Astronomers have detected an ultra-bright burst of radio waves from Relay 2, a NASA communications satellite launched in 1964 and silent since 1967. OzGrav Chief Investigator Adam Deller, Professor of Astrophysics at Swinburne University of Technology, was one of the principal authors of the discovery recently accepted for publication in the Astrophysical Journal Letters.

“This was a chance discovery made when looking for Fast Radio Bursts, which are millisecond-duration radio pulses that originate in distant galaxies. Despite FRBs being discovered almost 20 years ago, we still don’t know what can generate such short and bright radio emission, which is what is driving us to build better and better machines for finding them,” said Prof Deller. 

The pulse, captured on 13 June 2024 by the CRACO upgrade on CSIRO’s ASKAP radio telescope on Wajarri Yamaji Country in Western Australia, lasted under 30 nanoseconds, more than a million times shorter than the blink of an eye. However, the fact that it was so much shorter than a typical FRB wasn’t immediately apparent. 

“FRBs are intrinsically very brief flashes, but the radio pulse is spread out in frequency by the time they get to us on Earth. Longer wavelengths travel more slowly when passing through the ionised plasma in interstellar space, and so this millisecond pulse gets spread out by the time it reaches us, with the lower frequencies arriving hundreds of milliseconds to seconds later,” explained Prof Deller. “We can only correct for this spreading out roughly when doing the high-speed search for FRBs, but once we find a candidate, we can go back and find the absolute best correction, along with the true duration of the signal.” 

Because the Relay 2 signal showed virtually no dispersion in frequency, researchers immediately suspected a nearby origin rather than a distant galaxy. ASKAP imaging confirmed the burst came from roughly 4,500 km away—the satellite’s position at the moment of detection. 

The team’s pre-print, A nanosecond-duration radio pulse originating from the defunct Relay 2 satellite, outlines two likely causes: an electrostatic discharge (ESD) triggered by charge build-up on the spacecraft, or a fleeting plasma cloud created by a micrometeoroid impact. Either mechanism poses a recognised threat to operational satellites. 

“We were lucky to see it. It is certainly possible that there are many more such bursts happening from this or other satellites. However, in the detailed search that we can do with our ASKAP data, we wouldn’t mistake these as actual FRBs—the lack of spreading out of the signal in frequency is a dead giveaway,” said Prof Deller. 

Beyond protecting spacecraft electronics, studying nanosecond-scale ‘sparks’ can also help astronomers filter out false positives when hunting for genuine cosmic FRBs.  

“It was so totally unexpected to see such a short and bright radio pulse originating from a non-operational satellite – we’re both excited to see if this can be of use for identifying hazards for operational satellites, and hopeful that we can use what we learned to further improve the robustness of our FRB searches,” added Prof Deller. 

Collaboration 

The lead author of the paper is Dr Clancy James (Curtin University node, International Centre for Radio Astronomy Research), while other OzGrav contributors include Chief Investigator Prof. Ryan Shannon.

This work leverages the Commensal Real-time ASKAP Fast Transients (CRAFT) survey’s ability to produce rapid, high-resolution images—technology designed for deep-space FRB searches but now proving invaluable closer to home. 

ASKAP is part of the Australia Telescope National Facility and operates with generous support from the Wajarri Yamaji People, the Australian Government and the Pawsey Supercomputing Research Centre. 

Paper: James C. W. et al. (2025) A nanosecond-duration radio pulse originating from the defunct Relay 2 satellite (arXiv:2506.11462).  

Information reproduced in part courtesy of Charlene D’Monte, ICRAR.’Monte, ICRAR.