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It's well known that the shuttle's robotic arm is used to lift satellites out of the cargo bay, and that on the current mission a new version will be used to check the surface of the orbiter with a special camera. But the arm has also been used to "knock the ice off the shuttle's crapper," as one NASA scientist put it, and to smack the occasional balky communications satellite whose solar panels didn't unfurl properly.

"I think the arm has been used more for things it wasn't designed for than things it was designed for," one senior engineer said.

The shuttle twang

At the point that NASA calls "T minus 6.6 seconds," or launch time minus 6.6 seconds, the shuttle's massive engines fire. But it only takes about three seconds for them to get to full throttle, so why do they start at 6.6 seconds?

This is because when the engines start up, the force of that thrust actually bends the upper part of the external fuel tank backward by up to one metre, and it takes several seconds for it to swing back to vertical - a process NASA engineers call "the twang."

Once the twang is done, the shuttle is ready to go.

Bad jokes come in handy

Astronauts know a lot of bad jokes. During the launch countdown, they spend several hours lying flat on their backs, in full flight gear and space suit, unable to move. To pass the time, they often compete to come up with the dirtiest or stupidest joke -- and there is plenty of competition, members of the space program say. Because the only people listening to the audio channel at that point are the other crew members and NASA physicians, they don't have to worry about offending anyone. "You just have to make sure you don't hit the wrong button and put it on the public channel by mistake," one astronaut said.

Prone to pain

The amount of time astronauts spend on their backs in the orbiter before launch (up to six hours if there are problems or weather delays) can be hardest on the fighter pilots among the crew. This is because when pilots fly their high-speed manoeuvres, they are subject to severe gravitational forces that put a strain on their vertebrae. "We've had fighter pilots actually break their necks while they were flying" because of the gravitational pull, one astronaut who is also a pilot, said. This leads to back problems that are aggravated by lying motionless in a heavy flight suit for several hours.

The ice that wouldn't melt

You might think nothing could survive on the surface of the shuttle after its re-entry into the atmosphere when it is subjected to temperatures of up to 1,650 degrees Centigrade, but you'd be wrong, a NASA insider said.

On one mission, the liquid waste expelled from the toilet while in orbit created a giant, horn-like icicle that stuck up from the top of the shuttle. As the orbiter cruised to a landing after re-entry, a large frozen chunk of the horn slid off and landed with a thunk on the runway. "I guess we don't need any more insulation on that part of the shuttle," one of the NASA engineers said with a laugh.

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Mathew Ingram

Some little-known facts about the space shuttle