A factor that greatly simplifies the study of a specific pyrolytic graphite radiator design is the relationship of its size to that of the slotted waveguide radiator. The dimension of the heat radiator has to match the dimensions of the slotted waveguide radiator associated with it in the radiation module. The dimensions of the slotted waveguide radiator are quantized. It is assumed that each waveguide stick must have an even number of slots in it, and each set of slots is approximately 18.4 centimeters long. The dimensions of the area occupied by the magnetron directional amplifier and its associated waveguide section could therefore be 18.4 cm. 36.8 cm., 55.2 cm., 73.6 cm. etc. These dimensions are also associated with the number of waveguide sticks in the array of 2, 4, 6, and 8 respectively as suggested in Figure 1. For the same temperature drop in the radiator from the center to outside edge the mass goes up as the fourth power of the diameter while the heat radiated goes up as the square. This relationship causes an unfavorable increase in the mass of the radiator per unit of heat radiated as the size of the radiator is increased. Also the cost of the pyrolytic graphite per unit of heat radiated would increase with the diameter as would the cost of transportation into orbit. While the 55.2 cm diameter would be unfavorable from this point of view, the 18.4 dimension is probably much too small from the viewpoint of the greatly increased number of radiating modules that would be required, and also from the viewpoint of the difficulty of designing a magnetron that would operate with one kilowatt of power output at an anode voltage of 20 kilovolts. (The high voltage is a requirement of the system to reduce
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