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It takes an immense amount of energy to take an object into space. Almost all of this energy is used up within the first few minutes after launch for conventional rockets. The minutes immediately before and after launch are among the most important moments of a spacecraft's mission, and when most accidents and complications can occur.
After a spacecraft is assembled, it waits for the right moment to rise up into space. When the right launch window comes, the spacecraft is moved out to its launch site. The ideal conditions for a launch site are distance from population centers and proximity to the equator for low-inclination launches. Launches near the equator take advantage of Earth's rotation to give spacecraft an extra boost. A launch site must also have complex ground facilities such as a control center and a launch pad.
After a spacecraft such as the Space Shuttle is moved out on its launch pad, the clock starts running down toward launch. A few seconds before launch, the engines are turned on to less than their maximum capacity to test for problems. For the Space Shuttle, the liquid propellant engines are turned on at t minus 6.6 seconds, before the solid propellant engines, because they can be turned off in the event of an accident. At t equals 0 seconds, the engines are fired at 100% and the rocket lifts off the launch pad. About two or three minutes after launch, the first stage propellant runs out and the first stage detaches from the rest of the spacecraft. The rest of the spacecraft continues on, using as many as 5 different stages and discarding each one into the atmosphere when it runs out of fuel. For the Space Shuttle, the solid rocket boosters stop firing at t plus 2 minutes and are dropped down to Earth, to be recovered and used again, and the main external fuel tank burns up in the Earth's atmosphere after t plus 9 minutes. After using all of its stages, a spacecraft may use orbital maneuvering thrusters to place it in the right orbit, or send it on the right path out into the solar system.
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