Yeah, pretty impressive if they succeed. This engine might be used for their equivalent of Starship and eventually replace LM-9.
China's Space Program News Thread
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SpaceX has demonstrated that a methane engines are technologically feasible, so I don't see any reason why a Chinese equivalent couldn't be developed.
Particularly since the Raptor methane engines are higher performance and more reusable than the equivalent Merlin kerosene engines.
SpaceX has also demonstrated that the market for a common first-stage rocket engine can be measured in the thousands.
So low-cost mass-production of a proven engine design is the way forward.
First off, the proposed engine is a good prepare for the future. I am glad that China is betting on every technology path that has a potential.
Secondly, your statement that this engine has much deeper throttling than YF-100 is not true.
Here is an extraction from a research paper from 2018. It says that YF-100 (1200kN LOX/Kerosene) is targeted down to 10%. It is much lower that this Methane engine 25%. More importantly, it has conducted many ignition tests.
Thirdly, I don't think the proposed rocket can share anything with CZ-5. LH2 and Methane are just too different in characteristics to share the same facilities, storage tanks and plumbings of the launch facility for CZ-5 won't work with Methane rocket. Just wait and see if SpaceX will ever reuse NASA's launch facility for SLS for their Starship.
Lastly, the replacement won't happen, at least not in the way that you suggested "common first stage". Just think about it, first stage is LO2/Methane, second stage is LO2/LH2, two different liquefied gases with far different temperatures, that is a nightmare. Think again, why does SpaceX use only Methane for Starship and SH? why does Falcon 9 only use LO2/Kerosene?
It can only be total replacement (all stages), new rockets. In that case Methane engine must have a tremendous advantage over the current Kerosene engines to warrant forgoing all the investment in CZ-7/8/5/9 and 921. It is akin to dumping your one year old Mercedes for a new EV because the EV saves you 10% of fuel cost.
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The cost of fuel is negligible compared to the cost of the rocket.
Here are a few energy densities in MJ/kg
Kerosene 43.3
Methane 55.5
Hydrogen 142
So we can see Methane has 28% more energy than Kerosene.
And remember a rocket is carries a lot of fuel in terms of weight.
Any weight saving translates directly into increased payload.
Horses for courses
The CZ-5 uses Kerosene for its boosters and Hydrogen for its main stage, hydrogen provides much better performance in a vacuum. Kerosene is much easier to handle.
As the boosters are presently single use one needs to balance the cost/benefit of changing to methane boosters I doubt there is any.
As methane is not as efficient as hydrogen in a vacuum there's no benefit in swapping out the main stage engines, if the boosters aren't also methane fuelled.
The equation changes when the system becomes a reusable one since fuel reserves need to be factored in for the return and to achieve the same payload capacity a fuel with better energy density like methane provides benefits. Given the design characteristics of Chinese launchers
End of the day the rockets are just carriers the real valuable bit is what goes into orbit. Despite the plethora of LOX/RP1 and LOX/H2 engined carrier rockets available the work horses of the Chinese space program are still the N2O4/UDMH fuelled CZ-3 and CZ-4 not because they're technologically the best but because they do the job well.
To paraphrase Deng, it doesn't natter what fuel is used what matters is that the payload gets to orbit safely
What I talked about was the complexity of operating and maintaining three liquefied gas (O2, H2 and Methane) in gelgoog's proposal (common first stage) than two (O2, H2) in a CZ in a launch facility. Your reply is unrelated.
hkbc has answered your post very well. Methane is not the best in first stage, nor the upper stage (2 and or 3). It is ONLY best for the specific scenario such as only one fuel to maintain rather than Kerosene+H2.
Also, fundamentally people in rocketry talk about specific impulse in vacuum and mass specific impulse at sea level, not energy density. In this regard, Methane is worse than Kerosene at sea level and worse than H2 in a vacuum. This is a well-known fact. It has been repeated by Chinese studies in their road-map planning, a reason why China tested a 70t methane engine long before SpaceX, but choose not to continue. China does not see the meaningful advantage of it even for a full flow engine like Raptor.
Now China conducting study on Methane engine is a continuation of the strategy of 技术储备 (prepare the capability for possible use one day). It should not be overstated that China has changed mind and acknowledged the minimal and conditional advantage that Methane engine has overcome its drawback.
Another reason (not related to your post) why China does not see Methane engine much wanted is the "re-usability" advantage of it is a myth propagated by SpaceX fans. Oxygen rich close circle Kerosene engine has no more problem than Methane engine. That's why you are seeing YF-100 being developed to 10% for re-usability.
All this is to say that, China want to be prepared some time in the future for the next generation rockets in some decades, but not today. And CZ-5/6/7/8/9 and 921 will serve a long time (two decades) before being replaced, and Methane is not necessarily the only one candidate.
That sounds fishy to say the least. The RD-191 for example can only throttle down to 27% not 10%.
I guess I did not make myself clear. The whole idea is to use a common LOX/Methane first stage engine across all the rockets instead of the combined LOX/Kerosene and LOX/Hydrogen engines currently used or contemplated. The LM-7/8 use the YF-100. The LM-5 uses the YF-100 and YF-77. The Long March 9 will use YF-130 engines. That is three engine types you need to manufacture and certify. This way you need a single engine type for the first stage of all those launchers. That is why I said "common first stage engine" not "common engine".
What SpaceX does with a common first and second stage is kind of beyond the point. SpaceX doesn't want to spend the engineering resources to develop a whole new rocket engine for the second stage which will be manufactured in small numbers and would require the use of different fuel. It is much harder to have ground handling facilities for hydrogen than methane. Just look at the boiling point of both. Methane has similar boiling temperature range to oxygen. Hydrogen is way, way lower. 20.28K for hydrogen. That is 20 degrees above absolute zero. Methane is 111.6K. Oxygen is 90.188K. The Chinese already have hydrogen production, ground handling, and the second stage engines already are in production. So the calculus isn't the same. LM-7 uses the same YF-75 engines on the LM-3A/B/C. The LM-5 uses the YF-75D, which is new, but it is capable of multiple restarts unlike their previous engine.
The move to a common first stage engine has nothing to do with saving fuel cost. It is all about driving down production costs through reducing the types of parts you manufacture. If you have those YF-130 engines only on a LM9 rocket which is launched like only once every couple of years how much do you think you will need to spend to maintain those production facilities, tools, and retain trained staff specialized in manufacturing those engines? The costs will be immense. It makes no sense. They need to rationalize the production chain in the future.
The 5m fairing production cost reductions because the diameter is same as LM-5 have nothing to do with sharing the tank design schematics. It has to do with sharing tools, production facilities, and logistics facilities to move things around. They have existing tooling dimensioned for that already.
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Can't wait for the cargo supply mission! Side note, does anyone think the inflatable heat shield that was tested last year could be used on this spacecraft?
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