After 21 years, a defunct NASA spacecraft returns to Earth.

NASA's Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft is expected to reenter Earth's atmosphere Wednesday at approximately 9:30 p.m. ET. The 660-pound spacecraft is expected to burn up as it travels through the atmosphere, but some components are expected to survive. The risk of harm coming to anyone on Earth as a result of RHESSI's return is low - approximately 1 in 2,467. The spacecraft was equipped with an imaging spectrometer that recorded the sun's X-rays and gamma rays, and data from the spacecraft provided vital clues about the phenomena and their associated coronal mass ejections.

RHESSI documented the huge range in solar flare size, from tiny nanoflares to massive superflares that were tens of thousands of times bigger and more explosive. NASA and the Department of Defense will monitor the satellite's reentry into Earth's atmosphere.