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Old 04-16-2018, 09:16 AM   #11
Marasmusine
 
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Default Re: [Spaceships] Black powder Rockets?

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Originally Posted by Agemegos View Post
Bear in mind that in GURPS Spaceships' terms the model rocket motors you buy consist of a engine and some fuel tanks, not just an engine. Listed thrust-to-weight ratios in the spec will be for the fully-fuelled motor at ignition, not for the almost-empty motor at flameout.
I see, thanks. I'm now looking at http://www2.estesrockets.com/pdf/Estes_Engine_Chart.pdf which shows initial weight and propellant weight. It looks like, roughly speaking in Spaceships terms, half the components would be chemical rocket, and half would be fuel tanks.
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Old 04-16-2018, 06:06 PM   #12
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Default Re: [Spaceships] Black powder Rockets?

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Originally Posted by Marasmusine View Post
Yes I intend to give the rocket a good chance of catastrophic failure!
On the scale and at the TL you are talking, I'd suggest a Malf of about 6...maaaaybe 7. It'd probably be realistic to make it a Malf of 3....
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Old 04-17-2018, 02:38 AM   #13
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Default Re: [Spaceships] Black powder Rockets?

Here's what I think I've worked out for the Estes E9-6.
From their chart, it has 25 N of thrust, an initial weight of 56.7 g and a propellant weight of 35.8 g. Wikipedia says its Isp is 85.51

Its acceleration is 25 / (0.0567 * 9.8) = 45 G

If the whole rocket was a GURPS spaceship, it would have 13 chemical rocket components and 7 fuel tank components. So the acceleration of one chemical rocket is 45 / 13 = 3.46 G

The delta-v per tank is 85.51 / 3000 = 0.03 mps

Does this seem cromulent?
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Old 04-17-2018, 07:26 AM   #14
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Default Re: [Spaceships] Black powder Rockets?

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Originally Posted by Marasmusine View Post
Here's what I think I've worked out for the Estes E9-6.
Does this seem cromulent?
It seems unlikely to be related to your basic question.
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Old 04-18-2018, 02:44 AM   #15
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Default Re: [Spaceships] Black powder Rockets?

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Originally Posted by Fred Brackin View Post
It seems unlikely to be related to your basic question.
It gives me a ballpark figure? Thanks for helping.
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Old 04-19-2018, 02:12 AM   #16
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Default Re: [Spaceships] Black powder Rockets?

Quote:
Originally Posted by Marasmusine View Post
Here's what I think I've worked out for the Estes E9-6.
From their chart, it has 25 N of thrust, an initial weight of 56.7 g and a propellant weight of 35.8 g. Wikipedia says its Isp is 85.51
So its dry mass (without propellant) is 56.7 - 35.8 = 20.9 g. It is 35.8/56.7 = 63% propellant and 37% engine.

Quote:
If the whole rocket was a GURPS spaceship, it would have 13 chemical rocket components and 7 fuel tank components.
I make that 7.4 engine components and 12.6 fuel tank.

Quote:
So the acceleration of one chemical rocket is 45 / 13 = 3.46 G
I make that 45 gee / 7.4 = 6 gee per reaction engine.

Quote:
The delta-v per tank is 85.51 / 3000 = 0.03 mps
I[sub]sp[/sub] of 85.51 seconds means that 20 tanks of fuel could (except for the changing mass ratio) produce 85.51 gee-seconds. And a gee is, umm, 32.17 ft/sec≤. So that's 2751 ft/sec. And a mile is 5280 feet, so it's about 0.52 miles/sec. Divided by twenty tanks is 0.026 mi/sec per tank. Close enough.
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Old 04-19-2018, 11:29 AM   #17
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Default Re: [Spaceships] Black powder Rockets?

Mythbusters also took a shot at Lag‚ri Hasan «elebi, but really there were problems with both the Ming Dynasty Astronaut and Lag‚ri Hasan «elebi's vehicle, even beyond the propellant question.

The Ming Dynasty Astronaut's "vehicle" was said to be a throne. It was going to flip over and smash even if it didn't explode. Lag‚ri Hasan «elebi's vehicle is pretty sketchy in description, but generally is agreed to be a sort of open-topped barrel-type thing... which is neither aerodynamic, nor air-tight, and he was supposed to stand in it so even more unstable there. So both are (as originally told) pretty mythological («elebi's "parachute" is about as plausable as Icharus' wings too) even assuming modern motors.

The mythbusters used modern motors for both tests, btw, because of health-and-saftey concerns, not that this stopped the Ming Dynasty Astronaut test from exploding - they were not made to be packed in something like a 16x16 grid under a wooden throne with basically-simultaneous ignition.

Both stories, however, highlight the problem that the rockets are really only one of the problems that a TL 4-ish astronaut is going to struggle with. You need an aerodynamic stable body that isn't going to just flip over in flight, you really want to have some control over it beyond "light the fuse and pray to the deity of your choice", it has to be air tight, and you need to somehow bring enough air that your crew doesn't promptly suffocate (or you need a chemical air scrubber, which is even more technology and weight).
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Old 04-19-2018, 11:35 AM   #18
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Default Re: [Spaceships] Black powder Rockets?

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The Ming Dynasty Astronaut's "vehicle" was said to be a throne. It was going to flip over and smash even if it didn't explode. Lag‚ri Hasan «elebi's vehicle is pretty sketchy in description, but generally is agreed to be a sort of open-topped barrel-type thing... which is neither aerodynamic, nor air-tight, and he was supposed to stand in it so even more unstable there. So both are (as originally told) pretty mythological («elebi's "parachute" is about as plausable as Icharus' wings too) even assuming modern motors.
Speaking as a long time Kerbal Space Program player, those can all be solved with more struts and/or boosters.
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Old 04-19-2018, 11:41 AM   #19
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Default Re: [Spaceships] Black powder Rockets?

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You need an aerodynamic stable body that isn't going to just flip over in flight.
BP rockets are low enough temperature that you could structure your system with the payload behind the rocket. Still an explosion risk, of course, but not dynamically unstable.
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Old 04-19-2018, 11:59 AM   #20
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Default Re: [Spaceships] Black powder Rockets?

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BP rockets are low enough temperature that you could structure your system with the payload behind the rocket. Still an explosion risk, of course, but not dynamically unstable.
If you mean a pendulum rocket, unfortunately those are no more stable than conventional layouts. The force of the rocket is fixed along the axis of the rocket rather than the axis of gravity (As we would usually think of a normal pendulum), so it provides no correcting force.
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