You’ve probably used satellite today. Satellites allow us to stream our favorite shows, call and text friends, check weather and navigation apps, and make online purchases. Satellites also monitor the Earth’s climate, the extent of agricultural crops, wildlife habitats and the effects of natural disasters.
As we found more uses for them, the number of satellites increased. There are currently over 10,000 satellites in low Earth orbit. Another 5,000 decommissioned satellites drift through the region, along with more than 100 million pieces of debris, from spent rocket stages to flecks of spacecraft paint.
For MIT’s Richard Linares, the rapid ballooning of satellites raises pressing questions: How can we safely manage traffic and growing congestion in space? And at what point will we reach orbital capacity if adding more satellites is not sustainable and may actually endanger the spacecraft and services we rely on?
“It’s up to society to evaluate what value we get from launching more satellites,” says Linares, who recently received an associate professorship in MIT’s Department of Aeronautics and Astronautics (AeroAstro). “One of the things we’re trying to do is approach traffic management and orbital capacity as engineering problems.”
Linares directs MIT’s Astrodynamics, Space Robotics, and Control Laboratory (ARCLab), a research group that uses astrodynamics (the motion and trajectory of objects in orbit) to track and manage millions of objects in Earth orbit. The group is also developing tools to predict changes in space traffic and debris as operators launch huge satellite “mega constellations” into space.
He also studies the impact of space weather on satellites, as well as how climate change on Earth may limit the number of satellites that can safely orbit in space. Anticipating that satellites will need to be smarter and faster to navigate cluttered environments, Linares is researching artificial intelligence to lend a hand satellites learn and reason autonomously to adapt to changing conditions and solve problems on board.
“Our research is quite diverse,” Linares says. “But overall, we want to make available all the economic opportunities that satellites provide us. And we are looking for engineering solutions to make this possible.”
Grounding practical problems
Linares was born and raised in Yonkers, Modern York. Both of his parents worked as school bus drivers to support their children, and Linares was the youngest of six children. He was an vigorous child and loved sports, playing football throughout high school.
“Sport allowed me to stay focused and organized, as well as develop a work ethic,” says Linares. “It taught me how to work hard.”
“My interest in science came from the universe and trying to understand our place in it,” Linares recalls.
Deciding to stay close to home, he applied to in-state schools with forceful aerospace engineering departments and luckily landed at the State University of Modern York at Buffalo (SUNY Buffalo), where he eventually earned bachelor’s, master’s, and doctorate degrees, all in aerospace engineering.
As a student, Linares undertook a research project in astrodynamics, aiming to solve the problem of determining the relative orientation of satellites flying in formation.
“Formation flying was a big topic in the early 2000s,” Linares says. “I liked the math aspect that allowed me to go one layer deeper towards the solution.”
He developed calculations to show that when three satellites fly together, they essentially form a triangle whose angles can be calculated to determine where each satellite is in relation to the other two at any given time. His work introduced a novel control approach to enable satellites to fly safely together. The research had direct applications to the United States Air Force, which helped fund the work.
While expanding his thesis research, Linares also took the opportunity to work directly with the Air Force on satellite tracking and orientation issues. He completed two internships at the United States Air Force Research Laboratory, one at Kirtland Air Force Base in Albuquerque, Modern Mexico, and the other in Maui, Hawaii.
“Being able to work with the Air Force at that time kind of grounded the research in practical problems,” Linares says.
As part of his PhD, he tackled another practical problem of “uncorrelated tracks”. At the time, the Air Force was using a network of telescopes to observe more than 20,000 objects in space, and labeling and cataloging them helped track the objects over time. While object detection was relatively uncomplicated, the challenge was to associate the detected object with what was already in the catalog. In other words, was what they saw something they had already seen?
Linares developed image analysis techniques to identify key features of objects, such as their shape and orientation, which helped the Air Force “fingerprint” satellites and pieces of space debris and track their activity – and collision potential – over time.
After receiving his Ph.D., Linares worked as a postdoc at Los Alamos National Laboratory and the U.S. Naval Observatory. During this time, he expanded his aviation activities into other areas, including space weather, using satellite measurements to model the effects of Earth’s ionosphere – the upper layer of the atmosphere ionized by solar radiation – on satellite drag.
He then accepted a position as assistant professor of aerospace engineering at the University of Minnesota in Minneapolis. Over the next three years, he continued research into space weather modeling, tracking space objects, and coordinating satellites to fly in swarms.
Making space
In 2018, Linares moved to MIT.
“I had a lot of respect for the people and the history of the work that had been done here,” says Linares, who was particularly inspired by the legendary Charles Stark “Doc” Draper, who in the 1940s developed the first inertial guidance systems that enabled airplanes, submarines, satellites and spacecraft to navigate independently for decades to come. “This was essentially my field, and I knew MIT was the best place to pursue my career.”
As a junior member of the AeroAstro faculty, Linares spent his early years focusing on an emerging challenge: space sustainability. Around this time, the first satellite constellations launched into low Earth orbit using SpaceX’s Starlink, which aimed to provide global Internet coverage through a massive network of several thousand coordination satellites. Launching so many satellites into orbits that already housed other vigorous and inactive satellites, along with millions of pieces of space debris, raised questions about how to safely manage satellite traffic and how much traffic an orbit can withstand.
“At what level do we reach the tipping point when we have too many satellites in certain orbital regimes?” – says Linares. “It was a fairly well-known problem at the time, but there weren’t many solutions.”
Linares’ group used knowledge of astrodynamics and the physics of how objects move in space to find the best way to pack satellites into orbital “shells,” or paths, that would most likely prevent collisions. They also developed a state-of-the-art orbital motion model that was able to simulate the trajectories of over 10 million individual objects in space. Previous models were much more circumscribed in the number of objects they could accurately simulate. Linares’ open source model, the so-called MIT Orbital Capacity Assessment Toolor MoCAT, could account for millions of pieces of space debris, as well as many intact satellites in orbit.
The tools his group developed are today used by satellite operators to plan and predict unthreatening spacecraft trajectories. His team continues to work on issues of space traffic management and orbital capacity. They also deal with space robotics. The team is testing ways to remotely control a humanoid robot, which could potentially lend a hand build future infrastructure and perform long-duration tasks in space.
Linares is also researching artificial intelligence, including ways a satellite can autonomously “learn” from its experience and safely adapt to uncertain conditions.
“Imagine if each satellite had a virtual Doc Draper on board that could do the error corrections that we did from the ground during the Apollo missions,” says Linares. “This would make satellites instantly more robust. And it doesn’t take humans out of the equation. It allows for human augmentation. I think that’s within reach.”