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NASA: Sun Setting on Solar Satellite: Craft Oribited Poles for 18 Years
[June 22, 2008]

NASA: Sun Setting on Solar Satellite: Craft Oribited Poles for 18 Years

(Albuquerque Journal (NM) (KRT) Via Acquire Media NewsEdge) Jun. 22--For the last decade, Los Alamos scientists Ruth Skoug and John Steinberg have had a unique view of the sun.

Next month, that vista will go away with the retirement of Ulysses, a research satellite operated by NASA and the European Space Agency that has been orbiting the sun for nearly 18 years.

Its batteries, the space agencies announced earlier this month, are simply running out of juice, and Ulysses will be shut down July 1.

As spacecraft go, Ulysses is a geriatric trooper. Its demise comes after a useful lifespan four times longer than the original mission plan.

Satellite operators like to point out a central fact about their business. They're building and running machines they can never touch once they are turned on.

"It's fascinating to be able to send something and have it work," Skoug said in a recent interview.

Ulysses launched in October 1990, and followed a long, looping trajectory into an orbit no spacecraft had ever tried.

It carried with it instruments developed at Los Alamos National Laboratory, and lab scientists have worked throughout its nearly twodecade life to study the data Ulysses has collected.

Every other spacecraft launched has spent its life primarily orbiting around the equivalent of the sun's equator, the large flat pancake of space where Earth and the other planets reside.

For scientists trying to understand the sun, and especially the emanations known as the "solar wind," it was the equivalent of trying to understand Earth's climate with all your weather stations in the Amazon.

Ulysses changed that, Steinberg said, by putting the equivalent of a solar weather station in orbit about the sun's north and south poles.

By earthly standards, the vacuum of space is not a terribly windy place. But the sun is constantly spewing particles that make up the solar wind.

"They're boiling off into space because it's so hot," Skoug explained.

It is the solar wind, for example, that creates the beautiful ghostly night lights known as auroras when they reach Earth.

But what of the solar wind spewing off the sun's north and south poles? Is it the same as the wind coming off the sun's equator, toward Earth? That's the question the Ulysses team set out to answer.

The winds from the sun's equator are a messy affair, Steinberg explained -- sometimes fast, sometimes slow.

As Ulysses made its first pass around the north and south poles of the sun, the satellite found a fast, steady solar wind blowing.

But as often happens in science, the more data the satellite collected, the more complicated things became.

Similar to the seasons on Earth, the sun goes through long-term cycles -- an 11-year cycle of increasing and declining sunspots. As Ulysses made its second orbit around the sun, it found that the wind changed with the sunspot cycle.

Scientists had their ideas about how the solar wind worked before Ulysses launched, many of which turned out to be correct.

But Steinberg noted that there is no substitute for real data. "You always want to go there with your instrument," he said.

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