How does the space shuttle manoeuvre?

13 March 2011

Part of the show Why did a Laser Make My Nuts Glow?

Question

Hello Naked Scientists!

My name is Taylor and I'm from Vancouver, British Columbia in Canada.

I love the show and listen every week.

Since Discovery has just completed it's last launch, I've come up with a couple questions that I was hoping you guys could answer.

1. Why is it that the Shuttle's 3 main engines look like the very clean, directional flame from a jet lighter but the explosions coming out of the solid rocket boosters look like a huge mix of orange and yellow flame just bursting out?

2. How does the space shuttle maneuver at each point in it's flight? (liftoff, primary ascent, in orbit, re-entry)?? Does it use conventional avionics? thrusters positioned on the craft? engine throttling?

Thanks so much! I hope to hear the answers on the air!!

Keep up the great work guys, and for pete's sake, Chris.... get some sleep! you work too hard! hahaha.

Taylor Sharpe

Answer

Dave - Okay, to start off from the beginning, the two forms of rocket on the space shuttle are working very differently. The main engines on the back of the rocket are burning a mixture of oxygen and hydrogen. So we've got liquid oxygen and mix it with hydrogen in a big fuel tank. It's then piped into the engines. It's then burned, it heats up to 2,000 or 3,000 degrees centigrade, to form water. Essentially, you get very, very hot water shooting out at the back. It's very, very clean. There's almost no solids in it and water doesn't glow particularly in visible light, so the flame is almost invisible.

The solid rocket boosters on the other hand are burning a completely different fuel, they're burning aluminium and then they put an oxidiser on there as well. It's all mixed up and it's solid, and that burns, and it gets very, very hot and it produces an awful lot of thrust. It's kicking out a lot of solid particles and solid particles, when they get hot, they glow. It's a bit like if you cook, it gets very hot, it glows red hot. So these particles coming out of the bottom of the boosters are going to be glowing very brightly. They produce a lot of light and it's also coming out of much bigger holes. Everything is a bit less focused and a bit less clean.

How does the space shuttle manoeuvre? When it's in the take-off phase, so when it's going up, the main engines are gimballed. That means they can change the direction over them and so, if it's starting to go too far over the right, they kind of tip the engines around a little bit and it pushes the bottom of the rocket around. The main engines do most of the directional work of the shuttle as it goes up. They can throttle the engines a bit which would affect where it ends up, so it can do the boost, but the most control is by gimballing them.

When it gets actually up into space and it's manoeuvring just gently up there, it's dropped off all the main engines. The main engines don't work so they've got a few minor little thrusters which just act like very small rocket engines. They throw out stuff one way and it gets pushed the other way. And then for re-entering, they've got some slightly larger engines, not as big as the main ones, which can produce enough thrust to lose enough energy so they come down and hit the atmosphere and end up landing.