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I didn't see liquid methane (CH4) during my quick scan, is it covered in the book? In a victory of worse-is-better, SpaceX is using methane because it makes S

I didn't see liquid methane (CH4) during my quick scan, is it covered in the book? In a victory of worse-is-better, SpaceX is using methane because it makes Starship/Raptor simple, cheap, and more reliable (a passive cooling system is enough to store it, storable for a more extended period than hydrogen, does not leak, does not require insulation on the fuel tank, and rocket design is simpler) Methane makes in-space refueling easier, and methane can be produced, handled, and stored more readily on Mars. It also makes Starship rapidly reusable (unike Falcon, whose kerosene Merlin engines need to be cleaned between flights to remove soot)

perihelions 4y ago
I don't think they were thinking about reusable rocket engines at that point in time. The primary (?) advantage of methane over kerosene is that it doesn't deposit soot on engine parts, which is highly important for SpaceX today, but not really anyone else in history. Here's one reference to methane-LOX in the book ("nobody could see any point"): - "The VfR was completely unaware of all of this when they started work. Oberth had originally wanted to use methane as fuel, but as it was hard to come by in Berlin, their first work was with gasoline and oxygen. Johannes Winkler, however, picked up the idea, and working independently of the VfR, was able to fire a liquid oxygen-liquid methane motor before the end of 1930. This work led nowhere in particular, since, as methane has a performance only slightly superior to that of gasoline, and is much harder to handle, nobody could see any point to following it up." (pages 7-8) There's more references to methane + [exotic oxidizers], because (going off my memory) they were to trying to min-max Isp performance, for interplanetary probes, constrained to a certain cryogenic temperature range. (This predates radioisotope heaters, I believe. Not *electric* generators -- these little heater things [0]). Liquid CH₄ looked like a good match for the deep-space thermal environment. [0] https://en.wikipedia.org/wiki/Radioisotope_heater_unit https://en.wikipedia.org/wiki/Radioisotope_heater_unit - "Deep space probes, working at low temperatures, will probably use methane, ethane, and diborane for fuels, although propane is a possibility. The oxidizers will be OF₂, and possibly ONF₃ and NO₂F, while perchloryl fluoride, ClO₃F, would be useful as far out as Jupiter." (page 191) (If anyone at Google is reading this, could you consider adding search support for numerals in the superscripts and subscripts block [1]; they don't seem to be normalized in a sensible way. ClO₃F and ClO3F are entirely different searches). [1] https://en.wikipedia.org/wiki/Superscripts_and_Subscripts_(Unicode_block) https://en.wikipedia.org/wiki/Superscripts_and_Subscripts_(U...
- khuey 4y ago
  > The primary (?) advantage of methane over kerosene The other big advantage of methane for SpaceX is that it can (in theory) be synthesized chemically from the Martian atmosphere.
  - skykooler 4y ago
    Technically you could synthesize more complex hydrocarbons such as kerosene as well, it's just that it's way more complexity, energy, and infrastructure required.
- DylanSp 4y ago
  SpaceX isn't the only one looking at methalox engines for reusability, though they're definitely the farthest along. Blue Origin's BE-4 engines use methalox; New Glenn's planned to be at least partially reusable, and ULA might try to reuse them on Vulcan with SMART engine recovery.
- RcouF1uZ4gsC 4y ago
  > I don't think they were thinking about reusable rocket engines at that point in time. I think early on, the primary focus for rocket research was for missiles, and you don’t really care about reuse in those.
- avmich 4y ago
  > The primary (?) advantage of methane over kerosene is that it doesn't deposit soot on engine parts Some people would disagree. AFAIK, by professionals methane was always considered first for better Isp, even though Clark dismisses the advantage. Here's another example of disagreement, regarding virtues of hydrogen peroxide - https://yarchive.net/space/rocket/fuels/peroxide.html https://yarchive.net/space/rocket/fuels/peroxide.html - "It's only bad habit is that it decomposes exothermically -- and since the rate of decomposition is accelerated with temperature, this reaction can run away from you. But that hardly deserves the bad press it's gotten. LOX will also bite you, quite readily, if you're careless. "Wings" simply got it wrong. (Even _Ignition!_, while pretty sour on hydrogen peroxide due to the decomposition hazard, has the facts right, and only the emphasis is arguable -- I don't understand how someone can cozy up to ClF5 while considering peroxide dangerous; but that was Clark's position! )" Jeff Greason (of XCOR fame, among others)
dmurray 4y ago
There are plenty of references to methane, but no in-depth story about systems using it. The last part of the book, attempting to predict what fuels would be popular, prescribed methane for deep space probes, for many of the same reasons you give, but failed to foresee reusable boosters or other departures from the status quo. > as methane has a performance only slightly superior to that of gasoline, and is much harder to handle, nobody could see any point... > For the big first-stage space boosters we will continue to use liquid oxygen and RP-1 or the equivalent. They work and they're cheap — and Saturn V uses a lot of propellant! Later, we may shift to hydrogen as a first-stage fuel, but it appears unlikely. The development of a reusable booster won't change the picture, but if a ram-rocket booster is developed all bets are off. > For the upper stages, the hydrogen-oxygen combination of the J-2 is very satisfactory, and will probably be used for a long time. Later, as more energy is needed, there may be a shift, for the final stage, to hydrogen-fluorine or hydrogen-lithium-fluorine... > Deep space probes, working at low temperatures, will probably use methane, ethane, and diborane for fuels, although propane is a possibility. The oxidizers will be OF2, and possibly ONF3 and NO2F...

perihelions 4y ago

I don't think they were thinking about reusable rocket engines at that point in time. The primary (?) advantage of methane over kerosene is that it doesn't deposit soot on engine parts, which is highly important for SpaceX today, but not really anyone else in history. Here's one reference to methane-LOX in the book ("nobody could see any point"): - "The VfR was completely unaware of all of this when they started work. Oberth had originally wanted to use methane as fuel, but as it was hard to come by in Berlin, their first work was with gasoline and oxygen. Johannes Winkler, however, picked up the idea, and working independently of the VfR, was able to fire a liquid oxygen-liquid methane motor before the end of 1930. This work led nowhere in particular, since, as methane has a performance only slightly superior to that of gasoline, and is much harder to handle, nobody could see any point to following it up." (pages 7-8) There's more references to methane + [exotic oxidizers], because (going off my memory) they were to trying to min-max Isp performance, for interplanetary probes, constrained to a certain cryogenic temperature range. (This predates radioisotope heaters, I believe. Not *electric* generators -- these little heater things [0]). Liquid CH₄ looked like a good match for the deep-space thermal environment. [0] https://en.wikipedia.org/wiki/Radioisotope_heater_unit https://en.wikipedia.org/wiki/Radioisotope_heater_unit - "Deep space probes, working at low temperatures, will probably use methane, ethane, and diborane for fuels, although propane is a possibility. The oxidizers will be OF₂, and possibly ONF₃ and NO₂F, while perchloryl fluoride, ClO₃F, would be useful as far out as Jupiter." (page 191) (If anyone at Google is reading this, could you consider adding search support for numerals in the superscripts and subscripts block [1]; they don't seem to be normalized in a sensible way. ClO₃F and ClO3F are entirely different searches). [1] https://en.wikipedia.org/wiki/Superscripts_and_Subscripts_(Unicode_block) https://en.wikipedia.org/wiki/Superscripts_and_Subscripts_(U...

khuey 4y ago
> The primary (?) advantage of methane over kerosene The other big advantage of methane for SpaceX is that it can (in theory) be synthesized chemically from the Martian atmosphere.
- skykooler 4y ago
  Technically you could synthesize more complex hydrocarbons such as kerosene as well, it's just that it's way more complexity, energy, and infrastructure required.
DylanSp 4y ago
SpaceX isn't the only one looking at methalox engines for reusability, though they're definitely the farthest along. Blue Origin's BE-4 engines use methalox; New Glenn's planned to be at least partially reusable, and ULA might try to reuse them on Vulcan with SMART engine recovery.
RcouF1uZ4gsC 4y ago
> I don't think they were thinking about reusable rocket engines at that point in time. I think early on, the primary focus for rocket research was for missiles, and you don’t really care about reuse in those.
avmich 4y ago
> The primary (?) advantage of methane over kerosene is that it doesn't deposit soot on engine parts Some people would disagree. AFAIK, by professionals methane was always considered first for better Isp, even though Clark dismisses the advantage. Here's another example of disagreement, regarding virtues of hydrogen peroxide - https://yarchive.net/space/rocket/fuels/peroxide.html https://yarchive.net/space/rocket/fuels/peroxide.html - "It's only bad habit is that it decomposes exothermically -- and since the rate of decomposition is accelerated with temperature, this reaction can run away from you. But that hardly deserves the bad press it's gotten. LOX will also bite you, quite readily, if you're careless. "Wings" simply got it wrong. (Even _Ignition!_, while pretty sour on hydrogen peroxide due to the decomposition hazard, has the facts right, and only the emphasis is arguable -- I don't understand how someone can cozy up to ClF5 while considering peroxide dangerous; but that was Clark's position! )" Jeff Greason (of XCOR fame, among others)

dmurray 4y ago

There are plenty of references to methane, but no in-depth story about systems using it. The last part of the book, attempting to predict what fuels would be popular, prescribed methane for deep space probes, for many of the same reasons you give, but failed to foresee reusable boosters or other departures from the status quo. > as methane has a performance only slightly superior to that of gasoline, and is much harder to handle, nobody could see any point... > For the big first-stage space boosters we will continue to use liquid oxygen and RP-1 or the equivalent. They work and they're cheap — and Saturn V uses a lot of propellant! Later, we may shift to hydrogen as a first-stage fuel, but it appears unlikely. The development of a reusable booster won't change the picture, but if a ram-rocket booster is developed all bets are off. > For the upper stages, the hydrogen-oxygen combination of the J-2 is very satisfactory, and will probably be used for a long time. Later, as more energy is needed, there may be a shift, for the final stage, to hydrogen-fluorine or hydrogen-lithium-fluorine... > Deep space probes, working at low temperatures, will probably use methane, ethane, and diborane for fuels, although propane is a possibility. The oxidizers will be OF2, and possibly ONF3 and NO2F...