NEWS RELEASE, 8/12/96
Launch date set for FAST Explorer, a UC Berkeley satellite that will study the Northern Lights
Berkeley -- A UC Berkeley satellite, the second in NASA's highly touted "Small-Class Explorer" series of fast and cheap satellites, is set for launch early Sunday morning (8/18) to probe the mysteries of the Northern Lights.
Once in orbit the Fast Auroral SnapshoT (FAST) Explorer satellite will skim as low as 220 miles above the aurora borealis or Northern Lights, collecting detailed "snapshots" of the magnetic and electric fields above both the North and South Poles.
These fields accelerate electrons in the Earth's ionosphere to such high velocities that they smash into atmospheric atoms and generate the beautiful shimmering curtains of light that dominate the polar night sky.
The data from the satellite, which also include information on the energies and arrival direction of the electrons and ions, and the intensity of electrical currents, will be correlated with ground observations of the aurora, in an effort to explain the colorful and shifting sheets of light.
"The goal is to study the microphysics of the aurora," said project leader Charles "Chuck" Carlson, a research physicist at UC Berkeley's Space Sciences Laboratory. "One of the puzzles is how something global like the solar wind ends up creating a thin curtain of light around the North Pole."
The Earth's magnetosphere, or magnetic field, is a teardrop-shaped magnetic "bubble" that shelters the Earth from the solar wind and allows only a small fraction of solar wind particles through. Stretching for hundreds of thousands of miles into space, the magnetosphere nevertheless lets in energy from the solar wind, in the form of electrical currents that flow along magnetic field lines to the poles.
"The puzzle is how you can end up with very fine-scale features in the aurora," he said. "Some of the curtains stretch for hundreds of kilometers but are only a few hundred meters thick. It's as if all the water pouring over a waterfall, instead of spreading out, formed a single narrow sheet ribbon. "
The answer undoubtedly lies in how the electrons are accelerated by electric fields in the ionosphere above the pole, some 2,500 miles above the ground, he said. That is the area on which FAST will concentrate, as its highly elliptical orbit carries it over the pole at altitudes varying from 220 to 2,500 miles.
The visible aurora begins much lower, at an altitude of only 70 miles, where it forms a halo around the pole several thousand miles across. This is the region where the accelerated electrons first encounter Earth's dense atmosphere and collide with atoms or molecules of oxygen and nitrogen. The collisions give energy to the atoms and molecules, which they then release by emitting light.
The process is akin to what happens inside a TV set. Electric fields accelerate electrons toward the phosphor-coated screen, which emits light when the electrons collide with phosphor molecules.
While previous satellites and sounding rockets measured fields and plasma density on a kilometer scale, FAST will measure them on the scale of a few tens of meters. FAST also was designed to take data rapidly -- quick "snapshots" -- since things happen in the aurora on the scale of minutes to microseconds, Carlson said.
What's new about the satellite instruments is that much of the data selection is done onboard before it is relayed to Earth. Whereas most satellites have a fixed set of measurements that are collected and transmitted to the ground, FAST uses an onboard computer to analyze the data immediately and decide whether they are worth keeping. Once it decides, though, it collects rapid measurements which are stored in a large memory for later transmission to the ground.
With the satellite passing over the auroral region 11 times a day for at least the next year, Carlson and his colleagues will accumulate scads of new data.
"Much of what we know about aurora has been learned through observations on the ground, along with laboratory experiments," Carlson said. "But there are essential measurements you can't do in the lab, you have to do them from space."
To date most observations from space have been done with the occasional sounding rocket shot through the Northern Lights, plus a few satellites.
FAST is part of an international, multi-satellite program to study the solar wind and its interaction with the Earth's magnetosphere and ionosphere. It joins several other satellites already orbiting the Earth, most of which include instruments designed by groups at the Space Sciences Laboratory.
These satellites, part of NASA's Global Geospace Science Program, include WIND, positioned "upstream" from the sun-facing bowshock of the Earth where the solar wind rams into the Earth's magnetic field; POLAR, orbiting high above the polar regions; and Japan's GEOTAIL, spending most of its orbit in the downwind magnetic tail of the Earth. Another related mission, a four-satellite group called CLUSTER destined for an intermediate position between WIND and POLAR, was destroyed in early June when its launch vehicle, an experimental Ariane 5 rocket, went awry shortly after launch.
NASA will send the FAST Explorer into orbit aboard a privately developed air-launched space booster called Pegasus XL, which itself had serious problems that delayed the FAST launch for two years.
The launcher, dropped from an L-1011 jet cruising at 39,000 feet over the Pacific Ocean out of California's Vandenberg Air Force Base, failed its first test in 1994. Designer and builder Orbital Sciences Corporation of Fairfax, Virg., developed an improved version, but that too was destroyed last year after its first and second stages failed to separate after launch. Though the most recent version of this rocket successfully orbited several satellites this year, Carlson nevertheless keeps his fingers crossed.
After FAST has achieved polar orbit, NASA will turn over scientific operation of the satellite to a small band of physicists operating out of two third-floor rooms at the Space Sciences Laboratory, high atop the Berkeley hills. The advantage of the "small explorers" is that a small team -- in this case only about a dozen scientists and graduate students and a couple dozen technicians and engineers -- designs and builds the satellite.
Of particular interest to Carlson are the auroral substorms, sudden disruptions of the magnetosphere that cause intense brightening and rapid motions of the green and red colored curtains of light ringing the pole. He has stood for hours in the Alaskan cold admiring the Northern Lights while waiting for substorms to emerge from the aurora.
"The Northern Lights are really spectacular, you never get tried of it," he said. "It's a great light show."
Carlson's colleagues at UC Berkeley include Forrest Mozer and Robert Lin, both professors of physics; and research physicists Jim McFadden, Robert Ergun and Mike Temerin.
Collaborators include Los Alamos National Laboratory and UCLA, where the magnetic field instrument aboard FAST was built; Lockheed Palo Alto Research Laboratory and the University of New Hampshire, which collaborated with UC Berkeley to build the mass spectrograph; the University of Minnesota; and NASA/Goddard Space Flight Center, which supplied the spacecraft and overall project management.
Ground observations will be centered at the University of Alaska's Poker Flat Research Range, about 30 miles north of Fairbanks, where extremely sensitive video cameras will capture high-resolution pictures of the Northern Lights as FAST passes overhead.
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