It has to do with idealised models of the expansion process in the nozzle. Shifting equilibrium assumes chemical reactions continue to take place during the expansion process, while frozen assumes that mole fractions remain constant during the expansion process. If the reaction is very fast then Isp may be closer to shifting equilibrium Isp, otherwise it will be closer to the frozen value.
On a SpaceX thread the possibility of using gaseous hydrogen dissolved in liquid methane came up. It looks as if this is impractical since the solubility is far too low. Would it be possible to use slush methane in liquid hydrogen and if so would this be more practical than slush hydrogen?
I'm struggling a bit to understand the advantage of doing this. Is the hope that dissolved methane would add little to the volume, thereby increasing volume-specific impulse (at the cost of weight-specific impulse)?
Quote from: mmeijeri on 09/24/2011 05:47 pmOn a SpaceX thread the possibility of using gaseous hydrogen dissolved in liquid methane came up. It looks as if this is impractical since the solubility is far too low. Would it be possible to use slush methane in liquid hydrogen and if so would this be more practical than slush hydrogen?I'm struggling a bit to understand the advantage of doing this. Is the hope that dissolved methane would add little to the volume, thereby increasing volume-specific impulse (at the cost of weight-specific impulse)?
Quote from: Proponent on 09/26/2011 09:05 amQuote from: mmeijeri on 09/24/2011 05:47 pmOn a SpaceX thread the possibility of using gaseous hydrogen dissolved in liquid methane came up. It looks as if this is impractical since the solubility is far too low. Would it be possible to use slush methane in liquid hydrogen and if so would this be more practical than slush hydrogen?I'm struggling a bit to understand the advantage of doing this. Is the hope that dissolved methane would add little to the volume, thereby increasing volume-specific impulse (at the cost of weight-specific impulse)?Coming from Elon's Reddit AMA video responses:"We can certainly improve on the chemical propulsion that has been done thus far, and I think probably a very high efficiency light hydrocarbon that uses predominantly methane is probably a good way to go, and I think that's something SpaceX will end up working on."I was wondering what Elon was meaning and my idea was:Obtaining a (still unknown) mixture of liquid hydrocarbons that enables storing hydrogen at mild cryo temperature and low pressure would be a great advantage.Obviously adding solid methane to LH2 would be smaller advantage.As you said, trading density to ISP.
Hopefully basic orbital mechanics is like basic rocket science. Apologies if not.So the first thing you do when you're launching is loft yourself above the atmosphere, so it doesn't rob your v and crash you back down to Earth. Then you build up a bunch of v. (These are obviously happening concurrently e.g. with less-lofted launches.) I've seen the awesome Earth -> LEO chart circulating around here recently, and it lists that as costing 9.5 m/s. Does that include lofting costs?
What's the advantage of having multiple combustion chambers and nozzles on a given turbo machinery assembly instead of one larger chamber and nozzle? I know of one possible advantage on regenerative nozzles, but I'm thinking of other types such as on the Soyuz.