Do the boosters transfer fuel to the core before dropping out? Is there any indication of that happening?
China's Space Program News Thread
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The hydrolox upper stage, you mean YF-77, but isn't that third stage only going to be expected for orbits beyond LEO? (I.e. GTO or LTO?)
For a LEO payload of 70t, would we expect the YF-77 third stage to be used?
The specific impulse of YF-100 is said to be 300s, while the specific impulse of Merlin 1D is 282s, both at sea level.
Payload to LEO is basically a unit of measurement and does not mean the actual mission will be LEO.
Yes. Based on this picture you sent, the hydrolox third stage is the YF-75D, which is used for 70t LEO.
Yes, but a hydrolox vaccuum optimized engine can have Isp ~450, which is what allows for the high payload. The other reason why CZ-5DY without the third stage has lower payload could be because it is a smaller rocket.
In fact, the reason why it has more sea level thrust than Falcon 9 might be so that it can lift the third stage if needed. Sea level lift must exceed launch weight after all.
It is probably because the CZ-5DY has a higher dry mass than the Falcon 9.
Every pound you shave in dry mass is an extra pound you get in payload.
Launch site distance to the equator and upper stage performance is mostly irrelevant for LEO payloads.
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The single-core CZ-5DY is likely to be designed to be limited to a certain max LEO for cost-efficiency reasons.
With the higher total thrust of the single-core engines, they should have no problem designing the rocket to have a similar or even higher payload than 22000 t and with the same kind of efficiency as the Falcon 9, assuming the rockets' engines have similar ISP.
The problem is this would mean less cost efficiency when launching the usual kind of payload of 5 tons or so, for the reason of the hypothetical rocket having to carry the additional higher dried mass of the propellant tanks at the expense of payload, plus the additional cost of building a much larger tank needed for that kind of super-duper max payload.
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Not sure if this has been posted before but china is planning on using "tethered landing device" for its reusable first stage with hooks and to be caught with tightwires.
What do you guys think about this approach/design compared to legs one like SpaceX and everyone else who's trying to make reusable rockets? Also, what was wrong with the space shuttle design? Too expensive? Can't they redesign and make a better/safer/more economical version of that, or was space shuttle design(ie landing like a plane on a runway) fundamentally flawed in some way and better to just scrap and forget about it completely?
I guess the private companies are still going to develop reusable ones using legs like SpaceX so this will give china access to more solutions
Kinda reminds me of aircraft carrier tech to hook and slow down the planes but this is vertical instead of horizontal.
What do you guys think about this approach/design compared to legs one like SpaceX and everyone else who's trying to make reusable rockets? Also, what was wrong with the space shuttle design? Too expensive? Can't they redesign and make a better/safer/more economical version of that, or was space shuttle design(ie landing like a plane on a runway) fundamentally flawed in some way and better to just scrap and forget about it completely?
I guess the private companies are still going to develop reusable ones using legs like SpaceX so this will give china access to more solutions
Kinda reminds me of aircraft carrier tech to hook and slow down the planes but this is vertical instead of horizontal.
SpaceX has proposed something like that for Starship recovery. I personally think it is too complicated and finicky.
The Space Shuttle had terrible economics. You could in theory solve a lot of the problems in that design. But then you would end up with something much like Starship. I will give you some examples. The Shuttle used side-mounting. Because of this they lost one Shuttle when broken ice from the central tank fell into the Shuttle thermal protection system and broke the tiles. On reentry it just burned down. The Shuttle also had no crew escape functionality. You are SOL if you have any major problem.
I think it is just too complicated to work properly. I am a big fan of the VTVL approach like Falcon 9 myself. There is also plenty of evidence the extra weight not just in wings but the reinforced fuselage for horizontal landing costs about as much in weight as extra fuel for vertical powered landing. Winged design also complicates aerodynamic design of the vehicle a whole lot.
You can only justify winged design if you want to bring vehicle back to launch site.
I think besides looking at the thrust of every stage, the burn time (propellant volume) is also a critical factor to the payload.
From the slide that I got from this thread, I can see that the first stage of single stack CZ-5DY is shorter than the core of full-stack version. We also know that CZ-5DY's three first stages are of difference sizes, the center one is larger, having a longer burn time than the side boosters.
Falcon-9 and Falcon Heavy share the same boosters. Falcon Heavy would throttle down the center booster to extend its burn time.
If we trust the slide, I think CZ-5DY single stack configuration is using the smaller booster. So its burn time is shorter than the core, also shorter than a Falcon-9, therefor lower payload. There is no problem to reach a higher payload surpassing Falcon-9 by using the center booster as 1st stage. It is just unnecessary in China's plan, and it wouldn't be much effort to increase it when demand appears.
Your following sentence actually suggested 70t LEO can be a real mission payload.
The 70t to LEO is mass to orbit, a theoretic value. But it includes the 3rd stage as part of payload. The 3rd stage is not used to reach LEO.
Just think of it, is there any liquid rocket in China enters LEO with 3 stages? Is there any such rocket in the world?
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Indeed, which is the basis of my thinking.
So, the picture I sent describes the hydrolox third stage yes, but my interpretation is that would be for a LTO 27t mission profile.
For a LEO 70t mission, I suspect they would omit the third stage.
Here is an earlier, more detailed image of the CZ-57DY with all three stages and three cores on the left, and a single core LEO variant on the right, and as we can see the single core LEO variant only has two stages.
We can see that the side boosters on the three core variant and the first stage of the single core variant are substantially smaller/shorter than the central core first stage of the three core variant, with noticeably smaller fuel tanks.
Also, the second stage of the single core variant seems to only have one YF-77 rather than two YF-77s as on the second stage of the three core variant on the left.
Adapting the three core CZ-5DY image, I think this is what a LEO configured variant would look like -- i.e. removal of the third stage.
I suppose the difference between the three core CZ-5DY and the single core variant, versus Falcon Heavy and Falcon 9, is that the central core first and second stages of the three core CZ-5DY is substantially larger than the side boosters, yet the smaller side boosters are used for the single core variant.
I suppose that is why there is such a big difference.
Essentially what @taxiya wrote above.
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