Patent GB-919597-A (GB)
Title: A self-contained celestial navigation device
Inventor: WAGONER ROBERT VERNON
IPC: G01C21/02
Filed: 1961-12-18
Abstract: 919,597. Latitude and longitude instruments. GENERAL PRECISION Inc. Dec. 18, 1961, No. 45314/61. Class 97 (2). A celestial navigation device, particularly for use in space craft, uses the fact that if a star field D, Fig. 2a, contains a single star E at the zenith of an observer A on earth, an observer B on the earth at a point 90 degrees from A will see the right-hand half of star group D above his horizon with star E directly on the horizon in the centre of his field of view and an observer C at a height above the surface of the earth in the plane tangent at B will see the same view except that his horizon is curved. At any specified altitude therefore, the geographical position of the observer's sub-point on earth can be determined. In the apparatus, Fig. 1a, a transparent star globe 2 painted with phosphorescent paint at points corresponding to the positions of the major navigational stars as they would be viewed from the centre of the globe, and an opaque earth globe 3, are driven relative to each other by means of a sidereal clock 1, the star globe 2 being so mounted within a housing 6 that it may be manually rotated in any direction. A double spherical plano-convex plastic wide-angle lens assembly 7 focuses the image 11 of the earth's horizon and the stars above the horizon on to its back surface, and a beam splitting mirror 9 allows an observer looking through eyepiece assembly 22 to see the image of star field 10 on globe 2 superimposed on the image of the identical star field formed by real stars 11 on the back of lens assembly 7, the arrangement being such that the size and shape of the image of the real stars corresponds exactly to that painted on star globe 2. On looking through a window 14 displaced 90 degrees from the view of the earth globe 3 seen by mirror 9, cross-hairs 20, Fig. 1c, thereon indicate the position on earth of an observer at zero altitude, i.e. position B. To allow for altitude, the back surface of lens assembly 7 is inscribed with circle arcs 8 corresponding to the horizon outline of the earth as seen from various altitudes, so that by matching the viewed horizon with the corresponding arc 8, or by interpolation between two arcs, the altitude is determined. If altitude corrector 15 is pushed inwardly so that friction members 16 contact globe 2, and then rotated to the corresponding altitude as given by pointer 17 against scale 18, the globe 2 is rotated an amount corresponding to movement from B to C, Fig. 2a, so that the position on the earth globe 3 denoted by crosshairs 20 now gives the sub-point of the observer's position C. In modifications instead of moving the star and earth globes to correct for altitude, the cross-hairs in window 14 are arranged on a slide which moves over a rigid transparent plastic segment having altitude line inscribed thereon, or in another embodiment a plastic indicator inscribed with altitude indications and having a shape of one eighth the surface of a sphere fits between star globe 2 and housing 6. The relevant altitude marking is then brought into correspondence with the cross-hairs and the observer's position is located at the zero altitude point.