My Question: What is the nature of the "experimental passive radar reflector developed by the U.S. Navy’s Space and Naval Warfare Systems Command"? How does it work, and why does it work for only a narrow range of radar frequencies?
Related question: Are SpaceBEEs actually hard to track?
The IEEE News article FCC Accuses Stealthy Startup of Launching Rogue Satellites focuses mostly on the intrigue addressed in the question What checks are supposed to be carried out to prevent illegal satellite launches? but I'd like to focus on the technical issues raised.
The SpaceBee-1, 2, 3, and 4 spacecraft look like this:
above: From IEEE "Images: Top: ISRO; Bottom: Swarm Technologies"
These are 1/4 U cubesats, only about 2.8 cm tall.
According to the IEEE article:
he FCC is responsible for regulating commercial satellites, including minimizing the chance of accidents in space. It feared that the four SpaceBees now orbiting the Earth would pose an unacceptable collision risk for other spacecraft.
The article goes on to say:
“As an object gets below 1U in size, it gets difficult to track, which means it’s harder to predict if there’s going to be a conjunction with another satellite,” says Marcus Holzinger, an aerospace professor at the Georgia Institute of Technology and expert on orbital safety. “Anything that size impacting at orbital velocities can be catastrophic.”
Swarm Technologies had realized that the small size of its BEEs might be a problem. It installed a GPS device in each satellite that would broadcast its position when requested. It also covered each of the satellite’s four smallest faces with an experimental passive radar reflector developed by the U.S. Navy’s Space and Naval Warfare Systems Command. According to Swarm’s FCC application, this would increase the BEE’s radar profile by a factor of 10.
But the FCC was not buying it. After correspondence back and forth through the summer, the FCC sent Swarm a letter in early December. In it, Anthony Serafini, chief of the FCC’s Experimental Licensing Branch, noted that the radar reflector only operated in a certain frequency band, corresponding to “a small portion” of America’s ground-based Space Surveillance Network. He also worried that GPS data would only be available while the satellite was functional.
Holzinger shares the agency’s concerns. “If there’s a software glitch, the satellite is going to become a passive piece of debris,” he says. “And while the reflector is certainly more robust, it may not amplify radar from a sensor using [a different] frequency band.” (Emphasis added).
While still waiting for an answer, the question What would be a “big picture” understanding of how the orbits of Earth satellites are monitored? includes a brief discussion of both radar and optical tracking, and the answer to Are 1U cubesats sufficiently detectable to get at least minimally usefully predictive public TLEs, updated regularly? addresses the already present challenges with fully-1U cubesats.
I would have thought that the roughly 1 meter long antenna would have contributed significantly to the spacecrafts' radar cross section already, but this does not seem to have been enough to assuage regulatory concern.
Ideally looking for a(n at least somewhat) supported answer if possible, not just a "well it could be a..." Thanks!