Ed Lu, who has spent seven months of his life in space, can sometimes sound nonchalant about it. But he's really not.

"Yes, they managed to kick me off the planet three times," he said in a Newsmakers interview with ABC News and Yahoo! News. Lu, chosen as a NASA astronaut in 1994, flew twice on American space shuttle flights, and then spent six months on the International Space Station.

"It was awesome, best office in the world, view can't be beat, the work is interesting," Lu joked. "The food's good, but it gets boring."

These days, Lu spends a fair amount of his time worrying about protecting the planet he got to see from afar. Having left NASA in 2007 to work for Google and other technology companies, he is now CEO of the B612 Foundation, a nonprofit group that advocates action to prevent errant asteroids from hitting Earth.

Asteroids? Death from the sky? Yes, says Lu, the chances may be small - but it's a small chance of a big catastrophe, and that's something worth our attention. For the first time in history, we have the technology to detect incoming asteroids - and, if necessary, deflect them before they do us damage.

There was the asteroid that is believed to have wiped out the last dinosaurs, but that was 66 million years ago, and disasters of that magnitude are very rare.

Lu says he's more concerned about objects like the one that crashed near the Tunguska River in Siberia in 1908, decimating about a thousand square miles of forest. It was probably about 150 feet in diameter.

And it so happens there is another, of about the same size, that will pass the Earth on Feb. 15, missing by 17,200 miles. It is called 2012 DA14, and it's not missing by much when you consider the vastness of space.

"It's a wake-up call," said Lu, "because this asteroid is big enough, if it hit, to take out an area roughly the size of metropolitan D.C."

There are estimated to be a million asteroids of that size or larger. Telescopes on Earth have spotted about 10,000 of them. "So for every one of these out there that we see, there's 99 more we haven't tracked yet," said Lu. "Each and every day, think of it as sort of playing roulette with the Earth."

The B612 group's solution is to launch a telescope, called Sentinel, into space, where it can scan for objects whose orbits cross ours.

Lu says the project is technologically possible, and could be done with private funding, which he and his team are now trying to attract. They hope to launch Sentinel in 2018.

If Sentinel does spot something with our name on it, what then? Fifteen years ago, in the movie "Armageddon," Bruce Willis led a team of roughneck astronauts who tried to blow up a threatening asteroid with a nuclear weapon. Lu says the reality would be much less dramatic.

If you spot an incoming asteroid well in advance - and that's the idea behind Sentinel - you just have to nudge it ever so slightly.

Lu and his colleagues have proposed a space tug, a rocket that would rendezvous with the asteroid and push it just enough to make it harmless. If an asteroid is spotted and its orbit is calculated, scientists will be able to plot its path decades into the future. Changing its orbital speed by a few thousandths of a mile per hour now, he says, would head off a collision years from now.

"We can do something about it," said Lu. "It would be sort of the height of stupidity if we didn't do something about it. We could get wiped out, but we couldn't do anything about it because we didn't have the foresight to do so. We have the technology to do this."