The 660-pound Reuven Ramaty High Energy Solar Spectroscopic Imager — or RHESSI — has been in space for over 20 years. It was deployed to observe solar flares and clouds of plasma expelled from the sun, and it remained in orbit after it was decommissioned in 2018.
The Department of Defense forecasts that RHESSI will reenter Earth’s atmosphere around 9:30 p.m. Eastern time on Wednesday, plus or minus 16 hours, though the location of its crash was still unclear.
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Before it was decommissioned, the satellite recorded more than 100,000 solar events, capturing some of the first images in high-energy X-rays and gamma rays of solar flares.
Its observations helped “scientists understand the underlying physics of how such powerful bursts of energy are created,” until it was retired because of communication problems, according to NASA. It has also helped improve measurements of the sun’s shape, among other discoveries.
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The retired satellite has been orbiting our planet alongside tens of thousands of pieces of space debris, including other nonoperational satellites.
The United States requires operators to “deorbit” satellites within five years of completing their missions.
Satellites can malfunction or run out of fuel, becoming space junk circling Earth or burning up in its atmosphere when they plunge, including to a remote part of the southern Pacific Ocean known as the “spacecraft cemetery.”
Some satellites have also been blown up in space in destructive antisatellite tests, which the United States has called for an end to.
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NASA estimates that there are roughly 500,000 objects between one and 10 centimeters in diameter orbiting Earth, and that there are more than 100 million particles larger than 1 millimeter.
The scale has prompted calls to pour more resources into cleaning up space as Earth’s lower orbit gets crowded by objects such as satellites, spent rocket stages and debris from missile strikes and collisions.