Berkeley, NASA to launch satellite June 12

By Robert Sanders, Public Affairs


satellite dish

A dish built atop the Berkeley Hills, bottom, will collect the data as the satellite arcs over the Bay, 373 miles above the Earth.
Space Sciences Lab photo

06 June 2001 | A satellite dedicated solely to the study of solar flares, designed, built and operated by an international consortium led by scientists at Berkeley is set for launch on June 12, by the National Aeronautics and Space Administration.

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 Lin, professor of physics in the College of Letters & Science and principal investigator for the mission.

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 spacecraft scheduled for launch under NASA’s 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.

The 645-pound 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 above the Earth, inclined at 38 degrees to the equator.

Once in orbit, the satellite comes under Berkeley’s control, with commands uplinked and data downlinked through a 36-foot radio dish perched in the wooded hills above campus. From mission control in the nearby Samuel L. Silver Space Sciences Laboratory, HESSI mission operators will monitor the automatic pointing of the satellite toward the sun, deployment of the four solar panels and the spin-up of the satellite to about 15 revolutions per minute.

Information collected by HESSI is sent back to Earth, where computers translate the data into pictures of the flare every second or so. It is also possible to obtain the energy spectrum of the hard X-rays and gamma-rays at each location in the pictures.


Mission operators must cool spacecraft’s imager before mission begins


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