The U.S. Air Force has directed contractors working on a futuristic
space-based laser to only focus on the system as an anti-missile
weapon.
But this technology, said program officials, also opens the doors
to scientific and military applications other than the obliteration
of intercontinental ballistic missiles.
The space-based laser is an experimental satellite equipped with
a megawatt laser, scheduled to be launched in 2010 or 2011.
A flight test planned for 2013 will prove whether the laser can
zap a long-range ballistic missile in its boost phase. This technology
was the foundation of Ronald Reagan’s Strategic Defense Initiative,
dubbed “Star Wars.”
The test also has “secondary mission objectives,” said
Air Force Col. Neil McCasland. The Air Force Space Command, he said,
is interested in the use of directed energy and the sensors that
go with the laser for missions such as space-object identification
and tracking, space control, ground-target designation and illumination,
air-vehicle tracking or potentially air-vehicle attack in the higher
levels of the stratosphere.
“Those secondary missions,” McCasland stressed, “are
just about as demanding as ballistic-missile defense.” Even
if the experiment failed in its anti-missile role, the project still
would yield large amounts of scientific data, he added.
In addition to the megawatt killer laser, the SBL has a target-illumination
laser and a fine-tracking laser. These are medium-powered, not lethal,
but potentially could be used for ground illumination and to generate
imagery of space objects under laser light.
SBL comes with “very large optics,” said McCasland.
The experimental system will have an optical mirror at least 2.4-3.2
meters in diameter. An operational system may have an optical aperture
as big as 8-12 meters. “This opens the door to very powerful
sensing technology,” he said. The technical infrastructure
is suitable, particularly, for remote-sensing applications.
Three contractors currently are working on the $4 billion SBL flight
demonstration program.
The manufacturer of the SBL primary optics is Lockheed Martin Corp.
Art Woods, the company’s SBL program manager, agreed with
McCasland that imaging applications are feasible, but he cautioned
that the technology needs to mature in this area.
“Since we have a telescope, obviously, it could be used for
imaging,” said Woods. “However, that is going to be
a function of the optical coatings we have on the mirrors.”
Depending upon the reflectivity of the optical coatings in the
visible spectrum, said Woods, “you possibly could do some
imaging, but we don’t know that now, because the coatings
have not been finished or selected.”
The ability of the SBL telescope, or beam director, to generate
images depends on the focal planes used on the hardware, said Woods.
“Right now, there are no designs for focal planes that would
image in the visible spectrum. They will image in the spectrum we
use for locating the [missile] target.” The beam director
is designed to project the laser beam as accurately as possible
on the target.
Eventually, he said, “it would be very logical for a space-based
laser to have that ability, because it’s a large optic. I
would imagine that one would not waste the opportunity.” The
telescope could image space objects or, theoretically, any object
on the ground, or in the air.
“You could design the capability into an SBL to image stars,
for scientific purposes,” said Woods. “But it’s
not clear if anybody would ever be interested in that.”
These missions for SBL would be “a bit of a stretch,”
he noted. The Air Force has not tasked Lockheed Martin to design
the SBL beam director other than for missile defense applications.
Dan Wildt, SBL program manager at TRW Inc., agreed that the large
telescope on SBL could become a powerful imaging tool. TRW is developing
the laser for the SBL project.
Additionally, he said, “you could use the laser to help other
layers of the [theater ballistic missile] systems discriminate between
warheads and decoys, for missiles that have gotten through the boost
phase.”
Don Hockensmith, SBL program manager at Boeing Co., said that if
the Air Force chose to do so, it could add more capabilities to
the SBL satellite, such as surveillance and space-control missions.
But he warned that it would be premature to decide what the system
can do, before it’s fully developed. “When we do the
operational system, we will probably broaden our thinking.”
The optics used in SBL are “unique,” said Hockensmith.
Most space-based optical systems (used for surveillance or imaging)
are passive, because they receive energy from sources on the ground.
“The requirements on those optics are not nearly as stringent
as SBL,” he said. “We are going to be transmitting a
high-energy laser [beam] through these optics and we are going to
be receiving information back through the optics.”
The most stringent requirements are for the coatings that go on
the SBL mirrors, said Hockensmith. “Contamination is a big
issue [because it] can burn the coating.” Optical coatings
are evaporated chemical substances that are laid on the optics,
in a vacuum chamber. Then, they re-condense on the optics and become
a solid thin film. “These coatings have an extremely high
reflectivity,” he said. When light strikes the surface, it
is either reflected or absorbed. In the SBL, “we don’t
want to absorb much energy,” Hockesmith said. “We want
to reflect 99.9 percent [of the energy]. So it takes advanced coatings
to do that.”
A future system could be designed to produce images, he said. “You
could use the same set of optics to receive information from a long
distance and re-image it.”