China's Space Program News Thread

[Blitzo]

Payload to LEO is basically a unit of measurement and does not mean the actual mission will be LEO.

It means that it is a rocket designed for both LEO missions and LTO missions.

Yes. Based on this picture you sent, the hydrolox third stage is the YF-75D, which is used for 70t LEO.

Why do you think the third stage with YF-75D is used for 70t LEO?

They explicitly stated LTO 27t as the first payload, and it makes sense that a LTO payload would require a third stage.
By contrast, a LEO mission profile will not require a third stage.

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.

I feel like we are talking past each other.

Taxiya and I have already come to an agreement for why the single core CZ-5DY variant has a lower LEO payload than Falcon 9 -- and that's likely because the fuel tanks are smaller and the second stage has only one YF-100.

However, we are now talking about the three core CZ-5DY, which has boosters that have the first stage of the single core CZ-5DY, but that the central core first stage has much larger fuel tanks for longer burn and that the second stage also has two YF-100s rather than one.


What I am suggesting, is essentially this:

 

[Jason_]

It means that it is a rocket designed for both LEO missions and LTO missions.




Why do you think the third stage with YF-75D is used for 70t LEO?

Because that seems to me to be what the slide is saying. On the basis of the slide itself, there is no indication that a two-stage with booster configuration exists.

They explicitly stated LTO 27t as the first payload, and it makes sense that a LTO payload would require a third stage.
By contrast, a LEO mission profile will not require a third stage.

There is no particular reason why LEO rockets cannot have a third stage. The last Saturn V launch putting Skylab in LEO has three stages. The convention today is that rockets optimized for LEO missions have two stages, as that is sufficient. However, if you consider payload to LEO as a unit of measurement, this can easily apply to three stage rockets.

In other words, the fact that the slide used payload to LEO as a unit of measurement is in my opinion not indicative that the measurement is done on an LEO-optimized two stage rocket, as opposed to the LTO-optimized three stage rocket as shown hypothetically flown on an LEO mission.

I feel like we are talking past each other.

Taxiya and I have already come to an agreement for why the single core CZ-5DY variant has a lower LEO payload than Falcon 9 -- and that's likely because the fuel tanks are smaller and the second stage has only one YF-100.

However, we are now talking about the three core CZ-5DY, which has boosters that have the first stage of the single core CZ-5DY, but that the central core first stage has much larger fuel tanks for longer burn and that the second stage also has two YF-100s rather than one.

I think you are mistaken in focusing on thrust. Thrust has no bearing on payload capabilities. This is a consequence of the rocket equation.


As you can see, thrust simply is not part of the equation. The only factors that matter are specific impulse Isp and mass ratio mi/mf.

Of course, a real rocket's thrust must satisfy two constraints. For the first stage, the thrust at sea level must exceed takeoff weight. For the second stage, the thrust must accelerate the rocket to orbital velocity quick enough so that it does not crash into the atmosphere before that.

However, once these two constraints are met, there are no benefit to having even greater thrust, at least with respect to payload capacity. Therefore, a rocket having greater thrust does not imply more payload capacity.

What I am suggesting, is essentially this:

View attachment 84769

Yes, #2 might be what the slide is referring to, but it also might not be.

 

[Blitzo]

Because that seems to me to be what the slide is saying. On the basis of the slide itself, there is no indication that a two-stage with booster configuration exists.

It seems to me to be saying otherwise, that this is a rocket intended primarily for moon missions and it is depicted in a lunar mission configuration, however it also has a robust LEO mission profile, but as it is a secondary mission and of less public and scientific interest, they are only depicting the lunar mission profile.

There is no particular reason why LEO rockets cannot have a third stage. The last Saturn V launch putting Skylab in LEO has three stages. The convention today is that rockets optimized for LEO missions have two stages, as that is sufficient. However, if you consider payload to LEO as a unit of measurement, this can easily apply to three stage rockets.

In other words, the fact that the slide used payload to LEO as a unit of measurement is in my opinion not indicative that the measurement is done on an LEO-optimized two stage rocket, as opposed to the LTO-optimized three stage rocket as shown hypothetically flown on an LEO mission.


I think you are mistaken in focusing on thrust. Thrust has no bearing on payload capabilities. This is a consequence of the rocket equation.
View attachment 84770

As you can see, thrust simply is not part of the equation. The only factors that matter are specific impulse Isp and mass ratio mi/mf.

Of course, a real rocket's thrust must satisfy two constraints. For the first stage, the thrust at sea level must exceed takeoff weight. For the second stage, the thrust must accelerate the rocket to orbital velocity quick enough so that it does not crash into the atmosphere before that.

However, once these two constraints are met, there are no benefit to having even greater thrust, at least with respect to payload capacity. Therefore, a rocket having greater thrust does not imply more payload capacity.

Without us knowing how the numbers plug in, there is no credible way for us to know whether the third stage is somehow required for a 70t LEO mission.

However we do know that:
- virtually all contemporary LEO oriented rocket configurations are two stage
- the depicted three stage, three core variant is showing a lunar mission configuration

So the question we have to ask is whether that lunar mission configuration is also appropriate for a LEO launch configuration, and if not, then what may be changed or subtracted.

Yes, #2 might be what the slide is referring to, but it also might not be.

Is there something about #2 which is so difficult to believe for a 70t LEO configuration?

Because to me it looks exactly like what you would expect for such a mission, and is only natural to deduce when the depicted arrangement of the rocket is intended for a lunar mission profile given its primary role.

Isn't it more abnormal to consider that the rocket would have a LEO configuration that is identical to a lunar configuration?

 

[Jason_]

It seems to me to be saying otherwise, that this is a rocket intended primarily for moon missions and it is depicted in a lunar mission configuration, however it also has a robust LEO mission profile, but as it is a secondary mission and of less public and scientific interest, they are only depicting the lunar mission profile.




Without us knowing how the numbers plug in, there is no credible way for us to know whether the third stage is somehow required for a 70t LEO mission.

However we do know that:
- virtually all contemporary LEO oriented rocket configurations are two stage
- the depicted three stage, three core variant is showing a lunar mission configuration

So the question we have to ask is whether that lunar mission configuration is also appropriate for a LEO launch configuration, and if not, then what may be changed or subtracted.



Is there something about #2 which is so difficult to believe for a 70t LEO configuration?

Because to me it looks exactly like what you would expect for such a mission, and is only natural to deduce when the depicted arrangement of the rocket is intended for a lunar mission profile given its primary role.

Isn't it more abnormal to consider that the rocket would have a LEO configuration that is identical to a lunar configuration?

I would say that booster version do not have an LEO mission profile at all. Falcon 9 to date has flown 142 times. Falcon Heavy 3 times. All three Falcon Heavy launches are <10 ton payload to GEO/Mars orbit.

Satellite mass has been going down. The modern preferred approach is mass constellation of small sats on low orbit. A 14 ton payload is sufficient for 99% of LEO missions.

Which again shows the 70t is just a measurement and does not imply the existence of another configuration.

 

[Quickie]

Because that seems to me to be what the slide is saying. On the basis of the slide itself, there is no indication that a two-stage with booster configuration exists.


There is no particular reason why LEO rockets cannot have a third stage. The last Saturn V launch putting Skylab in LEO has three stages. The convention today is that rockets optimized for LEO missions have two stages, as that is sufficient. However, if you consider payload to LEO as a unit of measurement, this can easily apply to three stage rockets.

In other words, the fact that the slide used payload to LEO as a unit of measurement is in my opinion not indicative that the measurement is done on an LEO-optimized two stage rocket, as opposed to the LTO-optimized three stage rocket as shown hypothetically flown on an LEO mission.


I think you are mistaken in focusing on thrust. Thrust has no bearing on payload capabilities. This is a consequence of the rocket equation.
View attachment 84770

As you can see, thrust simply is not part of the equation. The only factors that matter are specific impulse Isp and mass ratio mi/mf.

Of course, a real rocket's thrust must satisfy two constraints. For the first stage, the thrust at sea level must exceed takeoff weight. For the second stage, the thrust must accelerate the rocket to orbital velocity quick enough so that it does not crash into the atmosphere before that.

However, once these two constraints are met, there are no benefit to having even greater thrust, at least with respect to payload capacity. Therefore, a rocket having greater thrust does not imply more payload capacity.

Yes, #2 might be what the slide is referring to, but it also might not be.

I recall that Skylab itself was actually a converted third stage without the engines and propellant.

"... Skylab had a mass of 199,750 pounds (90,610 kg) with a 31,000-pound (14,000 kg)

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(CSM) attached

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and included a workshop, a solar observatory, and several hundred life science and physical science experiments. It was launched uncrewed into

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by a

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rocket modified to be similar to the

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, with the

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third stage not available for propulsion because the orbital workshop was built out of it. ..."

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[Blitzo]

I would say that booster version do not have an LEO mission profile at all. Falcon 9 to date has flown 142 times. Falcon Heavy 3 times. All three Falcon Heavy launches are <10 ton payload to GEO/Mars orbit.

Satellite mass has been going down. The modern preferred approach is mass constellation of small sats on low orbit. A 14 ton payload is sufficient for 99% of LEO missions.

Which again shows the 70t is just a measurement and does not imply the existence of another configuration.

I think your interpretation of that slide and the information on it is being influenced by your perception of what does and does not constitute a reasonable LEO mission.

I am less interested in what the present norms for LEO payloads are, and more interested in what the rocket's intended LEO capabilities are, given we do not know what may constitute "reasonable" payload masses for LEO going into the next few decades.

 

[Jason_]

I think your interpretation of that slide and the information on it is being influenced by your perception of what does and does not constitute a reasonable LEO mission.

I am less interested in what the present norms for LEO payloads are, and more interested in what the rocket's intended LEO capabilities are, given we do not know what may constitute "reasonable" payload masses for LEO going into the next few decades.

It seems to me that you are making more assumptions than I am. Factually, we know:
1. The slide does not show or refer to a 2-stage with booster configuration. Only a 3-stage with booster configuration is shown.
2. Payload to LEO is a common method to measure rocket lift capabilities. It has been applied to rockets that are not designed for LEO missions, and have never flown LEO missions.

My argument on the basis of these two facts is that the 70t LEO figure refers to the 3-stage configuration as shown. This is clearly the most plain reading of the information presented.

In order to argue that the 70t figure actually refer to a hypothetical 2-stage with booster configuration, you would need to assume:
1. China has a need for a LEO mission that the no booster variant's 14t payload cannot satisfy
2. The 3-stage with booster variant designed for a moon mission can be modified as a LEO-optimized configuration simply by removing the hydrolox upper stage
3. The 70t figure refers to the LEO capability of this hypothetical configuration

It seems to me that assumption 1 is poor assumption since a) 14t can meet the need for most LEO missions b)Falcon Heavy, which most closely resembles the hypothetical 2 stage with booster configuration, has been launched very infrequently compared to Falcon 9, and when launched, were always used for non-LEO missions carrying payloads substantially below the theoretical 63.8t LEO payload

3 is also a poor assumption since payload to LEO is a common measurement and thus do not imply the existence of a new configuration.

 

[by78]

The "Tianqin-1" gravitational-wave observation satellite obtained a global map of Earth's gravitational field, which is a first for China, after the U.S. and Germany.

 

[Blitzo]

It seems to me that you are making more assumptions than I am. Factually, we know:
1. The slide does not show or refer to a 2-stage with booster configuration. Only a 3-stage with booster configuration is shown.
2. Payload to LEO is a common method to measure rocket lift capabilities. It has been applied to rockets that are not designed for LEO missions, and have never flown LEO missions.

My argument on the basis of these two facts is that the 70t LEO figure refers to the 3-stage configuration as shown. This is clearly the most plain reading of the information presented.

In order to argue that the 70t figure actually refer to a hypothetical 2-stage with booster configuration, you would need to assume:
1. China has a need for a LEO mission that the no booster variant's 14t payload cannot satisfy
2. The 3-stage with booster variant designed for a moon mission can be modified as a LEO-optimized configuration simply by removing the hydrolox upper stage
3. The 70t figure refers to the LEO capability of this hypothetical configuration

Yeah, I believe all of those three are very reasonable assumptions.

It seems to me that assumption 1 is poor assumption since a) 14t can meet the need for most LEO missions b)Falcon Heavy, which most closely resembles the hypothetical 2 stage with booster configuration, has been launched very infrequently compared to Falcon 9, and when launched, were always used for non-LEO missions carrying payloads substantially below the theoretical 63.8t LEO payload

3 is also a poor assumption since payload to LEO is a common measurement and thus do not imply the existence of a new configuration.

1. I strongly disagree. I think that in coming years and decades, there will be routine needs to be able to put multiple dozens of tons of payload per launch. The fact that there have been few launches of such large payloads into LEO is because of the lack of such rockets in quantity and affordability.
3. I never said that such a configuration "exists" -- obviously the pursuit of this rocket is prioritized for lunar missions, and a LEO configuration has yet to emerge. My argument is that if they want a rocket to actually be able to put the given 70t payload into LEO, the configuration they depicted does not make sense for it.


Isn't your argument a bit self contradictory? You are saying that a 70t LEO payload is unlikely and not currently needed, and that this 70t payload to LEO is only a "measurement" and doesn't represent a true configuration -- but then you were also simultaneously saying that the depicted rocket with three stages is what you believe a 70t to LEO capable configuration.

 

[taxiya]

It seems to me that you are making more assumptions than I am. Factually, we know:
1. The slide does not show or refer to a 2-stage with booster configuration. Only a 3-stage with booster configuration is shown.
2. Payload to LEO is a common method to measure rocket lift capabilities. It has been applied to rockets that are not designed for LEO missions, and have never flown LEO missions.

My argument on the basis of these two facts is that the 70t LEO figure refers to the 3-stage configuration as shown. This is clearly the most plain reading of the information presented.

In order to argue that the 70t figure actually refer to a hypothetical 2-stage with booster configuration, you would need to assume:
1. China has a need for a LEO mission that the no booster variant's 14t payload cannot satisfy
2. The 3-stage with booster variant designed for a moon mission can be modified as a LEO-optimized configuration simply by removing the hydrolox upper stage
3. The 70t figure refers to the LEO capability of this hypothetical configuration

It seems to me that assumption 1 is poor assumption since a) 14t can meet the need for most LEO missions b)Falcon Heavy, which most closely resembles the hypothetical 2 stage with booster configuration, has been launched very infrequently compared to Falcon 9, and when launched, were always used for non-LEO missions carrying payloads substantially below the theoretical 63.8t LEO payload

3 is also a poor assumption since payload to LEO is a common measurement and thus do not imply the existence of a new configuration.

I think you have been stick to the point that 70t LEO is purely theoretic figure on paper. For that you use falcon heavy as an example to illustrate the unnecessary capability.

If we look at the planned Europa clipper mission in 2024, you would agree that the 68t LEO payload is a must have because sending the 6t clipper to MTO needs 30 to 40t LEO. In this case, you would regard falcon heavy as a two stage LEO vehicle. On top of it, there is a stage to send the clipper to MTO. But you would not count it as part of falcon heavy, but part of the clipper complex.

Now, back to CZ-5DY's 3 stage configuration, it can send 12t to MTO with a LEO mass of 70t. Here you count CZ-5DY as a 3 stage rocket. The 3rd stage departing from LEO is counted in CZ-5DY.

Do you see the issue? It is only matter of how you count the stages. If you apply the Falcon Heavy counting method to CZ-5DY, then there is a 2 stage version of it and the 70t is not just figure on paper. In the other way around, the whole Falcon Heavy launch stack is a 3 stage rocket like CZ-5DY.

So, I don't think there is a point to reject the existence of 2 stage version as pure theoretic, it is always there, it exists in the moon landing version, it exists in all upcoming interplanetary missions. It is just how and where you draw the line between what is the launcher and what is the payload.