Space

Cost-effective laser-based asteroid defense system pitched to NASA

Artist's impression of a massive asteroid impact (Image: NASA/Don Davis)
Artist's impression of a massive asteroid impact (Image: NASA/Don Davis)
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Diagram of the laser fleet firing on an asteroid
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Diagram of the laser fleet firing on an asteroid
Artist's impression of a massive asteroid impact (Image: NASA/Don Davis)
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Artist's impression of a massive asteroid impact (Image: NASA/Don Davis)
Dr. Richard Fork says that the proposed system is scalable enough deal with wayward comets
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Dr. Richard Fork says that the proposed system is scalable enough deal with wayward comets

Last year, the University of Strathclyde in Glasgow put forward the idea of using fleets of laser-toting satellites to deflect potentially dangerous objects away from Earth. Now, Dr. Richard Fork, principal investigator for the Laser Science and Engineering Laboratory at the University of Alabama in Huntsville (UAH), and his team have refined the idea, saying that it’s not only feasible, but could handle anything up to the size of a comet.

If an asteroid 100 m (330 ft) across hit the Earth, it would be a bad day. The impact of a comet such as Halle-Bopp, which is about 70 km (43 mi) in diameter, would make for a very, very bad day. According to Fork, "[The Hale-Bopp comet] is enormous, and if it had been on a collision course with Earth we would have had only two years from the time it was first observed to the time it arrived at Earth. If the comet happened to be on track to hit us, there would have been nothing we could have done. We would have been toast."

Because of the remote, but still present, danger of such an event happening, finding ways to deflect asteroids is of great interest to scientists and engineers. The idea floated by researchers at Strathclyde University in 2012 involves sending a fleet of small satellites that fires lasers at a potentially dangerous asteroid. The purpose wouldn't be to destroy it in a spectacular Death Star-like explosion, but to nudge it into a new orbit.

Diagram of the laser fleet firing on an asteroid
Diagram of the laser fleet firing on an asteroid

Instead of one large laser blasting away at a space-going rock, several small ones from the solar-powered satellites would vaporize areas on the asteroid and this vapor and debris would act like a rocket thruster, pushing the asteroid away. The advantages of such a system are, among others, that it’s cheaper than ground-based lasers or a laser installed in a large spacecraft. Since it’s solar powered, the system would also require much less propellant than a single large space laser and could work at lower wattage than an Earth-based one.

Though similar, the UAH system is based on work started by Dr. Fork at Bell Labs in the 1980s. In the UAH approach, there’s also a fleet of mini satellites, by they are tended by a mothership that that powers the actual laser, which the mini satellites reflect onto the target.

If a threatening asteroid is detected, the satellites are dispatched, perhaps as a unit using an ion drive. On arrival, the mini satellites fan out and orbit the asteroid within a few kilometers. The satellites scan the asteroid and produce a submillimeter-resolution 3D map of the surface, which is constantly updated. This information is used to find flat surfaces that would be an optimal target for the lasers. These areas can be under a millimeter wide.

Dr. Richard Fork says that the proposed system is scalable enough deal with wayward comets
Dr. Richard Fork says that the proposed system is scalable enough deal with wayward comets

The mothership would supply the lasers, which the minisats reflect onto the asteroid. Coordinated bursts of optical laser blasts would be fired for only picoseconds at a time, vaporizing the rock surface. This may not seem like much, but Fork says that the effect is surprisingly large.

"The amount of average power to be delivered to the asteroid as coherent laser light can be comparable to the power, 10 kilowatts, supplied by the solar system to the currently existing Dawn spacecraft," Fork says.

"One pulse, during the brief time the propulsive force is applied, provides as much power as all three Space Shuttle main engines when they are firing together," continues Fork. "The challenging technical task our group is addressing is that of delivering the required total number of these pulses to an Earth-threatening asteroid so as to apply this highly effective propulsive force efficiently with each delivered pulse.”

There was some concern about the debris clouds interfering with the lasers, but the team concluded that these would disperse from the targets areas within three microseconds.

As the lasers are applied, the satellites continue to scan and to plot the asteroid’s trajectory; applying the necessary course corrections as needed. The lasers can also be used to make the asteroid stop spinning by strategically firing the lasers, so the debris jets act like the attitude control rockets on a spacecraft.

Presented to NASA because of its cost effectiveness, the system is designed to initially tackle small near Earth objects, specifically ones about 20 m (66 ft) in diameter, which is about the size of the one that exploded over Chelyabinsk, Russia earlier this year. Fork is confident that the technology to build such satellites already exists and it’s possible to deflect a small asteroid in the near future. He also says that the proposed system is scalable enough deal with wayward comets, providing enough power can be brought to bear with enough advance warning time.

A paper with the team’s results can be found at the Cornell University Library (PDF)

Source: University of Alabama in Huntsville

16 comments
Slowburn
The idea that the USofA could not launch multiple nukes on deep space trajectories on three months notice is ludicrous. So could Russia and I suspect that the PRC would toss a couple of their own as well.
jochair
This might just work, if the blasts are at the correct angle simultaneously. Glad nobody came up with the idea to move earth.
Strauski
Could also be used to deliberately target earth with a comet.
Fishing Zebra
The laser-based system could work on asteroids, but if time was off the essence explosives, preferably nuclear, could be more effective at a shorter time period. A fleet of small space probes that detonate at close proximity to a asteroid, at the same side of the rock over and over again, could gradely push it on a different course. Controlled blast at a distance would make better use of its energy than what a surface explosion would do. The atomic bomb that destroyed Hiroshima detonated 1,968 feet (600m) above the city. It was more efficient because of the distance that existed between center of explosion and ground. The approach described in this article could be effective against comets. A comet is a so-called dirty snowball, many small and big rocks held together by frozen water. Is more fragile and less dense than what a rocky asteroid is. A explosion could break the comet apart, but it would most likely continued on the same course. Explosives against comets is probably a bad approach.
Seth Miesters
Might as well use this same tech to shift useful material to L1 or lunar orbit.
zevulon
do the math,--moving a solid mass sphere of radius of 30km is ludicrously impossible to do for large distances, especially over short periods of time. i did the math of trying to crash phobos or deimos into mars and the energy required---assuming 100% of all energy necessary to move the mass is efficiently produced by a 100% energy efficient process-----is ludicrous. even deimos, with a radius of 6+ kilometers and moving at 1.35 kilometers a second relative to mars is nearly impossible to move and significant distance closer to the martian surface, even over a 100 year period. to theorize about asteroid deflection is one thing. however, if you take for granted that we have small tactical nukes that can be hoisted onto existing space rockets for TESTING on real asteroids, using 1 kiloton explosions for TESTS on real asteroids [ which are far more likely to hit earth than comets ]------------then you are actually looking into empirical testing. not theorizing. the best candidate for 'experimenting' with deflecting asteroids (for a madman perhaps?)-----is 1999 an10 http://www.halfbakery.com/idea/killasteroid#1380738091
frogola
Cost-effective to save the planet really.
kellory
And just what keeps those reflectors facing the "right" way? Could this not also be fired at dirtside targets? How much of that 10 kilowatts would make it through our atmosphere? With the precision required, perhaps even human targets?
Stephen N Russell
& how about a Lunar based remote Laser as well aside those Lasersats. Other problems with Lasersats: 1. Hacking 2. Use for war over Earth. Otherwise Yes, mass produce & launch in HEO or cisliunar orbit mode.
Gregg Eshelman
If there's something on a collision course with Earth, cost effective = whatever it costs to stop it from hitting Earth. Then just like Y2K there will be all the ninnies going on about all the hype over something that wasn't really a problem. Duh! It wasn't a problem because of all the effort and expense people put forth to ensure it wouldn't be one. If nothing had been done, they would've sure thought it was a problem to wake up on January 1st to discover all their power and gas shut off because the computers thought it was the year 19,100.
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