Hundreds of thousands of tiny pieces of space debris presently go untracked in Earth’s orbit, putting human use of space at risk.
With society growing ever more dependent on spaceborne assets such as communications, weather, and Global Positioning System (GPS) satellites, the threat posed by space debris — material left by human activity above our planet, such as launched rockets and deployed spacecraft – is surging.
Sizewise, space debris runs the gamut, from large defunct satellites to infinitesimal flecks of paint. All these objects, however, pose a severe threat to operational spacecraft, as well as to astronauts aboard them or working in space. That’s because objects in orbit above the Earth move at speeds approaching 20,000 miles per hour, packing a major punch should a collision occur.
Space debris greater than 10 centimeters can effectively be tracked using ground radar, with collision avoidance alerts going out to spacecraft operators to adjust their assets’ orbits accordingly. But small debris is an unaddressed and growing threat. Alarmingly, while estimates suggest that more than 100 million objects greater than a millimeter in size are whizzing around Earth, less than 1 percent of this dangerous debris is currently being tracked.
SRI researchers are seeking to address this growing and unaccounted-for menace with an innovative approach to tracking space debris. The researchers call it SOTERIA (Space Object Tracking and Evaluation via Radar Integration and Analysis), named after the goddess in Greek mythology for safety and preservation from harm.
“Space debris poses a serious threat to our continuing use of space across all domains of science, communications, commerce, and intelligence,” said Lin van Nieuwstadt, a senior engineer at SRI and principal investigator for SOTERIA. “With the SOTERIA project, we hope to extend reliable tracking of objects in space down to previously unobservable scales, thereby preserving humankind’s ability to utilize the final frontier.”
“We want to be able to track space debris particles that are merely the size of a grain of sand,” said Tony van Eyken, director of the Center for GeoSpace Studies at SRI and co-principal investigator for SOTERIA. “Particles that small can still impact with a tremendous amount of energy. If you’re a satellite operator, you care if your asset is in line to be hit by one of these specks.”
The premise of SOTERIA is to leverage existing ground-based radars, alongside a suite of detector instruments placed on spacecraft launched in coming years, to ubiquitously track small space debris through a host of signatures.
One such signature is the incidental illumination of objects by radio signals from ground radar that could reach back to our planet’s surface, so long as we know how to distinguish these faint signals. The scattered radio wave signatures might further be distinguishable via localized spaceborne sensors.
Another signature under investigation is the tiny “wakes” created by debris as it careens through plasma in the upper reaches of Earth’s atmosphere and in vast radiation clouds farther out in space.
To pursue these aims, SOTERIA was recently selected by the Intelligence Advanced Research Projects Activity (IARPA), the advanced R&D arm under the Office of the Director of National Intelligence, for further development as part of the SINTRA (Space Debris Identification and Tracking) program.
For the project, SRI is working on data collection and analysis, algorithm-development tracking, and overall project management. SRI is collaborating with two Virginia-based subcontractors: Leidos, a defense, aviation, and information technology company that’s doing plasma modeling, and space technology company SCOUT Space Inc., which is working on the spaceborne sensors and planning for their deployment.
With a long history of developing and implementing satellite tracking technologies, SRI brings significant expertise to the project.
“SRI researchers have decades of experience using ground-based radar for the detection and the tracking of objects in space,” said van Eyken. “Based on this legacy, we are excited to be a part of the SINTRA effort with SOTERIA.”
Developing new means of tracking
The SOTERIA team plans to collect and study data from multiple radar instruments to see how radar signals already being beamed into space from large transmitter antennas could incidentally bounce off small space debris and return to different receiver antennas, thus boosting tracking potential. To this end, SRI researchers plan to run a test using SRI’s steerable radio telescope — nicknamed the Dish and housed on Stanford University land — as the receiver.
For detecting plasma wakes, the researchers are examining how to better harvest these echolike signals when space debris passes through Earth’s ionosphere — an upper atmospheric layer extending 50 to 400 miles above our planet. Observational exploration for these signatures actually dates back to the Space Race days of the late 1950s, but signatures would routinely have been filtered out of tracking analyses since. “These plasma signatures might have been previously overlooked, naturally because we weren’t looking for them, not realizing their potential usefulness,” said van Eyken.
Regarding the development of spaceborne sensors, the SOTERIA project will conclude with the flying of a prototype sensor as a payload on a satellite. That test will be integrated with the infrastructure built and knowledge gained through the previous tasks.
The overall objective for SINTRA, through SOTERIA, is to extend reliable tracking capabilities to geostationary orbit — a region about 22,000 miles out into space, where commercial communications and key weather satellites are orbiting at the same rate as the rotation of the Earth, thereby maintaining a constant view of a portion of the planet.
“Our ultimate goal,” said van Nieuwstadt, “is to be able to keep track of small space debris particles anywhere within thousands of miles of the surface of the Earth, which represents an enormous volume.”
This research is based upon work supported in part by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), via 2023-23060200005. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of ODNI, IARPA, or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright annotation therein. IA52.205-714 Press Release (Announcement of Contract Award) (JUN 2017).