Bauer Ernest. Atmospheric effects on airborne lasers for tactical missile defense: clouds and turbulence

Institute For Defense Analyses, Alexandria, VA, 1993. — 54 p.In the context of Tactical Missile Defense (TMD), an Airborne (High- Energy) Laser (ABL) is investigated for its possible utility for boost-phase kill of a tactical ballistic missile, at a range of 100-1,000 km. Here we examine the effects of clouds and atmospheric turbulence, including possible compensation by Adaptive Optics (AO) techniques, which can interfere with the functioning of this concept. To avoid the effect of clouds, the aircraft carrying the laser should fly as high as possible, preferably above the tropopause. At 15 km (49 kft) there will be no problem at mid-and high latitudes, but in the tropics conventional aircraft cannot fly high enough to avoid possible interference from towering cumulonimbus, which have been found upon occasion as high as 20 km. Regarding the effects of atmospheric turbulence on beam propagation, if the airplane flies high enough that the optical viewing path avoids cloud, there would probably be no major problems with turbulence at ranges of not more than 100 km. However, for longer ranges, there may be significant effects of phase coherence, beam wander, and beam broadening that could require compensation by AO. There are critical uncertainties in models of atmospheric turbulence, suggesting that more data are needed. Work at USAF/ Phillips Laboratory and at MIT/Lincoln Laboratory is attacking the problems of appropriate compensation for atmospheric turbulence by AO techniques, but the current level of effort is not adequate to support deployment of an ABL system for TMD on a near-term basis.