Science and Exploration

Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) Spacecraft To Reenter

By Keith Cowing
Press Release
April 17, 2023
Filed under
Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) Spacecraft To Reenter
Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

NASA’s retired Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft is expected to reenter Earth’s atmosphere in April, almost 21 years after launch. From 2002 to its decommissioning in 2018, RHESSI observed solar flares and coronal mass ejections from its low-Earth orbit, helping scientists understand the underlying physics of how such powerful bursts of energy are created.

As of Monday, April 17, the Department of Defense predicted the 660-pound spacecraft will reenter the atmosphere at approximately 9:30 p.m. EDT on Wednesday, April 19 with an uncertainty of +/- 16 hours. NASA and the Defense Department will continue to monitor reentry and update predictions.

NASA expects most of the spacecraft to burn up as it travels through the atmosphere, but some components are expected to survive reentry. The risk of harm coming to anyone on Earth is low – approximately 1 in 2,467.

The spacecraft launched aboard an Orbital Sciences Corporation Pegasus XL rocket with a mission to image the high-energy electrons that carry a large part of the energy released in solar flares. It achieved this with its sole instrument, an imaging spectrometer, which recorded X-rays and gamma rays from the Sun. Before RHESSI, no gamma-ray images nor high-energy X-ray images had been taken of solar flares.

Data from RHESSI provided vital clues about solar flares and their associated coronal mass ejections. These events release the energy equivalent of billions of megatons of TNT into the solar atmosphere within minutes and can have effects on Earth, including the disruption of electrical systems. Understanding them has proven challenging.

During its mission tenure, RHESSI recorded more than 100,000 X-ray events, allowing scientists to study the energetic particles in solar flares. The imager helped researchers determine the particles’ frequency, location, and movement, which helped them understand where the particles were being accelerated.

Over the years, RHESSI documented the huge range in solar flare size, from tiny nanoflares to massive superflares tens of thousands of times bigger and more explosive. RHESSI even made discoveries not related to flares, such as improving measurements of the Sun’s shape, and showing that terrestrial gamma-ray flashes – bursts of gamma rays emitted from high in Earth’s atmosphere over lightning storms – are more common than previously thought.

After 16 years of operations, NASA decommissioned RHESSI due to communications difficulties with the spacecraft. RHESSI was a NASA Small Explorers mission, managed and operated by the agency’s Goddard Space Flight Center in Greenbelt, Maryland.

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.