Once the Space Shuttle is securely in place at either Launch Pad 39A or 39B, the final phase of launch preparations begin. Throughout this time, operations at the launch pad are controlled from the Launch Control Center (LCC), the electronic "brain" of Launch Complex 39.
Launch Complex 39's Pad A and Pad B were originally designed to support the Apollo program and were modified for Space Shuttle launch operations. Pads 39-A and 39-B are virtually identical and roughly octagonal in shape. The distance between pads is 8,715 ft. The pad base contains 68,000 cubic yards of concrete, and enough pipe to reach from Orlando to Miami.
A key milestone in the final preparations is the Terminal Countdown Demonstration Test (TCDT) which simulates with the crew and launch team the final hours of the countdown and serves as a dress rehearsal for the launch. The test ends in a simulated ignition and automated shutdown of the Orbiter's main engines.
TCDT supports an important function for the KSC launch team. During what is called the malfunction run, the test simulates real-time failures of vehicle and ground systems.
As launch day nears, propellants are loaded, flight crew equipment is stowed and range safety ordnance connections are completed just before the countdown starts. It is during this period that NASA conducts a comprehensive Flight Readiness Review to address every facet of the pre-launch process.
The Space Shuttle launch countdown is a routine and standardized timeline of events that begins about 43 hours before the launch with a call to stations from the Launch Control Center. This verifies that all required personnel are ready to support the countdown activities.
The final hours of the count include a final mission software update, completion of propellant system purges, propellant line chilling, crew ingress and lift-off.
The Space Shuttle is launched in a vertical position, with thrust provided by two solid rocket boosters, called the first stage, and three Space Shuttle main engines, called the second stage. The three main liquid fuel engines ignite 6.6 seconds before liftoff, followed by ignition of the twin solid rocket boosters at T -0. To achieve orbit, the Shuttle must accelerate from zero to a speed of almost 18,000 miles per hour, a speed nine times as fast as the average rifle bullet.
