Hundreds of millions of pieces of space junk orbit the Earth daily, from chips of rocket paint, to entire dead satellites. This cloud of high-tech detritus circles the planet at 17,500mph. At these speeds, even objects as small as a pebble can severely damage a passing spacecraft.
Aerospace engineers from MIT have developed a laser sensing technique that can decipher not only where but what kind of space junk may be passing overhead. The technique, called laser polarimetry, could be used to discern whether a piece of debris is bare metal or covered with paint. The difference, they say, could help determine an object’s mass, momentum, and potential for destruction.
“There have been two major collisions over the last 10 years that have caused pretty significant spikes in debris,” explains Michael Pasqual, a former graduate student in MIT’s Department of Aeronautics and Astronautics. “If you can figure out what a piece of debris is made of, you can know how heavy it is and how quickly it could de-orbit over time or hit something else.”
The team used a laser to measure a material’s effect on the polarisation state of light, which refers to the orientation of light’s oscillating electric field that reflects off the material. For instance, when the sun’s rays reflect off a rubber ball, the incoming light’s electric field may oscillate vertically. But certain properties of the ball’s surface, such as its roughness, may cause it to reflect with a horizontal oscillation instead, or in a completely different orientation, depending on the angle at which light hits it.
Each material they tested was found to have a sufficiently unique polarisation signature to distinguish it from the other samples. Pasqual believes other aerospace materials, such as shielding films, composite materials for antennas, solar cells, and circuit boards, may also exhibit unique polarisation effects. His goal is to use laser polarimetry to establish a library of materials and their polarisation signatures.