In April 2016, RHESSI successfully completed its fifth detector 'anneal' after over 14 years of successful operation. From February 23, 02:19 UTC to April 29, 03:48 UTC, the detectors were heated up to repair accumulated radiation damage and then cooled back down to operating temperatures. During that time, no science observations were made.

RHESSI is again obtaining science data, but with a reduced number of operating detectors in order to maintain optimal detector temperatures. See the RHESSI has resumed operations Nugget and the RHESSI 5th Anneal Nugget for more information, and the list of all anneal dates.




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