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HESSI Solar Explorer Delayed In Wake Of Pegasus Failure

A new launch date for the HESSI mission, originally scheduled for June 7, will be announced once NASA and Orbital have completed the investigation.
Dulles - June 5, 2001
Orbital Sciences said Tuesday that the launch of its Pegasus XL rocket carrying NASA's High Energy Solar Spectroscopic (HESSI) satellite has been postponed.

Orbital is supporting a NASA-led investigation to determine if there may be any associated technical issues between the X-43A/Hyper-X launch failure at Edwards Air Force Base on Saturday, June 2, and the Pegasus XL vehicle awaiting launch at Cape Canaveral Air Force Base, Florida.

A new launch date for the HESSI mission, originally scheduled for June 7, will be announced once NASA and Orbital have completed the investigation.

The HESSI spacecraft will be used to study 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."

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.

Related Links
HESSI at Goddard
HESSI at Berkeley
Orbital Sciences
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Pegasus Sends Gamma Ray Scope Soaring
Greenbelt - October 9, 2000
A new gamma ray burst mission, the High-Energy Transient Explorer (HETE-2), made its entrance into space Monday morning at 1:38 a.m. EDT from the Kwajalein Missile Range in the Marshall Islands. The launch was delayed 48 hours to repair a spacecraft ground support cable.

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