PASADENA, California — Send a robot into space. Grab an asteroid. Bring it back to Earth orbit.

This may sound like a crazy plan, but it was discussed quite seriously last week by a group of scientists and engineers at the California Institute of Technology. The four-day workshop was dedicated to investigating the feasibility and requirements of capturing a near-Earth asteroid, bringing it closer to our planet and using it as a base for future manned spaceflight missions.

This is not something the scientists are imagining could be done some day off in the future. This is possible with the technology we have today and could be accomplished within a decade.

A robotic probe could anchor to an asteroid made mostly of nickel-iron with simple magnets or grab a rocky asteroid with a harpoon or specialized claws (see video below) and then push the asteroid using solar-electric propulsion. For asteroids too big for a robot to handle, a large spacecraft could fly near the object to act as a gravity tractor that deflects the asteroid’s trajectory, sending it toward Earth.

“Once you get over the initial reaction — ‘You want to do what?!’ — it actually starts to seem like a reasonable idea,” said engineer John Brophy from NASA’s Jet Propulsion Laboratory, who helped organize the workshop.

In fact, many of these ideas have been on the drawing board for years as part of NASA’s planetary defense program against large space-based objects that might threaten Earth. And there’s no shortage of potential targets. NASA estimates there are 19,500 asteroids at least 330 feet wide — large enough to detect with telescopes — within 28 million miles of Earth.

Though rearranging the heavens may seem an excessive undertaking, the mission has its merits. The Obama administration already plans to send astronauts to a near-Earth asteroid, a mission that would coop them up in a tiny capsule for three to six months, and involve all the risks of a long deep-space voyage. Instead, robots could shoulder some of that burden by bringing an asteroid close enough for astronauts to get there in just a month.

Parking an asteroid in a gravitationally neutral spot between the Earth and the sun, known as a Lagrange point, would provide a stationary base from which to launch missions further into space. There are several advantages to this. For one, launching materials from Earth requires a lot of power, fuel, and consequently money, to get out of our planet’s deep gravity well. Resources mined from an asteroid with very little gravitational pull could be easily shuttled around the solar system.

And many asteroids have a lot to offer. Some are full of metals such as iron, which can be used to build space-based habitats while others are up to one-quarter water, which would be either used for life-support or broken down into hydrogen and oxygen to make fuel. As well, asteroid regolith placed around a spaceship hull would shield it against radiation from deep space, allowing safer travel to other planets.

An asteroid could be an alternative to setting up camp on the moon, or complement a moon base with more resources for heading further out in the solar system, said engineer Louis Friedman, cofounder of the Planetary Society and another co-organizer of the Caltech workshop.

There’s also the potential for mining asteroid materials to bring back to Earth. Even a small asteroid contains roughly 30 times the amount of metals mined over all of human history, with an estimated worth of $70 trillion. And astronomers would have the chance to get a close-up look at one of the solar system’s earliest relics, generating important scientific data.

Though technically feasible, budging such a hefty target — with a mass in excess of a million tons — would not be easy.

“You’re moving the largest mother lode imaginable,” said former astronaut Rusty Schweickart, cofounder of the B612 Foundation, an organization dedicated to protecting Earth from asteroid strikes.

Most asteroids are irregular chunks of rock that spin chaotically along irregular axes. Engineers would need to be absolutely certain they could control such a potentially dangerous object. “It’s the opposite of planetary defense; if you do something wrong you have a Tunguska event,” said engineer Marco Tantardini from the Planetary Society, referring to the powerful 1908 explosion above a remote Russian region thought to have been caused by a meteoroid or comet.

Still, these obstacles are like catnip to engineers, who love to go over every potential difficulty in order to solve it. Actually executing the asteroid retrieval plan would help demonstrate and greatly expand mankind’s space-based engineering capabilities, said Friedman. For instance, the mission would teach engineers how to capture an uncooperative target, which could be good practice for future planetary defense missions, he added.

And if the challenges for a large asteroid seem too daunting, researchers could always start with a smaller asteroid, perhaps six to 30 feet across. Gradually larger objects could be part of a campaign where engineers learn to deal with progressively greater complications.

Last year, Brophy helped conduct a study at JPL to look at the feasibility of bringing a 6.5-foot, 22,000-pound asteroid — of which there might conceivably be millions — to the International Space Station. This mission would help astronauts and engineers learn how to process asteroid materials and ores in space.

The JPL study suggested the asteroid could be captured robotically in something as simple as a large Kevlar bag and then flown to the space station or placed in a Lagrange point. Of course, such a small object might not have the same emotional impact as a larger destination. “NASA isn’t going to want to go to something that is smaller than our spaceships,” said engineer Dan Mazanek from NASA’s Langley Research Center.

No matter the size of the asteroid, these plans would require hefty investments. Even capturing a small asteroid would consume at least a billion dollars and anything larger would be a multi-billion-dollar endeavor. Convincing taxpayers to foot such a bill could be tricky.

Considering the resources available in any asteroid, private industry might be interested in getting involved. One possible mission would be to simply execute the first part of the plan — pushing the asteroid to near-Earth orbit — and then convene a commercial competition inviting anyone who wants to develop the capabilities to reach and mine the object.

Though the undertaking might be scientifically exciting, this wouldn’t be the primary motivation. An asteroid would provide great insight into the solar system’s formation, it’s not enough to justify the expense of bringing one to Earth. Any interesting science can be done much cheaper with an unmanned robotic spacecraft, said chemist Joseph A Nuth from NASA’s Goddard Spaceflight Center.

“Ultimately, we would be developing this target in order to help move out into the solar system,” Brophy said.

Though they did not reach a consensus on all the details, the group will reconvene in January to hammer out further specifications and potentially get the interest of NASA.

In the end, many agreed that bringing an asteroid back to Earth could create an interesting destination for repeated manned missions and that the undertaking would help build up experience for future jaunts into space.

Image: NASA/Denise Watt