Solid-Fuel Controls

Solid-fuel rockets are the dream weapons of military rocketeers. They have no pumps or valves to go wrong and are always ready to fire. Their big trouble is that they are harder to control than liquid-fuel rockets, whose small combustion chambers, fed by flexible pipes, can be mounted on gimbals. When a liquid-fuel rocket takes off, it can switch its gas jet from side to side, correcting any tendency to veer off course. But solid-fuel rockets have no separate combustion chamber, only a nozzle to form the gases into a high-speed jet. Usually the nozzle is an integral part of the rigid cylinder that contains the fuel.

This week, at the New York meeting of the Institute of Aeronautical Sciences, Engineer Harold W. Ritchey of Thiokol Chemical Corp. explained some of the tricks that are used to make solid rockets behave. One method, he said, is to put vanes in the gas jet. When their angles are changed, they deflect the stream of gas like a rudder. This system was used on the German wartime V2, but the vanes add a lot of drag, and they must be made of highly heat-resistant material if they are to last even the few minutes needed to do their job.

Hot Pipe. Another system is to mount the nozzle at the end of a large, flexible coupling so it can switch from side to side like the combustion chamber of a liquid-fuel rocket. This is extremely difficult because the flexible pipe must carry the giant flow of hot, high-speed, high-pressure gas without leaking or burning out. But Ritchey implied that it can be done in an efficient way that causes little drag loss.

For guidance and control purposes, solid-fuel rockets are normally loaded with fuel to full capacity. Thus when one of them is fired at a target short of the maximum range, something must be done to cut off or slow the thrust when the rocket reaches the necessary speed. The flow of liquid fuels can be controlled by valves or pumps. Comparable control can be achieved with solids, said Ritchey, by opening small apertures upstream from the nozzle. The gas that leaks out through them reduces the pressure in the combustion chamber, and the thrust falls.

Vacuum Extinguisher. If the power is to be cut off entirely, it can be done by extinguishing the rocket's fire. This is almost impossible at atmospheric pressure; if the flaming propellant is extinguished, it tends to relight. But in the vacuum of space all that is necessary is to blow off the rocket's nozzle. The vacuum outside strikes into the rocket's heart. The hot combustion gases are sucked away from the unburned fuel so quickly that they do not heat it to the kindling point. The rocket's fire goes out instantly.

Another control problem is how to supply small bursts of power to alter the course of a rocket deep in space, to land it softly on the moon or swing it around Mars. Fuel systems now in use do not operate efficiently at low throttle, and once the fuel is turned off they cannot be re-ignited easily. Last week the Naval Ordnance Test Station at China Lake, Calif, unveiled a fuel system that could solve this problem. It uses hypergolic fuel, i.e., two fluids that ignite as soon as they come in contact. A feed mechanism (using a $3.50 auto brake cylinder) squirts controlled amounts of fuel into the combustion chamber. They ignite when they mingle. So far, the system has been tested only in an experimental rocket engine on the ground. But if it can be developed, the Navy's feed mechanism could be made to obey radioed instructions from the earth, deliver thrusts to a space satellite varying from a massive push to the most delicate of nudges.

This file is automatically generated by a robot program, so reader's discretion is required.