Every day, the Earth is under bombardment from space. Not, of course, from alien invasion, but from debris. Current calculations indicate that somewhere between 18,000 and 84,000 meteorites weighing more than 10 grams (0.35 ounces) fall to Earth every year. Most of these don't do any harm, but a larger asteroid or comet that crosses Earth's orbit can pose significant risk.
A team of researchers, led by UCSB physicist Philip Lubin and California Polytechnic State University, San Luis Obispo professor Gary B. Hughes, are developing a system they are calling DE-STAR (Directed Energy System for Targeting of Asteroids and exploRation).
This will consist of a modular phased array of kilowatt lasers powered by photovoltaic panels, using the sun's mighty power to laser rocks away from Earth. In theory, the lasers would be placed in orbit around the Earth in increments (which would allow for costs to be spread out and for the system to be tested before full deployment).
Before any solar-powered lasers can be sent into space, though, the feasibility of the idea needs to be demonstrated. And, in a controlled, scaled-down lab setting, this is exactly what a team of students in Lubin's Experimental Cosmology Group have done.
To test the concept, the team used a small piece of basalt. Basalt is a volcanic rock that has a composition similar to the composition of asteroids. This was placed in a vacuum chamber, and heated with a laser to about 2,000 to 3,000 Kelvin. At temperatures this high, the basalt glows white hot, and material erodes from the surface. This is called laser ablation.
As material erodes from the rock, its mass changes, and the heat acts like a rocket engine. In the vacuum of space, this would be enough to propel the rock away from the laser.
"What happens is a process called sublimation or vaporization, which turns a solid or liquid into a gas," explained Travis Brashears, a freshman at UC Berkeley who led the experiments. "That gas causes a plume cloud -- mass ejection -- which generates an opposite and equal reaction or thrust -- and that's what we measure."
But asteroids are never stationary in space: According to Lubin, they're always spinning, even if it's just a tiny spin. To simulate a spinning asteroid, the team used magnets to rotate the basalt. The laser was then directed in the opposite direction, to gauge if it would have any effect on the rock's spin.
"Our video shows the basalt sample slowing down, stopping and changing direction and then spinning up again," Brashears said. "That's how much force we're getting. It's a nice way to show this process and to demonstrate that de-spinning an asteroid is actually possible as predicted in our papers."
Stopping or slowing the spin of an asteroid or comet would make it much easier to land a module on the surface, whether for research or for mining purposes, Although, it would take more time or a bigger laser for the larger objects. This would be what the team call DE-STARLITE, a smaller, individual system that could be deployed on a single launcher for dealing with larger hazards.
The paper on Brashears' team's research can be found online here.