Saturn V: Attitude control @ launch

(Hi, if this has been covered previously, apologies, I did search SDMB first as well as Nasa sites.)

How was the attitude of a Saturn V (or really any) spacecraft controlled during launch? The launches that I’ve seen typically show the spacecraft launching straight up and then pitching over after a while, sometimes quite a bit, presumably to meet it’s desired flight path.

This picture shows Apollo 13 at launch yawing over having just left the ground! The photo caption on this page states, “Apollo 13 yaws away from the launch tower during lift-off. It has risen about half its own height.”

It seems like quite a trick to pitch over a 36 story building under a million pounds of thrust. Or perhaps I’m easily impressed.

Okay, so how was the Apollo pitched over just after (or during in the case of Apollo 13) launch? My guesses:

[ul][li]Big freaking gyroscopes (like they can afford the weight??).[/li]
[li]Fine control of the main engines (boy, that sound easy to do: tilting or throttling the main engines of five rockets going full tilt. Nah.).[/li]
[li]Hi, Winnie![/li]
[li]Powerful side thrusters, like the small ones used in free flight (nah).[/li][/ul]


Aside from gyroscopes being used to measure attitude rather than directly control it you answered your own questions. What’s so amazing about any of the things you listed? They must have precise control of the main engines for symmetrical thrust so why not correction?

Padeye, sorry, I think I’m missing your point, or perhaps I haven’t explained mine very well.

Yawing over the spacecraft during ascent is a controlled maneuver; I’m just wondering what mechanical process (side thrusters, weight distribution, main engine control, something else) is providing that control. I’m not sure I agree that “They must have precise control of the main engines”, but I’m also not sure what you mean by ‘precise’.

It seems to me that for the main engines to control the direction of the vehicle would mean that either a) each of five engines can be tilted a reasonable enough amount to affect the flight path, or b) each or several engines can be directed to use a variable amount of thrust towards that same purpose. Sure, this seems possible but it also seems very hard (to me) to design a reliable set of engines that can retarget the thrust of such a huge vehicle.

This obviously isn’t my area of expertise, but wouldn’t the precise control of the main engines be more along the lines of on/off, or perhaps more/less-thrust, rather than ‘take a right, bob’ ? :slight_smile:

The Saturn V had gimbaled (movable) engines to control the attitude. You can get info on many web pages, such as this one. The Shuttle has a similar system - if you watch a detailed TV coverage of a launch, such as you get from NASA Select TV, you can see them move the three engines to test this system.

scr4 beat me to it. The engines are on gimbals. Think of it as balancing a long pole on your fingertip. It doesn’t take much movement to keep it centred.

Well, son of a gun. Who’da thought they could gimbal monster engines like the Saturn’s. I am in Awe.

Thanks for the info!!!

Well, you only have to gimbal the nozzles, and I don’t know if the Saturn V’s nozzles were gimbaled. Hmm… apparently they were.

It’s also quite possible to use liquid thrust vector control, wherein ports are made in a ring around the inside of the throat of the nozzle and hydrogen peroxide or some other reactive liquid is injected. This changes the dynamics of the plume and alters the direction of thrust a few degrees.

The engines I worked with at American Rocket Company a decade ago used this method.