An experimental satellite loaded with a megawatt laser could be
launched into orbit some time between 2010 and 2012. Its mission
would be to zap an intercontinental ballistic missile, fired from
a location on Earth, hundreds of miles away.
Exotic space-based beam weapons—the so-called Star Wars systems—have
been in and out of the spotlight for more than two decades. The
idea of a space-based shield against Soviet nuclear missiles was
embraced by Ronald Reagan in 1983. The plan faded away with the
end of the Cold War. In the early 1990s, the Pentagon shifted its
financial resources from celestial defenses to land-based theater
systems that would protect troops from short-range tactical missiles.
But the notion of deploying a missile-defense system in space did
not vanish entirely. Congressional Republicans, particularly, provided
funding for military space research, even when the administration
did not support the projects.
Space-based anti-missile weapons are banned by the 1972 Anti-Ballistic
Missile Treaty. But, from a technological standpoint, it appears
that such a system is achievable, provided that the Pentagon commits
the funding. Even though the treaty prohibits the deployment of
space-based missile defenses, it cannot stop the United States from
pursuing research and testing technologies.
That is exactly what the U.S. Air Force plans to do, under a program
called Space-Based Laser Integrated Flight Experiment (SBL-IFX).
The $4 billion program is co-sponsored by the Ballistic Missile
Defense Organization.
The Air Force expects to formalize the technical specifications
for SBL-IFX this fall.
The experiment currently is scheduled for 2013, which would require
that, by 2012, the Air Force launch what is expected to be a 40-foot
long, 40,000-pound spacecraft, loaded with a megawatt laser, beam-control
optical mirrors and a beam-director telescope.
Only a heavy Delta IV-type launch could lift the SBL-IFX, which
would be among the weightiest military payloads ever sent into low
orbit (about 250 to 300 miles high). By comparison, NASA’s
Hubble space telescope weighs about 30,000 pounds.
The program’s director, Air Force Col. Neil McCasland, cautions
that it is too early to label the SBL-IFX as a definitive missile-defense
option for the United States. “It is only a demonstration,”
he said in an interview. But there is potential, he noted, to evolve
the technology toward the deployment of a global network of space-based
interceptor satellites, which would destroy intercontinental-class
ballistic missiles (ICBMs) using directed energy.
Congressional supporters of the SBL would like McCasland to accelerate
the program, and aim for a 2010 launch. It is not clear, however,
how much it would cost to do that.
The Pentagon budgeted $138 million annually for the program for
the next two years, said McCasland.
According to a U.S. Senate source, there are “quite a few”
members of Congress who would like to move SBL forward at a faster
pace.
The source stressed, nevertheless, that additional funding for
SBL is not guaranteed, and that the system should not be viewed
as a reincarnation of Reagan’s Star Wars model, but rather
as a complement to the land-based national missile defense (NMD)
currently in development. “SBL would be the final stepping
stone” in a layered system, said the source.
The SBL-IFX is not about sending a robotic weapon into space, with
no humans in the control loop, McCasland said. It is not going to
detect, intercept and shoot autonomously, he explained. Like most
engineering tests, it will have a carefully planned test scenario.
The system will know where the launch is coming from, and the target
vehicle will be flown deliberately into the engagement range of
the laser. “There is no reason at this stage to make the system
capable of autonomous operations,” said McCasland. The ground
control station will be based at Cape Canaveral, Fla.
A full-fledged SBL constellation is not in the plans today and
may never be. But the Air Force has looked at notional systems,
which could range from 18 to 36 platforms. Other studies considered
the possibility of mixing shooter satellites with relay-only satellites,
which would not have a laser and, thus, would lower the cost of
the system. “It depends on the particular threat that we have
to engineer against,” said McCasland. “It depends on
the other layers in the NMD architecture.
“The Defense Department hasn’t made up its mind on
what it wants to do in this area yet,” he said. “It’s
way too early for it, frankly.”
If the U.S. government decided to deploy an SBL system, it would
violate the ABM Treaty, said Nicholas Berry, an arms-control expert
at the Center for Defense Information. Experiments such as the IFX,
however, are not prohibited.
To get ready for the SBL-IFX, the Air Force needs to build a new
test facility, a sophisticated vacuum chamber that will allow engineers
to shoot the laser in an atmosphere-free environment, as it would
in outer space. The home for this test site will be the Stennis
Space Center, Miss.
The laser technology has been in development for more than two
decades by TRW Inc. The company is one of three contractors that
share the SBL work. The other two firms are Lockheed Martin Missiles
& Space, and Boeing Space & Communications.
The three companies have received incremental contracts since February
1999. Their current contract is worth $240 million.
The three-contractor arrangement resulted from a “conscious
decision by the Defense Department to not run a competition for
this flight demonstration,” said McCasland. The idea is to
preserve an industrial base, in case the Pentagon decides to proceed
with full-scale development of an SBL constellation.
TRW is responsible for the laser payload and for building the test
facility at Stennis. The company has been testing lasers at its
Capistrano facility, near San Clemente, Calif. The SBL laser has
run 103 seconds so far. But that is not nearly enough, said McCasland.
“We need to accumulate a lot more test time.”
These lasers have to run in a vacuum, he said. “So we need
a test facility that is capable of evacuating all the air, and then
pulling the laser exhaust out of the chamber as fast as we burn
the fuel.”
A subscale model of the laser payload will continue to be tested
at Capistrano, and a design review is scheduled for 2005. The facility
at Stennis could take up to five years to complete.
Even though laser technology has matured significantly in recent
years, there is complex mechanical engineering required in the SBL
to reduce the number of parts and harden them to withstand the launch
shock, said McCasland. The spacecraft also has to be engineered
so it can operate unattended in space, for several years at a time.
“We are trying to verify all these things with this flight
demonstration.”
Another “really challenging area” is the so-called
close-loop control of the laser, McCasland said. The beam has to
project across hundreds of miles of space and focus on a small spot,
less than 2 feet in diameter, for several seconds. “That much
precision is a demanding thing,” he said.
The key is to control the wave-front quality of the laser source,
in order to project it across large distances, explained TRW’s
Dan Wildt.
In all waves, including light, the wave moves or propagates in
a direction perpendicular to the wave-front. A laser beam travels
in a direction perpendicular to the local orientation of the wave-front.
When the wave-front of light is perfectly flat, which is rare, all
the light moves in the same direction toward the target. However,
if the wave-front is irregular, the individual portions of the beam
move in slightly different directions. The result, if pointing toward
a distant target, is that the light spreads, causing some of it
to miss the target.
The high-power beam generated by the SBL-IFX laser is relatively
flat, but not perfectly flat. The beam control system measures the
wave-front of the laser beam, then “reshapes” a deformable
mirror in order to correct wave-front errors and make the beam flatter,
Wildt said. “By flattening the wave-front, we effectively
maximize the amount of energy that strikes the target.”
TRW has to assemble its megawatt laser with a beam-director telescope
made by Lockheed and the beam-control optics made by Boeing. “We
are responsible to make sure that the three work together,”
said Wildt.
The beam-control system is used to both minimize the jitter and
to flatten the wave-front.
Inside the atmosphere, jitter control is a more difficult challenge
than wave-front correction, while the opposite is true outside the
atmosphere, said Don Hockensmith, program manager at Boeing Space
& Communications, in Seal Beach, Calif. The reason is that the
atmosphere distorts the beam on the way to the target.
The beam-control system that Boeing developed is a collection of
optical mirrors that are steered. Some are flat mirrors, some are
deformable mirrors, Hockensmith said. When the beam comes out of
the laser, it’s somewhat corrupted, its wave-front is not
perfect and is jittery. The wave-front control is a very complex
system of mirrors, electronics and software, and its mission is
to correct the jitter before the beam is projected out of the beam-director
telescope.
The beam-director expands the small-diameter beam that comes out
of the laser into a larger beam, then focuses on a small spot on
the target, said Art Woods, SBL program manager at Lockheed Martin
Missiles & Space, in Sunnyvale, Calif.
The beam director primary mirror for the SBL-IFX is between 2.4
and 3.2 meters in diameter. The unit looks like a two-mirror telescope,
with a small mirror in front of a large one.
In an operational SBL system, the diameter would go up 8-12 meters,
said Woods. “There is a parallel program [at Lockheed Martin]
to develop that technology, which is not part of the flight experiment
program.”
Lockheed also is responsible for manufacturing the SBL-IFX spacecraft,
which will be a down-scaled version of an operational satellite,
said Woods.
He expressed some skepticism about Air Force studies that proposed
SBL architectures that mix relay platforms with laser spacecraft,
to cut costs. “Depending on technology development, there
may be an opportunity to intermix a relay satellite with space-based
laser satellites,” he said. The laser satellites would point
the beam toward the relay satellites, which in turn would bounce
the beam to the target. This concept, said Woods, is contingent
on “whether the right technologies can be developed.”
If the SBL-IFX takes place as planned, it would mark the first
time that the United States launched a space platform with a high-power
laser on board.
The SBL is a chemical hydrogen-fluorine (HF) laser. The hardware
makes up a large fraction of the space vehicle. It accounts for
about half the weight and one-third of the payload volume.
Chemical Laser
TRW also has developed a chemical oxygen-iodine laser for the Airborne
Laser, a jet-mounted system designed to shoot ballistic missiles
in their boost phase, but inside the atmosphere. The HF laser is
“ideal for space,” said Wildt, because the reactants
can be stored for long periods of time in space.
The HF laser device’s waste heat is exhausted into space,
with the spent reactants. The upshot, he said, is that “we
don’t have to deal with additional heat. Waste heat is a challenge
in space.”
Wildt would not reveal the exact wattage of the laser, other than
saying that it is in the “megawatt class.” He speculated
that it would be able to destroy an ICBM in seconds.
According to McCasland, the SBL potentially could attack aircraft
flying in the higher levels of the stratosphere. “We think
the laser will penetrate into the very highest levels of the atmosphere,”
he said.
That may or may not happen, said Wildt. The SBL laser wavelength
is 2.7 microns, a wavelength that would be absorbed by water vapor
in the atmosphere. “This laser does not penetrate the atmosphere
well,” he said. “It’ll all be absorbed by the
time you get to about 30,000 to 40,000 feet.”
As far as maintenance goes, said Wildt, SBL presents huge challenges.
The more formidable one is the idea that every glitch has to be
fixed or adjusted remotely, he noted. “We have to design a
robustness and flexibility so we can operate it from the ground.”