Missile Speedway

The world's longest straightedge is the 6 1/2-mile track at the Air Force Missile Development Center, N. Mex., which has started to flight-test missiles while they are still on the ground. The virtues of this system are many. Instead of destroying itself in a single flight, a missile shot along the track can be recovered undamaged and tested many more times. It can be timed accurately and photographed at close range.

Tangent or Great Circle? To build a track straight and level enough for missiles was a technical tour de force. Air Force experts selected a section of the Tularosa Basin, near Holloman, that is almost as flat as a frozen lake. While figuring theoretically how to lay out the 35,080-ft. track, they considered making it perfectly straight both up-and-down and sideways, but gave this up because the curvature of the earth (the earth considered as a sphere with a 4,000-mile radius) would require either a cut in the ground 35 ft. deep at the midsection of the track, or 35-ft. embankments at the ends. So the engineers compromised with nature by making their track a series of sections slightly less humpbacked than the earth's curve.

Hydraulic Stretch. The surveying had to be done at night because daytime heat foiled the accuracy of the surveyors' instruments. The next step was to pour a continuous slab of reinforced concrete 6 1/2 miles long with adjustable fasteners for the rails, which are 7 ft. apart and three times as heavy as railroad rails. They came in 3Q-ft. sections and were welded together on the spot into 10,000-ft. lengths. Merely fastening them to the concrete slab would not do; the temperature of the Tularosa Basin fluctuates between zero and 120DEGF. If the rails were fastened in cool weather, a hot summer day might make them expand and buckle out of line. So each 10,000-ft. length of massive rail was stretched 3 ft. by hydraulic jacks. At ordinary temperatures the rails are under tension like piano strings. Only on the hottest days do they barely relax. After the rails were stretched, they were aligned by special optical devices and bolted down so that they did not deviate from a perfectly straight line by more than five one-thousandths of an inch.

Nearly all of the track is in use now, and last week a sled carried a missile roaring along it at 3,000 ft. per second (2,000 m.p.h.), which is about the muzzle velocity of a high-power rifle bullet. The Air Force scientists expect much higher speeds. It is fortunate, they say, that the Tularosa Basin is not subject to earthquakes. Even a delicate motion of the earth might throw the track out of perfect alignment and wreck the next missile to be used on it.

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