Timeline for Pros and Cons of LH2/LOX vs Other Fuels
Current License: CC BY-SA 3.0
18 events
| when toggle format | what | by | license | comment | |
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| Jan 19, 2017 at 14:39 | comment | added | Uwe | Water is not a good choice for thermal nuclear rockets. If very hot metals get in contact with water vapour they react with the oxygen of the water and leave hydrogen. | |
| Jan 19, 2017 at 12:58 | comment | added | SF. | @RussellBorogove: IIRC: "if you isolate a house with aerogel and keep a lit candle in one of the rooms, in a few days living inside will be impossible due to the heat from the candle". It has truly miraculous thermal properties, but the manufacture process currently is too expensive for stuff like isolation on a non-reusable 10-ton tank of LH2. Although it seems such tank, or at least its isolation wouldn't have much problems landing in one piece on Earth. It's ludicruously light so it should brake to sane speeds long before entering dense atmosphere. | |
| Jan 19, 2017 at 12:54 | comment | added | SF. | @UIDAlexD: Thermal nuclear rockets may work on pretty much damn everything as long as its boiling temperature is less than the chamber melting temperature. They are way more efficient on hydrogen than anything else, but they won't suffer too badly if other, not too heavy elements are introduced into the mix. | |
| Jan 18, 2017 at 16:18 | history | edited | Russell Borogove | CC BY-SA 3.0 |
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| Oct 21, 2016 at 2:05 | history | edited | Russell Borogove | CC BY-SA 3.0 |
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| Aug 3, 2016 at 14:41 | comment | added | Russell Borogove | Yes. Kerolox = kerosene/LOX, methalox = methane/LOX. In casual rocket-engine-discussion use, these are synonymous with the name of the fuel by itself (because other oxidizers are rarely used with those fuels). | |
| Aug 3, 2016 at 12:02 | comment | added | uhoh | Does hydrolox = LOX/LH2? | |
| Jul 29, 2016 at 21:31 | history | edited | Russell Borogove | CC BY-SA 3.0 |
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| Jul 29, 2016 at 16:35 | comment | added | Russell Borogove | ULA has a white paper on insulation based strategies, but I think you need active cooling to really make it work, which means a lot of power and a bulky/massive coolant loop. | |
| Jul 29, 2016 at 16:35 | comment | added | Organic Marble | It's a tough problem. Shuttle-Centaur was going to have a thermodynamic vent system to mitigate the problem. Don't know if operational Centaurs ever used such a system. ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880006561.pdf | |
| Jul 29, 2016 at 16:31 | comment | added | UIDAlexD | There any way to avoid or prolong boiloff? Nuclear Thermal Rockets look great for deep space propulsion but they only function with Hydrogen. | |
| Jul 29, 2016 at 16:01 | comment | added | Russell Borogove | Saturn/Apollo is a terrific example of the tradeoffs in fuel selection. Kerosene first stage to meet the colossal liftoff thrust requirement and keep the stage diameter somewhat sane; hydrogen second and third stages to make the delta-v needed for orbital and translunar injection; hypergolics on the CSM and LM to store fuel for a two-week mission and start reliably, repeatedly, over many short burns. | |
| Jul 29, 2016 at 15:53 | comment | added | Russell Borogove | It depends on the timeframe under consideration. Hydrogen boil off rate for a stage like Centaur is about 4% per day, so it's not a major issue for typical LEO/GEO insertion operations, but a definite concern for lunar and a showstopper for interplanetary operations, which is why you see hypergolics used for orbital insertion on those kinds of missions. LOX boil off is about 2% per day, so kerolox has similar limitations. | |
| Jul 29, 2016 at 15:43 | comment | added | UIDAlexD | Yeah, that's a difference. I can see how it makes sense for upper stages now. What about orbital operations? I've been lead to believe the boiloff is considerable, but is it really that bad? | |
| Jul 29, 2016 at 15:35 | history | edited | Russell Borogove | CC BY-SA 3.0 |
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| Jul 29, 2016 at 15:24 | comment | added | Tristan | It's worth pointing out that one of the drivers in fuel selection for optimal Isp is to have the exhaust gases be as light as possible, as the maximum exhaust velocity is inversely proportional to the square root of molecular weight. A hydrogen-based engine will have almost exclusively water as its exhaust gas. Long chain hydrocarbons like kerosene will have (in addition to the water) carbon dioxide, which is much heavier, as well as other constituents due to incomplete combustion, like carbon monoxide (which is actually better than CO2) and residual unburned hydrocarbons (worse). | |
| Jul 29, 2016 at 15:20 | vote | accept | UIDAlexD | ||
| Jul 29, 2016 at 15:04 | history | answered | Russell Borogove | CC BY-SA 3.0 |