Phase distortion due to airflow over a hemispherical laser turret
Abstract
Compressible flow over a laser turret creates a phase distortion. To gain insight into this problem, a model of a hemispherical turret is developed. The flow field is obtained using a second order solution based on JanzenRayleigh expansion for the compressible potential flow equation. Contours of constant phase distortion were calculated; results at the critical Mach number are presented and discussed. It was found that the distortion at 0 degree elevation angle was equivalent to a positive lens, whereas at 90 degrees the distortion is similar to a negative lens. At 45 degrees the main effect is beam tilting into the wind. For a ratio of beam radius to turret radius equal to 0.5, the focal length at beam elevation angle of 0 degrees is 16.5km. At beam elevation of 54 degrees the beam tilt was found to be 26.5 microradians. Cruise missiles with intercontinental ranges may use celestial navigation which requires precise measurement of angular location of stars. A distorted lens created by the ambient flow field causes an error in measurement. Knowledge of the external aerodynamics is important.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 September 1976
 Bibcode:
 1976STIN...7723474F
 Keywords:

 Cruise Missiles;
 Lasers;
 Phase Shift;
 Aerodynamic Forces;
 Celestial Navigation;
 Laser Ranger/Tracker;
 Mathematical Models;
 Lasers and Masers