Shifting Orbits

Military satellites will be of little use unless they can change their orbits nimbly--either for evasion or positive action. Such skills are not easily built into rockets, but last week the Air Force launched a Titan III A to show that the task is all but done. The three-stage rocket took off from Cape Kennedy and climbed to slightly more than 100 miles before the "transtage" (third stage) fired briefly and accelerated itself into a near-circular orbit. Then, 90 minutes after launch, when the transtage had almost girdled the earth and was over the California coast, its engine fired for 37 seconds to put it into a climbing curve toward a new orbit. After circling the earth for three hours on an elliptical path ranging from 101 miles to 1,536 miles high, the engine fired a third time, parking the transtage in a third, almost circular orbit, near the high point of the ellipse.

The vehicle then ejected two secondary satellites. One was a dummy payload with 1,000 Ibs. of ballast; the other, a 69-lb. communications satellite, was supposed to fire its own little rocket engine and climb to 11,000 miles. The engine did not fire, but this fringe failure hardly diminished the orbit-shifting accomplishment. At week's end, satellite and Titan fragments were circling the earth in an orbit that may go on for 2,000 years.

If they are to serve as earth-circling military vehicles, later Titans will have to refine their orbit shifting still more. Besides changing altitudes, they will need the ability to skitter sideways, a difficult maneuver. Another job for Titan Ills may be to boost the Air Force's two-man satellite laboratory into orbit.

Another space vehicle performed equally agilely. Mariner IV, which started on its 7 1/2-month journey to Mars on Nov. 28, and will reach its target in mid-July, got a cautious checkup as electronic medicos at the Jet Propulsion Laboratory in Pasadena asked it twelve searching radio questions. With three-minute delays to permit the radio waves to cover 33 million miles at the speed of light, the answers came back clearly. The far-ranging spacecraft never felt better. All 38 parts of the TV apparatus that are scheduled to take pictures of Mars are in working order.

JPL also instructed Mariner IV to remove the camera's lens cap. The spacecraft obeyed, but the scientists kept their fingers crossed. Mariner IV steers itself by a star, Canopus, and they were afraid that microscopic dust particles released along with the lens cap might shine like stars in the sunlight and confuse the Canopus sensor. This did not happen; the spacecraft continued to cruise toward Mars, its sensor serenely fixed on its guiding star.

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