Some NASA critics have argued it should be sending astronauts back to the moon before aiming for an asteroid, which would take at least six months to reach.
A deep-space rocket-propulsion system is still not ready, and there has been no decision on which asteroid to go to.
For their part, NASA officials say an asteroid mission would finally bring manned flight completely out of the grasp of earth gravity, at last turning Star Trek into reality.
Al Jazeera's Tom Ackerman reports.
Source: Al Jazeera