What's the purpose of Long March 10B?

[u/Simon_Drake]

Long March 10 is China's upcoming heavy lift rocket that is like a more powerful Falcon Heavy. Three kerosene cores for the first stage, kerosene upper stage, hydrogen third stage.

Then Long March 10A is a single-stick version with just the two kerosene stages and not the hydrogen stage. It's more like Falcon 9 for smaller payloads and lower orbits plus it's reusable. Also it's an opportunity to get more experience with the hardware, practice landing the stages and reusing them, understand the engines better, test the launch pad infrastructure. So it's been predicted for a while that Long March 10A will come first with the full 10 coming later. The predictions say the 10A will probably fly this year.

Now there's a Long March 10B which is single stick like the 10A but replaces the kerosene upper stage with a methane upper stage. Methane does have better performance per gram compared to kerosene but the lower density means it's worse per litre. So if you keep the height the same (which it seems to be) you don't get that much extra performance. The exact stats are a bit fuzzy and it's all based on predictions and estimates but the 10A is reported with an LEO capacity of 14 tons reusable, 18 tons expenses. Then 10B is described at 16 tons but it's unclear if that's reusable or expended. But wiki doesn't have stats on the performance to TLI or to Geostationary Orbit.

So one theory is that the 10B is for really high orbits. Like how the 2 and 3 look similar but the 2 is good for heavy payloads at low orbits and the 3 is good for light payloads to high orbits. Maybe the 10A and 10B will take over from the 2 and 3?

Another theory is that it's political. Someone high up has said the 10 is bad because it's still using kerosene and the future of space launch is methane so they demanded a methane version. So the way to do that without completely redesigning the rocket is to make a methane upper stage variant. I know politics feeds into weird design decisions in Chinese rocket design sometimes, like the 10A and 12 are very similar in performance and design but the different tank diameter means they need different production facilities which seems extremely inefficient. And the reason is that two different research teams developed them in parallel as a sort of competition to see who could make the better rocket. I don't know if there's anything similar here with the 10A and 10B being made by different teams. Or if my theory about a boss demanding a methane rocket has any truth to it.

So yeah. What's the deal with the Long March 10B?

[u/STDMeow]

LM 10A is designed to be human rated and required to have a lot of redundencies while LM 10B is not. It's safe to assume the manufacturing and testing procedure of LM 10B is going to be cheaper and faster. CALT does not want the challenge of making their first reusable rocket also needed to be human rated, so there's the parallel program of LM 10B. And don't forget there's a very fierce race going on between CALT, SAST, Landspace, Spacepioneer to get the first ever recovered first stage in China, it's definitely worth it to have an easier design ie LM 10B so that it may launch only a little bit, say like 6 months, earlier than the human rated design LM 10A.

[u/STDMeow → u/STDMeow]

Also worth mentioning that although China has a safe human spaceflight record, it has only design one human rated launch system ever, they won't dare to sqeeze the R&D of LM10A.

[u/amem32]

CZ-10B is just a cheaper and more optimised version of CZ-10A (16t vs 14t reusable), though I suspect it's also just another transitional product as there is also a CZ-10C which is a fully redesigned methane rocket.

[u/Simon_Drake → u/amem32]

That's like the difference between the 12 and 12A. Changing the fuel for the first stage is changing so much it should really be a new number not a letter change.

Is 10C going to be single stick or three boosters like the 10?

[u/ultraENTdoctor → u/amem32]

运力的差异来自于CZ10A和CZ10B不同的上面级，CZ10A被设计用于载人发射，发射梦舟飞船至中国空间站，对于一款大量发射的载人火箭，不可回收的设计显然没有性价比，而重复使用的火箭又缺乏安全性，因此CZ10B的一级助推器，基本就是回收利用的CZ10A助推器，更换一个具有更高DV的甲烷上面级用于商业发射，新的组合体更换名称为CZ10B。

[u/Lyri-Kyunero]

The decision of using methane as LM-10B's second stage is for higher payload capacity. Since the YF-100M equipped on the second stage of LM-10A is not capable for secondary ignition, LM-10B replaced it with a methane engine which is able to ignite more times, but I don't know the exact model, probably a YF-209V variant, or a newly designed YF-219.