692 MECHANICAL DESIGN AND PACKAGING 



13-4 SOLAR RADIATION 



Solar radiation is included in the category of natural environments. 

 The intensity of the solar radiation acting on a body is directly 

 dependent upon the altitude of the body, the type of atmosphere (the 

 amount of dust, smoke, moisture, etc. which affect the absorption, scat- 

 tering, and reflection of the rays) and the angle at which the rays enter 

 the atmosphere. Thus a body can receive solar radiation either by direct 

 rays or indirect rays of varying intensity, depending upon the above- 

 mentioned conditions. 



Special design considerations are involved for electronic equipment 

 exposed directly to the sun's rays. However, this is not the normal situation 

 unless the electronic equipment is placed in an exposed place prior to the 

 actual installation in the aircraft. Special surface finishes, coatings, and 

 material would be required for directly exposed parts, since solar rgdiation 

 deteriorates materials like rubber, plastics, textiles, paints, etc. 



A body subjected to solar radiation will experience an increase of 

 temperature in the enclosed areas. As was pointed out in the discussino 

 on temperature, the design of electronic equipment housed in aircraft 

 compartments subjected to a solar radiation environment must consider the 

 increase of temperature for all phases of the equipment life. In general, the 

 thermal effects of solar radiation for airborne electronic equipment are 

 appreciable for ground operations and will dictate the volume and tem- 

 perature limits of the required ground cooling system to keep a satisfactory 

 ambient temperature within the electronic equipment compartment. How- 

 ever, the effects of solar radiation are small during flight when compared to 

 the other forms of heat generation and do not necessarily influence the type 

 of equipment cooling system required for satisfactory operation. 



The critical areas of the electronic equipment for solar radiation should 

 be determined, and their influence on the overall temperature problem must 

 be considered in assessing their effect on the equipment design criteria. 



13-5 NUCLEAR RADIATION 



The use of electronic equipment in nuclear-powered aircraft will subject 

 the equipment to the induced environment of nuclear radiation. This 

 environment is due to a high-intensity field of nuclear radiation emitted 

 from the nuclear reactor of the aircraft power plant. Radiation from a 

 nuclear reactor suitable for an aircraft power plant can be divided into three 

 types — beta particles, gamma rays, and neutrons. Beta particles are easily 

 dealt with, requiring very thin layers of material to stop penetration; they 

 thus present no major problem. Gamma rays are of high energy content; 

 the amount of attenuation of these rays depends directly upon the density 

 of the material. A very dense material like lead is often used for radiation 



