Using a method proposed by University of Michigan researchers, satellite and spacecraft operators may soon be able to detect small pieces of debris orbiting Earth.
“Right now, we detect space debris by looking for objects that reflect light or radar signals,” said Nilton Renno, the University of Michigan team’s principal investigator and a professor of climate and space sciences and engineering as well as aerospace engineering. “The smaller the objects get, the harder it becomes to get sunlight or radar signals strong enough to detect them from the ground.”
Objects larger than a softball are currently the only trackable pieces of “space junk,” which accounts for less than 1% of the nearly 170 million pieces of trash left over from rocket launches, spacewalks, and defunct satellites. The new method detects debris as small as one millimeter in diameter – about the thickness of a pencil lead.
Renno will co-present the findings with Yun Zhang, a postdoctoral researcher in climate and space sciences and engineering, at the Second International Orbital Debris Conference on December 5. The findings are part of a larger, collaborative project funded by the Intelligence Advanced Research Projects Activity’s Space Debris Identification and Tracking Program. Blue Halo, a military contractor, is leading the project, which also includes the University of Alaska Fairbanks.
Right now, we detect space debris by looking for objects that reflect light or radar signals. The smaller the objects get, the harder it becomes to get sunlight or radar signals strong enough to detect them from the ground.
Nilton Renno
Trash in space is not only unsightly; it is also dangerous. A plum-sized piece of space debris can collide with another object with the same energy as a car crash on the highway at a typical orbital speed of 22,000 miles per hour, potentially knocking a satellite offline. Even small pieces of debris can cause damage to spacecraft, so tracking them is critical for satellites and spacecraft that must take evasive actions.
The Earth’s orbit is becoming increasingly cluttered, making satellite protection much more difficult. Space debris frequently collides with one another, fragmenting larger pieces into small, undetectable fragments as a result. Some experts fear that the amount of space debris will grow exponentially as individual pieces collide, wreaking havoc on the infrastructure that we rely on for GPS, cell phone data, weather monitoring, and other services.
Collisions between space debris, while potentially disastrous, may turn out to be the best way to track tiny space junk. When small pieces of space debris collide, they explode into tiny fragments, some of which vaporize into a charged gas as a result of the impact’s heat.
“When the cloud of charged gas and debris fragments expands, it creates lightning-like energy bursts, similar to signals produced by static sparks that appear after rubbing a freshly laundered blanket,” said Mojtaba Akhavan-Tafti, an assistant research scientist in climate and space sciences and engineering, and a lead scientist on the project.
After this initial energy burst, charged solid pieces of debris fragments can create electric field pulses whenever they are close enough to each other, producing additional lightning-like bursts. These electric signals last for only a fraction of a second, but they could help track pieces of space debris and clouds of microscopic fragments that form when debris collides.
According to the team’s most recent computer simulations, when two pieces of aluminum collide at typical orbital speeds, they emit an electrical burst powerful enough to be detected from the ground by a 26-meter dish equipped with a high-quality radio receiver. More sensitive radio arrays, such as NASA’s Deep Space Network, should be able to detect the electric field pulses as well.
There is still much to be worked out. The frequency of the electrical signals can vary depending on the speed of the collision and the material of the debris, complicating detection. To be seen, the electric signals must be stronger than the background signals of the ground instrument and must pass through Earth’s upper atmosphere.
The team intends to improve their approach through additional computer simulations, real-world signal measurements with NASA’s Deep Space Network, and data analysis from hypervelocity experiments at the Naval Research Laboratory and NASA’s Ames Research Center. Using the lasers at the facility, the team can launch various types of debris at targets at various orbital speeds and measure the characteristics of the electric emissions produced by the impact. If such experiments reveal a method to detect a wide range of electrical signals generated during space debris collisions, they may be able to determine not only where space debris is, but also what it looks like and what it is made of.
