DEFENSE DEPARTMENT

Laser Satellite Potentially Useful for Imaging, Surveillance

6/1/2001
By Sandra I. Erwin

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.”

Topics: Missiles, Space, Lasers

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