Patent GB-973157-A (GB)
Title: Improvements in navigation and/or orientation control systems
IPC: G01S3/781
Filed: 1961-01-27
Abstract: 973,157. Photo-electric spectrum analysis. POLARAD ELECTRONICS CORPORATION. Jan. 27, 1961 [Jan. 28, 1960], No. 3325/61. Heading G1A. [Also in Division H4] A system for the orientation and/or navigation of a vehicle in space or for automatically controlling the orientation of a terrestrial telescope comprises space scanning means, means for forming the characteristic spectrum of the light received from each extra-terrestrial object scanned, e.g. a star, planet or meteor, means for comparing each spectrum formed with a plurality of known spectra corresponding to objects of known position and indicating when the formed spectrum of an object matches a known spectrum thereby identifying the object, means operative on identification of an object for locking the scanning means on to the identified object and means for utilising the direction of the identified object to control the orientation of the terrestrial telescope or to control the orientation and/or direction of movement of the vehicle. As shown as applied to controlling a vehicle, a conical space segment of apex angle 90 degrees defined by a window 202 in the surface 200 of the vehicle is scanned spirally by a plane mirror 204 which is nutated by a control circuit 206 and the light from any object incident on the mirror 204 is directed by a plane mirror 210 and Schmidt telescope 212 through a rotating chopper disc 18b, a diffraction slit 187 and an adjustable aperture 180 on to a prism 188 or diffraction grating which directs the spectral components of the light on to a bank of photo-cells 192a.. 192n each of which produces an output A.C. electrical signal of amplitude proportional to the intensity of the corresponding spectral component. Each photocell is preferably responsive to a narrow band of frequencies, e.g. by selection of the photo sensitive material or by using a filter. The A.C. outputs from the photo-cells 192a.. 192n are amplified and converted to D.C. in detectors 18a.. 18n and the maximum signal is selected by an amplitude selector 32 and applied together with a reference voltage of constant amplitude from a source 36 to a differential amplifier 54 whose output controls the adjustable aperture 180 via a servomotor 182 so that the maximum spectral component output is of predetermined amplitude, i.e. the output signals are normalised; alternatively the output from the differential amplifier 54 may control the sensitivity of the photo-cells 192a.. 192n. As shown the selector circuit 32 comprises a number of diodes each of which is back biased by the other diodes so that only the diode at which the maximum amplitude signal appears is allowed to conduct. The amplitude of each output component is then converted into a corresponding 4-digit parallel binary code in an analogue to digital converter 102 so that the formed spectrum is specified byn binary numbers The known spectra are stored in the same form in a memory storage 120 which may comprise magnetic tape, punched cards or a core matrix and the formed spectrum is compared sequentially with the known spectra in a logic circuit 115 which produces a recognition signal when the formed spectrum matches a known spectrum within predetermined limits. The recognition signal causes the scan control 20b to lock on to the object which has been recognised and the scan control 20b then supplies tracking information to a navigation computer 215 which is rendered operative by the recognition signal, the computer then functioning to produce control signals in accordance with a pre-set flight plan which are used to steer the vehicle, e.g. by actuating rudders and/or steering fins or by controlling the vehicle's main or auxiliary propulsion. In the case of a space satellite the control signal may release the satellite from the launching rocket The position of the vehicle in space may be determined by (1) measuring the directions of two stars from the vehicle relative to the direction of the sun to give the heliocentric latitude and longitude by means of apparatus according to the present invention using two tracking and recognition units if required and (2) measuring the distance of the vehicle from the sun, e.g. by measuring the suns apparent size by photo-electric measurement of the diameter of an image of the sun.