Laser asteroid defense

Could lasers protect the Earth from wayward asteroids? A number of schemes have been proposed for pushing asteroids gradually to move their orbits away from the planet. Now, two California professors are proposing a bold scheme to build solar-powered space lasers powerful enough to evaporate a 500 m asteroid in about a year--or to make short work of a 17 m asteroid like the one that exploded near Chelyabinsk, Russia, on February 15.

Philip Lubin of the University of California (Santa Barbara, CA) and Gary Hughes of California Polytechnic State University (San Luis Obispo, CA) began planning the project they call DE-STAR--for Directed Energy Solar Targeting of Asteroids and exploRation--a year ago. On February 14, they issued a press release timed to the close approach by asteroid 2012 DA14. They were as stunned by the Russian explosion as everyone else.

Their bold proposal seeks to take advantage of the dramatic improvements in high-power diode lasers and solid-state lighting to build giant orbital phased arrays of lasers powered by electricity from huge solar panels. They envision starting with a desktop 1 m array called DE-STAR 0, then scaling up to a 10 m array called DE-STAR 1. They have proposed that NASA support a conceptual study of scaling up to a 10 km DE-STAR 4 array, powerful enough to vaporize a half-kilometer asteroid 150 million kilometers away. Even bigger versions could be used for laser propulsion; they estimate that a 1000 km DE-STAR 6 array could accelerate a 10 ton spacecraft close to the speed of light.

Future DE-STAR array samples composition of an asteroid as it propels an interplanetary spacecraft. (Courtesy of Philip Lubin)

The scheme may sound fantastic, but Lubin says it violates no laws of physics and requires no "technological miracles." It merely envisions continuing technological progress at the rate of the past 50 years, which took us from the feeble LEDs and diode lasers of 1963 to today's powerful emitters. They assume photovoltaic cells that can convert 70% of incident solar energy into electricity, and diodes which can convert 70% of the input electrical power into light.

Lubin doesn't think it will be easy. He worries about issues including the mass needed to build the giant array, and controlling output phase across the array with the precision needed to tightly focus the emission. But he predicts his assumptions will be considered "extraordinarily conservative and modest" in 30 to 50 years.

That remains to be seen, but space-based solar-powered diode arrays are worth investigating. They could go beyond asteroid defense to could help move asteroids, collect valuable materials from them, or provide power resources in space--as well as inspiring some fun science-fiction stories.

New visions for space telescopes

NASA stumbled into a rare bit of good luck recently when the National Reconnaissance Office did some housecleaning. NRO decided that a pair of space-qualified 2.4 m telescopes dating from the late 1990s were no longer suitable for their original mission in spy satellites. So NRO offered the surplus optics to one of its poorer relations, NASA, for use in new space-based instruments. 

Unexpected hand-me-downs can bring opportunity, like the the piles of Scientific American and Sky & Telescope that came with a house my family rented when I was in high school. Astronomers and NASA scientists are pondering what to do with the windfall. The f/8 Cassegrain telescopes lack instruments, electronics, or spacecraft, but NRO long ago paid for the optics, saving NASA serious money. The Study on Applications for Large Space Optics workshop held February 5 and 6, 2013, in Huntsville, AL heard and discussed 34 proposals for building new instruments around the mirrors. They will be narrowed to six proposals and submitted to NASA management in May.

The range of ideas is impressive. Adaptive optics can do wonders on the ground, but ultraviolet astronomy must remain above the atmosphere, so three proposals call for studying the ultraviolet sky. Other common themes are spectroscopy, planetary science inside the solar system, and attempts to image challenging targets including extrasolar planets.

Bare-bones surplus telescopes inherited by NASA (Government work not subject to copyright)

Some proposals are intriguing. Alfred McEwen of the University of Arizona (Tucson, AZ) envisions the Mars Orbiting Space Telescope, and  Zachary Bailey of the Jet Propulsion Laboratory (Pasadena, CA) proposes "high-resolution surface science at Mars."  Rebecca Farr of the NASA Marshall Space Flight Center (Huntsville, AL) proposes using both mirrors as a deep-space binocular telescope stationed at the Lunar L2 Lagrange point.

Not everything is exactly a telescope. Abhijit Biswas of JPL wants to use a mirror as an optical communications node in space. J. H. Clemmons of the Aerospace Corp. (El Segundo, CA) wants to use one in a lidar to explore the Earth's thermosphere.  Richard Eastes of the University of Central Florida (Orlando, FL) has a plan for "Atmospheric TeleConnections on Earth."

There are plenty more listed on the program, and NASA will be recording the proceedings for later viewing. The ideas are not fully formed, of course, and some seem to duplicate others. But there are enough bright ideas to make one hope that NRO can find more goodies sitting in storage for its needy relatives.

Source:  http://science.nasa.gov/salso/telescope-characteristics-and-capabilities/