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Beam me up?
"Star Wars" lasers could make light work of launching future satellites
By Andy Walton
NEAR LAS CRUCES, New Mexico -- Leik Myrabo has a unique idea for launching satellites. He wants to beam them up.
This isn't a "Star Trek" fantasy. It's an experiment in a new form of propulsion, using only light and air. The test vehicle, a palm-sized flying saucer-like structure, is made of aircraft aluminum with no moving parts and no fuel. The heavy lifting is done by a laser on the ground.
The underside of the vehicle -- dubbed a Lightcraft -- is a parabolic mirror that focuses the laser toward the edge. There, at temperatures from 10,000 to 30,000 degrees Kelvin (about 18,000 to 54,000 degrees Fahrenheit), the air itself explodes, providing thrust. The launch leaves no chemical exhaust, no environmental impact at all.
Myrabo, an aerospace engineering professor at Rensselaer Polytechnic Institute (RPI) of Troy, New York, first had the idea for the Lightcraft 10 years ago. Developed as part of "Star Wars" anti-missile research, Lightcraft were limited to paper studies until about four years ago, when Myrabo and Air Force scientist Franklin Mead began trying it out.
"We're at the very beginning of this technology," Myrabo said. "I like to draw an analogy between where we are right now and where Robert Goddard, the father of liquid-propellant rocketry, was in 1926 when he launched his first liquid-propelled rocket.
"His first flight was about 41 feet (12.5 meters), which we passed last November," Myrabo said. "His second flight was 90 feet (27.4 meters), and we passed that in March."
Like a bat out of HELSTF
The flight tests are held at the Army's High Energy Laser Systems Test Facility (HELSTF), near Los Cruces, New Mexico, toward the southern end of the White Sands Missile Range. The power plant is the Pulsed Laser Vulnerability Test System (PLVTS), a 10-kilowatt carbon dioxide laser that the Army uses to test the vulnerability of its own systems to laser attacks. For the Lightcraft test, PLVTS produces 20 infrared pulses a second.
The PLVTS laser is mounted in a trailer for portability, with the power supply in a second trailer.
Inside the PLVTS trailer, one piece of equipment betrays the laser's origin as a weapon. A 50 centimeter swiveling "beam director" -- essentially a telescope -- focuses the laser beam, allowing it to hit targets several kilometers downrange.
For the Lightcraft tests, it's all done with mirrors, which are meticulously adjusted in a process that takes hours. Test firings scorch black marks on a sheet of paper, and the mirrors are tweaked until a mark is centered where the Lightcraft will be.
About 120 feet above the ground, a crane holds a black-painted board that catches any stray beams that miss the Lightcraft. This is a precaution to protect satellites with sensitive infrared sensors that could be "blinded" by the laser. Higher-altitude flights, without a backstop, will require clearance from the North American Aerospace Command, which handles traffic control in Earth orbit.
Before a launch, Myrabo positions the craft on a spindle and sets it spinning at about 6,000 revolutions per minute with a jet of nitrogen gas. Like a child's top or toy gyroscope, the spinning stabilizes the satellite on its axis. After a 5-second countdown, the laser fires with a rapid series of pops. Though the beam is not visible, the explosions on the Lightcraft produce bright flashes.
The craft lifts off the spindle and surges upward for a few seconds -- about a hundred feet into the air in the more successful trials. The test is over after about 100 laser pulses (or 5 seconds), when a metal band around the combustion chamber overheats and breaks. A cooling system is a priority for future tests.
The damaged Lightcraft falls away from the laser beam, which is quickly shut off; the craft then falls to Earth, where technicians wait to catch it with foam-padded swimming pool nets. Caught gently, many of the Lightcraft's parts can be recycled for future flights.
Space on a shoestring?
Future Lightcraft models will likely be built from exotic materials like composites or high-temperature ceramics. The plan is to launch a 1-kilogram (2.2 pound) satellite into orbit within five years.
In three years, the Air Force and NASA plan to use equipment already in the HELSTF inventory to assemble a 100-kilowatt laser, 10 times more powerful than the PLVTS -- which is now the most powerful laser of its kind in the United States. An orbital launch will require a megawatt laser, 10 times larger than the planned Air Force-NASA laser.
To get into orbit, Lightcraft will have to travel five to six times the speed of sound. They will also require fuel on board, likely liquid hydrogen, for use when the craft gets too high to use air as fuel. Adding fuel will increase the weight and require a more powerful laser. Tests with the PLVTS are limited to 50 grams (less than 2 ounces).
The challenges are many, but the potential payoff is enormous.
"The total cost of electricity to propel that 1-kilogram microsatellite into orbit will just be a couple of hundred dollars," Myrabo says. "Since the laser is always sitting on the ground and is never at risk, that huge investment you make [to build the laser] is amortized over many, many launches, whereas with chemical rockets, you launch it once and it's gone.
"A shuttle launch today costs you about $10,000 per pound of payload into orbit," Myrabo says. "We're trying to get that down by a factor of about one thousand, or at least [a factor of] a hundred within a few years."
White Sands is no stranger to breakthroughs in space technology. Goddard flew early liquid-fueled test rockets in nearby Roswell. And in the days following World War II, U.S. and German scientists conducted the first tests of captured German V-2 rockets at what was then called the White Sands Proving Ground. Those tests, conducted by Wernher von Braun and others, were the start of America's ballistic missile and space programs.
Today, the range -- larger than the states of Delaware and Rhode Island combined -- remains the primary missile test area for the U.S. military. It is also a backup landing site for the space shuttle, which landed there in 1982.
If the Lightcraft team -- essentially Myrabo and Mead, laser technicians from HELSTF, and help from RPI students -- has its way, White Sands is now bearing witness to another idea moving from science fiction to scientific fact.