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Getting ready for launch
Preparing a spacecraft for launch actually begins way before the finished version is despatched to the launch site.
One of the first versions of the spacecraft to be built is the thermal and structural model. This is thoroughly tested at ESA's European Space Technology Centre (ESTEC) to make sure it will survive the rigours of launch.
Each launch vehicle has its own unique properties, which include the amount of vibration created and the noise generated during take-off. So, a vital aspect of preparing a spacecraft for launch is the tests in ESA's acoustic chamber simulating the noise of launch and the vibration table that simulates the feeling of launch.
Once the thermal and structural model passes these and other tests, the actual flight model can be made. When it is finished and tested it must be taken to the launch site. This is usually Europe's spaceport at Kourou in French Guiana, or a Russian launch site, such as the Baikonur Cosmodrome.
Transporting the spacecraft is a risky business and is handled with extreme caution. Once the spacecraft arrives at its launch destination, it undergoes a major inspection to make sure it is still in perfect shape. The final check to make sure the spacecraft is ready to fly is known as the 'flight readiness review'. As soon as this is passed, the spacecraft is fuelled.
Fuelling is a hazardous operation because the some rocket propellants are extremely toxic. Technicians wearing protective plastic 'spacesuits' supervise the fuelling, which can take up to a week to complete. This is a painstaking process because it is also irreversible. Once loaded, the fuel cannot be drained without potentially seriously damaging the fuel tanks.
With a fully fuelled (or 'gassed-up') spacecraft, the next task is to mate the spacecraft with the upper stage. This is the rocket motor that will propel the spacecraft on its way, once it has been placed in Earth’s orbit by the launch vehicle. The spacecraft and upper stage are then encased in a protective shroud and fixed to the launch vehicle itself.
In the case of a launch on the European Ariane rockets, all assembly is performed with the rocket upright. On the Russian Soyuz rockets, however, the assembly is performed horizontally and the rocket is only hoisted upright when it arrives at the launch pad.
The roll-out to the pad takes place a few days before lift-off. The rocket itself, however, is not fuelled until shortly before blast-off time. In the last minutes before launch, lots of data pass between the rocket and mission control.
Computers verify that all systems are 'nominal' – the word that engineers use to refer to correct readings – and then the rocket's main engines ignite and the spacecraft begins its journey into space.
Last update: 13 September 2004
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