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Precision Guided Munitions - Texas Instruments GBU-10, 12, 16 Paveway

The Paveway "smart bomb" was the first laser-guided weapon to gain wider application and distinguished itself during the Vietnam conflict.

The Paveway is a modular guidance kit comprised of a Computer Control Group and Airfoil Group Assembly fitted to a standard Mk82, 83, 84 demolition bomb or SUU 54 cluster bomb. It functions as a semi-active laser-seeking ballistic projectile and requires no electrical connections with carrying aircraft prior to release.

The CCG consists of a laser energy sensor, a guidance command computer and a control actuator/control surface assembly (see diagram). The laser sensor is mounted in a gimballed, aerodynamically aligned (ring airfoil - it aligns the sensor assembly with the weapon's velocity vector) assembly. Laser light reflected off a target passes through a protective nose window and an infrared filter and is focussed by an aspheric lens on to a four-quadrant silicon photoelectric sensor. The sensor is slightly shifted along the longitudinal axis of the assembly so it lies in front of the focal plane of the lens and the image of the laser spot is slightly defocussed. If the spot is perfectly aligned with the weapon's velocity vector, all quadrants are equally illuminated. If the spot lies off-axis it will illuminate each quadrant differently. Each quadrant generates electric current proportional to its illumination. Voltages proportional to these currents are then amplified and fed into a mixer network which compares the signals and generates up/down, left/right commands - these are then fed into the guidance command computer.

Paveway uses a non-proportional 'bang-bang' guidance where control surfaces are not deflected proportionally to the guidance error, but are driven to the limit of their deflection; the guidance commands being up, down, left, right and no command. The computer receives the outputs from the sensor assembly and, after selecting the correct pulse code, it compares the outputs to select the appropriate control commands. Control actuation occurs if the difference between two channels exceeds a level given by the minimum guidance error; if not, the control fins are set to trail.

The control section is aft of the computer, it converts the computer's commands into control surface deflections and also powers the computer. The energy source is a hot gas generator which supplies electricity via a thermal battery and also supplies the high-pressure gas required to actuate the control surfaces.

The high-pressure gas is fed through a manifold into four piston/cylinder assemblies which are connected to the control surfaces. The gases are then vented through four solenoid valves which are controlled by the computer. A guidance command will shut a valve, allowing the full pressure of 7.5 MPa to build up, which will generate a torque acting on the control surface, deflecting it.
If no command is present the surfaces trail, any motion being damped by oil dampers which are necessary to avoid flutter during carriage. For safety reasons, the gas generator cartridge is ignited two seconds after release, which results in a necessary unguided flight-time of at least two seconds. The wing assembly mounts on the rear of the bomb body and the wings deploy after release, when a retaining latch enables four coil springs to extend the wings.