Why RHESSI?

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.   Real Video - Hi or Low Bandwidth 
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• Why is this mission happening, and why was it considered important enough for NASA to fund it?  
  RHESSI may help to answer one of the most fundamental questions about how the sun works:  How do solar flares release such large quantities of energy in such a short span of time? (A single flare can be as powerful as ten million volcanic explosions!).  For an excellent scientific overview and a complete rationale for the mission, read the RHESSI  Online Brochure  (http://hesperia.gsfc.nasa.gov/hessi/brochure.htm)

  
  

• Why must RHESSI make observations of the Sun from space?  Can't the same data be collected from Earth?
  A very large part of the expense of the RHESSI mission is allocated to its launch into space. This is necessary because x-rays and gamma rays do not penetrate the Earth's atmosphere. RHESSI's observations must be made from space. In fact, before the advent of space-based observatories, there were only limited astronomical observations done in the high energy portion of the electromagnetic spectrum. To understand why, see Atmospheric Transmission, or study this diagram (scroll down to the bottom of the page).

  
  

• What is special about the RHESSI mission?
  The centerpiece of the RHESSI mission is the imager, which uses a new technology to capture images and spectra of high energy solar flares.  The imager uses a method which is quite unlike the cameras and telescopes that are familiar to us; it has no lenses!  Learn more about the RHESSI Imager.