I'm guessing Raptor is just another one of those optimized compromises; a higher Isp might have been possible via much higher SSME-type pressure and temps, but that gets difficult and expensive fast. Here's hoping they can get that 470 sec performance figure. It won't be any less of a design challenge.
Quote from: Malderi on 07/31/2010 01:08 amAlso, anyone see how they're planning on Raptor having a 470s vacuum Isp? That's a *very* tall claim, which I'm likely to call Incorrect on unless they've got some very good numbers or hotfire tests to back it up. SSME is 453s vacuum, by comparison.I agree that 470s is a tall claim, but remember that the SSME is a ground-lit engine, which generally means the vacuum Isp is less than an equivalent air- or vacuum-lit engine. It still gets good vacuum Isp only because its chamber pressure is so high. If you put a big bell on the SSME, you'd get somewhat better Isp than 453s (perhaps around 470s), but it wouldn't work at sea level anymore.
Also, anyone see how they're planning on Raptor having a 470s vacuum Isp? That's a *very* tall claim, which I'm likely to call Incorrect on unless they've got some very good numbers or hotfire tests to back it up. SSME is 453s vacuum, by comparison.
Quote from: neilh on 07/30/2010 11:32 pmIt's also interesting that they're sticking with gas generator cycle for the Merlin 2 instead of staged combustion. Not surprised one bit about this. A simpler engine cycle plus it solves the problem of having a separate roll control system when it's used as drop in replacement for F9 first stage (look at the diagram in the 2nd post).
It's also interesting that they're sticking with gas generator cycle for the Merlin 2 instead of staged combustion.
* WTF is with the dead sea scrolls reference?
It's a joke. Black water (=oil) shall elevate thy children (=mankind) to the heavens (=space). But I don't get the other part. Probably because I am not familiar enough with ancient hebrew units of currency and measurement :-)
nor shalt thou burn rocks
The greatest sin of the budget debate will be choosing a no-competition rocket. Crushing the ambition and capabilities of such unique companies (like ULA and SpaceX) will be a real sin. But the demand for "job creation" is stronger than just about anything else.
Quote from: moose103 on 07/31/2010 12:28 amThe greatest sin of the budget debate will be choosing a no-competition rocket. Crushing the ambition and capabilities of such unique companies (like ULA and SpaceX) will be a real sin. But the demand for "job creation" is stronger than just about anything else.Or maybe they want something derived from a vehicle that already works and is minimum risk, cost and schedule to develop
I am not sure if they are planning to use the gas generator exhaust for roll control. It looks like they plan to feed it into the engine bell like the f1 did.
So why is SpaceX developing HLVs beyond Saturn V when we are told incessantly by the NuSpace crowd they are not necessary ? Also why would the DoD develop a 1.7mlbf RP-1 engine now if SpaceX are already doing this and NASA won't be doing one now ?
Quote from: marsavian on 07/31/2010 11:11 amQuote from: moose103 on 07/31/2010 12:28 amThe greatest sin of the budget debate will be choosing a no-competition rocket. Crushing the ambition and capabilities of such unique companies (like ULA and SpaceX) will be a real sin. But the demand for "job creation" is stronger than just about anything else.Or maybe they want something derived from a vehicle that already works and is minimum risk, cost and schedule to developYou mean the altas V? Ares V is a completely new launch vehicle where the biggest commonality with shuttle is the color scheme.
Quote from: marsavian on 07/31/2010 11:11 amSo why is SpaceX developing HLVs beyond Saturn V when we are told incessantly by the NuSpace crowd they are not necessary ? Also why would the DoD develop a 1.7mlbf RP-1 engine now if SpaceX are already doing this and NASA won't be doing one now ?A proposed evolution plan and actually developing are two very different things. Which part of the presentations indicated to you they actually are developing any of this?
A SD-HLV will be cheaper and quicker to the 75-130 tons requirement than any Atlas V derivative.
SpaceX are not going to stop at Falcon 9 (Heavy) if they can help it.
So just what makes Saturn V class launch vehicles sustainable in these peoples eyes while everyone else says they are not and that we could never have sustained them in the first place?