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 of the launch platform, which has the flame deflection structure to withstand the intense heat and load generated by rocket engines during liftoff.
Most cryogenic launch vehicles need to be continuously topped off as scheduled liftoff approaches. This is particularly necessary as various holds are placed on the liftoff and then removed as support personnel correct problems or verify they are not serious. Without the ability to top off the launch vehicle, the launch would have to be scrubbed when problems slowed down the countdown. 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.
Read more about Launch Pad: Transport of Rockets To The Pad
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