HOW A ROCKET’S MOTORS WORK
Rocket engines are complex machines that must endure ferocious heat and pressure
Modern rocket motors have come a long way from fireworks. Relatively simple solid rockets, most often used as boosters to provide extra thrust at launch, still rely on the same basic principle of igniting a tube containing a combustible mix of fuel and oxidant. Once ignited, a solid rocket will burn until its fuel is exhausted, but the rate at which fuel is burnt – and thus the amount of thrust – can be controlled by changing the amount of surface exposed to ignition during different times in the rocket’s flight by packing the fuel-oxidant mix with a hollow gap down the centre, running along the length of the rocket. Depending on the profile of this gap, which may be circular or star-shaped, for instance, the amount of exposed surface will change during the flight.
The more widespread liquid-fuelled rockets are far more complex. Typically, they involve a pair of propellant tanks – one each for the fuel and the oxidant – connected to a combustion chamber through a complex maze of pipes. High-speed turbopumps driven by their own independent motor systems are used to deliver liquid propellant into the chamber through an injection system. The rate of supply can be throttled up or down depending on requirement, and fuel can be injected as a simple jet or a fine spray. Inside the combustion chamber, an ignition mechanism is used to begin combustion – this may be a jet of high-temperature gas, an electric spark or a pyrotechnic explosion. Rapid ignition is critical – if too
