http://www.cnn.com/2008/TECH/05/18/solar.probe/index.html
(NASA's Solar Probe, shown in this artist's conception, will get closer to the sun than any spacecraft before it.)
By Elizabeth Landau
CNN
(CNN) -- Its heat powers the solar system. Its light makes life on Earth possible. Its gravitational pull keeps planets in orbit around it.
The sun is, in every sense of the word, a superstar. But despite its familiarity, there is a lot we don't know about it.
Now, scientists are planning humanity's closest visit yet to our most familiar star. The NASA Solar Probe, an unmanned spacecraft scheduled for launch in 2015, will explore some of the burning questions scientists have about the sun.
The probe "takes us to where space weather and, indeed, everything that directly affects life on Earth, starts," said Loren Acton, research professor of physics at
The project, which costs around $750 million, will be able to withstand inconceivably high temperatures -- up to 2,600 degrees Fahrenheit. The probe is being developed at
Scientists hope the probe will help them better understand and forecast solar storms, which occur when the sun accelerates energetic particles that travel to the Earth along magnetic field lines at super-high speeds.
Such storms can disrupt power grids and communication satellites that affect cellphones and GPS navigation. In 1989, a solar storm caused the HydroQuebec Power Grid to lose power in
Astronauts in space during a solar storm are also at risk for absorbing dangerously large amounts of solar radiation.
In the same way that hurricane predictors must consider how the ocean accelerates and powers hurricanes, scientists hope to understand how the sun accelerates particles in solar storms.
"This isn't a space weather satellite, but if you do want to have any hope of predicting solar storms, you have to have a better understanding of this mechanism than we have," said Andrew Dantzler, Solar Probe project manager at the Applied Physics Laboratory.
Scientists currently believe the storms have to do with the activity of sunspots, regions of relatively low temperatures where magnetic field lines have breached the sun's surface. A strong sunspot cycle may signal strong solar storms, but researchers still have a lot to learn about forecasting.
Scientists also want to know why the sun's outer atmosphere, called the corona, is several hundred times hotter than the visible solar surface, which is where sunlight comes from.
The corona, whose temperature is about 1.8 million degrees Fahrenheit, seems mysteriously warm considering that the sun's surface layer, much closer to the star's core, is less than 11,000 degrees Fahrenheit.
The probe will capture images to help solve these puzzles over a period of almost seven years. During this time, the probe will fly by Venus seven times, gradually reducing the size of its orbit.
At its closest, the probe will get about 4.1 million miles from the sun. That may not seem so near, but consider that the sun is about 93 million miles from Earth. The probe will come about eight times closer to the sun than any spacecraft before it.
The NASA probe will also achieve a top speed of 450,000 miles per hour, which is three times the record of any man-made object in space, Dantzler said.
During loops around the inner solar system, two sets of solar arrays will extend or retract, regulating the temperatures and power levels of the probe's panels, according to preliminary designs. The probe itself will weigh about 1,000 pounds, with a shield filled with carbon foam 9 feet in diameter and 6 inches thick.
"Everything on Earth is affected by the sun. We can't turn off the sun or change anything about it," Dantzler said. "You can't change or turn out a hurricane. But you can prepare for it."
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