Lost Satellite Discovered
The S73-7 satellite, measuring just 26 inches wide and orbiting at a high altitude of 500 miles, has been missing from radar since the 1990s.
Historic Launch and Deployment
Launched into space on April 10, 1974, as part of the United States Air Force's Space Test Program, the Infra-Red Calibration Balloon satellite (S73-7) was part of the Hexagon System. S73-7 was deployed from a larger satellite in space.
Unexpected Discovery
Originally intended to inflate and become a calibration target for remote sensing devices, the mission failed, leaving the satellite adrift as space junk until its recent rediscovery last month, according to a report by Live Science on May 6. Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, studied archival data and found that S73-7 had actually been missing from radar twice before - once in the 1970s and again in the 1990s.
Challenges in Tracking Space Debris
"The issue here is that S73-7 either has a very small radar cross-section, or what's being tracked is a non-deploying piece of the satellite that is non-metallic and not showing up well on radar," McDowell explained.
Knowing the location and identity of every object in orbit is no easy task, with over 20,000 currently cataloged. Experts track space debris using ground-based radar and optical sensors, but accurately identifying each object remains a challenge. Sensors may detect an object in orbit, but it then has to be matched to a satellite with a known flight path.
Recovering Lost Satellites
After launch, engineers have a good idea of where the satellite will go and the altitude it is expected to reach. Using this information, they can look back through the satellite's history and compare it to where it is now being observed. However, if there were any changes to the original flight plan or if the satellite went astray, engineers would have their work cut out for them in trying to relocate it.
Importance of Discovery
This is why the rediscovery of S73-7 is a triumph for those working to keep track of the tens of thousands of defunct satellites and other objects orbiting Earth. But as more satellites are launched into space, understanding exactly what is up there and the potential hazards it poses becomes increasingly challenging.
"If you miss one or two objects, it's not a huge risk," McDowell said. "But you want to do as good a job as you can."
Summary
The S73-7 satellite, missing for almost 30 years, has been rediscovered in orbit. Despite challenges in tracking space debris, experts continue to work tirelessly to monitor the growing number of objects surrounding Earth for potential risks to space missions and communications.