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Article 2007

From The Baltimore Son, January 26, 2007

Scientists wowed by Sun images

By Frank D. Roylance
Janurary 26, 2007

Two Maryland-built satellites, launched in October aboard the same rocket, have pulled off separate pirouettes around the moon and headed off in opposite directions to begin a series of stereoscopic observations of the Sun.

"Everything has been picture-perfect up to this point," said Ron Denissen, mission project manager at the Johns Hopkins University Applied Physics Laboratory for NASA's $520 million STEREO mission.

All the instrument doors, solar panels and the high-gain antennas on both craft opened or deployed as planned. "Both spacecraft are very complicated. That's always a concern," he said.

The first pictures and scientific data are streaming back to APL. "All the teams are extremely excited about the images they're getting. Everything seems to be working better than expected," Denissen said. "We had a review here at the lab yesterday and I heard 'phenomenal' a lot of times from all the instrument teams."

Scientists have already been treated to images of several solar flares and eruptions, and even a passing comet, said Therese Kucera, a deputy project scientist for STEREO at the NASA Goddard Space Flight Center, who's enjoying the first mission she's been with from launch.

"People plan and build for years and finally it goes up, things work and you get your data," she said. "It's neat to be involved in it."

Scientists hope the first-ever stereo images of the Sun, expected in April, will reveal the Sun's corona in unprecedented detail, and track the evolving structure of coronal mass ejections -- huge bubbles of electrically charged solar particles -- as they erupt from the Sun's surface and fly off into space.

These solar storms can race across the solar system at a million miles per hour. If they're powerful enough, and aimed at the Earth, they can damage satellites, pose radiation hazards to astronauts and cause geomagnetic storms that disrupt radio communications and bedevil electric power distribution systems.

Existing solar observatories provide important warnings when solar storms erupt. But they can only see in two dimensions, making scientific observations and space weather forecasting less precise.

The instrument-packed STEREO mission was designed to address the problem. But getting twin spacecraft to split up and fly far enough apart to provide stereo photos after their launch was a challenge.

After sending them into similar orbits around the Earth and moon, APL scientists ordered a series of thruster blasts that sent each craft into a slightly different lunar flyby.

On Dec. 15, STEREO's "A" craft flew within 4,550 miles of the lunar surface. The moon's gravity then flung the satellite into an orbit around the Sun that's slightly closer to the Sun and faster than Earth's.

On Sunday, spacecraft "B" whipped around the moon, passing 7,300 miles from the surface. That swing hurled it into an orbit slightly farther from the Sun than Earth's, and therefore slower.

Relative to the Earth, the A observatory is now drifting ahead, while the B craft falls behind -- hence their letter designations. Relative to each other, they're separating at a rate of nearly 44 degrees per year -- almost precisely as planned. "They did a very good job," Denissen said.

By April they'll be far enough apart to provide solar scientists with nifty 3-D images of the Sun -- just as the separation between human eyes provides us with a stereoscopic view of the world and depth perception.

All of the prime science for STEREO data will be collected within the first 150 days. There is funding to carry the mission for two years, by which time the spacecraft will be separated by almost 90 degrees.

There are no plans for observations beyond that. "A two-year mission will give us all we need," Denissen said.

But the two spacecraft will keep on flying. After eight years they will pass each other on the opposite side of the Sun from Earth, returning separately to our neighborhood after 16 years.

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