RHESSI celebrated its 16th anniversary on February 5, 2018. It continues to be the only active observatory that can provide imaging spectroscopy of the energetic electrons that carry such a predominant part of the energy released in a flare.

RHESSI has now covered more than a complete 11-year solar cycle and is continuing to make observations as activity decreases to solar minimum (expected in ~2019). During that time it has recorded over 114,000 X-ray events, 42 with gamma-ray emission above 300 keV, and 27 with gamma-ray line emission.

The RHESSI spacecraft and instrument continue to operate well. The slowly rising detector temperature resulting from decreasing cryocooler efficiency is of concern, and only two of the nine detectors are turned on during periods of low solar activity to minimize the temperature increase. When there is enhanced activity and during short observing campaigns with other space- and ground-based observatories, we will turn on additional detectors for optimum coverage. In this way, we expect to be able to maintain RHESSI's unique hard X-ray imaging spectroscopy capability for the foreseeable future.



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