4 ms·
The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a
by danaliv 7y ago
The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a measly 8500.
- Ididntdothis 7y agoInteresting! I didn't think about volume. Is that why the Saturn V first stage also used kerosene?
- m4rtink 7y agoPretty much - the rocket is smaller & you can usually also get more thrust, while loosing some efficiency. There are were more rockets like this (kerolox for first stage & hydrolox for upper stage), like for example Atlas 5. Other rockets used kerolox boosters, such as for example Energia & IIRc some of the new Chinese rockets.
- labster 7y agoThat probably went into the decision, but rocket science is complicated. While not on the Saturn V, you there’s a good discussion on fuel tradeoffs here, after explaining the engine cycles: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
- danaliv 7y agoOh, good question - not a rocket scientist but this history seems to say that’s the case: https://history.nasa.gov/SP-4206/ch7.htm https://history.nasa.gov/SP-4206/ch7.htm ”Liquid hydrogen was only one half as dense as kerosene. This density ratio indicated that, for the necessary propellant, an LH2 tank design would require a far larger tank volume than required for RP-1. The size would create unacceptable penalties in tank weight and aerodynamic design. So, RP-1 became the fuel.” (RP-1 And Jet A are almost identical.) In applications where cross-sectional area is an exponential factor (read: atmospheric flight), volume is significant!