"We were aiming for the peak of solar activity in mid-2000, so we have been lucky solar activity has continued to stay high," said Robert Lin, a University of California Berkeley physics professor and principal investigator of NASA's High Energy Solar Spectroscopic Imager.
"We still think we will image around 1,000 solar flares, though whatever we see will be new and interesting," he said.
HESSI is designed to spend two to three years capturing pictures and data of high-energy X-ray and gamma-ray emissions during solar flares. The radiation emanates from electrons and ions whipping around during the flare. Scientists expect HESSI to capture image sequences showing -- for the first time -- explicit details about what is happening to the most energetic particles when flares erupt from the surface of the sun.
The spacecraft has one instrument -- an imaging spectrometer -- that will construct flare images from patterns of light and shadows produced by high-energy radiation as it passes through the instrument.
Scientists hope to learn more about conditions that trigger flares, where they form and how they generate such enormous power. In addition to gaining better understanding for forecasting potentially dangerous flares that affect Earth and Earth-orbiting satellites, the studies are an opportunity for scientists to learn how to interpret similar high-energy processes elsewhere in the universe.
"The sun is a perfect natural laboratory for exploring plasmas and high-energy processes," said John Brown, a HESSI investigator at the Department of Physics and Astronomy at Scotland's University of Glasgow.
"The universe is teeming with accelerated particles from explosive events such as supernovae," said Brown. "The sun gives us a nearby test bed to study these particles."
If HESSI weathers the space environment as well as it has shouldered its launch delays, scientists will be relieved. The satellite was severely damaged in March 2000 during a botched vibration test that delivered more than 10 times the forces HESSI was designed to withstand. The satellite's graphite hull was damaged and two of its four solar arrays cracked.
Additional delays last year were due to problems with the spacecraft's launch vehicle. The 645-pound craft is air-launched from a Pegasus booster that is carried into the skies by a specially modified L-1011 jet. The Pegasus, which carries the HESSI satellite, will be dropped from beneath the plane's wing at an altitude of about 39,000 feet. The rocket ignites to hurl HESSI into its targeted orbit 373 miles above Earth. Launch is scheduled to take place between 3:21 and 5:21 p.m. EST over the Atlantic Ocean.
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