nortex97 said:
that's funny. BO should somehow be able to at least produce some tanks by now, one would think.
This just looks very complicated vs. Raptor 2.0, with a lot of what surely are hand-built parts/tubes all over it.
They've had so many problems with this thing running reliably and engine durability, it makes me think that they really do have some fundamental challenges which may impact especially the durability of this engine. I read this elsewhere and have no idea if it is right but it sounds believable to my somewhat ignorant non-rocket engineer mind, re our earlier speculation about 'super cooled' or cryogenic methane vs. the fuel for BE-4;
Quote:
One key point of difference between these engines is that BE-4 uses LNG (basically liquid methane, with minor amounts of ethane, propane, and butane - but it is almost entirely methane in practice), whereas Raptor uses only highly purified methane - and subcooled methane, at that, for improved density (as with their oxygen, which they also subcool, for the same reason - just as they do with their Falcon 9 rockets).
I doubt BE-4 can subcool its LNG fuel, as it's likely that those higher alkane (ethane, et al.) impurities would solidify, and complicate matters, especially in the turbopumps, and if not that, the injectors. They could subcool the oxygen, though - however, I'm not sure if they are doing this (they probably should… it's not a small performance benefit - it's pretty substantial).
Edit: as Enzo Piacitelli has commented in regard to, my discussion on LNG vs purified methane is actually moot, as it was subsequently clarified by an official that BE-4 will actually be using purified methane, not LNG (were an engine to actually use LNG proper, however, as had previously appeared to be the case for BE-4 absent further clarification, again, my points regarding the possible disadvantages of this would still apply). Additionally, my commentary on the subcooling of this methane and oxygen still fully applies.
SpaceX's Raptor may run a bit more nicely than BE-4, since both oxidiser and fuel are in the gaseous state when introduced into the engine, thus ensuring nearly perfect mixing - no incredibly complicated injector designs needed here! This probably cuts out a whole class of potential combustion instability issues right there. How much this will translate into more reliability and performance I'm not sure, but I am confident that it is a distinct advantage - and possibly even makes it cheaper to manufacture (injectors are some of the most complex parts to get right, and to manufacture, and it is critical that they are right if you are to avoid performance loss and combustion instabilities!)
I really don't think this guy knowns what he is talking about.
Injectors for supercritical fluids, which is what the raptor is, would not be less complex just because the fluid is supercritical. They can be made complex or simple. More thought has to be given to keeping the injector face cool because the propellants are heated by the stage combustion process so don't provide as much cooling to the injector as unheated liquid propellants would. At supercritical conditions the reactions occur immediately where fuel and oxidizer meet, any small recirculation zones with flame holding could melt your injector or chamber wall. There is need for more complex cooling schemes like film cooling. Keeping the injector face and chamber walls safe from heat damage is easier with liquid propellants because the phase change from liquid to gas provides a cooling effect absorbing some of the combustion heat and also delaying the reaction, keeping it away from the injector. Yes, supercritical fluid mixes and combusts well, but it's not without its own challenges.
Raptors architecture, full flow staged combustion, is going to be more complex than what Blue Origin is doing with ox rich staged combustion. Yet this author makes silly statements that the added complexity of raptor will make it cheaper to manufacture and more stable just because it's supercritical phase.
Remember when Musk said Raptor development costs almost bankrupt them?
The real challenge is not any single component, but balancing them all working together. Slight change in the behavior of one, effects all of the others because on rocket engines all of the fluid systems are linked. This is why full flow staged combustion is so hard in practice, the number of components that have to work together is higher, you have two pumps, 3 combustion chambers. You need more man hours to design and do analysis on all of the components, and you need more testing time to get it all working together, and you need more parts to manufacture, track and integrate.
I don't get why everyone hates so much on Blue Origin just because they aren't SpaceX.
Also, not sure what he is saying about LNG impurities solidifying. The hydrocarbon mixture will have a freezing temperature. Think of antifreeze being added to water. The water doesn't solidify or freeze at the same temperature it does as a pure substance because it's a new mixture. This guy is just bull****ting to hate on Blue Origin.
