Pegasus Launches HESSI

A Pegasus XL successfully launched NASA’s High Energy Solar Spectroscopic Imager (HESSI) at 2058:17 UTC (12:58 p.m. PST) on February 5. The US$85 million mission was air-launched into a circular orbit 600 km (324 nmi), inclined at 38 degrees. The launch occurred flown 75 miles off the coast of Palm Bay, Florida, with the release from a modified Lockheed L-1011 jetliner. The initial look at the orbit data shows a perigee of 586.85 km, an apogee of 600.24 km,  and inclination of 38.023 degrees.

For at least two years, HESSI will use an imaging spectrometer, to construct pictures of solar flares in x rays and gamma rays. HESSI's solar flare observations will try to identify what kinds of particles are accelerated as well as where and when they are accelerated, to assist in developing an understanding of what activates a solar flare and how it releases energy. The pictures HESSI takes will create the first high-fidelity color movies of solar flares from these high-energy emissions.

The 293 kg (645 lbm) spacecraft was designed by engineers at the University of California, Berkeley. The satellite was built by Spectrum Astro. Robert Lin is the project's principal scientist at the University of California, Berkeley. Mission operations will be managed by the university. HESSI is the sixth Small Explorer spacecraft from NASA's Explorers program. The mission was supposed to begin a year and a half ago. If HESSI had launched in mid-2000, as planned, the satellite would have taken observations during the peak of the 11-year solar cycle and probably would have measured close to 2,000 solar flares. Managers have asked for a US$2 million, six-month extension to the two-year mission. Their goal is to measure about 1,000 solar flares. The spacecraft was delayed 19 months due to damage incurred during a vibration test, followed by several problems with rockets similar to the Pegasus. All of the delays cost about US$13 million.

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