Instead, "we would go around the equator," Dantzler said.
That had its own benefits, giving scientists more opportunities - 24 in all - to fly through the corona at speeds up to 125 miles per second.
And by flying "downhill" - almost straight down the sun's gravity "well" - the spacecraft makes its first approach to the sun just three months after launch. That change also shortened the mission from 10 years to seven, further cutting total costs.
After rounding the sun, Solar Probe will soar back out as far as Venus' orbit and use seven such Venus flybys to shrink its orbit and edge closer to the sun.
But buzzing the sun repeatedly demands a tough spacecraft. Solar Probe - 9 feet long and 1,000 pounds - will need to shield its instruments and communications gear from temperatures up to 2,600 degrees Fahrenheit.
Coronal temperatures can top a million degrees, Guhathakurta said. But the particles at those temperatures are so far apart that Solar Probe will not experience temperatures that high. Even so, planners elected to double the minimum distance they had originally planned, just to be safe.
APL's designers are working on a 6-inch-thick solar shield made of advanced carbon-carbon foam. It must always be pointed toward the sun, keeping the craft's camera and sensors at room temperature.
The spacecraft will also require secondary solar panels that can continue to produce power under very high temperatures. These small, blue panels will retract into the craft's shadow as it flies nearest to the sun, exposing only as much area as needed.
Dantzler said the mission, now in its very early development, will last 14 years in all, eventually employing perhaps 100 people. Most will be drawn from other APL projects. "We don't envision some major hiring for this," he said.
Solar Probe adds to APL's contributions to the study of links between the sun and Earth. They include NASA's Advanced Composition Explorer (ACE), launched in 1997; TIMED, studying Earth's outer atmosphere since 2001; And STEREO, twin craft providing three-dimensional images of solar events since 2006.
frank.roylance@baltsun.com
Mission to the sun
Launch: 2015
Cost: $750 million (in 2007 dollars)
Duration: 7 years
Closest approach to sun: 4.1 million miles
Highest temperature: 2,600 degrees F
Each orbit around sun: 88 days
Number of orbits: 24
Highest speed: 450,000 mph, (three times the current record for a manmade object in space)
[ Source: JHU Applied Physics Lab]
