Riding Laser Beams to Space
Source: Space.com
July 5, 2000
WASHINGTON -- 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.
Test time
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.
By Leonard David
Senior Space Writer
http://www.space.com/businesstechnology/technology/laser_propulsion_00
0705.html