Manage space traffic

You are probably already using satellites today. Thanks to satellites, you can stream your favorite shows, call or text friends, check weather and navigation apps, and make purchases online. Satellites also monitor Earth’s climate, crop coverage, wildlife habitat, and the effects of natural disasters.

The number of satellites has exploded as more uses are found. Currently, more than 10,000 satellites operate in low Earth orbit. Another 5,000 decommissioned satellites are floating around the region, as well as more than 100 million pieces of debris, made up of everything from spent rocket stages to bits of spaceship paint.

For MIT’s Richard Linares, the rapid expansion of satellites raises pressing questions. How do we safely manage space traffic and growing congestion? And at what point do we reach orbital capacity where adding more satellites is not sustainable and may actually endanger spacecraft and the services we depend on?

“What value is gained by launching more satellites is a decision that society has to make,” says Linares, who recently received tenure as an associate professor in MIT’s Aeroastrology Department. “One of the things we’re trying to do is approach these issues of traffic management and track capacity as engineering problems.”

Linares leads the MIT Astrodynamics, Space Robotics, and Control Lab (ARCLab). ARCLab is a research group that applies celestial mechanics (the motion and trajectory of orbiting objects) to help track and manage the millions of objects in orbit around the Earth. The group is also developing tools to predict how space traffic and debris will change when operators launch mega-constellations of large satellites into space.

He also investigates the effects of space weather on satellites and how climate change on Earth limits the number of satellites that can safely orbit in space. And anticipating that satellites will need to become smarter and faster to navigate more cluttered environments, Linares is considering artificial intelligence that would allow satellites to learn autonomously, adapt to changing conditions, and autonomously assist with reasoning to solve onboard problems.

“Our research is quite diverse,” says Linares. “But overall, we want to enable all these economic opportunities that satellites bring, and we’re coming up with engineering solutions that enable that.”

Grounding in practical problems

Linares was born and raised in Yonkers, New York. Both parents worked as school bus drivers to support their children, and Linares was the youngest of six children. He was an active kid who loved sports and played soccer throughout high school.

“Sports were a way to stay focused and organized and develop a work ethic,” Linares says. “It taught me to work hard.”

When applying to colleges, Linares looked for programs that were strong in science, specifically aerospace, rather than aiming for a Division 1 school like some of his teammates. Growing up, he was fascinated by Carl Sagan’s documentary “Cosmos.” Due to its proximity to Manhattan, he also regularly visited the Hayden Planetarium to view the center’s immersive space projections and the technology used to explore them.

“My interest in science came from space and trying to understand our place in it,” Linares recalls.

Choosing to stay close to home, he applied to in-state schools with strong aeronautical engineering fields and was lucky enough to attend the State University of New York at Buffalo (SUNY Buffalo), where he eventually earned a bachelor’s, master’s, and doctoral degree in aerospace engineering.

As an undergraduate, Linares worked on a research project in celestial mechanics, trying to solve the problem of how to determine the relative orientation of satellites flying in formation.

“Flighting in formation was a big topic in the early 2000s,” says Linares. “I liked the flavor of the mathematics involved. It allowed me to go deeper towards solutions.”

He calculated the mathematics to show that when three satellites fly together, they essentially form a triangle, and by calculating their angle, you can determine where each satellite is relative to the other two at any given time. His research introduced new control approaches to enable satellites to fly together safely. The U.S. Air Force directly applied for and helped sponsor the study.

In expanding his research into a master’s thesis, Linares also had the opportunity to work directly with the Air Force on satellite tracking and orientation issues. He completed two internships at the U.S. Air Force Research Laboratory, one at Kirtland Air Force Base in Albuquerque, New Mexico, and one on Maui, Hawaii.

“Being able to work with the Air Force at the time made the research feel more grounded in practical problems,” Linares said.

For his Ph.D., he turned to another practical problem: “uncorrelated tracks.” At the time, the Air Force operated a network of telescopes that observed more than 20,000 celestial objects in space, labeling and cataloging them so they could be tracked over time. However, while discovering objects was relatively easy, the challenge was associating detected objects with those already in the catalog. In other words, was what they were seeing something they had already seen?

Linares has developed an image analysis technique that identifies important features such as an object’s shape and orientation. This has helped the Air Force take “fingerprints” of satellites and space debris and track their activity and potential collisions over time.

After receiving his Ph.D., Linares worked as a postdoctoral researcher at Los Alamos National Laboratory and the U.S. Naval Observatory. During that time, he expanded his aerospace research into other areas such as space weather, using satellite measurements to model how Earth’s ionosphere (the upper layer of the atmosphere ionized by the sun’s radiation) affects drag on satellites.

He then accepted a position as an assistant professor of aerospace engineering at the University of Minnesota, Minneapolis. For the next three years, he continued his research, including modeling space weather, tracking space objects, and coordinating satellites flying in swarms.

make space

In 2018, Linares moved to MIT.

“I had great respect for the history of the people and the work that was done here,” Linares says. Linares said he was especially inspired by the legendary Charles Stark “Doc” Draper, who developed the first inertial guidance system in the 1940s. This system will enable autonomous navigation for planes, submarines, satellites, and spacecraft for decades to come. “This is essentially my field of expertise, and I knew MIT would be the perfect place to continue my career.”

As a junior faculty member at AeroAstro, Linares spent his first few years focused on the emerging challenge of space sustainability. Around that time, SpaceX’s Starlink was launching the first constellation of satellites into low Earth orbit. Starlink was intended to provide worldwide internet coverage through a huge network of thousands of coordinating satellites. The launch of so many satellites, along with millions of pieces of space debris, into orbits where other operational and non-operating satellites were already present raised questions about how to safely manage satellite traffic and how much traffic the orbits could sustain.

“At what level do we reach a tipping point where there are too many satellites in a given orbit regime?” Linares said. “Back then, it was kind of a known problem, but there weren’t a lot of solutions.”

Linares’ group applied an understanding of celestial mechanics and the physics of how objects move in space to figure out the best way to squeeze satellites into orbital “shells,” or lanes that are most likely to prevent collisions. They have also developed a state-of-the-art orbital traffic model that can simulate the trajectories of more than 10 million individual objects in space. Previous models were much more limited in the number of objects that could be accurately simulated. Linares’ open source model is MIT Orbital Capacity Evaluation Toolor MoCAT, could account for millions of pieces of space debris in addition to many intact satellites in orbit.

The tools his group developed are currently used by satellite operators to plan and predict safe spacecraft trajectories. His team continues to work on space traffic management and orbital capacity issues. They are also branching out into space robotics. The research team is testing ways to remotely control humanoid robots. This could help build future infrastructure and perform long-duration tasks in space.

Linares also researches artificial intelligence, including how satellites can autonomously “learn” from their experiences and safely adapt to uncertain environments.

“What if each satellite had a virtual Doc Draper onboard that could do the debugging that we did from the ground during the Apollo mission?” Linares says. “Then the satellites will become instantly more robust. And it doesn’t take humans out of the equation. It allows humans to be enhanced. I think it’s within reach.”