A launch pad is designed and built to meet a launch vehicle's special needs and requirements. For example:
1. Most cryogenic launch vehicles need to be continuously topped off as scheduled lift off 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. Gantrys 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.
2. 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 use of exploding bolts to connect the launch vehicle to the pad. When the vehicle is stable and ready to fly the bolts are exploded, this severes the vehicle's ties to the launch pad and structures on the ground.
