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Discoverer is an ambitious craft. It car ries in it a complicated guidance system that watches the horizon with infra-red eyes and shoots high-pressure gas through a series of jets to keep the rocket horizontal in respect to the ground below. When a Discoverer — and there have been eleven fired so far — has circled the earth 17 times on a polar orbit, it passes over Kodiak, Alaska, where a radio control station sends an order that sets the guidance system on a new track, tilting it 60° from the horizontal. An electric impulse fires explosive bolts to kick off a re-entry capsule, a retrorocket slows the capsule's speed, a drag parachute pops out, a radio beacon shrills signals, and aluminum chaff is released to show on the radar screens of the recovery aircraft and ships waiting anxiously below. All this must be accomplished on a rigid time schedule with millisecond accuracy if the Discoverer is to be successfully recovered.
So far it has not been — a fact that fails to bother its sponsors. Says an Air Force officer involved in the program: "With the Discoverer, we sort of rigged our own public relations trap, because recovery was the last item on our laundry list of objectives. But Discoverer is really the test bed from which an awful lot of earth satellite systems will flower.''
They have already begun to flower. Midas profited from the "capability" lessons taught by Discoverer. Samos will certainly profit. And so will some of the most elegant of the other systems now being developed.
Moon Orbiters. Preparations for one of those systems are under full steam at the Space Technology Laboratory, which will have two tries next fall at putting a satellite in orbit around the moon. Boosted away from earth by an Atlas missile and two smaller upper-stage rockets, the moon satellite will weigh 350-400 Ibs. It will be spin-stabilized by ten small rockets and will get electric power for its instruments and controls from four paddle-wheels covered with 8,800 solar cells. All this has become standard U.S. practice. What is novel about the moon orbiter is a restartable engine technique for on-course guidance.
To have a chance of going into orbit around the moon, a space vehicle must make its approach at just the right speed and angle. To chivy itself into this ideal situation, the S.T.L. moon orbiter will have two engines—one firing forward and the other backward. The backward-pointing engine will have four tubes, each with two explosive valves, permitting it to be started and stopped four times by signal. The forward-pointing machine will have two tubes, giving it two starts and stops. Ground-controlled alternate firings of the forward and rearward engines are calculated to keep the orbiters on the right course, ease them into moon orbit at a speed of 5.000 ft. per sec. If the first shot works. S.T.L. may use its second or biter for a long-range crack at Venus which will be in a fairly good position next January.