Piers Sellers describing the seconds before takeoff:
At exactly 10 seconds before launch, all the navigation instruments go from a rest position to active, you can see that navigation is tracking, that it knows where it wants to take the shuttle. A few seconds after that, the main engines light. You can't really feel or hear much at that point. You see the power come up on the indicators in the cockpit, you see the thrust go up from zero to 100% on three engines and then you feel the whole stack sway forwards towards your feet, and that is because the thrust of the engines is so great that it bends the shuttle and stack on its hold-down bolts, and pushes it to one side. They call that the twang. The twang goes all the way, about 4ft, and then the whole stack bounces back. And at exactly the right moment, zero, the solid rocket boosters light and the hold-down bolts explode and off you go. It feels as if someone lit a bomb underneath your back. You just go flying up into the air, like a gigantic hand pushing you up into the sky. You see the launch tower fall by down one side and you are headed upwards into the sky.
Scott Altman on returning to Earth:
You're coming through the atmosphere and if it's night where you are, you look out of the overhead window and you start seeing this little green glow, which is the atmosphere heating up by the friction of the shuttle smashing through it. As you go further and lower, you start to notice it going a little bit darker, into the yellows. On my second entry, I was looking out at that and I started to see it get a little bit darker, so I floated up in my seat a little bit and looked towards the nose and I could see it transitioning from yellow to kind of pink and I floated up a little higher and it was starting to go red, and it was like - "I don't know if I want to look any more" - so I floated back down in my seat because it just looked too hot, too brutal out there.