How were Space Shuttles Launched - The Initial Preparation of a Space Shuttle Launch
The launch of the space shuttle began in the Orbiter Processing Facility (OPF). This was a relatively squat (95 ft high) building next to
the huge Vertical Assembly Building (VAB) [see below]. In the OPF, the shuttle orbiter was inspected, refurbished and tested. The mission payload was installed and tested, and a power up test of the shuttle carried out.
During this time, the Solid Rocket Boosters (SRB) and External Tank were being mated in the huge VAB. They were resting on the Mobile Launch Platform, secured by four huge nuts and bolts on each of the SRBs
that are severed at liftoff by small explosives. With the shuttle, the entire stack, as it is called, would be carried to Pad 39A or 39B by the Crawler-Transporter. The SRB seals were inspected and integration tests performed during this time.
Once all this was completed, the orbiter was moved from the OPF to the VAB where it was mated to the SRBs and external tank. Integration tests were performed, and the giant crawler-transporter lifted the Mobile Launch Platform off its supports and began the slow, five hour, 3.4 or 4.2 mile journey to the launch pad.
When the crawler got the Mobile Launch Platform and Shuttle to the pad, it lowered its cargo onto the pad supports and backed away to return to the crawler bay.
On the pad, further checks were performed and the shuttle and payload were prepared for flight.
The Clock Has Started
The actual countdown began at about T-43 hours, depending on the mission. All launch activities were conducted from the Launch Control Center (LCC) adjacent to and connected to the VAB. With built-in holds, a shuttle launch actually took about 72 hours.
At T-43 hours, the LCC was manned and system checks performed, including a power up of the orbiter. The SRB seals were again inspected.
At T-28 hours, the orbiter’s fuel cell systems were loaded. From then to T-11 hours, the orbiter and its propulsive units were prepared for flight. The payload bay doors were closed, and all valves set for fuel loading. During this time, the launch crew made its first pass through some 25,000 measurements and criteria that had to be met before the shuttle could be launched.
At T-9 hours the external tank was prepared for loading of liquid hydrogen and liquid oxygen. From then until loading began, the pad was prepared for launch. The rotating service structure was rolled back. Time critical flight crew equipment was installed in the cockpit, and the crew escape pole was installed in the orbiter.
Fuel loading began at T-6 hours. It took three hours. When completed at the T-3 hour mark, an automatic two hour hold was initiated. At this time only specialized launch teams were permitted on the pad. One was the Final Inspection Team, nick-named the ice team. Its task was to conduct a walking inspection of the vehicle and pad to look for any anomalies that might be of concern.
Another ice team prepares the white room, ensures the orbiter cockpit was properly configured and assist the astronauts’ entry into the orbiter.
GO for Launch
At T-20 minutes the LCC was locked down and the launch crew made its first run through a set of 2300 Launch Commit Criteria. These included weather, all tracking stations up, an acceptable level of hydrogen gas on the pad, and hundreds more. If the Launch Director got a GO from everyone, the countdown proceeded to T-9 minutes, at which time a built-in hold initiated. During this time, the Launch Director polled the team again to ensure the Launch Criteria were met. If they were, the Ground Launch Sequencer (GLS) was started, and the countdown proceeded under computer control.
The GLS monitored every system on the shuttle. If it detected an incorrect reading, it automatically stopped the countdown.
At T-9 seconds, the orbiter’s main engines were put through a gimble test by the GLS. If that is successful, a pyrotechnic device just beneath the orbiter’s main engines ignited. At that time the pad sound suppression system was initiated. This consisted of a spray of 900,000 gallons a minute of water into the flame deflectors through the holes in the Mobile Launcher.
Sound suppression is necessary because the shuttle at liftoff produced one of the loudest sounds ever heard on Earth—215dB. To put that in perspective, a sound level of 111 dB causes a human so much pain it is unbearable and will cause permanent hearing loss. Without suppression, that level would damage the launch platform, and the reflected sound would damage the shuttle. The thousands of gallons of water spraying into the flame deflectors reduce that to 142 dB—still a very high level of sound but not enough to damage the pad or shuttle.
At T-6.6 seconds fuel had begun pumping into the main engines and they ignited. By T-3 seconds they have built up to 90 percent thrust and were put into liftoff position.
At T-0 the explosive holddown bolts securing the shuttle to the launch platform were severed. The SRBs were ignited by a pyrotechnic device inside the rocket motor that fires down the entire length of the propellant grain. As soon as the SRBs ignite the shuttle lifted off for another trip into space. The white smoke billowing up around the pad was not from the SRB exhaust. It was from the sound suppression water pouring into the flame deflectors—it was steam.
Launching a Shuttle was a Complex Dance
The Space Shuttle was the most complex machine ever designed by Man. It is no surprise then that to launch it requireed a complex series of preparations, checks and operations.
- All photos: NASA