LAUNCH VEHICLES

Stages Large rockets that launch spacecraft are often not just one rocket, but two, three or more stacked on top of each other. This is callled "Staging" and each individual rocket is a Stage. Each rocket is used in turn, from the bottom up, to lift the spacecraft as high as possible before it burns out. Once it is burned out it is useless and just unwanted weight, so it is allowed to drop off, or rather it is blown off with explosive bolts. The next rocket stage then starts and the spacecraft moves on up towards orbit. Discarded stages fall to Earth or burn up as they re-enter the atmosphere. This is why most space vehicles are launched over unpopulated sea or desert. You don't want to be in the way when a spent rocket comes down. They are big and weigh several tonnes.   Fuel Rockets are the size they are because most of what is in them is fuel. Rockets use huge amounts of fuel, but they generate huge amounts of energy too. When the Saturn 5 Rocket (left), that sent men to the moon, was built it was the world's most powerful machine. It weighed over 300 tonnes when empty, but ten times that when full of fuel, and it stood 365 feet high. All this just to get three men to the Moon and back! Return

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