In June 2015, the NASA Senior Review Panel affirmed RHESSI's value as a participant in NASA's Heliophysics System Observatory (HSO) and approved it for extended operations. The RHESSI extended mission proposal received evaluations of "compelling" for “Overall Scientific Merit” and “Value to the HSO”. (See the full proposal and report.)




The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a NASA Small Explorer Mission, launched on February 5, 2002.

RHESSI's primary mission is to explore the basic physics of particle acceleration and explosive energy release in solar flares.  This is achieved through imaging spectroscopy in X-rays and gamma-rays with fine angular and energy resolution to reveal the locations and spectra of the accelerated electrons and ions and of the hottest plasma.

Solar flares and their associated coronal mass ejections are of great scientific interest since they are so little understood. They present severe challenges to explain how the energy equivalent of billions of megatons of TNT is released in the solar atmosphere on time scales of minutes, and how so many electrons, protons and heavier ions are accelerated to such high energies. These super-energetic solar eruptive events are the most extreme drivers of space weather and present significant dangers in space and on Earth.



What is a solar flare?
How does RHESSI work?
What are the scientific objectives?
How does RHESSI make images?
RHESSI Spectroscopy