99% of Space Junk is Undetectable. That Could Change Soon

Private and military organizations are tracking some of the 170 million pieces of space junk orbiting the planet, but they’re limited to how small an object they can detect. Only chunks larger than a softball can be tracked with radar or optical systems, and that only accounts for less than 1% of the junk out there.

But a new technique is being developed to resolve space junk to pieces smaller than one millimeter in diameter.

Called Space Debris Identification and Tracking (SINTRA), the project will test out a new technique that uses the state-of-the-art sensors to detect plasma waves created by fields of debris. The new sensors are used along with existing sensors, such as ground-based radar, tracking satellites, and optical sensors in order to identify and track space debris in the one-millimeter size range.

“Right now, we detect space debris by looking for objects that reflect light or radar signals,” said Nilton Renno, from the University of Michigan and a professor of climate and space sciences, and engineering and 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.”

SINTRA is a 4-year project that will help advance the sensors needed for detecting orbital debris signatures. SIINTRA is a collaborative project funded by the Intelligence Advanced Research Projects Activity’s Space Debris Identification and Tracking Program. The project includes military contractor Blue Halo as well as several universities, such as the University of Michigan and the University of Alaska Fairbanks as well as MIT Lincoln Laboratory, Naval Research Laboratory, Los Alamos National Laboratory, and JHU Applied Physics Laboratory.

Low Earth Orbit
Estimated number of objects in low Earth orbit. Credit: NASA

The idea behind SINTRA is to search for the electrical signals emitted by clouds of space debris. Colliding pieces of space debris explode into tiny fragments, some of which vaporize into a charged gas due to the heat created by the impact. 

“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 for the University of Michigan.

The charged gas and debris fragments can create electric field pulses whenever they come close enough to each other, producing additional electrical bursts. These 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.

For example, when two pieces of aluminum collide at typical orbital speeds, they emit an electrical burst strong enough for a 26-meter dish with a high-quality radio receiver to detect from the ground, according to the University of Michigan team’s most recent computer simulations. The electric field pulses should similarly be detectable with more sensitive radio arrays, such as NASA’s Deep Space Network.

A piece of space junk punched this hole into the hull of NASA’s Solar Max spacecraft. Image credit: NASA Orbital Debris Program Office.

If successful, SINTRA would enable the first tracking capability for the ultra-small debris population, reducing risk to worldwide space operations. Space debris in low Earth orbit (LEO) have an average impact velocity of 36,000 km/hr (22,500 MPH). Therefore, even the smallest of debris can cause significant damage to operational satellites.

But there’s a lot of work yet to do in making the SINTRA concept work. The frequency of the electrical signals can vary with the speed of the collision; additionally, what the debris is made of also changes many variables, which could complicate detection.

In a press release from the University of Michigan, Akhavan-Tafti said that to see the electric signals, they need to be stronger than the ground instrument’s background signals and pass through Earth’s upper atmosphere.

For the project, the team will start by measuring real signals with NASA’s Deep Space Network, and analyze data from hypervelocity experiments at the Naval Research Laboratory and NASA’s Ames Research Center. Using the facilities’ lasers, the team can launch different kinds of debris at targets over a range of orbital speeds and measure the characteristics of the electric emissions resulting from the impact. If such experiments reveal a way to detect a wide range of electrical signals generated during space debris collisions, they could determine not just where space debris is, but what it looks like and is made of.

In a press release earlier this year, the US Intelligence Advanced Research Projects Activity agency said the goal of the SINTRA program is to fill gaps in current space debris-monitoring systems, which currently only track and monitor debris objects larger than four inches across. They said the detection, tracking, and characterization of lethal non-trackable space debris would support the safe operation of valuable space assets worldwide.

For more information, see the SINTRA website.