Patent SE-323434-B (SE)
Inventor: KNOWLES P
IPC: F41G7/30
Filed: 1964-06-16
Abstract: 1,024,616. Interception computers. DECCA Ltd. June 3, 1964 [June 17, 1963], No. 24089/63. Heading G4G. In an apparatus for use in the control of an interception between an interceptor and a target, signals representative of the instantaneous position of the interceptor and target, of the velocity vector of the target, and of the orthogonal components of a proposed velocity vector of the interceptor are generated. Arrangements are incorporated for varying the signals representative of the proposed components with time to simulate a changing course, for comparing the vector signals and for generating signals representative of the velocity vector of the interceptor relative to the target for the proposed interceptor velocity. An arrangement is incorporated for determining whether the relative velocity vector passes through the instantaneous positions of both target and interceptor. The signals representing the proposed velocity of the interceptor may then be adjusted until the relative velocity vector passes through the positions of the target and interceptor. Where the target and interceptor are aircraft or missiles, the information regarding the instantaneous positions of the target and interceptor and the velocity of the target may be derived from radar apparatus, and the relative velocity vectors are displayed on the screen of a radar display in the intervals between radar scans. In a particular embodiment, it is required that the interceptor should attack at a specified angle, e.g. 90 degrees to the target heading, and should have a certain minimum " attack time ", during which it flies in a straight line' immediately before the attack. The vectors for such a system are shown in Fig. 1, the points 29 and 30 being the present positions of the target and interceptor, respectively, while the vector 31 represents the target velocity, vector 33 represents the desired interceptor velocity and vector 38 represents the relative velocity between target and interceptor. In practice, trial command headings are adjusted until the vector 38 passes through and beyond the point 30, and then the vector length is adjusted so that the end of the vector 38 coincides with the point 30, to determine the time to interception. In a system for displaying the vector 38 on the cathode ray display tube 40 (Fig. 2) signals representing the target position are supplied from a source 41 to the shift control inputs of a waveform generator 42. The generator 42 provides the two orthogonal deflection arrangements of the cathode ray tube with sawtooth voltage waveforms, each waveform starting from a datum level determined by one input control voltage (the shift control voltage) and having a slope determined by a second control voltage (the scan control voltage). Signals representing the target velocity from a source 43 are fed to the subtracting units 56, 57. Since immediately prior to attack the interceptor is travelling at a predetermined angle to the target, the direction represented by the target motion signals can be changed to give the final attack path of the interceptor, and this is achieved by supplying the target velocity signals via potentiometers 46, 47 which are set according to the interceptor speed to a rotor circuit 51 which is set according to the required attack angle 52. This rotor circuit comprises two integrator circuits and an inverter connected in a loop to constitute an oscillator. The initial conditions of the integrators are set in from the lines 48, 49, thus setting in a unique vector. Integration causes rotation of the vector, and after a predetermined time set by the control 52 oscillation is stopped. The vector is thus rotated by an angle dependent on the setting of the control 52. The outputs from the circuit 51 are fed to a further angle control 55 and thence to the subtraction units 56, 57, where the potentials representing the interceptor velocity are subtracted from those representing the target velocity. On the output lines 58, 59 thus appear signals representing the X and Y components of the relative velocity between interceptor and target, and these are fed to the scan controls of the waveform generator 42 so as to provide the display on the tube 40. The initiation of the vector generation is achieved by means of a start pulse over the line 61 from a timing unit (not shown). This pulse is fed to the generator 42, so that operations commence, and also to a delay 63, set by a control 64 in accordance with the straight line attack time required by the interceptor. When this time has elapsed, the pulse from the delay initiates a turn control 66 which operates on the rotor circuit 55, which shifts the vector, to give the vector section 39 (Fig. 1). The rate at which this is carried out is set by the control 67 and the period is determined by the start pulse emerging from a further delay 71, adjusted by a control 72, to act on the control 66 so as to switch off the angle control. Thereafter the angle stays constant for the remainder of the trace. Thus by adjusting the control 72, the relative vector trace can be swept through a certain angular range, and made to pass through the indicated present position of the interceptor. The necessary command heading for the interceptor may then be read from an indicator 73.  The outputs from the waveform generator 42 are also fed to a coincidence detector 74 which is supplied with information representing the interceptor position from a unit 75. When coincidence is detected, an output pulse is supplied to a timer 77 to cut off the trace 38 so as to terminate at the interceptor position. A clock unit 78 and an indicator 79 enable the time required to the start of the turn on to the final attack course to be determined. Although manual control has been described, adjustments may be effected automatically. Furthermore, other parameters, such as acceleration of the interceptor, may be allowed for in the apparatus.