Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

RHESSI is a NASA Small Explorer Mission dedicated to the study of particle acceleration and explosive energy release in solar flares. The satellite was launched by a Pegasus rocket into a low earth orbit on February 5th, 2002. The single instrument on board is an imaging spectrometer operating in the hard X-ray and gamma ray regime. For the first time, simultaneous, high resolution imaging and spectroscopy of solar flares from 3 keV X-rays to 17 MeV gamma rays with high time and energy resolution can be obtained. The mission was designed and carried out by teams from the United States (UCB Berkeley and Goddard Space Flight Center) and Europe (Paul Scherrer Institut and ETH Zurich).

A solar flare is the rapid release of a large amount of energy stored in the solar atmosphere. In less than an hour, an amount of energy sufficient to cover the world's energy need for more than 10000 years is liberated. A significant fraction of this energy is contained in energetic electrons. These electrons generate hard X-ray radiation when interacting with the solar atmosphere. Thus, X-ray spectra and images yield crucial information on
particle acceleration processes in flares. Since energetic electrons are also creating radio radiation, radio observations such as those conducted by our group offer an important complementary approach to the problem of particle acceleration.

Germany is involved in the RHESSI mission in a threefold manner

  • the ground station Weillheim of the German Space Operation Center (GSOC), operated by the German Space Agency DLR, provides additional data downlink capacity for RHESSI whenever the need arises. This represents a service to NASA of 74000 € per year.
  • the radio data of the Observatory for Solar Radioastronomy in Tremsdorf are provided to the RHESSI data center.
  • the Group for Solar Radioastronomy at the AIP participates in the joint analysis of RHESSI- and radio data.

The practical relevance of this area of research is the study of solar activity and its influence on Earth and mankind. Termed space weather.