About the RHESSI Mission

Principal Investigator:     Sam Krucker

University of Applied Sciences, Northwestern Switzerland (FHNW) and
Space Sciences Laboratory, University of California, Berkeley, CA

Mission Scientist:Albert Shih     Goddard Space Flight Center, NASA, Greenbelt, MD



RHESSI is the result of a collaboration between 

Primary Mission Objective:

Explore the basic physics of particle acceleration and energy release in solar flares

Science Objectives


  • Determine the frequency, location, and evolution of impulsive energy release in the corona
  • Study the acceleration of electrons, protons, and heavier ions in flares
  • Study the heating of plasma to tens of millions of degrees and determine its relationship to particle acceleration
  • Study the propagation and evolution of energetic particles in flares
  • Determine the relative abundances of accelerated and ambient ions in flares


  • Obtain images and spectra of the Crab Nebula with 2 arcsecond spatial resolution and ~1 keV spectral resolution
  • Detect and obtain high resolution spectra of gamma-ray bursts and cosmic and terrestrial transient sources over a large fraction of the sky
  • Search for cyclotron line features in gamma-ray bursts and cosmic transient sources
  • Obtain high resolution spectra and search for line features in steady X-ray and gamma-ray sources

Primary Observations:

Simultaneous, high resolution imaging and spectroscopy of solar flares from 3 keV X-rays to 17 MeV gamma rays with high time resolution

 Expected Numbers of Flares:

  • Tens of thousands of microflares
  • Over a thousand X-ray flares with crude imaging and spectra to >100 keV
  • Hundreds of flares with >1000 counts per second above 20 keV, allowing spatial changes to be followed on timescales of 0.1 seconds.
  • Tens of flares sufficiently intense to allow the finest possible imaging spectroscopy
  • Up to 100 flares with the detection of gamma-ray lines
  • Tens of flares with detailed gamma-ray line spectroscopy and the location and extent of the source determined to ~40 arcseconds

 RHESSI "Firsts":

  • Hard X-ray imaging spectroscopy
  • Hard X-ray and gamma-ray imaging above 100 keV
  • Imaging in narrow gamma-ray lines
  • Determination of solar gamma-ray line shapes
  • Combination of spatial, spectral, and time resolution that is commensurate with physically relevant scales for energy loss and transport of >10 keV electrons
  • Dynamic range to both detect microflares and make quantitative spectral measurements of the largest flares
  • High resolution X-ray and gamma-ray spectra of cosmic sources
  • Hard X-ray images of the Crab Nebula with 2 arcsecond resolution