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HESSI
Mission Questions & Answers
What will HESSI study?
The
High Energy Solar Spectroscopic Imager (HESSI) will study the most energetic explosions
in our solar system – solar flares. The explosions fire solar gas, heated to tens
of millions of degrees, causing it to sizzle with high-energy radiation (X-rays
and gamma rays). HESSI will focus on this radiation, providing researchers with
insight into how this process happens. Why
is it important to study solar flares? Studying
solar flares is vital to protecting our resources both in space and on Earth.
The intense energy released by flares can result in damage to a spacecraft’s electrical
system, affect ground-based communications, as well as astronaut activities. What
firsts will HESSI accomplish? HESSI
is the first solar science mission to produce high-resolution spectrographic X-ray
and gamma-ray pictures of flares. This will enable scientists to see, for the
first time, where the high-energy events in flares take place. HESSI
also has the finest angular and spectral resolution of any hard X-ray or gamma-ray
instrument ever flown in space, so it will allow researchers to see the development
of the high-energy reactions within flares. [NOTE:
Angular resolution is the ability to see fine detail in an image, and spectral
resolution is the ability to distinguish the component "colors," or
wavelengths, of light.]
How
does HESSI fit into NASA's solar science objectives? HESSI
ties into the Office of Space Science Sun-Earth Connection (SEC) theme, which
focuses on the physical processes that link the Sun and the Earth.
What
instruments will HESSI use during its mission? HESSI
carries one instrument – an imaging spectrometer – which produces pictures of
flares using a method unlike any conventional telescope or camera. This spectrometer
has no lenses and no mirrors to focus the light and form an image. Instead,
detectors aboard HESSI count the number of X-ray and gamma-ray photons passing
through pairs of grids and measures their energies with exceptional precision.
Astronomers will then use the variable rates of photons detected as the spacecraft
rotates to make high-resolution pictures of a flare, showing their "color"
or energy.
How
will the HESSI data be distributed? Data
obtained throughout the HESSI mission will be on the Internet – available not
only to scientists worldwide, but also to anyone who has computer access. Within
a few short hours of receiving data on the ground, people around the world will
be able to view X-ray images and spectra of flares that occurred during the day-time
portion of HESSI’s orbit.
When
will the spacecraft be launched and from where?
The
HESSI spacecraft is scheduled to take off June 7, 2001 at 9 a.m. EDT from Cape
Canaveral Air Force Station, FL. The Stargazer L-1011 aircraft will take off carrying
HESSI inside a Pegasus rocket. The Pegasus drop is scheduled for 10:05 a.m. EDT. How
long is the HESSI mission? The
planned mission lifetime is two to three years. How
much does the mission cost? Costs
for the development of the HESSI spacecraft, instrument payload, ground station,
and launch vehicle is about $75 million. An additional $10 million is reserved
for ground operations, mission operations, and data analysis, for a total mission
cost of $85 million.
Who
sponsors and manages HESSI? NASA's
Goddard Space Flight Center in Greenbelt, MD manages the overall mission for NASA’s
Office of Space Flight in Washington, DC. The
Principal Investigator for HESSI is Dr. Robert Lin of the University of California,
Berkeley (UC Berkeley). Lin is responsible for most aspects of the mission, including
the instrument and spacecraft, integration and testing, and operations and data
analysis after launch.
Who
built the spacecraft and science instrument? The
University of California, Berkeley, in collaboration with Goddard and the Paul
Scherrer Institut, Switzerland, designed, constructed, integrated, and tested
the payload and will perform data analysis. Spectrum Astro of Phoenix built the
spacecraft for UC Berkeley. A
complete list of names and affiliations are included at: http://hessi.ssl.berkeley.edu/
Why
was the HESSI launch delayed? The
spacecraft suffered a vibration mishap at NASA’s Jet Propulsion Laboratory in
March 2000. Significant damage was incurred to the spacecraft and solar panels.
Recovering from this incident delayed the launch to March 2001. Issues
surrounding the Pegasus rocket further delayed the launch until June 2001.
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