Can giant lasers save us from asteroids?

Editor's note: This story was originally posted 16 Feb 2013, but it's now graduated and become part of Astronomy 101!  Please be aware that any references to events that seem current may not actually reflect events happening right now.

In what has to be the most well-timed announcement ever, a pair of California scientists are suggesting that we deploy giant lasers to space.  Unlike the ill-fated Star Wars project of the 1980's, however, these lasers will be pointing away from Earth, not towards it.  Instead of shooting down missiles, the DE-STAR system would protect us from asteroids.

The lasers would work by collecting energy from the Sun with large solar panels and then redirecting that power out through a giant laser.  The Sun shines with an enormous amount of power, so such a setup could lead to a very powerful laser.  Three different sizes of laser are proposed by the California researchers.  The smallest, about the size of the International Space Station, would have enough power to slowly deflect the path of an asteroid away from the Earth.  The second system would be one hundred times larger and be capable of outright destroying rocks up to ten times the size of the asteroid which barely missed the Earth on Friday.  An even larger system is proposed, but not described.

An orbiting laser could save the Earth from a killer asteroid, but who will pay for it? (Image source: Philip M. Lubin)

The principle of using lasers to deflect or destroy an asteroid is a solid one.  I think that there is little doubt that a large enough laser could indeed protect us from some asteroids.  The problems arise in building and employing this weapon.  No matter what the size of the laser, we will need plenty of advance notice to begin redirecting or destroying a space rock.  And, as we learned in Russia yesterday, sometimes that notice simply doesn't exist.  Asteroid detection is getting better and better, but this system could never completely protect us.

More problematic than even that, however, is who would pay for it.  A truly devastating asteroid, such as the one that hit Russia in 1908, is expected to come around once every hundred years, at most.  The United States (including the largely unpopulated Alaska) makes up just 2% of the world's surface area.  Taken together, this means that (as a very rough estimate) an orbital laser would, on average, save American lives once every 5,000 years.  At a cost which is sure to be in the tens of billions, would the US be forward looking enough to spend that kind of money? Doubtful.  Even if a consortium of countries were to build it, chance are high that it would never be used during its operational lifetime.  Imagine trying to build a replacement for a facility that was never used - that'd be a tough sell!

As these scientists point out, such powerful laser systems could also be used to propel high-speed spacecraft as they explore the solar system.  While this might be plausible, I doubt it will be enough to save this project.  Until a major asteroid is guaranteed to hit us, I doubt much can.

Source: UCSB