That’s because even though Congress assigned the space agency this mission four years ago, it never gave NASA money to build the necessary telescopes, the new National Academy of Sciences report says. Specifically, NASA has been ordered to spot 90 percent of the potentially deadly rocks hurtling through space by 2020.

Even so, NASA says it’s completed about one-third of its assignment with its current telescope system…

NASA calculated that to spot the asteroids as required by law would cost about $800 million between now and 2020, either with a new ground-based telescope or a space observation system, Johnson said. If NASA got only $300 million it could find most asteroids bigger than 1,000 feet across, he said.

But so far NASA has gotten neither sum.

It may never get the money, said John Logsdon, a space policy professor at George Washington University.