Project Hot Rod was actually a giant balloon eight thousand feet in diameter, one-half "silvered" with a greenish reflective surface inside that reflected only that light that could be utilized by the ruby rods at its long focal center; and that absorbed the remainder of the incident solar radiation, dumping it through to its black outside surface, and on into the vastness of space. This half of the big balloon was the spherical collector mirror, facing, through the clear plastic of its other half, the solar disk.
Well inside the balloon, at the tip of the ruby barrel that was its heart, were located the boiler tubes that activated the self-centering inertial orientation servos which must remain operational at all times. If the big mirror were ever to present its blackened rear surface to the sun for more than a few minutes, the rise in temperature would totally destroy the entire project. Therefore, these servos had been designed as the ultimate in fail-safe, fool-proof control to maintain the orientation of the mirror always within one tenth of one degree of the center of Sol.
Their action was simplicity itself. The black boiler tubes were shielded in such a way that so long as the aim was dead center on the sun they received no energy; but let the orientation shift by a fraction of a degree, and one of these blackened surfaces would begin to receive reflected energy from the mirror behind it; the liquid nitrogen within would boil, and escape under pressure through a jet in such manner as to re-orient the position to the center of the tracking alignment.
Since the nitrogen gas escaped into the balloon, the automatic pressure regulator designed to maintain pressure within the balloon would extract an equal quantity of gas, put it back through the cooling system on the back side of the mirror, and return it as liquid to the boiler.
These jets were so carefully and precisely balanced that there was virtually no "hunting" in the system.
The balloon itself was attached to its anchor tube by a one hundred meter cable that gave free play to these orientation servos. The anchor point was the exact center of the black outside surface of the mirror-half of the balloon; and beside that anchor point was the air lock to the control center, to which Steve was now going.
From the control room, a column extended up through the axis of the balloon for thirty-five hundred feet—and most of the surface of this column was covered with the new type, high power ruby rods, thirty feet long and one-half inch in diameter, mounted in tubular trays of reflective material which took up sufficient space to make each rod occupy two inches of the circumference of the tube on which it was mounted.
These ruby rods were the heart of the power system, converting the random wave fronts of noncoherent light received from the mirror into a tremendous beam of coherent infrared energy which could be bundled in such a pattern as to reach Earth's surface in a focal point adjustable from here to be something between twenty-two feet in diameter to approximately one mile in diameter.
The banks of rods were so arranged that each of the one hundred sections comprising the three thousand feet of receptive surface at the focus of the mirror formed a concentric circle of energy beams; each circle becoming progressively smaller in diameter, so that the energy combined into one hundred concentric circles, one within the other, as it left the rods; but these circles were capable of the necessary focusing that could bring them all together into a single small point near Earth's surface.