China's Space Program News Thread

[by78]

A few more screen captures from the latest space walk.

 

[by78]

A very high-resolution images of the robotic crawler arm of the Chinese space station.

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for the original resolution (3072 x 4096) version.

 

[by78]

The Mars rover has travelled a total of 1253 meters.

Meanwhile, the Tianwen orbiter has begun carrying out remote sensing of Mars. The orbiter has been in Mars orbit for 473 days.

 

[enroger]

Electric pump engines' thrust may be too low for any practical landing. The best is 25kN (Rutherford). Compared to YF-100's 1200kN or Merlin's 854kN. For a size of Falcon 9 (the only successful VTVL so far), the lowest thrust is 482kN (one engine throttled to min) at 16% of total takeoff thrust. The prefered thrust is about 13% depending on the dry mass. So let's say the right thrust is about 450kN. This is 18 times of 25kN, 18 such engines with their battery pack is a huge dead weight. Ironically dead weight is good for landing because of less throttling, but then what is the point of having a rocket?

I think with today's battery and electrical motor technology level, electric pump rocket engine does not have a role in 1st stage of main stream launchers (CZ-2,3,6,7,8, Falcon 9 etc.), not even as a landing engine.

There is no reason you can't scale up the system, unless electric motor power is a limiting factor. Low TWR is a real problem, as you mentioned battery weight sucks. But considering Rocket Lab's Electron has it's entire first stage powered by electric pump rocket it can't be that bad?

As you said landing engine only needs 13%-16% of total thrust, the mass penalty is even lower.

Yes having something like Merlin engine is probably more ideal, but if you can't then the next best thing is to have quick and easy electric pump fed rocket for landing.

 

[taxiya]

There is no reason you can't scale up the system, unless electric motor power is a limiting factor. Low TWR is a real problem, as you mentioned battery weight sucks. But considering Rocket Lab's Electron has it's entire first stage powered by electric pump rocket it can't be that bad?

As you said landing engine only needs 13%-16% of total thrust, the mass penalty is even lower.

Yes having something like Merlin engine is probably more ideal, but if you can't then the next best thing is to have quick and easy electric pump fed rocket for landing.

Electric motor's power density is one of the two limiting factors, the other is the energy density of the battery. Both sucks compared to gas turbine and chemical feul. With these two limits unchanged, you will just scale up the dead weight together when you scale up the thrust.

Electron's LEO payload is 1.8% of its takeoff mass. The figure for CZ-7 is 2.3% which is a very low figure among its contemperaries, Russia's current rockets are over 3%, Falcon 9 is over 4%. So Electron is very bad.

Let me be clear, Merlin is a good engine in its class (open circle), but it is just one of many good engines depending of the application situation. It is NOT neccerarily an ideal VTVL engine either. "Falcon 9 using nine Merlin" is the key for its success in VTVL. By shutting down 8 out of 9 at landing, Falcon 9 BYPASSED the demand of deep throttling. It is a clever approach of system design, not because the engine is perfect. This is an approach that China is doing too in CZ-5DY, 7 YF-100 in one core with a even better deep throttling capability.

As it stands today, electric pump fed engine for VTVL is an approach both far distance and far difficult than conventional engines.

 

[tiancai8888]

Shenzhou-13 astronauts complete first spacewalk

By the way , Why you closed the comment section of your youtube channel?

 

[tiancai8888]

This is one of the more interesting developments coming from civi aerospace companies, I remember there is another Chinese company also tested electric pump rocket and even tested it on a vtol test.

Electric pump system inherently has lower TWR compared to say staged combustion cycles (due to mass of battery). However they have ridiculously good throttling range and response they make for ideal vertical landing engines.

My prediction is future Chinese reusable rocket will still use traditional pump cycle to provide main thrust but rely on electric pump systems for landing, honestly this seems to be the ideal setup.

The other company is Deep Blue Aerospace. The Link Space was "dead" for a while. Link Space is the first Chinese company to do the VTVL test 3 years ago. IMO the E-pump engine is optimal for the small rocket company, easier ,cheaper and more "wow" moments when doing the VTVLs

 

[Quickie]

Some great Mars Terrain CGs in this video with some of the imaging in the first half either real imaging or CGs based on the real images? It's getting difficult to differentiate between real and computer imaging nowadays.

 

[enroger]

Electric motor's power density is one of the two limiting factors, the other is the energy density of the battery. Both sucks compared to gas turbine and chemical feul. With these two limits unchanged, you will just scale up the dead weight together when you scale up the thrust.

Electron's LEO payload is 1.8% of its takeoff mass. The figure for CZ-7 is 2.3% which is a very low figure among its contemperaries, Russia's current rockets are over 3%, Falcon 9 is over 4%. So Electron is very bad.

Let me be clear, Merlin is a good engine in its class (open circle), but it is just one of many good engines depending of the application situation. It is NOT neccerarily an ideal VTVL engine either. "Falcon 9 using nine Merlin" is the key for its success in VTVL. By shutting down 8 out of 9 at landing, Falcon 9 BYPASSED the demand of deep throttling. It is a clever approach of system design, not because the engine is perfect. This is an approach that China is doing too in CZ-5DY, 7 YF-100 in one core with a even better deep throttling capability.

As it stands today, electric pump fed engine for VTVL is an approach both far distance and far difficult than conventional engines.

Rutherford is powered by two 37kW motor, current top of the line E-car has motor output of 2MW, so motor power is not that much of a limiting factor.

You're right battery weight is more of an issue. Lets run the number with Electron payload fraction 1.8%, lets simply assume all the excess mass of Electron is due to battery mass/motor weight compared to Falcon 9's 4% payload fraction, so 4-1.8 = 2.2% dead weight. Now since we only need say 15% thrust for landing: 2.2% * 0.015 = 0.033%. Subtract that from Falcon 9's 4% we get 3.967% payload fraction, not so terrible I'd say?

Remember the above calculation is certainly over simplified since I did not consider staging, and I have no data on the mass fraction of first and second stage, also Electron do jettison some battery mid-flight so it's more complicated.

Basically I'm saying E-pump might have terrible TWR, but if you only use it for 15% of the thrust it is not that terrible. Those 0.033%-ish weight penalty buys you a simple reliable landing system. I still think it is one of the more promising way to do it.

 

[enroger]

The other company is Deep Blue Aerospace. The Link Space was "dead" for a while. Link Space is the first Chinese company to do the VTVL test 3 years ago. IMO the E-pump engine is optimal for the small rocket company, easier ,cheaper and more "wow" moments when doing the VTVLs

Ah yes that's the one. I there're too many companies at the moment. Some consolidation and merger would be good for the industry.