China's Space Program News Thread


Status
Not open for further replies.

ougoah

Brigadier
Registered Member
Please, Log in or Register to view URLs content!

Did someone say China needed a starlink-like constellation?

Things like Starlink constellations in LEO and whatnot truly are a backup military constellation and the associated launch capabilities that make a fast and numerous constellation possible. China sort of doesn't quite need such a thing as the US does. Why? Because China's military posture is very defensive and regional where they already have numerous types of very fast and extremely high altitude reconnaissance and communications drones that probably can perform many other duties tasked by satellites. Regional advantage means easier to deploy and continue deploying these drones as opposed to sending them and somehow fueling them halfway around the world like the US would need to do if their mainstay satellites are disabled. Regional wars also mean you don't quite have as much comprehensive need for these sorts of satellites for targeting, comms, and navigation.

Of course all of this progress is still very valuable because one never knows when certain technologies become useful in myriad of other unexpected ways. It still pays to start working on relatively pointless tools today when you have the time and money.
 

gelgoog

Brigadier
Registered Member
China already does more satellite launches than either the US or Russia. Their satellite networks are mostly global but they will tend to go global in due time much like what happened with Beidou. This without the new generation rockets being in full production even. Once they enter full production I expect China to increase its global coverage more.

PS: Do the Chinese have electric propulsion technology for satellites? That is one of the main technologies behind Starlink.
 

ougoah

Brigadier
Registered Member
China already does more satellite launches than either the US or Russia. Their satellite networks are mostly global but they will tend to go global in due time much like what happened with Beidou. This without the new generation rockets being in full production even. Once they enter full production I expect China to increase its global coverage more.

PS: Do the Chinese have electric propulsion technology for satellites? That is one of the main technologies behind Starlink.

But the important thing is the Starlink style projects are built on very impressive LEO launch technologies that are cheap, numerous, and effective. So China needs to also develop similar capabilities and accessibility which will be done but it's just yet another thing to give attention to.

China will need to bridge the widening gap in booster tech, rocket engines, and various forms of economical advantages. Re-usable is a a really good solution for SpaceX because their boosters, rockets, and engines are undoubtably very expensive whereas Chinese ones probably can achieve desired function at much lower costs, therefore making reusables a more questionable endeavor. But there are other ways to lower costs and reusable is definitely still going to be worth pursuing for Chinese launchers even if the benefits won't be as considerable compared to the benefits for US launchers.
 

gelgoog

Brigadier
Registered Member
China until quite recently used hypergolic rockets. Not something exactly easy to reuse. You need special suits and a special environment to refill a rocket like that. Their most recent engines and rockets however are more amenable to reuse. One of the private Chinese companies is developing rockets with a similar guidance profile to the Falcon 9 in terms of reuse back to land. I think it is a question of time until other nations start doing rocket reuse too. One example is Japan. The engine on their H-III rocket is really well suited for reuse, even more than SpaceX's. The H-III could be redesign into a reusable rocket if they wanted to. Thing is they do so few launches it will probably not be cost competitive to reuse. China does many launches so it will be profitable to reuse rockets.
 

taxiya

Brigadier
Registered Member
PS: Do the Chinese have electric propulsion technology for satellites? That is one of the main technologies behind Starlink.
Yes, China has it for years, as early as 2014 on DFH-3B platform. The recent CZ-5 launch in 2019 was DFH-5 platform which also uses electric propulsion. If an earlier CZ-5 launch did not fail, DFH-5 would have been in orbit in 2017.
 

taxiya

Brigadier
Registered Member
China until quite recently used hypergolic rockets. Not something exactly easy to reuse. You need special suits and a special environment to refill a rocket like that. Their most recent engines and rockets however are more amenable to reuse. One of the private Chinese companies is developing rockets with a similar guidance profile to the Falcon 9 in terms of reuse back to land. I think it is a question of time until other nations start doing rocket reuse too. One example is Japan. The engine on their H-III rocket is really well suited for reuse, even more than SpaceX's. The H-III could be redesign into a reusable rocket if they wanted to. Thing is they do so few launches it will probably not be cost competitive to reuse. China does many launches so it will be profitable to reuse rockets.
The first Chinese reusable rocket is probably named CZ-8R. The non-reusable variant is scheduled to be launched this year. The 8R is rumored to be launched in 2021. Just wait and see.
 

taxiya

Brigadier
Registered Member
China until quite recently used hypergolic rockets. Not something exactly easy to reuse. You need special suits and a special environment to refill a rocket like that. Their most recent engines and rockets however are more amenable to reuse. One of the private Chinese companies is developing rockets with a similar guidance profile to the Falcon 9 in terms of reuse back to land. I think it is a question of time until other nations start doing rocket reuse too. One example is Japan. The engine on their H-III rocket is really well suited for reuse, even more than SpaceX's. The H-III could be redesign into a reusable rocket if they wanted to. Thing is they do so few launches it will probably not be cost competitive to reuse. China does many launches so it will be profitable to reuse rockets.
I highly doubt that. Here is my thought.

The H-III's main engine is LE-9. The throttle range is down to 63%. The core stage can have 2 or 3 LE-9s. Only the variant of 3 is possible to be reused. When landing, two engines will be shutdown, that leaves one engine, its full thrust being throttled down to its minimum 63% will give the minimum thrust at 0.63/3=21% of the liftoff thrust.

We know that rocket using LOX/Kerosene like Falcon 9 need to throttle down to 10% to make around 1:1 thrust/weight ratio to enable powered landing. The last moment is like hovering over. If the thrust is more than that, the rocket will not land but go up instead. To couple with larger than 1 ratio, the engine has to be shut down when the rocket is just a meter or so above ground, essentially smashing the rocket on ground. This is doable as SpaceX has done it in early days with higher chance of failure of course. The 10% figure is based on the fact that the dry weight of a rocket (tank almost empty) is about 10% of liftoff mass. This is determined by the type of fuel Kerosene that determines the size of the tank and additional structures for it. LH2 is much light but its tank is much bulkier for the same payload, so the key question is what is the dry mass to liftoff mass ratio? If it is around 21%, then fine. But I seriously doubt that Japan is that bad in making a light weight tank for LH2 even if we take into consideration of the bulkiness of LH2 tank. Take Saturn V's second stage as a reference, its dry mass was 9.7% even better than 10%. Japan should not be much worse than that considering Japan has been working on LH2 rocket for decades and it has a good material manufacturing foundation. So its ratio could be just above 10%, still too light for the minimum thrust of 21%. To reach around 10%, LE-9 has to be further throttled down half to 30%. A LH2 engine of this thrust class (>100 tonne) to 30% is nothing easy, even the most experienced and still the most advanced countries in LH2 engine (U.S. and Russia) have not done it, and probably not able to do it in the near future.

In conclusion, LE-9 and H-III in their current design specifications are very unlikely to be converted to being reusable, almost impossible. It would be another rocket and engine if they choose to do so.
 
Status
Not open for further replies.

Top