NASA has no need to pay for the Grashopper RLV.
There's that, too. Mars ISRU.And another thing, that maybe I didn't made clear. Only the Russians have develop a metallurgy able to make Oxygen Rich Stage Combustion. Both Rocketdyne and Aerojet, due to their RD-180 and NK-33 contracts have access to this technology. But, as far as I'm aware, SpaceX isn't. The beauty of methane, according to the Energomash paper, is that fuel rich is more efficient. And you have lower pressure losses if you use it as the chamber cooling liquid. So, apparently, SpaceX wouldn't need to develop any significant advancement in metallurgy to use fuel rich combustion if using methane. I guess that's the key of the analysis.
Quote from: baldusi on 10/06/2011 06:00 pmThere's that, too. Mars ISRU.And another thing, that maybe I didn't made clear. Only the Russians have develop a metallurgy able to make Oxygen Rich Stage Combustion. Both Rocketdyne and Aerojet, due to their RD-180 and NK-33 contracts have access to this technology. But, as far as I'm aware, SpaceX isn't. The beauty of methane, according to the Energomash paper, is that fuel rich is more efficient. And you have lower pressure losses if you use it as the chamber cooling liquid. So, apparently, SpaceX wouldn't need to develop any significant advancement in metallurgy to use fuel rich combustion if using methane. I guess that's the key of the analysis.SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.
Quote from: Robotbeat on 10/06/2011 07:01 pmQuote from: baldusi on 10/06/2011 06:00 pmThere's that, too. Mars ISRU.And another thing, that maybe I didn't made clear. Only the Russians have develop a metallurgy able to make Oxygen Rich Stage Combustion. Both Rocketdyne and Aerojet, due to their RD-180 and NK-33 contracts have access to this technology. But, as far as I'm aware, SpaceX isn't. The beauty of methane, according to the Energomash paper, is that fuel rich is more efficient. And you have lower pressure losses if you use it as the chamber cooling liquid. So, apparently, SpaceX wouldn't need to develop any significant advancement in metallurgy to use fuel rich combustion if using methane. I guess that's the key of the analysis.SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.The RS-84 is oxygen-rich if thats the engine you are talking about.
Quote from: notsorandom on 10/06/2011 07:09 pmQuote from: Robotbeat on 10/06/2011 07:01 pm...SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.The RS-84 is oxygen-rich if thats the engine you are talking about. Yeah, that's it. I think SpaceX has access to that engine's design.Not saying they'll do anything with it.
Quote from: Robotbeat on 10/06/2011 07:01 pm...SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.The RS-84 is oxygen-rich if thats the engine you are talking about.
...SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.
could you add an 'all H2' set of numbers to the list? same assumptions, so equal sized grain of salt..
Would one of these engines be suitable to getting a manned vehicle off the mars surface and back to Orbit? If you're doing in-situ Methane/Lox production of course. Elon's far reaching goals would seemingly be better served by al Methane over combinations of other fuels.
Not sure I'm sold on the 400s claim for vac isp- don't believe I've seen such a high number before.
Would be rather over-sized for any near-term sort of Mars vehicle. Unless you made a CH4 version of Kestrel.Not sure I'm sold on the 400s claim for vac isp- don't believe I've seen such a high number before.
Quote from: Kaputnik on 10/06/2011 07:38 pmWould be rather over-sized for any near-term sort of Mars vehicle. Unless you made a CH4 version of Kestrel.Not sure I'm sold on the 400s claim for vac isp- don't believe I've seen such a high number before.You shouldn't be. Zubrin's 380s was overzealous. 400s would need an expansion ratio over 1000.
You can't gain so much ISP switching to LCH4
In the Energomash paper the expansion ratio of the RD-191 is 29 (is area/area, like (1430/262.4)², right?). Let's not forget that this thing has something like 262Bar of chamber pressure. So the expansion ratio is normally very high.The Merlin 1C has an expansion ratio of 14.5, and the vacuum has an expansion of 117. If we scaled the 29.6 of the RD-191, that would mean an expansion ratio of 240 for the vacuum version. How much extra isp would it get, if the "stock" vacuum isp was 360?
Quote from: baldusi on 10/06/2011 08:25 pmIn the Energomash paper the expansion ratio of the RD-191 is 29 (is area/area, like (1430/262.4)², right?). Let's not forget that this thing has something like 262Bar of chamber pressure. So the expansion ratio is normally very high.The Merlin 1C has an expansion ratio of 14.5, and the vacuum has an expansion of 117. If we scaled the 29.6 of the RD-191, that would mean an expansion ratio of 240 for the vacuum version. How much extra isp would it get, if the "stock" vacuum isp was 360?I'd have to run the numbers, but the thing is that your thrust coefficient (which is what you increase with higher expansion ratio) flattens out asymptotically. 400s is just way too high for CH4. I can post some plots later tonight maybe.
Quote from: cambrianera on 10/06/2011 08:38 pmYou can't gain so much ISP switching to LCH4You are not reading what I'm writing. The 360 vacuum is for fuel rich methane variation of an RD-191. The switch is not from going to methane from RG-1. The Switch is from an expansion of 29.6 to 240.BTW, RD-160/1 both had expansion ratios of 355. I'm not guessing the switch from RP-1 to methane, I'm talking about the change in expansion ratio and how much can it add.