June 20, 2001
The High Energy Solar Spectroscopic Imager (HESSI) spacecraft is due to be launched today on a Pegasus XL rocket - it will be launched from a L1011 aircraft over Kennedy Space Center in Florida. The above is an artist's conception of HESSI in orbit. HESSI's orbit will place it approximately 600 km above the Earth. While the primary mission objective of HESSI is to explore the basic physics of particle acceleration and energy release in solar flares, there are a number of other solar science objectives and non solar objectives as well, such as obtaining images and spectra of nebulae.
HESSI 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. These observations need to be made from space since the physical properties of x-rays and gamma rays limit what can be observed using surface-based sensors and telescopes.
UPDATE: The HESSI launch has been postponed to allow NASA to fully investigate a Pegasus failure on June 2 at Vandenberg Air Force Base in California.