Patent GB-1218051-A (GB)
Title: A method and a device for measuring the sighting error of an optical apparatus
Inventor: POUBEAU PIERRE
IPC: G01S3/782
Filed: 1968-01-25
Abstract: 1,218,051. Optical direction finder. NORDAVIATION SOC. NATIONALE DE CONSTRUCTIONS AERONAUTIQUES. 25 Jan., 1968 [27 Jan., 1967], No. 4050/68. Heading H4D. The Specification describes an optical direction finder for use for example in a satellite star tracker. In general, the image of the star is focused on a photo-detector through alternate opaque and transparent sectors of a rotating disc obturator, one of said opaque sectors being longer than the rest and producing an anomaly in the output of the detector for deriving an image position mark T(M1), Fig. 3, in the output of the detector. The position of the obturation is defined by means of a magnetic fixing signal T(M2) stored on a magnetic disc rotating with obturator disc. Co-ordinates # of the image's position are determined in terms of the interval F between the occurrence of a fixing signal and the image position mark, said interval being determined by counting the number I(#) of timing pulses I(M3) occurring during said intervals, said timing pulses also being stored on said magnetic disc. In a first embodiment, Figs. 5, 7, 10, 11 and 13, the star image 0<SP>1</SP>, Fig. 5, is focused by means of a Cassagrain, optical system 5a, 5b, Fig. 7, on to a photo-detector d, lying on the axis Z-Z<SP>1</SP> of the arrangement, via the obturator disc E. Each small segment of the obturator E, Fig. 10, has an opaque portion Pio and a transparent portion Pit with the position where the two portions join, changing round the obturator according to a predetermined low. The magnetic disc B, Fig. 7, having the fixing signal T and timing pulses recorded thereon rotates with and below the obturator E and detector, and in operative contact with magnetic detectors M2 and M3 detecting the fixing signal and timing pulses, and a detector M detecting the output (top line Fig. 11) of the detector d. The output of the detector d starts with a wide 0 signal S'o due to the wider opaque segment, So and then continues with alternate 1 and 0 signals, until the image crosses the joint of opaque and transparent segment portions whereas two consecutive 0 signals (1 signals possibly) are produced. This anomaly causes the production of a signal S (bottom line). The polar angle co-ordinate 0 of the image 0<SP>1</SP> with respect to the detector centre 0 and axis z-z<SP>1</SP> is determined by the interval between the signal T and signal S and is produced by a counter counting the timing pulses I through a gate, opened by signal T and shut by signal S. The polar radius co-ordinate # of the image 0<SP>1</SP> is determined from the interval between the end of the signal So<SP>1</SP> and signal S and may be in terms of the number of 1 signals therein (e.g. 11). In a second embodiment, Figs. 4, 6, 8, 9, 12 the optical arrangement is such that two images are produced on areas 0, O<SP>1</SP> subtending 90 degrees to the centre a of the obturator disc E. The obturator is formed with continuous alternate opaque and transparent strips So, St, Fig. 8, with one wide opaque strip So 2 . The two images are superimposed in Fig. 8 together with the adjacent obturator portions. Thus one detector will produce a signal S, which together with the corresponding fixing signal T1 will enable the determination of the angle # 1  between the star image 0<SP>1</SP> and the centre of the detector C<SP>1</SP>2 and the other detector will correspondingly enable the determination of angle # 2 . Several consecutive measurements may be integrated (Fig. 14, not shown) and averaged.