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NASA’s retired Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft is expected to re-enter Earth’s atmosphere in April, nearly 21 years after launch. From 2002 until the mission’s shutdown in 2018, RHESSI observed solar flares and coronal mass ejections (CME) from its low Earth orbit, helping scientists understand how such powerful bursts of energy form.
As of Monday, April 17, the U.S. Department of Defense predicted that the 700-pound spacecraft will enter the atmosphere on Wednesday, April 19 at approximately 9:30 p.m. EDT, with an uncertainty of +/- 16 hours. NASA and the Department of Defense will continue to monitor the return and update forecasts. NASA expects most of the spacecraft to burn up as it travels through the atmosphere, but some parts are expected to survive reentry. The risk of something happening to someone on Earth is small, about 1 in 2,467.
The spacecraft was launched aboard an Orbital Sciences Corporation Pegasus XL rocket whose mission is to image the high-energy electrons that provide much of the energy released by solar flares. RHESSI achieved this with its only instrument, an imaging spectrometer, which recorded X-rays and gamma rays from the sun. Before RHESSI, no gamma-ray or high-energy X-ray images had been made of solar flares. The data from RHESSI provided vital clues about solar flares and associated coronal mass ejections (CME). These events release the energy equivalent of billions of megatons of TNT into the solar atmosphere within minutes and can have impacts on Earth, including the disruption of electrical systems. Understanding it has proved challenging.
During its mission, RHESSI took more than 100,000 x-rays, which allowed scientists to study the energetic particles in solar flares. The imager helped researchers determine the frequency, location and motion of the particles, helping them understand where the particles were being accelerated. Over the years, RHESSI has documented the vast array of solar flares, from tiny nanoflares to massive superflares tens of thousands of times larger and more explosive. RHESSI has even made discoveries unrelated to solar flares, such as better measurements of the sun’s shape, and has shown that terrestrial gamma-ray bursts — bursts of gamma rays high in Earth’s atmosphere during thunderstorms — are more common than previously thought.
After 16 years, NASA has decommissioned RHESSI due to communication problems with the spacecraft. RHESSI was a NASA Small Explorers mission managed and operated by the Goddard Space Flight Center in Greenbelt, Maryland.
Bron: NASA
