Adam Battle, University of Arizona; Tanner Campbell, University of Arizona; Roberto Furfaro, University of Arizona; Vishnu Reddy, University of Arizona
Keywords: LEO, cm-size, Debris, NaK, RORSAT
Abstract:
As technologies evolve and adversaries in the space domain implement new tools, the observing community must continue to push the limits of telescopes to counter those measures. Although much of the current focus is on catalog maintenance, characterization of active satellites and debris especially in low Earth orbit (LEO) is critical for a comprehensive Space Domain Awareness (SDA) mission. The Mission Extension Vehicle (MEV) satellites were experiments to demonstrate that a smaller satellite could rendezvous and dock with another geostationary satellite on-orbit and perform certain specialized tasks. Similarly, the early 2023 breakup of the 1-3 ft diameter Russian LEO, Kosmos 2499, caused people to speculate about its former mission, with many believing that it was an experimental anti-satellite weapon.
In order to exercise the tracking and characterization capabilities of the Robotic Automated Pointing Telescope for Optical Reflectance Spectroscopy II (RAPTORS II) on centimeter-size objects, we performed a test set of observations on leaked sodium-potassium (NaK) coolant from the Soviet Radar Ocean Reconnaissance (RORSAT) satellites nuclear reactors.
The RORSATs were Soviet LEO radar reconnaissance satellites used to monitor ocean traffic. Thirty-three of these satellites were launched between 1967 and 1988 at a relatively low altitude of 200 250 km. In order to avoid the drag that solar panels would have produced at this altitude, the RORSATs were equipped with nuclear reactors to provide the high-power requirements of the onboard radars. When these satellites were successfully retired, the reactors were ejected into a higher altitude graveyard orbit with the hope of keeping radioactive material from reentering Earths atmosphere. Upon ejection, however, droplets of the NaK liquid metal leaked from the coolant lines of the ejected reactors into the space environment. Due to the prolonged exposure with the nuclear reactor, these droplets and the spacecrafts remain radioactive.
The RORSATs have historically been the focus of other environmental accidents in addition to the on-orbit NaK coolant blobs. In 1978, the Soviets lost control of RORSAT Kosmos 958 and its reactor failed to eject. The satellite and its nuclear reactor reentered Earths atmosphere over North-West Canada and spread debris over a 300-mile-long swath of land. Operation Morning Light was a joint US-Canadian effort to clean up the wreckage which included over 100 pieces of radioactive debris, some of which were radioactive enough that they could have caused sickness within a few hours of exposure.
Although most of the orbits of the millimeter to 1-cm-sized droplets have decayed, most droplets larger than 1 cm will remain on orbit for several decades. Despite their small size, the velocity at which the debris travels means that they carry enough energy to cause serious damage to on-orbit assets. Their small size is part of what makes them dangerous. Objects between 1-10 cm are successfully detected by static SSA radar sensors. Current optical tracking systems typically cannot track particles of this size in LEO due to their faintness and fast rate of motion.
We performed observations of five of these coolant blobs on 14 Oct. 2022 to test the capabilities of our systems on these small, fast-moving LEO debris. Based on documented radar cross sections, these objects have diameters on the order of a few inches and the observed visual magnitude ranged from ~13 – 16. We present the results of our photometry of these objects and spectroscopy of one object, demonstrating our ability to track and characterize small, high-albedo targets with a small aperture telescope.
Date of Conference: September 19-22, 2023
Track: Space Debris