According to NASA, there are more than 500,000 pieces of debris, or space junk orbiting the Earth. At least 20,000 of those objects are larger than a softball. All of the objects, which travel at speeds up to 17,500 mph, pose potential dangers to satellites orbiting the Earth, both now and in the future.
One way to potentially reduce these hazards, and the costs and risks of launching new satellites, would be to build and launch an on-orbit recycling system. Notionally, the system would have the ability to vaporize small existing space debris; recycle and recover manufacturing materials from existing satellites; and even perform in-space manufacturing of structural elements for new satellites.
“Think of this space recycler as an on-orbit refinery, powered by that amazing source of energy in space called the sun,” said Howard Eller, Advanced Missions Tech Fellow, Northrop Grumman Aerospace Systems.
Bringing the Sun into Focus
In its basic form, the recycler would include a large parabolic reflector, perhaps 50 to 100 feet in diameter; a spherical crucible made of material with an extremely high melting point; a set of compartments in which different types of salvaged materials could be stored; and several robotic
arms for capturing “dead” satellites or other space debris.
The recycler’s reflector would concentrate solar energy into a small spherical space, creating an intense source of heat. The heat could be used either to simply vaporize existing small debris, or to heat larger pieces of space debris in the recycler’s crucible. The crucible could be rotated through the thermal flux like a rotisserie grill to heat the debris to a desired and uniform temperature.
Using this approach, explains Eller, “we could selectively melt and capture material of type A, heat the crucible more to melt and capture material of type B and so on.”
Materials melted and captured at each stage of the recycling process could be stored in separate compartments in the form of ingots, or perhaps piped in real time to another part of the recycler as source material for in-space manufacturing operations. Any unneeded leftovers from the recycling process could be compressed into small pieces and vaporized by the solar concentrator.
There could also be self-sustaining aspect to this recycler, adds Eller. “If the mirrored surface of the solar concentrator became contaminated, the recycler could vaporize a piece of scrap aluminum in such a way that material is deposited as a new thin and highly reflective layer on the mirror, effectively recoating it,” he said.
Scavenging the Graveyard
An ideal source of dead satellites for the recycler would be so-called “graveyard” orbits several hundred kilometers above geosynchronous (22,500 miles) altitude. Satellites are typically safe-d (batteries drained, propellant tanks emptied) and placed in a graveyard orbit at the end of their operational lives to reduce the chance of colliding with an operational spacecraft.
According to Eller, a recycler could either be placed in a relatively fixed location in orbit where dead satellites could be brought for recycling, or the entire facility could maneuver from satellite to satellite in a graveyard orbit. In theory, an in-space 3-D manufacturing facility could be attached to the other end of the recycler. As old satellites are ingested (think PacMan) and converted to raw materials, new satellite structures would be produced and pushed out the other end for in-space assembly.
Smarter, Lighter, Cheaper
The ability to perform on-orbit recycling and manufacturing could also enable a new generation of simpler, lighter and potentially more capable satellite systems. Free from the impact of gravitational forces during launch, satellites could be assembled in space using simpler designs and materials with far less mass and structural strength. As a result, they might look very different from traditional spacecraft buses, which are essentially boxes with one or more solar array appendages.
“If we built a satellite in space, it could be a single panel of any desired length,” explains Eller. “One side could be an array of RF [radio frequency] elements and electronics, like a single large circuit board. You could produce additional panels to serve as solar arrays, or perhaps attach solar cells to the back of the original panel.”
After building this “panelsat” in orbit, you could plug in a module launched from Earth containing all of the electronic components that are currently too difficult to produce in space.
Working the Vision
In the end, admits Eller, space recycling is a vision that should be driven by economics. It makes perfect sense to recycle existing satellites because they are made of the materials most often needed to make new satellites. “But right now there is no financial incentive to get rid of space debris,” he says. “That’s why we should develop this or similar concepts as a nation. If we can figure out a way to convert dead satellites from a waste product into an economic benefit, recycling in space will happen.”