At the movies, the best way to stop an asteroid from wiping out Earth is to lob a few nuclear missiles at the rocky beast or blow it apart from the inside with megaton bombs.
While those methods promise some fantastic explosions — and maybe a blockbuster hit — engineers are looking at a more patient approach. Their weapon: a swarm of nuclear-powered robots that could drill into an asteroid and hurl chunks of it into space with enough force to gradually push it away from an Earth-impacting course.
"We're aiming to examine the whole idea of these robots," said Matthew Graham, design project manager for the study at SpaceWorks Engineering Inc., an engineering consulting and concept analysis firm in Atlanta.
SpaceWorks researchers have completed a preliminary study into the robots, called Modular Asteroid Deflection Mission Ejector Node spacecraft, or MADMEN. The work was done under a grant awarded by the NASA Institute for Advanced Concepts, or NIAC, to come up with new techniques to defend the planet against pesky near-Earth objects.
"Previous studies by NASA and NIAC focused on concepts that could detect asteroids or bump them using propulsion systems of nuclear weapons," NIAC director Robert Cassanova told Space.com. "[MADMEN] was rather unique in that it would nibble away at the asteroid."
Mass drivers wanted
At the heart of the MADMEN concept is a mass driver, which would eject asteroid material as it is drilled out of the rock and sling it out into space using electromagnetic acceleration. The recoil from that ejection would push against the robot, and therefore the asteroid, imparting a small amount of force for each shot.
"It's like throwing rocks from inside a rowboat," Graham said in a telephone interview. "Over time, you end up moving the boat."
A preliminary design for a MADMEN spacecraft outlines a 1-ton robot that would stand about 36 feet (11 meters) high, just slightly taller than NASA's Apollo moon lander, on an asteroid’s surface. The mass-driving ejector, a self-assembling tube, would extend out toward space ready to start its slow, steady push against the rock at a rate of one shot a minute or so. A liquid-propellant booster rocket could deliver the lander to its cometary or asteroid target.
But the push would be small, and more than one MADMEN spacecraft would be required to constantly shove a space rock in one, uniform direction.
A MADMEN swarm
Since each MADMEN robot could only give a small push to an asteroid over time, Spaceworks researchers envision sending an entire fleet of them to a potential Earth impactor. The key, they said, is to have a lander on each face of an asteroid working together autonomously to push the space rock in one direction as it tumbles through space.
In a presentation to NIAC, MADMEN researchers compared their robotic devices to the cybernetic "Star Trek" juggernaut, the Borg, a species that overlooks individual casualties in pursuit of its goals.
"The benefit of the swarm is redundancy," Graham said. "Some could be destroyed, others lost, and the rest can still challenge the asteroid."
To build a swarm, MADMEN robots would have to be manufactured well before a potentially Earth-threatening asteroid was discovered. A stockpile of inert MADMEN spacecraft — each with its own fuel reserve — could be gathered into nearby parking orbits where they could be called upon if a stray space rock wandered too close.
Deciding how many MADMEN to send, thousands or maybe just four or so, would depend on the lead time before a potential impact, researchers said.
"If you have a good amount of warning, like 10 years, then you don't need to send many," Graham added.
More study needed
There are still a number of technological hurdles facing researchers before the first MADMEN robot could start its Earth-protecting mission — not the least of which is the mass driver machinery needed to eject asteroid chunks into space.
"People have not made a production versions of this," Graham said, adding that MADMEN mass drivers would have to fire away ejecta continuously on time scales of a year. "So something very reliable and light and strong and accurate is needed."
A lightweight space nuclear power plant also requires further study, as well as the drilling system that would eventually eat away at offending asteroids or comets.
"Drilling systems today mainly use water to move mass up the tube and away from the bit," Graham said. "In space, you need to develop a closed system to do that."
Waiting for a go-ahead
With the first phase of MADMEN study complete, SpaceWorks is awaiting a decision from NIAC on whether to fund a second round of research that would focus, among other things, on the design of a technology-testing precursor mission to be carried out in the next decade.
"Phase two means going into more detail, building a roadmap to develop the enabling technology for these projects," Casanova said. "We'd like to think that NASA would be interested in these projects once a phase-two study is finished."
Graham said it could be several months before phase-two approval for the MADMEN project is awarded. He is confident, however, that if the need were urgent enough, Earth scientists would be able to step up to the task of defending the planet with MADMEN robots or some other method.
NASA, Graham explained, has already demonstrated its ability to land on as asteroid when the NEAR Shoemaker spacecraft came to a soft landing on the asteroid Eros. Meanwhile, the European Space Agency's Rosetta mission is expected to drop its own lander, Philae, on a comet sometime in 2014.
"If it's a world-killing asteroid, well, then it's all about motivation," Graham said.