Low Earth Orbit crowding
Almost 20,000 satellites orbit Earth today, driving Low-Earth Orbit toward its physical limits, Universe Today reported.
More than 3,500 of those objects are defunct or silent zombies. A collision between two space assets could trigger the Kessler syndrome.
Growing congestion statistics
Tracked objects in Low-Earth Orbit jumped from about 13,700 in 2019 to more than 24,000 in 2025, according to Universe Today. That sharp increase leaves operators with little time to manual-pilot spacecraft from the ground.
Communication delays and sunlight illumination windows complicate manual interventions. Spacecraft require autonomous systems to track uncooperative targets safely.
Cortex framework design
Researchers published a CORTEX study in Acta Astronautica detailing an autonomous framework for close-range rendezvous operations. Minduli Wijayatunga, an aerospace engineering faculty member at The Grainger College of Engineering at the University of Illinois Urbana-Champaign, led the research.
“Rendezvous and Proximity Operations are shifting from bespoke demonstration missions such as Northrop Grumman’s Mission Extension Vehicles, China’s Tianyuan–1, and Astroscale’s ADRAS-J, to routine missions due to the growth of in-orbit assets and the resulting demand for inspection, servicing, assembly, and debris mitigation,” the authors wrote.
“These spacecraft must be able to track the trajectories of uncooperative objects autonomously but also make go/no-go decisions without waiting for the ground to decide,” Wijayatunga said.
Trajectory planning methods
Convex optimization allows a servicer spacecraft to approach a client using mathematical trajectories rather than manual input commands. The algorithm minimizes fuel use while respecting keep-out zones around sensitive instruments.
Cortex incorporates sunlight windows and a replanning architecture. “I wanted to bring that same idea into developing CORTEX and expand it, taking into consideration sunlight windows so we don’t have to operate in darkness,” Wijayatunga said.
“CORTEX has trajectory design and guidance, so if you deviate significantly from your nominal mission trajectory, it replans the trajectory and re-approaches unless you are in severe violation of your keep-out zone, in which case it returns to a passively safe orbit,” she added.
Hardware testbed validation
Testing involves an In-orbit Servicing Assembly and Manufacturing scenario with a client spacecraft object in Low-Earth Orbit. Hold positions at the fly-around and final approach stages allow the servicer to pause during eclipses.
Tests simulated unexpected solar storms and thruster failures. “In all cases, the framework either recovered successfully while respecting safety constraints or executed a safe retreat before entering unsafe regions,” the authors wrote.
“In some of the hardware tests, if the servicer violates the approach corridor, it leaves the keep-out zone and retreats to a safe position and in others, the servicer is able to recover and carry on with its mission,” Wijayatunga said.
Astroscale demonstration flights
Demonstration missions are already underway. The Japan Aerospace Exploration Agency launched Astroscale’s ADRAS-J spacecraft in 2024.
The vehicle maneuvered within 50 meters of an uncooperative spent rocket stage. It captured multi-angle images using onboard sensors and autonomous steering.