Satellite Lost in Space for 25 Years Reappears

S73-7 may have disappeared into a radar blind spot
By Arden Dier,  Newser Staff
Posted May 2, 2024 11:26 AM CDT
Updated May 5, 2024 11:05 AM CDT
Satellite Lost in Space for 25 Years Reappears
A depiction of satellites in orbit around Earth.   (Getty Images/yucelyilmaz)

A small, experimental satellite launched in failure in 1974 and lost to ground-based sensors for a quarter century has suddenly reappeared. On April 10, 1974, the large reconnaissance satellite KH-9 Hexagon ejected a much smaller, 26-inch-wide satellite, the Infra-Red Calibration Balloon or S73-7, which was supposed to inflate a balloon in low Earth orbit and "serve as a calibration target for remote sensing equipment," Gizmodo reports. But its deployment failed. Radars tracked the satellite for a while in the 1970s before losing it. The satellite reappeared in the 1990s but was lost yet again.

Except for what Interesting Engineering reports was a brief appearance around 2002, the satellite has been unaccounted for ever since. How does one lose a satellite? It's relatively easy, considering the 27,000 objects in orbit around our planet, ranging from dead satellites to used rocket boosters. A global network of sensors identify a satellite by looking at its orbit and seeing if it matches the expected movements of a particular one. But "if an object in the crowded region of space has not been observed for a while, matching its orbit can be challenging," per Interesting Engineering.

In the case of S73-7, it could be "the thing that they're tracking is a dispenser or a piece of the balloon that didn't deploy right, so it's not metal and doesn't show up well on radar," astrophysicist Jonathan McDowell tells Gizmodo. Plus, there are no radars to monitor objects directly above the equator, so "if you hug the equator, you can hide from the tracking." It was McDowell who announced Monday the satellite had reappeared on April 25. He credited an analyst with the 18th Space Defense Squadron for making the identification. Data suggests the satellite has dropped a little in altitude over its 50 years in space, from a height of 500 miles to about 491 miles, per Interesting Engineering. No word on its space adventures. (More space stories.)

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