the Sun, comes between the Earth tracking station and the spacecraft, where the signal would be degraded by passing through the solar plasma.”
Losing contact isn’t disastrous, though. “We have high-fidelity predictions of the spacecraft trajectory which are easily good enough to resume tracking the spacecraft when the event causing a communication loss is over,” Stanbridge said.
What route will Lucy take once its mission is complete, nearly 15 years from now? “We’re just going to leave it out there,” Englander said. “We did an analysis to see if it passively hits anything, and looking far into the future, it doesn’t.” The Lucy team has given the spacecraft a clear path for thousands of years, long after Lucy has rewritten the textbooks on our solar system’s history.
The Lucy mission is led by Principal Investigator Dr. Hal Levison from Southwest Research Institute in Boulder, Colorado. NASA Goddard in Greenbelt, Maryland, manages the mission. Lockheed Martin Space in Denver will build the spacecraft and conduct mission operations.