Nasa is going on an asteroid rodeo. In plans that sound like science fiction but that are aimed at becoming science fact, the US space agency has revealed its ambitions to lasso an asteroid and drag it back to the Earth. Nasa scientists are engaged on a hunt for a suitable space rock that can be the target of the mission, which has been scheduled tentatively for 2019.

"It really is a clever concept. Go find your ideal candidate for an asteroid. Go get it robotically and bring it back," said Florida senator Bill Nelson as he unveiled the plans at a press conference.

Nelson, who is chairman of the Senate science and space subcommittee, said President Barack Obama would put $100m aside for the mission in next week's budget for 2014. The cash will be used to find a suitable small asteroid – currently expected to be around 25ft and weight 500 tons. As it stands, the mission would use a robotically-controlled spacecraft to approach the asteroid, attach a large version of a "baggie with a draw string", and then drag the captured rock back to near Earth.

Once the asteroid arrives it will be easier to send up astronauts to examine it close-up. The aim of the mission would be to explore the idea that eventually asteroids could be mined for resources; the sample would also likely provide clues about the sort of material that made up the early solar system.

Last year, the Keck Institute for Space Studies proposed a similar mission for Nasa with a price tag of $2.6bn. There is no cost estimate for the space agency's version. Nasa's plans were first reported by Aviation Week.

Of course, such a scheme does sound a little like the plot of a Hollywood disaster movie, in which an errant space mission could lose control of the asteroid and accidentally send it hurtling towards Earth. Such thoughts are high on the agenda of many scientists who have recently seen a dramatic meteor burn through the skies above Russia with enough force to shatter windows and injure hundreds of people. But scientists insist this mission is foolproof, because the asteroid being captured and brought home will be small enough to burn up in the atmosphere if it does end up on a collision course with Earth.

While there are thousands of asteroids around 25ft, finding the right one that comes by Earth at just the right time to be captured will not be easy, said Donald Yeomans, the head of Nasa's Near Earth Object program, which monitors close-by asteroids. He said once a suitable rock was found it would be captured with the space equivalent of "a baggie with a drawstring. You bag it. You attach the solar propulsion module to de-spin it and bring it back to where you want it."

These types of asteroids are closer to Earth – not in the main asteroid belt between Jupiter and Mars. The robotic ship would require a high-tech solar engine to haul the rock through space. Then Nasa would use a new large rocket and the Orion capsule – both under development – to send astronauts to the asteroid. There would be no gravity on the asteroid so the astronauts would have to hover over it in an extended spacewalk.

Exploring the asteroid "would be great fun," said the Apollo 9 astronaut Rusty Schweickart, who is head of the B612 Foundation, a non-profit concerned with dangerous space rocks. "You'd have some interesting challenges in terms of operating in an environment like that."

Senator Nelson said the mission would help Nasa develop the capability to nudge away a dangerous asteroid if one headed to Earth in the future. It also would be training for a mission to send astronauts to Mars in the 2030s, he said. But while the project would be helpful for planetary defence, Schweickart added, "that's not your primary mission".