Illustration courtesy NASA

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A hypothetical robotic asteroid capture is illustrated above.

Illustration courtesy NASA

NASA Announces Plan for Capturing Asteroid

The space agency wants to tow an asteroid back to our planetary neighborhood.

NASA wants to identify an asteroid in deep space, figure out a way to capture the spinning and hard-to-grab orb, nudge it into our planetary region, and then set it into orbit around the moon, the agency announced Wednesday.

The capture would be performed robotically, and the relocated asteroid would become a destination for astronauts to explore—and, possibly, for space entrepreneurs to mine.

The idea may sound more like science fiction than national policy, but it actually fits in with key goals of the Obama administration and the space community.

Those goals include learning how to identify asteroids heading toward us and to change their course, finding destinations where astronauts can go as they try to learn how to make the longer trip to Mars, and providing opportunities for space investors. (Related: Psychological Challenges of a Manned Mars Mission.)

"This mission represents an unprecedented technological feat that will lead to new scientific discoveries and technological capabilities and help protect our home planet," NASA administrator Charles Bolden said in a statement before the plan was announced on Wednesday.

"This asteroid initiative brings together the best of NASA's science, technology, and human exploration efforts to achieve the president's goal of sending humans to an asteroid by 2025," his statement continued.

Planning for the effort has just begun, and Bolden said teams will meet over the summer to work out how to select the right asteroid, how to get a spacecraft to it, and how to tow it many millions of miles to our moon.

As envisioned in a new NASA video (below), the asteroid would be caught and then surrounded by a large, flexible covering that will be towed by a spacecraft with two large solar arrays.

The NASA idea is similar to one developed by scientists at the Keck Institute for Space Studies at the California Institute of Technology, and proposed by them last year.

A robotic spacecraft could drag a 23-foot, 500-ton near-Earth asteroid (NEA) using currently available technology, the Keck scientists concluded, though that technology would have to be modified somewhat. That team estimated that the project would cost $2.6 billion, but NASA officials say its effort would cost much less.

That's because NASA will look much closer to earth for their target asteroid, and because the agency will already be spending millions on related rocketry and technology.

The asteroid proposal was part of the NASA budget rollout for 2014, part of the broader federal budget that President Barack Obama unveiled Wednesday, which included an initial $104 million for the project.

But Bolden said the plan could go forward only if the federal government could roll back the cuts made as a result of the recent sequester.

In a presentation, NASA associate administrator Robert Lightfoot laid out the agency's timeline for the mission: target selection in 2016, asteroid capture in 2019, and the first astronaut visits to the relocated rock in 2021.

As explained by Paul Dimotakis, one of the Keck scientists who worked on the project, the physics of the endeavor requires NASA to target a relatively small asteroid of 500 to 1,000 tons.

Asteroids come in many forms, from rubble piles barely held together by their own gravity to dense balls of iron and nickel. Dimotakis said the asteroid to capture needs to be the consistency of dried mud.

Finding the right asteroid to capture will not be easy, Dimotakis said. Because of the limited size and nudging or towing power of the capsule that will be sent to the asteroid, the rock itself cannot be more than 1,000 tons.

What's more, it needs to be on a trajectory that would take it close to the Earth and moon even without a tow. The capture spacecraft, Dimotakis said, would not have enough power and fuel to dramatically change the direction of an asteroid of 500 to 1,000 tons.

By far the largest concentration of asteroids in the solar system orbit in the main belt between Mars and Jupiter. But NASA will be looking for one in Earth's extended neighborhood.

Bolden and Dimotakis listed numerous reasons for undertaking the project, but emphasized three in particular.

Because asteroids are among the oldest objects in the solar system, Dimotakis said, bringing one to a place where it could be studied intensely would allow scientists to gain a much better understanding of what that early solar system was like. He said having an asteroid nearby that could be constantly visited would likely lead to scientific breakthroughs.

And if the long-term goal of American space exploration is to send astronauts to Mars—which President Obama has proposed for the 2030s—then space program managers need achievable milestones to prepare for that mission.

An asteroid orbiting the moon, or at the unique second LaGrange point near the moon where the gravitational pull of Earth and the moon are about equal, would provide such a destination. It would also provide a use for the Orion capsule and Space Launch System now being developed by the agency.

Additionally, the issue of asteroid hazards has taken on a greater urgency of late.

Although tons of material fall every day from space down onto Earth, most is in the form of dust or the fist-sized rocks that become "shooting stars." NASA has long had a program to identify and study near-earth asteroids, but its focus and budget have been growing only in recent years.

Then in February an 11,000-ton meteorite exploded 10 to 16 miles above the skies of the Russian city of Chelyabinsk. The explosion, which was 20 to 30 times more powerful than the atomic bombs dropped on Hiroshima and Nagasaki, caused more than 1,500 injuries, mostly from broken glass. (Video: Predicting Asteroid Impacts.)

A significantly larger asteroid passed by Earth only 16 hours later. That one flew by harmlessly, but further increased concern about the hazards of the many asteroids in our solar neighborhood and supported the case for giving greater attention to what is termed "planetary defense."

An additional reason given to support the asteroid retrieval project involves the fast-growing number of commercial space companies and projects. Several companies have proposed mining asteroids for the rare and valuable metals they are believed to carry, and having a potential mining site so close could quickly spur development.