The B612 Foundation - named after a fictional planet in the book "The Little Prince" - is counting on private donors to raise money for the wide-angle, infrared telescope and its operations, estimated at a few hundred million dollars.

The goal is to chart 500,000 asteroids that fly relatively close to Earth.

The telescope, called Sentinel, will be positioned closer to the sun than Earth so it can look outward and track approaching asteroids for months, Apollo astronaut Rusty Schweickart, chairman emeritus of B612, said during a conference call.

The technology exists to deflect an asteroid, provided it is found in time, added former shuttle and space station astronaut Ed Lu, the foundation's chairman and chief executive.

The goal is to have decades of notice, Lu told Reuters.

"I think it would be embarrassing if we were to be struck by a major asteroid in the next few decades simply because we didn't choose to do the mapping that's needed to find these asteroids," he said.

Schweickart said it wasn't a question of if Earth will be hit by an asteroid, but when.

The planet bears the scars of past events. An impact 65 million years ago is believed to have triggered a change in Earth's climate that killed off dinosaurs and other life.

In 1908, an incoming asteroid or comet blasted apart over Siberia, Russia, leveling 830 square miles (2,150 square kilometers) of trees.

"You don't want to put off for some future date, if you can make a difference now, something which relates directly to human lives and public safety," Schweickart said. "That's why we've taken the initiative."

During its planned 5 1/2 year mission, Sentinel should be able to find 90 percent of near-Earth asteroids that are 460 feet in diameter or larger, and about 50 percent of asteroids 130 feet in diameter.

In addition to looking out for potentially dangerous asteroids, the information could be used for proposed asteroid mining projects and by researchers.

The telescope will be built by Ball Aerospace and operated by the University of Colorado's Laboratory for Atmospheric and Space Physics in Boulder, Colorado.

It is expected to be launched in 2017 or 2018 aboard a Space Exploration Technologies' Falcon 9 rocket.

(Editing by Kevin Gray and Stacey Joyce)

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