Electronics: Low-Flying Navigator

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Low-level bombing in bad weather is a deadly job. The same radar used to find targets can help a plane to navigate safely past hills or mountains, but it may also alert defenders equipped to pick up its blips. Navigation with the help of ground-based radio-beam transmitters can rarely be counted on over enemy territory. What pilots need is a system that will lead them along their chosen route without signaling their presence to enemy trackers.

To supply a "silent" electronic navigation system, Northrop engineers, led by James Campbell, project manager, have borrowed a technique that radio astronomers use to study the sun and the planets. They are tuning in on the faint thermal radio waves that are emitted by every natural body, whether celestial or earthly. At altitudes of less than 1,000 ft., a pair of highly directional antennas pick up that radiation from objects below the plane. And since one antenna points behind the other, it picks up the same radiation at a slightly later time. That time lag, along with the plane's altitude, supplies enough information for an on-board computer to calculate the plane's ground speed.

If a crosswind is causing the plane to drift sideways, the pilot may have to swing the rear antenna to right or left before it picks up the proper pattern of ground radiation. In that case, the amount of antenna swing is also fed into the computer, which then cranks the drift angle into its computations. Working with direction, ground speed, drift angle and flight time from a known point of departure, the pilot's computer becomes an accurate navigator.

Known as microwave radiometry, the system would be less vulnerable to the enemy than radar, and much less expensive than inertial navigational systems. It has thus far been shrouded in military secrecy, but it is no secret that it holds obvious advantages for planes on low-flying bombing missions.