A 1992 picture (left) of the two million-degree solar atmosphere glowing in soft X-rays, taken with the Soft X-Ray Telescope on the joint Japan-U.S. Yohkoh mission. At right is a blow-up of a flare as seen with Yohkoh in soft and hard X-rays. (hi-res version) NASA photo

Berkeley — A satellite dedicated solely to the study of solar flares and designed, built and operated by an international consortium led by scientists at the University of California, Berkeley, is set for launch on Thursday, June 7, by the National Aeronautics and Space Administration (NASA).

The High Energy Solar Spectroscopic Imager, or HESSI, will embark on a two- to three-year mission to look at high-energy X-ray and gamma ray emissions from solar flares — enormous explosions in the solar atmosphere. Though various satellites have made X-ray and gamma ray observations of flares, HESSI will be the first to snap pictures in gamma rays and the highest energy X-rays.

"With intense flares, we can take X-ray images with very high resolution, very fast, and create movies of flares lasting from 10 seconds to tens of minutes," said Robert P. Lin, professor of physics in the College of Letters & Science at UC Berkeley and principal investigator for the mission. Lin also is director of UC Berkeley's Space Sciences Laboratory.

Using these images, plus X-ray and gamma-ray spectra with unprecedented energy resolution, the scientists hope to discover what triggers flares and how energy stored in the solar magnetic fields is suddenly released to accelerate particles to very high speeds and to heat the gases in the solar atmosphere to tens of millions of degrees.

"From these hard X-ray and gamma-ray measurements, we can reconstruct the energy distribution of the particles and trace back to where everything was accelerated," Lin said.

The mission begins near the peak of the sun's 11-year cycle of activity, providing an unprecedented opportunity for study of these explosive events. What scientists learn will give insight into the processes that accelerate other particles whizzing at nearly light-speed through the universe.

HESSI is the sixth Small Explorer (SMEX) spacecraft scheduled for launch under NASAÕs Explorers Program. Total cost for the mission, including the spacecraft, launch vehicle and mission operations, is about $ 85 million.

Solar flares, along with the often associated explosions called coronal mass ejections, are the solar events that most affect "space weather." The intense energy associated with these events — up to the equivalent of a billion megatons of TNT — and the energetic particles they throw out impact the Earth's magnetic field, compressing it and interfering with radio communications on Earth. Astronauts and cosmonauts aboard the International Space Station or the Space Shuttle also can receive dangerous doses of radiation from the high-energy particles.

HESSI project manager Peter Harvey. Lauren Garcia photo

"Coronal mass ejections sometimes have flares associated with them and sometimes don't," said Brian Dennis, HESSI mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "We don't understand why this should be or what the relationship is between these two types of events."

The 645-pound (293 kilograms) HESSI satellite will be launched atop a Pegasus XL rocket dropped from the belly of an L-1011 aircraft flying out of Cape Canaveral Air Force Station, Florida. After the plane reaches an altitude of about 40,000 feet over the Atlantic Ocean, the rocket will be released to free-fall in a horizontal position for about five seconds before igniting its first stage motor. The three-stage rocket will place the spacecraft into a circular orbit about 373 miles (600 kilometers) above the Earth, inclined at 38 degrees to the equator.

HESSI project manager Peter Harvey details satellite launch and orbital insertion.
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