I read a Wikipedia article on the SRB's and it quoted it using a linear shaped charge, but where exactly is the charge located, and what/how does it destroy the SRB ? Cut it in half, cut the nozzle off etc.... ??
(...)Any other propellant combinations the readers here would like me to try?
strangequark, I wrote two papers on this subject which are attached. In a first stage performance is limited by propellant volume. I show in my paper that the criteria for choosing a fuel for a first stage is its impulse density Id, equal to the product of the propellant density (kg/L) and the exhuast speed (m/s). A list of propellants is given belowPropellants MR dp (kg/L) ve (m/s) Id (Ns/L)O2/H2 5.0 0.3251 4455 1448O2/H2 6.0 0.3622 4444 1610O2/H2 7.5 0.4120 4365 1798O2/CH4 3.6 0.8376 3656 3062O2/C2H6 3.2 0.9252 3634 3362O2/C3H8 3.1 0.9304 3613 3362O2/C3H4 2.4 0.9666 3696 3573O2/RP–1 2.8 1.0307 3554 3663O2/C7H8 2.4 1.0954 3628 3974HTP/C3H4 6.5 1.2553 3319 4166HTP/RP–1 7.3 1.3059 3223 4209HTP/C7H8 6.6 1.3496 3288 4437HTP is 98% hydrogen peroxide, RP-1 is rocket grade kerosene and C7H9 is quadricyclene or RP-X2 (an exotic hydrocarbon fuel). O2/H2 (liquid oxygen and liguid hydrogen) has the best exhaust speed, but a very poor density, which makes it a bad choice as a first stage propellant (that's why the Delta-IV is so huge). A good combination is O2/RP-1, but there are better combinations, such as HTP/RP-1 which will give 15% more performance, plus it has the advantage of being non-cryogenic at the disadvantage of being unstable in the presence of impurities.So in answer to your specific question about O2/CH4, that performs worse than O2/RP-1 in a first stage. This means your fuel tanks will need to be about 20% larger in order to have the same performance as O2/RP-1. Against O2/H2 it performs much better. Your fuel tanks will be about 47% smaller (the actual percentage depends on the required delta-v for the first stage, larger values will decrease this amount, but even to orbital speeds, O2/CH4 will still perform better).For an upper stage, mass is all important, so the high exhaust speed of O2/H2 means that's the best propellant to use.By the way, for single stage to orbit, my second paper shows that any combination O2 or HTP with any other hydrocarbon fuel will outperform O2/H2. A good choice is O2/RP-1, but O2/C7H8 gives 13% more performance.
Propellants MR dp (kg/L) ve (m/s) Id (Ns/L)O2/H2 5.0 0.3251 4455 1448O2/H2 6.0 0.3622 4444 1610O2/H2 7.5 0.4120 4365 1798O2/CH4 3.6 0.8376 3656 3062O2/C2H6 3.2 0.9252 3634 3362O2/C3H8 3.1 0.9304 3613 3362O2/C3H4 2.4 0.9666 3696 3573O2/RP–1 2.8 1.0307 3554 3663O2/C7H8 2.4 1.0954 3628 3974HTP/C3H4 6.5 1.2553 3319 4166HTP/RP–1 7.3 1.3059 3223 4209HTP/C7H8 6.6 1.3496 3288 4437
This "density impulse" you use, it looks like it arbitrarily assumes that mass ratio scales linearly with propellant density. Tank mass seems like it roughly would (assuming: constant pressure, spherical tanks or constant height/radius cylinders), but I was curious if there's anything empirical covering the other systems as well. Or am I looking too much into it, and first stage tank mass so dwarfs the other components that a linear scaling is fair?
Secondly, I was a bit thrown off by the assumption used in defining density impulse. You basically use the ln(1+x)=x assumption, but that's only valid for pretty small x, say about 0.1. So that assumption would only work for mass ratio of 1.1, at best (assuming ~450 Isp, to high-side ballpark) a first stage delta-V of just 421 m/s.
Propellants MR dp (kg/L) ve (m/s) Id (Ns/L)O2/H2 5.0 0.3251 4455 1448O2/H2 6.0 0.3622 4444 1610O2/H2 7.5 0.4120 4365 1798O2/NH3 1.4 0.8896 3399 3024O2/CH4 3.6 0.8376 3656 3062O2/C2H6 3.2 0.9252 3634 3362O2/C3H8 3.1 0.9304 3613 3362O2/C3H4 2.4 0.9666 3696 3573O2/RP–1 2.8 1.0307 3554 3663O2/C7H8 2.4 1.0954 3628 3974N2O4/NH3 2.0 1.0428 3097 3230N2O4/UDMH 2.9 1.1823 3350 3961N2O4/MMH 2.4 1.2051 3366 4056N2O4/N2H4 1.4 1.2156 3371 4097HTP/NH3 3.1 1.1216 3068 3441HTP/C3H8 7.8 1.2286 3240 3981HTP/N2H4 2.2 1.2608 3283 4139HTP/C3H4 6.5 1.2553 3319 4166HTP/RP–1 7.3 1.3059 3223 4209HTP/C7H8 6.6 1.3496 3288 4437F2/H2 14.6 0.6553 4704 3083F2/H2O 2.1 1.2942 2876 3722F2/HTP 0.88 1.4689 2966 4357F2/NH3 3.4 1.1770 4115 4843F2/N2H4 2.3 1.3073 4212 5506
Quote from: Steven Pietrobon on 03/24/2009 05:48 am(...)Any other propellant combinations the readers here would like me to try?Given the perfect impulse density which F2/NH3 offers, not to mention nice exhaust velocity, practically in the O2/H2 ballpark (see RS-68), I'd like to ask you how would the ammonia perform combined with other oxidizers, like O2, HTP, or N2O4? Would any of these combinations ever work?
Would you like to read reports about poisonous spills from US rockets?
Steven,Thanks for reminding me about HTP. I might have to think about acquiring some for my garage project. The catalytic decomposition eases ignition, and it doesn't have any nitrogen in it to murder your Isp.
Does anyone know a good reference text for ascent trajectories? I found some old Pascal code by our very own Steven Pietrobon and some papers that didn't go into a lot of depth. I'd like to write some code to get decent payload estimates to L1 for various Jupiter variants. I have a couple of years of experience with numerical simulation, but I know next to nothing about aerodynamics.
Attached is a small simulation I wrote in Quick Basic. It has a very efficient numerical integration routine and the basics of aerodynamics built in. You should be able to use the aero stuff in what you are doing.