Dolores Beasley
Headquarters, Washington, DC              June 1, 2001
(Phone: 202/358-1753 )

Susan Hendrix
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-7745)

RELEASE: 01-103

HESSI SPACECRAFT TO STEAL EXPLOSIVE SOLAR 
SECRETS WITH X-RAY VISION

     A new NASA spacecraft will soon be studying gigantic 
explosions in the atmosphere of the Sun with a unique kind of 
X-ray vision, producing the first high-fidelity color movies 
of solar flares in their highest energy emissions.
 
"The Sun has a trick that nobody totally understands," said 
Dr. Richard Fisher, Chief of the Laboratory for Astronomy and 
Solar Physics at NASA's Goddard Space Flight Center, 
Greenbelt, MD. "It can take magnetic energy and turn it into 
a stunningly powerful blast of heat, light and radiation. 
NASA's High Energy Solar Spectroscopic Imager (HESSI) will 
finally unlock the secrets of the initiation and onset of 
flares."
 
HESSI is scheduled to take off June 7 at 9 a.m. EDT from Cape 
Canaveral Air Force Station, FL aboard a Stargazer L-1011 
aircraft. The Stargazer cradles HESSI under its belly, stored 
inside A Pegasus rocket. At 10:05 a.m. EDT, the aircraft 
should release the Pegasus and deliver the spacecraft to its 
circular orbit 373 miles above the Earth, inclined at 38 
degrees to the equator.

Within the gigantic flare explosions, magnetic fields twist, 
snap and recombine, blasting particles to almost the speed of 
light, firing solar gas to tens of millions of degrees. This 
action causes the solar atmosphere to sizzle with high-energy 
X-rays and gamma rays  and accelerate proton and electron 
particles into the solar system. Radiation and particles from 
solar flares sometimes affect orbiting spacecraft, 
interfering with communications and astronaut activities.

In order to understand what triggers a solar flare and how it 
explosively releases energy, scientists must identify the 
different kinds of particles being accelerated, locate the 
regions where the acceleration occurs and determine when the 
particles get accelerated. The most direct tracer of these 
accelerated particles is the X-ray and gamma ray radiation 
that they produce as they travel through the solar 
atmosphere.  

To understand the physical processes and conditions inside 
flares, HESSI will create images in gamma rays and the 
highest energy X-rays emitted by the flare. These images will 
be the first to simultaneously measure the location and 
energy content of radiation from the flare material. This 
kind of data is expected to improve predictability of flare 
occurrence at the Sun and the subsequent consequences we 
experience here on Earth. Using the Sun as a laboratory, 
where such high-energy events take place, will provide 
scientists insight into interpreting similar high-energy 
activity that originate elsewhere in the universe.

Because HESSI has the finest angular and spectral resolution 
of any hard X-ray or gamma ray instrument ever flown in 
space, it will enable researchers for the first time to look 
at the development of high-energy reactions in flares. 
Powerful X-rays and gamma rays penetrate all materials, to 
some extent, and cannot be easily focused, so researchers are 
using another technique to form images. HESSI's sole 
instrument - an imaging spectrometer - will construct a flare 
image from patterns of light and shadows produced by high-
energy radiation that passes through the telescope's grids 
while the spacecraft rotates. Using this new method, HESSI is 
expected to gather data on thousands of flares during its 
two-to-three-year mission.  

Working together with other solar spacecraft - Yohkoh, the 
Solar and Heliospheric Observatory (SOHO), Geostationary 
Operational Environmental Satellites (GOES) and the 
Transitional Regional and Coronal Explorer (TRACE) for flare 
radiation, and Wind, the Advanced Composition Explorer (ACE), 
Ulysses, and Voyager for particle detection ­ HESSI will 
provide vital insight into the impulsive energy release and 
particle acceleration processes at the Sun.   

The HESSI mission costs about $85 million, which includes the 
spacecraft, launch vehicle, mission operations and data 
analysis. NASA's Office of Space Science, Headquarters, 
Washington, DC, provided funding for HESSI, and the Explorers 
Program Office at Goddard provides management and technical 
oversight for the mission.  

For more information on the Internet about the spacecraft and 
science mission, go to: 
           http://hesperia.gsfc.nasa.gov/hessi
              http://hessi.ssl.berkeley.edu/

                            -end-