NASA is considering a mission to capture an asteroid and drag it into the moon's orbit for study, researchers in California have confirmed.

Scientists at the Keck Institute for Space Studies said the space agency is looking over the institute's proposal to build a robotic spacecraft that would latch onto a small asteroid and transport it to a high lunar orbit, NewScientist.com reported.

The mission would cost about $2.6 billion, about the same as NASA's Mars rover Curiosity mission, and could be ready by the 2020s, the Keck institute said.

The Obama administration has said it wants to send astronauts to a near-Earth asteroid but such a mission would take about six months and expose astronauts to long-term radiation beyond Earth's protective magnetic field, the Keck researchers said.

Using a robot spacecraft to move an asteroid to the moon would be a better first step, they said, because an object orbiting the moon would be within easier reach of robotic probes and manned missions.

The Keck team is proposing a slow-moving spacecraft that would approach an asteroid, no more than 20 feet across, then gather the space rock up in a bag measuring about 30 feet by 45 feet and begin a return journey to the moon.

Such a mission with a slowly moving spacecraft would take about six to 10 years to place the asteroid into a lunar orbit, the Keck researchers said.