Reuven Ramaty High Energy Solar Spectroscopic Imager

The X-ray telescope orbits the earth since 2002, delivering data until 2018.
RHESSI is the precursor of the STIX X-ray telescope.


> Data management: data browser, host of the RHESSI European Data Centre

> Image processing: compressed sensing algorithm

> Science: analysis of solar flares, particle acceleration

Project lead at I4DS: André Csillaghy

Partners: international consortium led by University of California at Berkeley

Start: 2002
Decommissioned: 2018
Science exploitation: ongoing

Keywords: space sciences, solar physics, X-ray imaging, data archiving


2023: Rhessi re-entered the atmosphere in the night of April 19-20 over the Sahara desert.

2019: After more than 16 years of successful operations since its launch in 2002, RHESSI has been decommissioned on October 1, 2018. The on-board receiver has been slowly degrading since 2017, and commanding from the ground has become increasingly difficult. We have not been able to send commands successfully since mid-July 2018. Find more information on the RHESSI mission website.


RHESSI is a NASA-satellite designed and built with Swiss participation (Paul Schärer Institute and ETH) with an X-ray solar telescope on board observing solar flares. It delivered data from 2002 – 2018, much longer than the initially planned two years. Scientists and engineers at the Institute for Data Science have been involved in all aspects of the mission even before the institute existed. Since 2013, Säm Krucker is the principal investigator of the RHESSI mission through his affiliation with University of California at Berkeley.


Dr. Marina Battaglia

Solar Physicist

Laszlo Etesi

Computer Scientist

Dr. Matej Kuhar

Solar Physicist

Roman Bolzern

Computer Scientist

until 2018

Simon Felix

Computer Scientist

Dr. Diego Casadei

Solar Physicist

until 2017

Dr. Lucia Kleint

Solar Physicist

Prof. Dr. André Csillaghy

Head I4DS

Prof. Dr. Säm Krucker

Principal Investigator



Artist rendition of RHESSI spacecraft. Credits: NASA

The spacecraft tube (image above) and the grid trays (image below) were produced by PSI in Switzerland. Credit: SSL Berkeley

Nine grids were mounted on a grid tray at each end of the telescope tube. The grid pairs modulate the transmission of solar flare x-ray and gamma-ray emissions through to the detectors as the spacecraft spins around the axis of the telescope tube. The modulated count rates in the nine detectors are used in computers on the ground to construct images of solar flares in different energy bands. Credit: SSL Berkeley

The spectrometer contains nine germaniumdetectors that are positioned behind the nine gridpairs on the telescope. Credit: SSL Berkeley

Reconstruction of a solar flare image from X-ray raw data. Column left: back projection, column right:  image processed by the compressed sensing algorithm developed at I4DS. Credit: Simon Felix, Roman Bolzern
RHESSI and Solar Dynamis Observatory observed a solar flare at the solar limb. RHESSI’s observations are in blue (gamma-ray) and red (X-ray). This flare has been studied in detail at I4DS. Credit: Marina Battaglia
A multi-mission view of a solar flare: SDO, IRIS, RHESSI. During the height of the flare, we see gamma-ray emission (violet) observed by RHESSI. Credit: NASA’s Scientific Visualization Studio
The Solar Dynamics Observatory and RHESSI observed magnetic reconnection during a solar flare. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio