Most Powerful Engines In The World

Press, Volume CII, Issue 30130, 14 May 1963, Page 11

Most Powerful Engines In The World

The engines which propel large rockets into space are, for their size, by far the most powerful devices ever built. In principle rocket motors are the simplest prime movers of all —far simpler than the internal combustion engines which drive our cars or the gas turbines which propel jet aircraft. In practice this is true of solid-fuel rocket motors but not of their more efficient brothers: the liquid-fuel rocket motors, which are much more complex. The added complexity arises from the need to pump liquid fuels at a high rate into the combustion chamber to be burned, whereas a solidfuelled rocket has a very large combustion chamber with all the fuel packed in it from the start. Most of the present-day space successes are achieved by rockets lifted off their launch pads by liquid-fuelled motors of the S-3 family, developed by the Rocketdyne Division of the North American Aviation Company. The Thor, Atlas and Saturn first stages rely on variants of this well-designed rocket motor. The British Blue Streak rocket is powered by two Rolls Royce RZ.2 motors which are also closely related to the Rocketdyne S-3 series. Each of these engines uses the same propellant combination —kerosene and liquid oxygen. The kerosene, which is referred to as the fuel, burns with oxygen stored in liquid form at minus 300 degrees Fahrenheit and referred to as the oxidiser or oxidant. There are many other liquid propellant combinations but this is the one most widely used by large rockets. The motors of the Rocketdyne S-3 family each weigh about three quarters of a ton and produce about 75 tons of thrust—in other words, they can lift one hundred times their own weight. This requires the consumption of a ton of propellant every three seconds of burning time. The resulting jet of flaming gas roars out of the exhaust nozzle at a speed of nearly two miles a second and has a temperature of over 5000 degrees Fahrenheit. The power generated by a rocket motor of this size works out at two and a half million horsepower and is maintained for up to three minutes, depending on how long the supply of propellant lasts. A typical rocket vehicle powered by one of these motors reaches a height of 50 miles and a speed of 5000 miles an hour before running out of prooellant.

The key to this incredible performance lies in the transfer of a third of a ton of fuel and oxidiser every second from the propellant tanks to the combustion chamber. This is accomplished by a compact turbopump unit which produces 2500 horsepower at a rotational speed of almost 30,000 r.p m. Again, this is an incredible performance from a unit which weighs only as much as a small motor car engine. In both illustrations turbopump units may be seen mounted close to the rocket motors. The picture of a Rolls Royce RZ.2 motor reveals a spherical gas generator in which a small proportion of propellant is burnt to drive a turbine. The turbine shaft drives the fuel and qxidiser pumps via reduction gears. Turning now to the operation of a rocket motor, the action of pressing the start button in the control room initiates a sequence of events which must take place in a precise order, otherwise

the motor is shut down. In the case of the RZ.2 an electropneumatic sequencer controls every step automatically. First all tanks are pressurised and the pyrotechnic igniter inside the combustion chamber is fired. When an electrical link in the igniter burns through it signals the main liquid oxygen valve and the igniter fuel valve (fed from a ground starter tank) to opeh. This allows a small flow of fuel and low pressure liquid oxygen to enter the combustion chamber and be ignited, whereupon the resulting flame burns through an ignition

detector wire stretched across the exit of the exhaust nozzle. Breaking this wire fires the gas generator igniters and when they are Lit successfully the main fuel valve is opened. This in turn enables the gas generator to start supplying hot gas to the turbine, speeding up the pumps which commence feeding propellants at high pressure to the combustion chamber. Thrust builds up very quickly at this stage. The whole operation, from pressing the start button to full thrust, takes only four seconds. So much for what are nowadays classed as medium sized main-stage rocket motors. Advancing in size we come to motors such as the mighty Rocketdyne F-l. capable of producing 750 tons of thrust and said to be the largest rocket motor ever fired. Since this monster gulps three tons of propellant every second, one can imagine the tremendous fuel consumption of the Saturn

C-5, which employs five F-l motors in its first stage. The best idea of their power output is given by the fact that a single F-l motor can produce over thirty times the total power capacity of Benmore. It goes to show that getting to the moon takes quite a lot of effort—both financially and mechanically. Trips to the planets, especially the far ones, will require even greater power. Chemically propelled rockets are no longer adequate. Nuclear power coupled perhaps with electrical propulsion. might be the answer but it is too early to be certain.