A launch pad is the area and facilities where rockets or spacecraft lift off. A spaceport (or rocket launch site) can contain one or many launch pads. A typical launch pad consists of the service and umbilical structures. The service structure provides an access platform to inspect the launch vehicle prior to launch. Most service structures can be moved or rotated to a safe distance. The umbilical structure has propellant loading, gas, power, and communication links to the launch vehicle. The launch vehicle sits atop the launch platform, which may contain a flame deflection structure to withstand the intense heat and forces generated by rocket engines during liftoff. Large amounts of water are often used to deaden sound waves and this requires nearby water towers. Lightening arrestors are also frequently located nearby on large towers.
Cryogenic propellants (liquid oxygen oxidizer, and liquid hydrogen fuel) need to be continuously topped off (replace boil-off) as scheduled liftoff approaches. This is particularly necessary as complex launch sequences (countdowns) may be interrupted by planned and unplanned holds to account for the handling of problems. Gantries are commonly designed and constructed on launch pads to meet these types of servicing requirements both during launch and in the preparation period leading up to it.
Most rockets need stable support for a few seconds after ignition while the engines ramp up and stabilize at full thrust. This stability requirement is commonly met by the use of explosive bolts to connect the launch vehicle to the pad. When the vehicle is stable and ready to fly the bolts explode, severing the vehicle's ties to the launch pad and structures on the ground.
There are several different types of launch site, determined by the means by which the rocket gets to the pad.
The first large rocket, the V-2, travelled horizontally with its tail forward to the launch site at Peenemünde. This is the most common method of transport to the pad and was used for all large Soviet rockets, even Buran.
In a similar manner, at the Soviet launch site near Volgograd, a silo used to launch test rockets would have its top opened and a second stage and payload would be driven in horizontally and tilted on top of a first stage already in the silo, the nose cone and some of the second stage remaining visible above ground. Hence no surface pad is used; Russian silos are reusable. This method was only used for the Cosmos series of small satellite launching vehicles.
At Cape Canaveral Air Force Station, two parallel standard gauge railroad tracks were used to transport the Titan launch vehicle and its mobile launcher platform from the integration building to the launch areas at Complex 40 and 41, and continue to be used for the Atlas V.
In the 1920s, Hermann Oberth described a method in which the rocket is assembled vertically on a floating barge, which he used in the movie Frau im Mond. This has never been used, although it was seriously considered for use at Kennedy Space Center Launch Complex 39 for the Saturn V. It was rejected for that application due to the instability of the top-heavy unfuelled rocket and gantry.