RHESSI is being funded by NASA's  Explorers Program (http://explorers.gsfc.nasa.gov/) under the category of  "Small Explorers."   These are relatively low cost missions, which have specific scientific objectives that are in line with a list of NASA space science priorities.

RHESSI Science
Principal Investigator Robert Lin explains sun science and RHESSI mission objectives.  Featuring satellite data and images of the Sun.
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