Steam Powered Spaceship

When you run a huge SteamEngine?, you typically tune it using a big "governor", which is two spinning balls on arms. If the governor goes faster the arms go up, and these pull up on a ring. You tune the engine by calibrating the height of this ring, so the governor maintaining a steady speed controls the steam flow in the engine. " DynamicEquilibrium?".

But because the governor's controlled by gravity, these kinds of steam engines are not recommended for use in outer space.

> What happens the the space ship stops?

Assuming you mean "free fall", the engineer sets the highest calibration on the sliding ring to put the engine into its "idle" state. Assuming they dig speed before the engine stops.

I'm unsure how to achieve the alternative kind of stop, "station-keeping", aboard a steam-powered spaceship.

See StatisticalQualityControl?.

Of course, in space, no gravity for the governor is the least of your problems.

I HaveThisPattern: I've heard people give silly little reasons why something doesn't work while missing the bigger reasons.

These threads failed to cover one trivial but important point explicitly: The acceleration of the spaceship works as a stand-in for gravity. But (because we just traded to a variable from a constant), the rotational speed of the governor must therefor be made constant. And this is impossible if the only power available is steam!

Not quite. If you bend the rules a bit to allow electronics, provided that the electronics are powered by a generator which runs off a portion of the steam engine's power, you can do it. -- DanielKnapp

Have I missed the point or could you not use a spring?

Well: If the spring is wound by anything except the steam, it counts as a separate power source, and then the spaceship isn't "steam-powered" anymore. More importantly, springs don't release power regularly. I suppose that you could use an escapement - the mechanism that keeps clocks ticking properly - on the spring and then use that power to regulate the steam engine. Come to think of it, couldn't you just have the steam turn a gear, use an escapement on that gear, and use the regulated torque to regulate the engine?

They meant a spring to push down the governor.

A stationary steam engine mounted on a planet can use a governor pushed down by gravity.

It still won't push down with constant force - the force applied will be less when the governor is farther down. I think figuring out whether it would work regardless requires going into the mathematics of the situation, though - intuition is out of its depth.

Hmm. Sounds like a good way to kill an afternoon. Anybody have information on said mathematics?

It's comparatively trivial to change the linkage on the governer to match the linear behaviour of the spring. I've done it on the back of an envelope (literally). You then mount the governor so that its axis is perpendicular to the direction of thrust.

From the XpMailingList (Principia Programmatica thread, August of 2000)...

 > Actually, I don't see a problem with using a modified governor system in
 > low to no
 > gravity situations (I think a very low drag ratio may be important too).
 > An engine
 > exists to provide thrust or energy. When providing thrust, the
 > acceleration of the
 > system provides simulated gravity. If the governor is designed such that
 > the thrust
 > will always be large enough to keep the balls from reaching a "horizontal"
 > position,
 > you can use horizontal as an indicator of the fact that you are not
 > providing thrust,
 > merely energy and tune accordingly.
 >
 > I may have missed something, I often do.

Gravity is a constant, so you can calibrate against it.

The governor I described is used on stationary steam engines.

Nice idea about the thrust providing the downward drag on the arms, but this would _OverControl_ the situation. The arms would be influenced both by variable acceleration and by the variable rotational force inspiring them to straighten their arms out. If acceleration is constant then only the rotational force controls the arms, so they can be calibrated safely. Over-control can't be calibrated. This is a common Statistical Quality Control situation; engineers are advised to sample only one variable at a time, not two mixed together. And they should not constantly "tweak" the calibration; this mixes in the new independent variable of "human interference". Only long runs with constant settings should be analyzed to provide feedback as metrics. The intriguing thing to me in this thread is the design, which seems somewhat allegorical.

We start off with a reaction which generates a significant expansion: converting water in to steam. Then we use this expansion to move pistons up and down, generating linear motion. This motion is then converted into rotational motion. In order to stop a runaway, we need a governor. The design team is sending memos back and forth on how this governor should work.

Meanwhile, no one's asked how we could actually use a rotating shaft to make a vehicle suspended in space move, nor why we're not just blowing the steam out the back.

This is the evil that is BigDesignUpFront.

D.....oh. I feel really stupid. Hell, I even remember some Pournelle book involving a spacecraft which did exactly that.

Too true. Try Googling for Steam Rocket, if you want to see how steam power has been used to produce serious acceleration.

I assumed that the steam engine was for some internal machinery, not propulsion.