This 2001 NASA Solar and Heliospheric Observatory image of the Sun shows a solar flare leaping out from an active sunspot.
Credit: AFP
WASHINGTON, 18 August 2006: A pair of spacecraft NASA plans to launch on August 31 will take stereoscopic pictures of the sun to give the first-ever three-dimensional views of its massive, weather-disrupting eruptions, U.S. scientists said on Thursday.
The twin spacecraft, each the size of a small car, will join the Earth in its orbit, one moving ahead of the planet and one trailing, in the US$478 million project.
By simultaneously measuring and recording solar flares and coronal mass ejections, huge eruptions that blast solar plasma into space, the two craft will give a "unique and revolutionary view" of the flow of energy between the Sun and Earth.
It will also cut by half the time it takes, currently about 12 hours, to get warnings of geomagnetic storms headed toward the Earth that were produced by the eruptions, said Michael Kaiser, project scientist for NASA's Solar Terrestrial Relations Observatory, or STEREO.
Such storms can wreck satellites and cause power and telecommunications outages on Earth. They can also endanger astronauts on journeys beyond the Earth's magnetic field.
"In terms of space-weather forecasting, we're where weather forecasters were in the 1950s," Kaiser said.
"They didn't see hurricanes until the rain clouds were right above them. In our case, we can see storms leaving the Sun, but we have to make guesses and use models to figure out if and when they will impact Earth."
The twin STEREO craft will add a new dimension to other Sun-observing spacecraft under NASA's Heliophysics Division, said National Aeronautics and Space Administration scientist Madhulika Guhathakurta.
Set on either side of the Earth in the same solar orbit, they will take views of the Sun with the kind of three-dimensional depth perception a person's eyes provide looking at an object.
That will give more thorough views of solar eruptions, including the direction of the energy emitted, which currently can't always be determined, said Guhathakurta.
It could help weather scientists better predict the disruptions to the Earth's magnetic field of solar storms.
"Space weather is beginning to affect all nations which do business in space," she said.
"STEREO will play a very central role in this heliophysics observatory."
NASA will put the two spacecraft together aboard a single Delta rocket slated for launch August 31, according to Nicholas Chrissotimos, STEREO project manager.
After being released from the rocket, the two will make several massive elliptical orbits around the Earth, crossing the Moon's orbit. On September 15, they will get within a few thousand kilometres of the moon and tap its gravitational pull to be flung further away from the Earth, while still travelling in its solar orbit.
One of the two will take a slightly different path, and move back towards the Moon a month later to be pushed out into the Earth's orbital wake.
Over the two-year mission cycle the two will slowly drift further apart while tracking the Earth around the Sun.
NASA says the current launch window is five days, in case of weather or technically-forced delays, and that a new launch could be scheduled within two weeks.
It also said that if the planned August 27 launch of the Atlantis space shuttle is delayed into the STEREO launch window, NASA would be able to get the STEREO launch off in as little as 24 hours after the shuttle liftoff.
