Posted with permission from Popular Science

Earth’s orbit is becoming dangerously crowded with space junk.

Brane Craft capturing space debris.
An artist's rendition of a Brane Craft capturing space debris.

The Aerospace Corporation

Last year, the European Space Agency’s Sentinel-1A satellite collided with a tiny chunk of debris. Fortunately, the resulting damage to its solar panel turned out to be minor. But it got lucky. If the piece of space trash had been slightly larger, it could have shattered the entire panel, according to Holger Krag, head of the agency’s Space Debris Office who spoke about the incident at this past spring's 7th European Conference on Space Debris.

Earth’s orbit is littered with bolts, flecks of paint, dead satellites, and other leftovers from past missions. More than 500,000 pieces of space debris hurtle around our planet at speeds up to 17,500 miles per hour. Space trash is accumulating, and scientists fear that collisions will become more common, creating even more debris. This could trigger a domino effect where bits of shrapnel crash into other objects, creating more and more projectiles to clutter low Earth orbit.

“If that ever happens it will make space unusable essentially, and we’re pretty close to that,” says Jason Derleth, program executive of the NASA Innovative Advanced Concepts (NIAC) Program.

Some researchers want to take action now, before the problem inevitably grows. This past spring, the NIAC awarded researchers at The Aerospace Corporation in El Segundo, California $500,000 to continue development of an unusual-looking spacecraft that's meant to mop up small pieces of space debris; almost like a space vacuum cleaner. Called Brane Crafts, the tiny ships are about a yard across and thinner than a human hair. Each one would wrap around a chunk of debris and yank it down to into the atmosphere, where it would heat up and eventually be incinerated about 155 miles above the Earth’s surface.

“You can essentially think of it as one giant piece of saran wrap covered with thrusters, and you can curl it however you want,” Derleth says.

Each Brane Craft, its creators hope, will be incredibly lightweight and fuel-efficient. That means it could be ideal for more than just cleaning up space junk. One day, these tiny ships could be sent to visit asteroids, moons, and other planets.

On the prowl

To create Brane Craft, developers had to think beyond conventional spacecraft as they aren't really suited to chase down space debris. “Trying to catch something that’s going that fast is really, really hard,” Derleth says. “Docking with a piece of debris means you have to match that orbit exactly.”

To rendezvous with a piece of debris that is literally traveling faster than a speeding bullet, dispose of it, and then hunt down the next piece of trash would also call for immense amounts of fuel, making it extremely costly.

“The Brane Craft idea is to take a spacecraft and reduce it to its absolute minimum mass,” says Siegfried Janson, a senior scientist at The Aerospace Corporation. Currently, it can cost around $250,000 to launch a CubeSat, a kind of miniaturized satellite, that is about 11 pounds, Janson says. His goal is to make spacecraft that are so light that they would cost only $5,000 each to launch.

The current design is a membrane-like ship that is three square feet in size and weighs less than a banana. Each spacecraft will be made from flexible plastic sheets 10 microns thick (our hairs tend to be up to 180 microns thick) printed with a fine film of solar cells and electronics. Liquid propellant will be stored in the 15 to 20 micron gap between these sheets.

The solar cells will power a type of engine called an electrospray thruster that uses propellant very sparingly, Janson says. The whole ship will be bendy, too. “Basically it’s got thin muscles integrated into the structure,” he says. These “muscles” are made from a polymer sandwiched between two metal plates that can change shape when an electric current is run through them, causing a voltage difference.

These slender spacecraft are meant to be light enough to travel to space en masse. Janson envisions a batch of 50 or more Brane Crafts “like a stack of pizzas” launched together into orbit. Once they reach the International Space Station or another point in low Earth orbit, each one could be sent directions to its target piece of debris (radar stations track more than 18,000 objects in orbit, most of which are space debris).

It might take five days for the Brane Craft to maneuver up to the debris and envelop it. The Brane Craft would then fire its thrusters to push in the opposite direction to the one the debris was traveling in. This would slow the object down, causing it to gradually sink into the atmosphere. After 10 days or so, the debris would be low enough to burn up.

Typically, the Brane Craft would be incinerated along with its quarry; the spacecraft are intended to be light and cheap enough to be sacrificed at the end of the mission.

It will still be quite some time before Brane Crafts are unleashed upon the hordes of space junk orbiting our planet. Janson estimates that the ships could be ready for launch in about 10 years. He and his team are planning to use their most recent round of NASA funding to refine their design and start testing super-thin electronics.

One challenge they still need to overcome is how to protect the spacecrafts from radiation. The razor-thin ships won’t have shielding to protect their sensitive electronics from radiation. Janson and his crew are designing carbon-nanotube circuits that can survive for a month near the outer edge of low Earth orbit.

And there are drawbacks to building spaceships to be so thin. As Brane Craft closes in on a piece of debris, it will likely be clobbered by other tiny detritus. “The micro-meteorite environment in low Earth orbit is normally just a pain for spacecraft; you get little dings in your solar cells and windows,” Janson says. Bits of rock or manmade trash too small to even make a dent in a rocket might puncture a Brane Craft. “We have to…design the Brane Craft to be bulletproof to these really tiny bullets.”

Outward bound

To start, Janson and his crew are planning to use Brane Craft on small pieces of space debris about five to 10 centimeters in size (roughly two to four inches). The ships won’t be able to get rid of bulky space junk, like used upper stages. However, if scientists predict that a collision is imminent, a group of Brane Crafts could be sent to push this debris off track.

Super-thin ships like Brane Craft aren’t the only tech under construction to wrangle space debris. The European Space Agency is also considering robotic arm grippers, nets, harpoons, and tethers. Another European team is planning to launch its RemoveDebris mission in late 2017 or early 2018, which will practice capturing CubeSats with a net and harpoon. Aeroscale, a satellite services company based in Singapore, is planning to capture debris using magnets. And researchers at Stanford University and NASA’s Jet Propulsion Laboratory in Pasadena, California have designed a gripper inspired by gecko feet that could latch onto satellites and other large debris.

Researchers have even considered zapping debris with a ground-based laser. “You can slow things down just as they come over the horizon by pointing these very high-powered lasers at them,” Derleth says. This would gobble up much less energy than launching a spaceship and sending it after individual chunks of debris. However, such a laser could potentially be turned into an anti-satellite weapon.

All of these approaches will have to prove their mettle. One advantage to Brane Craft’s design, though, is it's potential to be put to work far beyond Earth’s orbit. Brane Craft will be so fuel-efficient that one of these tiny ships could travel all the way to Mars and back, or make multiple trips between the moon and low Earth orbit. “You can visit just about [anywhere] in the solar system,” Janson says.

Brane Craft could also be used to explore and mine asteroids, he says. It would be ridiculously expensive to build thousands of conventional spacecraft and send them traveling to individual asteroids. But perhaps swarms of Brane Crafts could visit the asteroid belt between Mars and Jupiter, and return carrying samples.

Eventually, these tiny spacecraft could even help protect the Earth, Janson says. We could manufacture larger versions or mass-produce thousands of Brane Crafts and send them out to deflect incoming asteroids.

“It’s a new kind of spacecraft that nobody’s ever seen, and I hope people can get really creative with it,” Derleth says.