Science: The Heat Seeker

First U.S. air-to-air missile to be tested in real combat is the Navy’s Sidewinder, which was adopted by the Air Force and used to equip Chinese Nationalist Sabre jets flying out of Formosa (TIME, Oct. 6). During one air operation against the Chinese Communists, the Nationalists used Sidewinders to knock down an estimated ten Red jets while coming off unscathed themselves. The Sidewinders given to the Chinese were an early model, but their general design, with improvements, is still in use.

The Sidewinder is a small (9.5 ft. long, 5 in. diameter) rocket driven by a solid propellant. In its nose is a sensing device containing lead sulphide, which is sensitive to infrared radiation from hot objects like the tailpipes of jet engines. When the sensing device “sees” something hot in its 20° field of vision, it turns toward it. The Sidewinder turns too, homing accurately on the hot object. The system is so simple that pilots can use it in combat with scarcely any special training.

When the pilot starts his attack on an enemy airplane, the Sidewinder tells him by a buzzing signal when it “sees” an object that it can home on. When the target is close enough, the pilot presses a button. The Sidewinder fires and is thereafter on its own, pursuing the target relentlessly. Its range is up to 20,000 ft., depending on many factors, including direction, altitude and speed of both airplanes. Frequently a Sidewinder gets in a jet’s wake and flies right up the tailpipe before it explodes.

The Sidewinder has disadvantages too, like all weapons. An enemy airplane cannot be attacked from the front; its hot parts must be in sight, and they are visible only from favorable angles. The attacking pilot must keep track of the sun’s position. If his Sidewinder sees the sun, it may vainly attack it.

The airplane under attack can foil the Sidewinder under some conditions by firing a flare or other hot object to deceive it and lure it away. This is not easy, and not always effective. The flare must be nearly as hot as the jet exhaust, and it must be released at exactly the proper moment.

The hot parts of the latest military jets are carefully shielded to make them “ess conspicuous to the Sidewinder’s infra—ed eye. As a result, the most recent Sidewinders have acquired electronic guidance o supplement their infra-red eyes.