China's Space Program Thread II

[taxiya]

You won't have to know the volume of the booster and density of propellant and the such of that. The 150 tons of propellant took 115 seconds to burn through which would give you an idea of the propellant burn rate (the equivalent to the expended fuel mass flow rate for a liquid rocket engine).

Here is my thought, 150t burnt in 115s gives the overall (averaged) burn rate.

Obviously, the real problem is what kind of methods to determine the actual thrust and burn rate of the solid rocket motor and how they vary throughout the test.

The inner side of the solid propellent is carved into star shaped grooves, the grooves' depth can change along the length, or the grooves' cross-section can change along the radius depends on design. So the burning surface changes which lead to the instantaneous burn rate changes over the 115 seconds, therefor instantaneous thrust changes over time.

I don't know the impact of what I am saying to the calculation of specific impulse however. But this explains the variation of thrust over time.

 

[Quickie]

Here is my thought, 150t burnt in 115s gives the overall (averaged) burn rate.

The inner side of the solid propellent is carved into star shaped grooves, the grooves' depth can change along the length, or the grooves' cross-section can change along the radius depends on design. So the burning surface changes which lead to the instantaneous burn rate changes over the 115 seconds, therefor instantaneous thrust changes over time.

I don't know the impact of what I am saying to the calculation of specific impulse however. But this explains the variation of thrust over time.

The specific impulse should be about the same throughout the burn because of the same type of propellant although the thrust may vary for various reasons.

 

[Helius]

Recap of Mengtian docking and transposition -

 

[Helius]

You won't have to know the volume of the booster and density of propellant and the such of that. The 150 tons of propellant took 115 seconds to burn through which would give you an idea of the propellant burn rate (the equivalent to the expended fuel mass flow rate for a liquid rocket engine).

Obviously, the real problem is what kind of methods to determine the actual thrust and burn rate of the solid rocket motor and how they vary throughout the test.

I take back what I said, I made the calculations way more complicated than it needed to be.

Getting mass flow rate from the simple burn rate of 150t in 115s got me the same ballpark in Isp at 383s.

Then I did it the hard way just to verify by making some assumptions of my own like substituting the missing values with those from the Space Shuttle and applying that to the same burn rate, which also got me a similar ~1,300kg/s mass flow rate. Totally unnecessary...

From there getting the exhaust velocity is easy, but 3,760m/s for this 150-tonner is really high for an SRB. That's almost 50% more powerful than the SSSRB at 2,571m/s.

 

[davidau]

Recap of Mengtian docking and transposition -

thanks so much. Nice selfies from Mengtian!

 

[by78]

The Chinese space station transiting the sun.

 

[gelgoog]

I take back what I said, I made the calculations way more complicated than it needed to be.

Getting mass flow rate from the simple burn rate of 150t in 115s got me the same ballpark in Isp at 383s.

There is no way the Isp is that high. That is the Isp of a staged combustion LOX/Kerosene engine. At best a solid rocket should be in the high 200s.

 

[Helius]

There is no way the Isp is that high. That is the Isp of a staged combustion LOX/Kerosene engine. At best a solid rocket should be in the high 200s.

Yeah that's what I thought at first. I had it pegged at the mid-270s intitially.

But then I tried to follow Quickie's math and it seems to check out -



m-dot = 150,000kg / 115sec = 1,304.35kg/s



Pretty impressive stuff if that's really what CSAC has managed to achieve.

 

[by78]

A model of YF-102 at Zhuhai Airshow.

 

[Kalec]

Yeah that's what I thought at first. I had it pegged at the mid-270s intitially.

But then I tried to follow Quickie's math and it seems to check out -

View attachment 100937

m-dot = 150,000kg / 115sec = 1,304.35kg/s

View attachment 100938

Pretty impressive stuff if that's really what CSAC has managed to achieve.

Dude, it is absolutely no way that any solid engine can have 383.9 Isp, except adding black magic into propellant.

Typical NEPE has a Isp around 260s at the sea level, and HTPB around 248s. China's best propellant is around 271-273s at sea level, by replacing Al with AlH3 into propellant. But it can't be mass produced as AlH3 has discrepancy between batches.