GB911914A - Improvements in or relating to astronomical, navigational and like apparatus - Google Patents

Abstract

911,914. Navigational instruments. UTTLEY, A. M., JONES, S., and MANNS, L. Dec. 13, 1947 [Sept. 24, 1946], No. 28576/46. Class 97 (2). [Also in Groups XXXV and XL (c)] Two telescopes 10, 11 are adapted to view two chosen stars and electric signals are produced measuring misalignment of their axes from the directions of these stars, and converted automatically into error voltages which are fed into driving means adapted to nullify the misalignment. The telescopes are clamped in positions determined by the declinations of the chosen stars S<SP>1</SP>, S<SP>2</SP> to rails 12, 13 fixed to rings 16, 17. The rings 16, 17 and an intermediate ring 18 are free to rotate about a vertical axis within a ring 19 which is gyro-stabilized horizontally. A prism 20, in the form of a truncated pyramid having base angles of 45 degrees and parallel silvered faces, is rotatable about a horizontal E-W axis and is correctly aligned when a telescope at 10<SP>1</SP> points towards the North or South celestial Pole P. A mask comprising opaque spokes, Fig. 5a, is associated within each telescope with a motor-driven scanning mirror to cause the star image to follow a circular locus 23. When the locus 23 is eccentric, as shown, the pulse signal sent by an electron multiplier photo-tube is frequency-modulated as starlight passing the spokes falls on the cathode of the tube in unequal flashes. A.C. misalignment signals Sd<SP>1</SP>, Sh from telescope 10 and Sd<SP>2</SP> from telescope 11 are obtained from the frequencymodulated pulse signals. These misalignment signals are in polar co-ordinates and are converted in a computer to error voltages #l #C, #h in cartesian co-ordinates representing changes in latitude course and hour angle. These error voltages are amplified and applied to two-phase servomotors 61, 60, 59 which drive the prism 20, ring 18 and rings 16, 17 respectively. The rings 16, 17 are connected to shafts 78, 79 and are driven in part by a clock 68 keeping sidereal time and in part by the motor 59. The latitude l and the angles h<SP>1</SP>, h<SP>2</SP> and h<SP>2</SP>-h<SP>1</SP> are supplied to the computer 50 and manual controls 74, 75, 82 are provided for initial setting of the sidereal hour angles of both stars and the declination of one star. The servomotors also operate a device 81 displaying navigational data such as course, latitude and longitude or may effect guiding adjustments to an aircraft in which the apparatus is mounted. The viewing means shown in Fig. 1 is unsuitable in equatorial regions and for these regions the device is modified by fixing the prism 20 and providing the rings 16, 17 with rotation about a horizontal N-S axis, Fig. 2 (not shown).