Here to There, Accurately

On a blustery February morning in 1953, a B-29 took off from Massachusetts' Bedford airport and pointed its nose along the great-circle route to Los Angeles. There were eight people aboard the big bomber, but after take-off no one worked the controls. For two hours, a pilot sat watching the instruments. Then he got bored and let the plane fly itself. It did, making minor corrections for each gust of air. It rose to 21,000 ft. to traverse the Rockies, stayed on course through a 100-m.p.h. wind shift over Nevada. Finally, 13 hours and 2,520 miles from Bedford, the pilot took over, took the aircraft the remaining ten miles to Los Angeles International Airport. To the jubilant M.I.T. scientists aboard the plane, he lamented: "I've just lost my job."

Since that historic flight, kept secret until last week, Inertial Guidance--the gyroscopic navigational system that guided the B-29 without visual or electronic aid from earth or stars--has been an obvious choice to control the U.S.'s ultimate earth-to-earth weapon: the pilotless intercontinental ballistic missile (TIME, Jan. 30, 1956). Last week in Cambridge. Mass., a pudgy, square-faced engineer who presides over an aging red brick factory building (still labeled "Home of Whittemore Shoe Polishes," but listed on Massachusetts Institute of Technology records as the Instrumentation Laboratory) outlined the details of Inertial Guidance, just declassified.

Three Virtues. The great virtues of the new system for the 5,000-mile ICBMs, according to Dr. Charles S. Draper (TIME, Dec. 10), head of M.I.T.'s Department of Aeronautical Engineering: extreme accuracy, interference-proof operation (weather, sunspots and enemy jamming attempts have no effect), and radio silence (no signal is sent or received).

Like the gyrocompass, the gyroscopic ship stabilizer and the Mark 14 antiaircraft gun sight (developed by Dr. Draper and his associates at M.I.T. in 1941), Inertial Guidance is based on the familiar principle that keeps a child's gyroscopic top from falling: a rapidly spinning wheel will resist forces working to twist it from the plane in which it is revolving. A gyroscope sufficiently free of outside disturbances--e.g., friction--will maintain an unvarying spin axis in relation to the "fixed" stars--or any other points of reference--no matter on what path it is carried by the motion of a vehicle or the rotation of the earth. Such a gyroscope is one element of Inertial Guidance. The other element is an electronic "Schuler pendulum" that always points toward the center of the earth, regardless of an aircraft's acceleration (speeding up or slowing down).* The unchanging gyroscope line and the line of the plumb bob, which tells which way is down, form an angle that changes as the plane follows the earth's curved surface. This angle is the self-contained milepost by which Inertial Guidance determines and sets its course (see diagram).

In a Closet. The Instrumentation Laboratory's most important technological advance in building the jam-proof navigational system was the development of the Hermetic Integrating Gyro (HIG), a 3-in. long package containing a gyroscope spinning at 12,000 r.p.m. in an inner cylinder pivoted on virtually friction-free bearings and floated in a heavy liquid. Three HIGs --one to "memorize" each coordinate of a point'on an imaginary star line at take-off --and three accelerometers (to measure change of speed in each direction) are fixed to a gimbals-mounted, free-swinging platform unaffected by changes in the plane's movements.

From the angle made by the platform and the Schuler-pendulum, corrected by a chronometer which allows for the earth's rotation, exact readings of a plane's (or missile's) latitude and longitude are made, then translated into instructions for the servomechanisms that operate the controls. (A variant of this layout, not described by Draper, uses similar gyros to fix position, radios continuously back to home base for flight instructions.) Throughout the flight, the control system also operates like a normal automatic pilot, making necessary minor corrections for pitch, yaw and roll.

The Inertial Guidance system that guided the 1953 flight with nearly pinpoint accuracy weighed a hefty 2,700 Ibs., got the tag "navigation in a closet." To be effective in a missile where each pound of excessive weight exacts a heavy toll in lost speed and distance, the mass of wires, tubes and gyros would have to be slimmed down from closet to pocket size. Advances in accuracy and miniaturization since the first flight are classified, but the M.I.T. scientists, who have been working on Inertial Guidance since 1939, serve as consultants to the Air Force and Navy on such systems, and are known to be designing the Inertial Guidance system of the Navy's 1,500-mile Polaris missile. These scientists say carefully that "efficiency of the equipment is known to have become even greater than in 1953." When the U.S.'s first rocket-powered, space-tunneling ICBM rises on its maiden test flight some time this spring, the chances are that a tiny, precocious descendant of M.I.T.'s 1953 navigator may be at the throttle.

* Dr. Maximilian Schuler, a German professor of applied mechanics, discovered in 1923 that acceleration would have no effect on a hypothetical pendulum the length of the earth's radius; the M.I.T. device simulates Schuler's effect electronically.

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