Patent GB-847232-A (GB)
Title: Rocket launch control system
IPC: F41G9/00
Filed: 1955-06-13
Abstract: 847,232. Analogue computors. HUGHES AIRCRAFT CO. June 13, 1955, No. 17026/55. Class 37. The invention relates to a computor for determining the correct instant to launch a rocket from an interceptor aircraft in air-to-air combat. THE VECTOR PROBLEM. The Specification discusses an attack vector diagram relative to ground Fig. 1 (not shown) and the effect of vertical drop in the rocket trajectory Figs. 2, 3 (not shown) and then considers the vector diagram relative to the attacker craft A at the instant of firing, Fig. 4, which shows the rocket trajectory intercepting the range rate vector #R of the target at X and the elevation and deflection components of these vectors. From, Fig. 4. (1) RweT=F cos # sin E+ G+JF. (2) RwDT=-F sin # (3) R+RT= F cos # cos E where the symbols have values as shown in the diagram. To.compute an approximate " timeto-go " Tc before firing, it is assumed that the rocket has missed by a small amount in elevation and deflection, but the range is correct, and equation (3) is solved for Tc and this value is used to determine the approximate miss in elevation and deflection from equations (1) and (2) rewritten:- (4) ME=-RwET-F cos # sin E+G+JF. (5) MD=RwDT+F sin #. The attacker is then oriented to reduce the miss components to zero. By continuous computation, as the computed Tc approaches the true " time-to-go " T the approximations become more accurate and the miss components reach zero together as the attacker attains the correct heading. The Computor; Fig. 6, for solving these equations is shown in block diagram form and is largely self-explanatory. It is fed from a conventional radar tracking set Fig. 5 (not shown) with range R, azimuth #, elevation E, elevation rate WE, and deflection rate WD signals and a preset voltage F representing the predetermined length-of-rocket-trajectory. From these inputs the computor provides signals representing (i) G/T; F/T cos # sin RwE to an adding circuit 28 to provide an output #EL (equation (1). (ii) F/T sin #; RWD, to an adding circuit 29 to provide an output #AZ (equation (2)), and a time-to-go signal f(T) which is compared with the preset rocket-trajectory signal at 3G-to fire the rocket. The signals #EL and #AZ are applied to a steering indicator and or an autopilot. Modifications (1) Fig. 7 (not shown). The time of firing may be altered slightly to compensate for small errors in course. When #AZ is not zero a signal proportional toF. e.g. #AZ may be produced e.g. by a potentiometer and the rocket fired by the comparator circuit when f(T)= F + F. #AZ (Fig. 7 not shown). (2) Fig. 8 (not shown). When the attacker is on the approximate lead collision course the azimuth miss is assumed to be zero, and the length of the rocket trajectory computed i.e. from equation (5). MD=O=RwDT+f sin # .À. f=RwDT sin # This computed value of f is used in place'of F to find the " time-to-go " t and these values of f and t are used to determine the elevation. As described in Fig. 8 (not shown) a switch 54 driven by the " time-to-go " servo closes, when the " time-to-go " has decreased to six seconds, and energises a relay 58 to connect the computor for this second mode of operation i.e. fixed azimuth course and variable "time-to-go". Since, however, azimuth errors can not be corrected by variation-of firing time in a tail chase or head-on-attack, a switch 60 gauged to the radarazimuth drive to operate a relay whenever the bearing angle is less thah 23  so that the computor remains in its first mode of operation i.e. preset, firing time producing azimuth and elevation steering signals. Additional features Fig. 8 (not shown) (1) A resistance 66 may be temperature sensitive to correct for variations due to the temperature of the rocket propellant. (ii) A signal from a lift accelerometer 68 may be included in the elevation steering signal. (iii) A steering filter system 71 may be used to remove radar tracking noise. The steering signals are separated into two components by a roll resolver controlled by a gyro vertical, and these signals are filtered separately.