Documents / Report
The Defense Intelligence Agency produced this reference document, dated 31 March 2010, under its Advanced Aerospace Weapon System Applications (AAWSA) Program. It reviews the state of the art and likely evolution of high-energy laser weapons, including chemical, solid-state, fiber and free-electron lasers, as well as beam control and the history of DoD laser research. It concludes that electrically powered lasers could make megawatt-class weapons practical and that spacecraft laser weapons are conceivable within 20 years. It also recommends ways to protect spacecraft from laser damage.
UNCLASSIFIED/ ,'FOR OFFllil-,L 1!1!11! 911E I completely in the vacuum of space, there is obviously no need for target loop adaptive optics. The measure of a beam control system's performance is its ability to maximize the HEL beam's average irradiance (watts/cm 2 ) in the focused spot on the aim point and maintain it there while sufficient fluence (watts/cm 2 x time or joules/cm2 ) is accumulated. The total power in this focused spot is typically about one-half of the laser's output power further reduced by losses in the beam control system's optical train and the atmosphere. The laser beam's spot size on the target has many contributors. Optical diffraction establishes the spot's minimum area at approximately (R!c/D)2 where R is the range to the target, /, is the laser beam's wavelength and D is the diameter of the pointing telescope. Improvement can be only achieved by reducing the range to the target, using a laser with shorter wavelength or increasing the pointing telescope's size. This ideal (diffraction limited) spot area, is unachievable in a real system. Additional contributors to the actual spot area include a less-than-perfect laser beam (beam quality greater than one), mechanical jitter of the beam control system from the tracker, the alignment systems, or base motion disturbance and atmospheric distortions from turbulence or thermal blooming. Each of these contributors to the laser beam spot's area serve to reduce the irradiance by spreading the laser power over a larger area. Figure 10 is a cartoon of the gimbaled portion of a beam control system and is used to illustrate basic servo control functions. A tracking telescope and optical sensor are mounted on the elevation over azimuth gimbal. Their purpose is to generate an electronic image of the target and send it to the tracker. This tracker is a special- purpose computer which then processes the target image, identifies the desired aim point and measures the angle between it and the optical boresight of the telescope. Its output is a command to the gimbals to rotate until the optical axis of the tracking telescope is following the target and pointing at the aim point. If the gimbals are mounted on a moving or vibrating platform, these disturbances introduce additional tracking errors. Unlike target motion, this base motion disturbance can be directly measured using gyros and accelerometers which are attached to the telescope. This package, called an Inertial Reference Unit (IRU), provides an additional command to the gimbals which stabilizes the telescope and improves the tracker's ability to measure target motion errors. The HEL, shown simply in this cartoon as a box, provides the weapon beam to a pointing telescope which is then mechanically boresighted (optical axis made parallel) to the tracking telescope. Finally, the range to the target must be measured so that a parallax correction can be applied to the pointing telescope. This slightly tilts its optical axis to intersect the tracking telescope's optical axis at the range of the target and thus place the HEL beam on the aim point. 13 UNCLASSIFIED/ ,'P8"2 IIFFlliliR.k Wilii O•ik:w'
Not linked to a story yet.
Report, from the dia collection. The PDF is mirrored here; the original link is above. 31 pages are in the text index: search them above, or from the library's search.