NASA gets ready for 3D view of the sun

Studies of solar magnetic storms, the solar system's most violent explosions, will soon come in 'stereo'.

Two nearly identical robotic spacecraft known as Solar Terrestrial Relations Observatories (or STEREO) are in development and testing by NASA to capture high-definition 3D images of the sun and solar wind -- the first-ever stereoscopic measurements of the sun's explosions.

NASA expects to launch the two-year mission this spring after it completes testing of the crafts at Goddard Space Flight Center in Maryland this winter.

The $520m project is the next frontier for scientists observing the sun and coronal mass ejections (CMEs), powerful solar eruptions that can disrupt the protective magnetic field surrounding Earth, as well as the general environment in space. Related to solar flares (scientists still don't know which come first), CMEs can pack a punch equivalent to a billion megaton nuclear bombs.

Scientists believe that with more understanding of CMEs they can better forecast weather in space and mitigate their negative effects on satellite operations, polar aviation, communication systems, power grids and astronauts in space. Radiation from the eruptions can harm astronauts while they're on missions, for example.

Scientists believe the mission will also prove beneficial for understanding the sun and its essential relationship to Earth.

"Although coronal mass ejections are the main subject of study of this mission, it will give a deeper understanding generally of our sun as a star -- its stability and future effects on Earth's atmosphere, climate and conditions," said Laurance Doyle, co-founder of stargazing software company PlanetQuest and a principal investigator at the Search for Extraterrestrial Intelligence (SETI) Institute.

"We really have so much more to understand about the sun, and yet it is the very basis of all ecosystems on Earth's surface," he added.

Scientists from NASA discussed the mission last week in San Francisco at the annual fall meeting of the American Geophysical Union.

Michael Kaiser, project scientist for NASA, said that the spacecraft will launch in late May from Cape Canaveral. At liftoff, the craft will be merged in one rocket and then split off after several days, when one will swing around the moon to a position trailing behind the Earth in its orbit and the other in a position just ahead of it. One will complete its orbit in 344 days, the other in 388 days.

Each craft is roughly the size of a golf cart, but when the solar arrays are extended in space they expand to the size of a football net. Each craft carries 16 instruments that were developed in labs around the world and assembled at Johns Hopkins Applied Physics Lab.

One of the key tools is SECCHI (Sun-Earth Connection Coronal and Heliospheric Investigation), which includes an extreme ultraviolet imager, two white-light cronographs and a heliospheric imager. The imaging telescopes are designed to take pictures within one second of each other and correct the difference in light-travel time from the sun to each spacecraft.

The instruments are designed to study the 3D evolution of CMEs from their start near the sun's surface through the corona, its outer atmosphere, and into interplanetary space. From there, it captures their effect on Earth.

CMEs are giant clouds of plasma travelling in space, and they are caused by the buildup and sudden release of magnetic stress in the solar atmosphere.

After about 90 days in space, the craft will begin taking observations. A beacon on each spacecraft transmits data to the National Oceanic & Atmospheric Administration, Kaiser said.

The STEREO mission builds on satellites already observing the sun and earlier missions like the Solar and Heliospheric Observatory (SOHO), a full-sun view chronograph. Still in operation, SOHO takes images of the sun every 10 to 15 minutes. But with the images, scientists still can't tell whether CMEs are coming towards the Earth or moving away from it. In order to see the trajectory of CMEs, scientists will need three-dimensional images.

Part of the project is to look at various technologies to forecast the movement of CMEs and construct a better model of what's happening in the solar system, Kaiser said. For example, scientists need to understand how fast the force is travelling and how one structure interacts with another.

"In terms of space weather forecasting, we're where weather forecasters were in the 1950s. 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 it will impact Earth," Kaiser said in a statement.

"Why do we care? Because the sun is the star that matters most to us," Kaiser said.