Riding Laser Beams to Space
Traveling light today? That takes on new meaning given upcoming tests of small laser-propelled craft that zip through the sky on pulses of light.
These research flights are setting the stage for future launches of ultra-tiny satellites into low Earth orbit. Ultimately, human-carrying spacecraft may be boosted into space via lasers.
NASA and the U.S. Air Force are slated to launch laser-propelled vehicles, dubbed "Lightcraft", in mid August. The series of tests will take place at the White Sands Missile Range in New Mexico.
The Army’s 10-kilowatt, pulsed-carbon-dioxide laser is on deck to send Lightcraft high over the desert scenery. Lightcraft fly atop a beam of laser light, harnessing its energy and converting it into propulsive thrust.
The laser energy strikes a parabolic condensing reflector mounted on the bottom of the Lightcraft. This area is lined with a thin coat of propellant. Struck by laser pulses, the propellant detonates and thrusts the Lightcraft upward.
Lightcraft come in various designs, but weigh around an ounce or two (28 to 56 grams) and measure just a few inches (centimeters) across.
Arguably, a Lightcraft looks like a cross between a giant acorn and a highly polished hubcap stolen off a car of tomorrow.
Lightcraft have already accumulated significant air time.
"We did our first test in July 1996. So we’ve been at this for about four years," said Franklin Mead, project manager, for the Air Force Research Laboratory’s Propulsion Directorate at Edwards Air Force Base, California.
"There’s a lot of historical aspects to this work. We’ve done things that nobody else has ever done," Mead told SPACE.com.
Over 140 flights of the saucer-sized disks have been completed to date. The highest altitude reached by a Lightcraft has been 128 feet (39 meters), a record set nearly a year ago last July.
Lightcraft flights last only seconds. As the vehicle rides on the light beam, it smacks into a black-painted plywood board that is positioned over the test site.
Mead said a goal of the next tests is setting a new record.
"We’re trying to attempt something on the order of 1,000 feet (305 meters)," Mead said. Gone will be the backstop, with the Lightcraft, hopefully, speeding past its current altitude record, he said.
The new series of open-air tests is being coordinated with the Air Force Space Command, which keeps track of Earth-orbiting spacecraft. Bursts of laser light will be timed so as not to blind sensors on satellites that are passing over New Mexico, Mead said.
On the beam
Mead said another possible goal for the upcoming flights is routing the laser beam on the ground from one set of optical gear to another while the Lightcraft is in flight.
By handing off the light beam to successively larger optics, the laser energy hitting the Lightcraft can be sharply focused while the vehicle climbs higher and higher. In essence, these "beam directors" act like stages of a rocket, needed to hurl a payload toward space.
"Flipping the beam around is likely a technique needed for launching Lightcraft into low Earth orbit," Mead said. "It’s more a laser-learning experience than it is a Lightcraft experience," Mead said.
Great progress has been made over the last few years in launching Lightcraft, said Leik Myrabo, chief executive officer of Lightcraft Technologies, Inc., Bennington, Vermont.
He has doggedly pursued laser-propulsion ideas since the late 1960s, working with both the Air Force and NASA.
Myrabo is also a professor of engineering physics at Rensselear Polytechnic Institute in Troy, New York.
Putting on the power!
Myrabo’s novel Lightcraft design work has proven that it is possible to send a small satellite weighing just a few pounds into orbit via laser propulsion.
But reaching a 1,000 feet is a far cry from beam blasting a satellite into orbit.
Myrabo quickly points out that the Lightcraft flights are a 21st-century equivalent of step-by-step experiments done by American rocket pioneer, Robert Goddard, starting in the late 1920s. Goddard built and flew the first liquid-fueled rockets nearly 75 years ago.
"We know we need 10 times the laser power, so we can fly to the edge of space. That’s the kind of trajectory taken by sounding rockets that go up to suborbital heights," he said.
Jointly funding the Lightcraft test program with the Air Force is NASA’s Marshall Space Flight Center in Huntsville, Alabama.
"We could be launching nano- or microsatellites into orbit within five years, given sufficient funding," said Sandy Kirkindall, leader for advanced systems and for laser propulsion at Marshall.
Kirkindall said that the 10-kilowatt laser now used could launch a Lightcraft that weights about as much as an empty coke can. More funds are needed to upgrade that laser by a factor of 10. It could then crank out as much as 150 kilowatts of energy, he said.
"With that upgraded laser we can boost things to the edge of space," Kirkindall said.
The big push
NASA and Air Force studies indicate that about a megawatt of laser power could toss a microsatellite weighing around a kilogram into orbit. Given more megawatts, heavier payloads can be heaved spaceward, Kirkindall said.
Work underway on miniature devices, such as tiny thrusters, gyroscopes and sensors, are giving rise to a whole new breed of spacecraft -- nanosatellites.
"Work in that area looks right on schedule, and would mesh about the right time with laser-propulsion work," Kirkindall said.
In the future, he envisions rapid firing of nanosatellites by laser, one after another.
"Get range clearance. Fuel it up. Put it on the launch stand. Fire up the laser. Boom, you’re out of there," Kirkindall said.
"I don’t see any showstoppers. It’s demanding, but I don’t see anything that you have to build out of ‘unobtainium’," Kirkindall said.
Light on money
While the next test series is meant to fine-tune laser-light-beam-propulsion concepts, finding funds to keep up the work is more a walk in the dark.
NASA’s total budget for laser propulsion is $100,000 dollars. Air Force monies for the joint work are meager as well.
NASA’s Kirkindall, along with Mead of the Air Force, both say future progress in laser propulsion "is a matter of money."
"Funds are minuscule. They are extremely meager," adds John Cole, NASA’s manager of the space transportation research project office at Marshall Space Flight Center.
"Beamed energy is one of the avenues we’ve got if we’re ever going to get the cost of access to space down," Cole said.
Cole sees a 21st century where passenger-carrying space vehicles might be powered upward on laser light. That laser would churn out 100 gigawatts of power, he admits.
"That’s 10,000 times bigger than any laser that’s been built. But, hey, I’ll take whatever works," Cole said.
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Updated: Saturday 23rd, February, 2013