The solar power plant for that purpose (Figure 77) represents, therefore, one of the most important systems of the space station. It delivers direct current, is equipped with a storage battery and is comparable in principle to a standard steam turbine power plant of the same type. There are differences, however: the steam generator is now heated by solar radiation, which is concentrated by a concave mirror in order to achieve sufficiently high temperatures (Figure 77, D); and cooling of the condenser occurs only by radiating into empty space, so it must be opened towards empty space and shielded from the sun (Figure 77, K).
Figure 77. Diagram of the solar power plant of the space station.
Key: 1. Steam turbine; 2. Shaft; 3. Storage battery; 4. Electrical generator; 5. Solar radiation; 6. Steam generator; 7. Concave mirror; 8. Pump; 9. Condenser; 10. Radiation out into empty space.
In accordance with our previous explanations, this causes both the steam generator and condenser to be painted dull black on the outside. In essence, both consist only of long, continuously curved metal pipes, so that the internal pipe walls, even in a weightless state, are always in sufficiently strong contact with the working fluid flowing through them (see Figure 77).
This working fluid is in a constant, loss-free circulation. Deviating from the usual practice, rather than water (steam), a highly volatile medium, nitrogen, is used in this case as a working fluid. Nitrogen allows the temperature of condensation to be maintained so low that the exceptional cooling potential of empty space can be used. Furthermore, an accidental escape of nitrogen into the rooms of the space station will not pollute its very valuable air.
Since it is only the size of the concave mirror that determines how much energy is being extracted from solar radiation, an appropriately efficient design of the power plant can easily ensure that sufficient amounts of electrical and also of mechanical energy are always available on the space station. Furthermore, since heat, even in great amounts, can be obtained directly from solar radiation, and since refrigeration, even down to the lowest temperatures, can be generated simply by radiating into empty space, the conditions exist to permit operation of all types of engineering systems.