Computer modeling of infrared head-on emission from missile noses

Abstract

A computer model that takes into account the effect of aerodynamic and solar heating, sky irradiation, and radiative cooling on infrared emission from missile noses is presented. The heat transfer equation was solved with numerical techniques both in the steady-state (constant speed and altitude flight of cruise missiles) and in the nonstationary regime (quickly variable speed and altitude of short to medium range ballistic missiles) to give the temperature distribution on the skin surface. The corresponding head-on absolute infrared emission in the 3 to 5 pm and 8 to 12 jim spectral bands was computed as a function of time of flight and missile altitude. Results show a strong dependence of temperature and radiant intensity distributions on thermal and geometrical properties of the skin material, on the character of the aerodynamic flow (laminar or turbulent boundary layer), and on the physical characteristics of the atmosphere. By varying these parameters into reasonable ranges, infrared emissions spanning over more than an order of magnitude were obtained. The comparison with data corresponding to a skin uniformly kept at the boundary layer effective temperature showed that huge overestimates of the infrared emission can be found when the target is flying at high speed and high altitude. By computing the ratio of the in-band total radiant intensity in the 3 to 5 p.m and 8 to 12 p.m spectral regions, the relative merits of these regions for the detection of a given target are given as a function of missile altitude.