A small NASA explorer satellite to investigate the basic physics of particle acceleration and the explosive energy released in solar flares. It was launched on 5 February 2002 with Reuven Ramaty's name added to the mission; he was a founding member of the HESSI team and died in 2001. Its objectives include discovering the location, frequency, and evolution of impulsive energy in the Sun's corona; studying the acceleration of electrons, protons, and heavier ions in flares; and investigating the heating of plasma to tens of millions of degrees. The sixth Small Explorer (SMEX) mission, it is expected to have a life of up to three years.
Hard X-ray (high-energy X-rays) and gamma-ray imaging will be used during the mission. Besides the Sun, RHESSI will also study the Crab nebula and other areas of the sky.
http://hesperia.gsfc.nasa.gov/hessi/ Full details of the workings, scientific goals, and status of the High-Energy Solar Spectroscopic Imager (HESSI). The site's articles are clearly laid out and easy to read. There are animations, an image gallery, and even a downloadable paper model of the HESSI spacecraft.
Subjects: Astronomy and Astrophysics.