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/