![]() To keep the launch teams in practice, NASA runs a series of simulations at the Kennedy Space Center in Florida, similar to the mission simulations that train astronauts in Houston. You have normal and emergency procedures, and you better know your emergency procedures or you're not going to be doing the normal ones for very long." I don't want to ever have to do that.' It's just like flying airplanes. In other words, you can't sit there and say 'I hope this never happens. "You have to know your procedures, and you have to be willing to execute them. "The real key to handling an emergency as serious as an engine abort is practice," says Bartolini. If certain limits are exceeded, the computers command an abort.Ī launch pad abort is a safety measure, but it creates a whole new set of problems since it leaves an enormous amount of potential chemical energy sitting on the pad. If all three engines reach 90 percent of maximum thrust by T minus three seconds and all parameters are within limits at T minus zero, the shuttle computers send out commands for pyrotechnics to ignite the SRBs, split the bolts holding the shuttle to the pad, and release the umbilical cord to the external tank. Fifty times a second, a computer on each of the three main engines examines close to 30 critical parameters, including sensor function, fuel pressures, temperature, vibration, fuel flow rates, and power status. "There's too much stuff going on in too short a time for a human being to make a decision and then take action," Bartolini says. "You're going flying." The liquid-fuel engines ignite 6.6 seconds earlier than the solids, giving the computers a narrow window in which to call off the launch. "When those SRBs light, there is no recall," says Bruce Bartolini, a launch team manager with Lockheed Martin Space Operations. The T-zero event is the ignition of the solid rocket boosters, propellant-filled towers that generate 71 percent of the thrust the shuttle needs to leave the ground. Plowden, who manages the Rocketdyne team that services the shuttle's main engines. "We are not willing to lift off if we lose redundancy before we get to T-zero," says John B. And, almost exactly a year later, less than two seconds before the solid rockets were to ignite, an oxidizer pump overheated. August 12, 1993: A faulty sensor indicated abnormal fuel flow. March 22, 1993: An oxidizer purge valve jammed on a chunk of O-ring. July 12, 1985: A chamber coolant valve refused to close. June 26, 1984: A main fuel valve actuator in one of the engines stuck. It has happened only five times in shuttle history: The three main engines on the orbiter ignite, computers monitoring them detect a problem, and the space shuttle onboard computers shut the engines down. It's really hard to feel it, but the vehicle continues to sway back and forth." Five to ten seconds after it's happened, all the noise has gone away, all the vibration. "It's very loud and it's obvious that something's wrong. "The first thing that catches your attention is the master alarm," he remembers. You can almost feel the shock waves as they develop out of the engine." Bursch's biggest surprise of the day, however, came seconds later, when the engines shut down. "On the pad the engines create a lot of noise, a lot of vibration. "It really does feel like these engines are strapped to your back," he says. Bursch, a Navy commander and test pilot, describes a sensation that the shuttle simulator couldn't quite replicate. Bursch was mildly surprised by the violence of the main engine firing. On his first space shuttle mission, astronaut Daniel W.
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