Solar Probe's instruments will measure high-energy protons and electrons in the sun's "atmosphere," as well as the strength and direction of its magnetic field and the amount of dust swirling around it.
"I find this to be really exciting. It's going to be a really fun mission," Dantzler said. "It doesn't even seem possible when you first take a look at it."
Three decades of earlier studies reached the same basic conclusion. Sending a probe into the solar corona - that shimmering halo of glowing gas that becomes visible around the sun during total eclipses - was technically too difficult, too expensive, or both.
In 2005, APL tried again, but its proposal to NASA contained two deal-killers.
It would have required a "radioisotope thermoelectric generator" (RTG) to supply electrical power. An RTG's energy comes from heat produced by a decaying bit of plutonium 238. On past missions, that design has drawn protests from people who feared a launch accident.
The mission also carried a prohibitive price tag of $1.2 billion.
Worse, from a scientific standpoint, it would have given scientists just one or two swings through the corona.
"That's really putting all your eggs in one basket, and that's a lot of eggs," Dantzler said. "So we took another look at the study."
First, APL ditched the plutonium-powered generator. Should a mission to the sun not use solar energy for electrical power?
The answer isn't simple. In fact, "It's counterintuitive," Dantzler said.
It turns out that to reach the sun, the original mission would swing by Jupiter first - too far from the sun for solar panels to do the job.
That route seems even more counterintuitive. What could be easier than flying - falling, really - into the sun's gravitational pull?
"It's not that easy," Dantzler said.
In order to get close to the sun and fly over its poles, where the solar physicists want to be, the craft would need an enormous amount of energy, he said. First it would have to shed the momentum it inherited at launch from Earth's speed around the sun. It would need more to climb above the plane of Earth's orbit, and up, over the sun's pole.
The best place to get all that energy free of charge is to swing by Jupiter and gather momentum from its gravitational pull. But with the plutonium generator and solar panels both ruled out, APL decided to abandon its plan for a polar solar orbit.
