Patent GB-1025740-A (GB)
Title: Proportional navigation system for a spinning body in free space
IPC: F41G7/22
Filed: 1964-09-04
Abstract: 1,025,740. Self-propelled missiles. W. B. McLEAN, and W. G. G. FINCH. Sept. 4, 1964, No. 36438/64. Heading F3A. [Also in Divisions F1 and G3] A space vehicle, when travelling in free space and spinning about its central axis, thus acting like and having all the properties of a gyroscope, is steered by a proportional navigation system comprising seeker means mounted on the spin axis of the vehicle for detecting electromagnetic radiation from a target body and generating electrical signals in response to this radiation, said electrical signals being proportional to the bearing of the target body relative to the spin axis of the vehicle and being zero when the spin axis is pointing directly at the target body, and means responsive to these electrical signals for operating propulsion means in the vehicle in a manner to process the vehicle to point its spin axis directly at the target body and to move the vehicle along a collision course with the target body. As illustrated in Fig. 1, a space vehicle 10 has a seeker 12 comprising an image chopper or reticle (not shown) mounted at the focal plane of a folded reflecting telescope, having primary and secondary optical mirrors 18 and 19, whose optical axis coincides with the spin axis of the vehicle, a photo-detector cell 22 being mounted directly behind the image chopper and converting the pulsed radiation signal it receives into an alternating current which is fed to an amplifier 14. The image chopper 20 may be a disc divided into two main sections of 180 degrees one being transparent to the incident radiation and the other opaque (Fig. 2, not shown), and since it rotates with the vehicle, a pulsed electric signal is obtained from the photo-detector cell 22, the amplitude of which depends on the extent to which the vehicle is off course and the phase of which depends on the direction of the target relative to the telescope axis. Because the electronic circuitry used rounds-off the pulses, the current from the amplifier 14 is undulating, while still containing both phase and amplitude information, and is fed (Fig. 8) to the solenoid coil 24 of a solenoid-operated valve 26 which feeds correct amounts of fuel and oxidizer into a combustion chamber 27 from which extend two jet nozzles, one being a processing jet nozzle 16 mounted at the periphery of the vehicle and extending parallel with its spin axis and the other being a lateral jet nozzle 32 positioned 90 degrees around the periphery from the processing jet with its thrust axis passing through the centre of gravity of the vehicle. The reaction force from the jet nozzle 16 exerts a processing torque on the vehicle until its spin axis points directly at the target and the target image is centred on the chopper 20, the magnitude of the electric signals from the photo-detector cell 22 then being reduced to zero. A preferred form of chopper 20 has one half opaque and the other half comprising alternating clear and opaque sectors (Fig. 12, not shown,) which pattern gives the chopping frequency a more convenient value for electronic amplification and reduces background noise. Since the target image is of finite size, when it nears the centre of the chopper 20, the narrow ends of the pie-shaped sectors only partially obscure and partially transmit the image radiation and hence the vehicle will receive smaller processional torques when the image is only slightly off-centre than when it is well away from the centre. The jet nozzle 32 provides the vehicle with a lateral acceleration in the plane determined by the sequential positions of the sight line from vehicle to target and of a magnitude proportional to the sight line rate so as to establish a collision course between the vehicle and the target. The phase of the signal pulses from the photo-detector cells 22 can be adjusted relative to the angular position of the jet nozzle 16 about the spin axis of the vehicle, so that the direction of the precession is such as to achieve straight line progression of the vehicle in realigning the spin axis with the sight line, by means of a phase shift circuit in the amplifier 14. Alternatively, the phase may be adjusted by physically orienting the clear opaque sectors of the chopper 20 about the spin axis with respect to the jet nozzle 16. Although the gas pressures at both jet nozzles 16, 32 are equal to each other at all times, the cross-sectional areas of the nozzles are of different sizes in order to establish the correct proportionality between the lateral acceleration and the sight line rate. Less thrust will usually be necessary to precess the vehicle than will be needed to move the vehicle on a collision course. Where forward velocity additional to that imparted to the vehicle at launching is desired, the lateral jet nozzle 32 may be canted back at an angle to give a forward thrust vector as well as the lateral thrust vector. By properly directing a single jet with respect to the centre of gravity of the vehicle in order to generate a pulsating torque equivalent to that of the processing jet above-described, the single jet can be used to achieve the processing mechanism as well as lateral and forward thrust.