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Trying to find out if earth lights can give navigation fixes to moon-bound spacecraft, Cooper successfully sighted a 3,000,000-candlepower ground light at Bloemfontein, South Africa. Surprisingly, he saw the normal lights of a nearby village before locating the bright one. Cooper took photometer readings of stars to measure the extent to which his window attenuates light. He snapped numerous photographs with special cameras to study the halolike zodiacal light, a mysterious night airglow layer, and the horizon itself. Scientists hope that the horizon may also provide a sharp enough line for navigational fixes from space vehicles.
Cooper's capsule carried Geiger counters to measure the radiation it encountered throughout its flight. The experts were most interested in learning whether an artificial belt, created over eastern South America and the South Atlantic by a high-altitude U.S. nuclear explosion last summer, was decaying as anticipated. Cooper wore four film patches beneath his pressure suit to record radiation reaching his body. Scientists estimated that he was exposed to less radiation than that of a normal chest X ray.
In other tests. Cooper deployed a 28-ft. antenna to check its high-frequency transmitting ability from both a horizontal and, by rolling his capsule 90°, a vertical plane. He shut off the cabin cooling system for a time, found that his pressure-suit cooling system kept him at about a comfortable 65°. In a long space flight, power could be saved by using, at least part of the time, the suit cooling alone. At one point, a gadget carrying condensed air out of his suit broke down, and Cooper began sweating profusely. Complained he: "I'm having a continuing battle with the plumbing." To get comfortable, he had to change his suit cooling control periodically.
Engineers later said that they were satisfied with television pictures transmitted to earth from a 10-lb. camera that Cooper could direct either at himself or out of his window. In the process of converting these signals for rebroadcast on regular TV channels, however, the pictures lost their clarity—and looked to the layman like mush. In one lighthearted moment, he held in front of the camera a small hand-lettered sign that read: "Go 22."
Throughout his flight, Astronaut Cooper performed magnificently. Where both John Glenn and Scott Carpenter had yielded to a pilot's instinct to maneuver their capsules manually, thereby using up precious hydrogen-peroxide fuel, Cooper kept hands off as much as possible. He came up to his final orbit with 70% of the fuel for his manual control system still unused. Early in the flight. Communicator Alan Shepard had kidded Cooper: "You're getting kind of chinchy on using this fuel up there." And Cooper managed his own oxygen supply so well that Shepard told him laughingly: "You can stop holding your breath any time and use some oxygen if you like."