Discussion
saaby93 said:
Eric Mc said:
All went well.
Over exuberant commentator aside?As an aside I do like that older engineer chap who does some of the Falcon 9 for SpaceX - did the starship launches too. He gets it right.
Dog Star said:
saaby93 said:
Eric Mc said:
All went well.
Over exuberant commentator aside?Dog Star said:
As an aside I do like that older engineer chap who does some of the Falcon 9 for SpaceX - did the starship launches too. He gets it right.
John Insprucker - yes he's great. I think it's fair to say he knows what he's talking about. He's also the Principal Integration Engineer at SpaceX & is ex-US Air Force with a long history in the rocket business. Very true. Blue can't make 2, SpaceX can't make 200. Still, shows that it's not easy, this rocket science stuff.
I am surprised by the Raptor difficulties, given the sheer number they have produced, tested and flown. I guess mass production is massively harder than hand-building a small run.
I am surprised by the Raptor difficulties, given the sheer number they have produced, tested and flown. I guess mass production is massively harder than hand-building a small run.
Flooble said:
Very true. Blue can't make 2, SpaceX can't make 200. Still, shows that it's not easy, this rocket science stuff.
I am surprised by the Raptor difficulties, given the sheer number they have produced, tested and flown. I guess mass production is massively harder than hand-building a small run.
Elon was very clear in the recent video by Tim Dodd that manufacturing success was the key to all this. More so than the tech and science.I am surprised by the Raptor difficulties, given the sheer number they have produced, tested and flown. I guess mass production is massively harder than hand-building a small run.
garyhun said:
Flooble said:
Very true. Blue can't make 2, SpaceX can't make 200. Still, shows that it's not easy, this rocket science stuff.
I am surprised by the Raptor difficulties, given the sheer number they have produced, tested and flown. I guess mass production is massively harder than hand-building a small run.
Elon was very clear in the recent video by Tim Dodd that manufacturing success was the key to all this. More so than the tech and science.I am surprised by the Raptor difficulties, given the sheer number they have produced, tested and flown. I guess mass production is massively harder than hand-building a small run.
- Issues with single crystal casting, both yields and quality, this is a black art and I would not be surprised if they are having problems
- Issues with tolerances on the bearing surfaces in the turbopumps resulting in wear, vibration and ingress of corrosive fluids
- Issues with not being able to slacken off tolerances because they don't really know where they can afford to let them go which results in few conforming parts, need for part matching (e.g. to get something to fit you select specific components from a batch) and/or processes where parts are machined to fit.
To try and keep this a little on topic. Are the issues SpaceX have likely to be in any way similar to those that Blue Origin face?
SpaceX appear to be able to make a small number of engines which are reliable enough to launch and and their rocket (although they had restart issues with 9 and 11). Blue seem to be okay making the "test run" engines - not sure if I have the correct term. But the "flight" engines don't seem to be coming out the factory.
Not sure what the difference is, but could that be similar manufacturing challenges?
"single crystal casting"
Any chance of an idiot explanation of this? A quick google (and my memory) suggests its like Rolls Royce do with fan blades on their jet engines - trying to make the material strong in the correct direction instead of a jumble?
SpaceX appear to be able to make a small number of engines which are reliable enough to launch and and their rocket (although they had restart issues with 9 and 11). Blue seem to be okay making the "test run" engines - not sure if I have the correct term. But the "flight" engines don't seem to be coming out the factory.
Not sure what the difference is, but could that be similar manufacturing challenges?
"single crystal casting"
Any chance of an idiot explanation of this? A quick google (and my memory) suggests its like Rolls Royce do with fan blades on their jet engines - trying to make the material strong in the correct direction instead of a jumble?
Flooble said:
To try and keep this a little on topic. Are the issues SpaceX have likely to be in any way similar to those that Blue Origin face?
SpaceX appear to be able to make a small number of engines which are reliable enough to launch and and their rocket (although they had restart issues with 9 and 11). Blue seem to be okay making the "test run" engines - not sure if I have the correct term. But the "flight" engines don't seem to be coming out the factory.
Not sure what the difference is, but could that be similar manufacturing challenges?
"single crystal casting"
Any chance of an idiot explanation of this? A quick google (and my memory) suggests its like Rolls Royce do with fan blades on their jet engines - trying to make the material strong in the correct direction instead of a jumble?
Single crystal casting is the process for making a metallic part which has no grain boundaries ergo it's a single crystal. It is achieved by casting the metal in a vacuum furnace, using a water cooled chill to start the casting freezing in a reservoir which is connected beneath the part(s). The grains then start growing linearly from the chill (think Giant's causeway). SpaceX appear to be able to make a small number of engines which are reliable enough to launch and and their rocket (although they had restart issues with 9 and 11). Blue seem to be okay making the "test run" engines - not sure if I have the correct term. But the "flight" engines don't seem to be coming out the factory.
Not sure what the difference is, but could that be similar manufacturing challenges?
"single crystal casting"
Any chance of an idiot explanation of this? A quick google (and my memory) suggests its like Rolls Royce do with fan blades on their jet engines - trying to make the material strong in the correct direction instead of a jumble?
The reservoir is connected to the part by a pig tail shaped connection, as the grains grow up the pig tails all but one of them eventually hit the side and stop, thus it is a single grain that starts growing in the part as it cools. The difficulty is getting the cooling rates to proceed linearly up the part and part design right so that the metal is freezing only where the grain is growing. If it starts freezing anywhere else or a bubble remains liquid beneath where the grain growth is happening then you end up with other crystals forming.
How to do this is deliberately poorly documented (pushing on an open door!), stored on multiple air gaped computers and in the heads of multiple people.
As to why you do it, the grain boundaries in the metal are primary sites for chemical attack and high temperature creep (metal stretches under load/temperature). Both of these are generally a limiting factor for gas turbine life. I would be surprised if creep is really an issue on the rocket engines as they aren't particularly hot and they don't have very long run times so it is mainly being used to allow turbines to survive in high pressure oxygen rich gasses.
I should also add the Russians got staged combustion to work in the 60's without single crystals by using ceramic coatings. These are also a famously low yield manufacturing process which again could be part of their issue.
Difficulty in the rocket is almost always now almost always in the dynamics of the turbo-pumps and the combustion of in the pre-burner or gas generator. The actual rocket nozzle, main burner and structures is pretty much solved and tends to work the same way whatever the rocket is.
Regarding BE4 vs Raptor the BE-4 runs at less than half the chamber pressure of the Raptor so should be a fair bit easier to engineer in theory given that people have pushed the same cycle harder with more difficult propellants. The Raptor is a lot more novel, in theory the engine should run a lower turbine temperatures, but it still runs at beltingly high pressures and the fuel rich closed cycle turbo pump is novel. The other main difficulty it getting everything to work together given you have two linked closed cycle systems.
I would presume that at some stage BO will turn the wick up on the BE-4 and get it to similar performance to the Raptor.
Elon has said Raptor will get replaced pretty soon, whether this is a full flow staged combustion engine or a new direction is something not explained.
If I were guessing, other directions would be to go to a dual expander cycle and use the ability to 3D print the combustion chamber to add heat exchange surface in it to get around the size and chamber pressure limitations that normally come with that engine type.
Flooble said:
Thanks for that, it's like an encyclopedia entry in it's own right!
Used to work in turbine systems at RR, I'm extrapolating to rocket design but the materials and processes are very similar. We don't use copper very much though as we don't have cryogens to cool it and we tend to always operate in an oxidising environment.Amazon are buying up to 83 launches for their Project Kuiper satellite internet system. These are with Blue Origin (good luck with that), ULA and Arianespace. All 3 are with rockets that haven’t flown yet.
https://press.aboutamazon.com/news-releases/news-r...
https://press.aboutamazon.com/news-releases/news-r...
Blue Origin have posted some new pictures of the big BE-4 engine on their twitter account.
Here’s one:
The engine bell alone is about 6 foot tall. It’s a test engine, so it’s wired up like a Christmas tree.
They’re getting up to 572,000 lbf thrust apparently. The smaller Raptor 2 engine is about 510,000 lbf (so far) by comparison.
Here’s one:
The engine bell alone is about 6 foot tall. It’s a test engine, so it’s wired up like a Christmas tree.
They’re getting up to 572,000 lbf thrust apparently. The smaller Raptor 2 engine is about 510,000 lbf (so far) by comparison.
Beati Dogu said:
Blue Origin have posted some new pictures of the big BE-4 engine on their twitter account.
Here’s one:
The engine bell alone is about 6 foot tall. It’s a test engine, so it’s wired up like a Christmas tree.
They’re getting up to 572,000 lbf thrust apparently. The smaller Raptor 2 engine is about 510,000 lbf (so far) by comparison.
Running at less than half the chamber pressure of the Raptor will do that!Here’s one:
The engine bell alone is about 6 foot tall. It’s a test engine, so it’s wired up like a Christmas tree.
They’re getting up to 572,000 lbf thrust apparently. The smaller Raptor 2 engine is about 510,000 lbf (so far) by comparison.
I think its safe to say that Blue Origin have under specced the BE-4 and frankly it doesn't appear to have helped them on the development program which has presented just as many issues as a lot less conservative design. The fact that their programme has had relatively few test engines almost certainly hasn't helped. This most likely was driven from the New Glenn programme which is based on the assumption that they never expend a vehicle.
Ergo by mid 2021 they had apparently built only 9 BE4! Which might make sense if the programme intent was that there would only ever by ~5 New Glenn first stages with 35 engines on them. Only in practice most successful rapid engine development programmes have been "hardware rich" with a rapid feedback loop between development testing and development engine build.
As an aside, we also don't know how much a BE4 weighs. For comparison an RD-170 has a chamber pressure of 270 atmospheres (bar) and a thrust to weight of 78, whereas a NK-33 has a chamber pressure of 143 bar and a thrust to weight of 137. Both of these are Russian closed cycle RP1/LOX engines, though I suspect that the NK-33 is somewhat more optimized for lower weight at a cost in money and durability.
This demonstrates a trade between efficiency and engine weight, the higher pressure can be turned into greater expansion and therefore higher exhaust velocities. I did some calcs a few years ago on a Falcon 9 with Merlin and with RD-180 and worked out that for an expendable booster trading a heavier engine for better fuel efficiency made sense.
The heavier engine didn't make that much difference to the total mass of empty booster and full second stage + payload but the improved specific impulse of the engine meant that you could carry much more second stage fuel or payload. However when you want to recover the second stage and either want to decelerate it and land or a barge or turn around and return to launch site the mass of the engine really makes a difference as it is 25-35% of the mass of the first stage. In these circumstances having a lighter but slightly less efficient engine makes more sense and in fact the Merlin actual beats the RD-180 in these circumstances while also being much cheaper to make.
This all might explain the choices behind the BE-4, but I suspect ultimately they didn't push themselves and SpaceX will probably have an engine that is more powerful, more efficient, lighter and cheaper to make.......
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