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The Sciences

The Satellite That Aims to Succeed Where Icarus Failed

NASA's Solar Probe Plus study the sun from close up, braving temperatures that would melt stainless steel.

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If you are taking a trip to the sun, you’d better plan on bringing some shade.

That is the guiding principle behind NASA’s $740 million Solar Probe Plus, scheduled to blast off in 2015. At its closest it will be within 4 million miles of the roiling solar surface, known as the photosphere. (For comparison, scorched Mercury circles the sun at an average distance of 36 million miles.) No spacecraft has attempted anything like this. Swooping so close to the sun means braving temperatures of 2,600 degrees Fahrenheit, above the melting point of stainless steel.

To survive, the probe will hide behind a nearly three-yard-wide thermal shield. The shield is designed to keep the probe’s scientific instruments at a comfortable average of 86°F and to constantly adjust its orientation while the spacecraft races along at up to 450,000 miles per hour. “If anything is exposed that shouldn’t be exposed, the damage would happen very quickly,” says Solar Probe Plus project manager Andrew Dantzler, an engineer at Johns Hopkins University’s Applied Physics Laboratory. “Every element of the spacecraft is designed to dissipate heat.”

Scientists hope that the probe will help solve some crucial mysteries about the sun: How can the corona (the outer layer of the sun’s atmosphere) be millions of degrees hotter than the solar surface? How do solar wind particles accelerate to a speed of 1 million miles per hour? These are not just academic concerns. When the sun is active, chunks of its atmosphere break off and race through the solar system, crashing against Earth’s magnetic field. The resulting electromagnetic mayhem can damage satellites and knock out power grids on the ground. Variations in solar activity also seem to affect global weather. “We know so much about the sun, but we don’t really understand the mechanism that is the powerhouse behind the corona and the solar wind,” Dantzler says. Soon that should change.

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