The realization of space tractor beams could soon move beyond science fiction

On February 10, 2009, disaster struck hundreds of miles over the Siberian Peninsula. That evening, an invalid Earth-orbiting Russian satellite collided with a communications satellite called Iridium-33, which was moving at thousands of miles per hour. Both spacecraft exploded into shrapnel, sending more than 1,800 pieces of debris spiraling around the world.

No other spacecraft (or humans) were harmed, but for many space engineers, the event was a sign of things to come. The space seemed crowded.

NASA estimates that about 23,000 pieces of debris the size of a softball or larger are currently orbiting through space. All this junk means that another collision like the one that destroyed Iridium-33 becomes increasingly likely every year – only this time, the fallout could be much worse.

“The problem with space debris is that once there’s a collision, you create more space debris,” said Julian Hammerl, a doctoral student in aeronautical engineering sciences at CU Boulder. “You have an increased probability of causing another collision, which will create more debris. There is a cascading effect.”

Hammerl and a team led by Professor Hanspeter Schaub have a plan to stop the waterfalls before they start. Researchers rely on one of the oldest tropes in science fiction: tractor beams like those used by the Starship Enterprise to move asteroids safely out of its path.

Imagine this: In the not too distant future, a fleet of tiny spacecraft could orbit the Earth, meeting up with dead lumps of metal in geosynchronous orbit around the planet. Then, using devices called “electron beams,” these space garbage trucks will slowly move that debris to safety without you even having to touch it—all by tapping the same kind of physics that makes your socks stick to your pants in the dryer.

“We create an attractive or repulsive electrostatic force,” said Schaub, chair of the Ann and H.G. Smid Department of Aerospace Engineering Sciences. “It’s similar to the tractor beam you see in Star Trek, although not quite as powerful.”

First, Schaub and colleagues must solve a series of challenges that they describe in Many recent studies. Researchers are using, for example, a new facility to replicate the surprisingly complex environment around Earth. They also set their sights on how tractor beams might one day clear debris from the region of space between Earth and the Moon.

“Touching things in space is very dangerous. Things move very quickly and often unexpectedly,” said Kaylee Champion, a doctoral student working with Schaub. “This could open up a lot of safer avenues for servicing spacecraft.”

space in the box

Champion and her fellow researchers are now exploring those avenues from the lab with a view of the Flatirons on the university’s East Campus.

A few students gather around a cylinder the size of a whiskey barrel. It’s made of a thick layer of stainless steel with several slit-like windows to peek inside. This vacuum chamber, called the Electrostatic Charge Laboratory for Interactions between Plasma and Spacecraft (ECLIPS), is now open at its base. But as the engine hums, the cylinder slowly drops lower until the clamps close.

Soon, the pump will start depressurizing the room. In about a day, there’ll be no air left inside—a tiny pocket of space right in the middle of Boulder. Schaub and his team designed the chamber themselves, and it is unlike any other research facility in the country.

This space in miniature takes center stage in the group’s experiments with electrostatic tractors. Inside, the group can reproduce the environment around Earth, which is not empty but is, instead, engulfed in a thin gas of free electrons and charged atoms called plasma. The group can even simulate the debris in this room by using cubes or more complex shapes made of metal.

Today, researchers are trying to mimic conditions in what Schwab called an “expensive patch of real estate” in space.

About 22,000 miles from the planet’s surface, a geosynchronous orbit, or “geo,” begins a journey far beyond low Earth orbit, or “low Earth orbit,” where Iridium 33 met its demise. There, you can find some of the most expensive satellites ever built – military and telecommunications spacecraft that are the size of school buses and weigh more than a ton.

“Geo is like the Bel Air of space,” said Schaub.

It’s also crowded. Engineers estimate that there are about 180 geosynchronous orbital parking spots where satellites can squeeze into. They are all claimed or already occupied.

Tractor beams may be able to move older spacecraft safely out of their way, Schwab said, making room for the next generation of satellites.

default chords

For Hammerl, the research project is one he could only dream about as a young student in his home city of Vienna, Austria. Hammerl studied mechanical engineering as an undergraduate, but transferred to Boulder for graduate school to pursue his passion for space exploration. (Austria does not have its own space programme.)

When he arrived, he had no idea how complicated this seemingly empty space was.

In a simple sense, he explained, the team’s concept of an “electrostatic tug” is a bit like rubbing a balloon on your head to make your hair stand on end. First, the service ship will approach an abandoned satellite from a distance of about 15 to 25 meters (49 to 89 feet), and then blast off with a beam of electrons. These electrons will give the space debris a negative charge, while making the server more positive.

As the saying goes, opposites attract.

“With that attractive force, you can basically pull the debris away without ever touching it,” Hammerl said. “It behaves like what we call a virtual rope.”

Seems to work too. Based on experiments in ECLIPS and computer models, the researchers estimated that an electrostatic tug could pull a multi-ton satellite about 200 miles in two to three months. That’s a slow pace, but it’s good enough to remove what are essentially glorified paperweights from your precious orbital slots.

Scientists have proposed other strategies for removing debris from orbit, such as capturing stray satellites with harpoons. But all of these methods require direct contact with the scrap.

However, in practice, using a tractor beam in space is fraught with complications.

For a start, decommissioned satellites don’t usually stay put and can meander wildly through space. In studies, Schaub and his students have shown that if you hit these pieces of metal with a rhythmic pulse of electrons, rather than a steady beam, they can potentially slow their rotation — making the satellites safe to tow away or even close in for repairs.

away from home

The team also began considering a region of space where there are few pieces of debris today but is about to get busier: “cislunar” space, or the region between Earth and its moon. Here, conditions can get really wild.

Champion explained that the Sun spews out a near-constant stream of plasma, referred to as the solar wind. Outside of Earth’s protective magnetic field, the plasma environment can become unpredictable. Vehicles flying through them can disturb the plasma flow and generate ions left behind, like sailboats jumping into the water. These wakes can, in turn, affect the tractor’s electrostatic performance.

“That’s what makes this technology so challenging,” said Champion. “You have very different plasma environments in low Earth orbit, versus geosynchronous orbit versus lunar orbit. You have to deal with that.”

To do just that, Champion and her lab colleagues augmented ECLIPS with an “ion gun,” a device that can create fast-moving streams of argon ions inside a chamber.

She hopes her work will one day aid NASA’s efforts through the Artemis program to return humans to the moon — and from there on beyond.

“Once we get people back on the moon, that’s a stepping stone to traveling to Mars,” Champion said.

Schwab noted that space tractor beams may not be the stuff of science fiction for long. With the right funding, he expects his team to be ready to launch a prototype electrostatic tractor into space in just five to 10 years.

“The exciting thing about this technology is that the same service vehicle can move two, three or even dozens of objects over its lifetime,” Schaub said. “This significantly reduces cost.” Nobody wants to spend a billion dollars moving trash.