United States Patent im
mi 3,712,391  Jan. 23, 1973
 MOLE GUIDANCE SYSTEM
 Inventor: James Christopher Coyne, New Providence, N.J.
 Assignee: Bell Telephone Laboratories, Inc., Murray Hill, Berkeley Heights, N.J.
 Filed: June 28, 1971
 Appl. No.: 157,570
Related U.S. Application Data
 Continuation of Ser. No. 792,893, Dec. 27, 1968.
 U.S.C1 175/26, 175/45,175/61
[51 ] Int. CI E21b 47/022, E21b 47/024
 Field of Search 175/26, 45; 61/72.7; 340/32;
114/21 R, 21 W, 23
 References Cited
UNITED STATES PATENTS
3,461,979 8/1969 Newfarmer 175/56 X
3,525,405 8/1970 Coyne et al 175/45 X
3,529,682 9/1970 Coyne et al 340/32 X
3,544,957 12/1970 Smetanin et al 175/45 X
3,589,454 6/1971 Coyne 175/26
FOREIGN PATENTS OR APPLICATIONS 1,240,830 7/1971 Great Britain 175/45
Primary Examiner—Samuel Feinberg
Assistant Examiner—James M. Hanley
Attorney—R. J. Guenther et al.
A subterranean missile is equipped with three mutually orthogonal coils in its body and a fourth suitably fixed in an articulatable steering member. The missile is guided along any desired underground trajectory defined with reference to a coordinate system including the plane of a dipole-quadrupole antenna system laid on the ground above. Voltages induced in the noncenterline body coils are used in a closed feedback loop to maintain the resultant magnetic field circularly polarized at the mole location. Heading errors are then revealed as a voltage phasor on the centerline coil. Rotation of the steering member sufficiently to bring the voltage induced in its coil into phase with the centerline coil voltage also aligns the steering member such that its articulation will reduce the heading error to zero. Any new trajectory may be defined as a suitable new voltage added to the centerline coil voltage.
1 Claim, 13 Drawing Figures