Now they just need the money. The group is negotiating the final price with Ball.
The dropping cost of computers, telescope components and rocket launches made the project feasible, Lu said.
But another expert is skeptical that the telescope will cost just "a few hundred million" dollars. Tim Spahr of the Minor Planet Center in Cambridge, Mass., which tracks asteroids — and which would eventually analyze data from Sentinel — was part of a team that in 2003 proposed a similar mission to NASA. The cost of that unbuilt project: $400 million.
Spahr is also skeptical that Sentinel will spot every possible threat. "It is a spectacular challenge," he said. The telescope will miss some asteroids that take a long time to orbit the sun and will have to track each asteroid for "years" to determine whether it hit Earth, Spahr said.
Still, Lu is confident that his group can pull off the mission. "We'll be successful," he said.
And what will donors get for their contributions?
Said Lu: "You get to take part in saving the Earth."