Author Topic: Long March  (Read 3283 times)

Offline Obviousman

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Long March
« on: February 11, 2017, 10:15:55 PM »
This is about the Chinese space programme, so apologies if I am in the wrong section of the board (it seemed appropriate here).

I was watching the launch of a manned Long March 2F booster (Shenzhou 7). From what I saw, I thought that - different from the Saturn and STS - it did not seem to have any hold-down clamps, and launched immediately upon booster ignition. I didn't see any thrust build up before release.

Is this correct?

Offline ka9q

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Re: Long March
« Reply #1 on: February 12, 2017, 04:38:23 AM »
The Long March uses hypergolic propellants, so ignition might look a little different from rockets burning either kerosene or solid fuels. Sure that's not it?


Offline Obviousman

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Re: Long March
« Reply #2 on: February 12, 2017, 06:01:42 PM »
If you have a look at this video, there is a slight delay; perhaps I just didn't notice it in the clip I originally saw?



The delay doen't seem as long in this one:



Offline smartcooky

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Re: Long March
« Reply #3 on: February 12, 2017, 07:09:47 PM »
This rocket seems rather precariously balanced.

If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline bknight

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Re: Long March
« Reply #4 on: February 12, 2017, 07:16:28 PM »
There should be some supports that retract just before liftoff otherwise it wouldn't stand long with high wind conditions.
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Offline Dalhousie

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Re: Long March
« Reply #5 on: February 13, 2017, 02:04:13 AM »
The Long March uses hypergolic propellants, so ignition might look a little different from rockets burning either kerosene or solid fuels. Sure that's not it?

LM-1 through to LM-4 have ICMB antecedents (hence their propellants) and you would expect a reasonably energetic departure from the pad.

Offline smartcooky

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Re: Long March
« Reply #6 on: February 13, 2017, 03:16:49 AM »
The Long March uses hypergolic propellants, so ignition might look a little different from rockets burning either kerosene or solid fuels. Sure that's not it?

Is this why the exhaust looks more "pinkish" and "see-through" rather that the bright orange/yellow we are used to seeing with LOX/Kerosene?
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline Dalhousie

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Re: Long March
« Reply #7 on: February 13, 2017, 03:56:07 AM »
The Long March uses hypergolic propellants, so ignition might look a little different from rockets burning either kerosene or solid fuels. Sure that's not it?

Is this why the exhaust looks more "pinkish" and "see-through" rather that the bright orange/yellow we are used to seeing with LOX/Kerosene?

Yes.  More recent rockets use different propellants - LM-5 LH-LOX and RP1-LOX, LM-6 RP1-LOX, LM-7 RP1-LOX.

Offline ka9q

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Re: Long March
« Reply #8 on: February 14, 2017, 02:36:17 AM »
Is this why the exhaust looks more "pinkish" and "see-through" rather that the bright orange/yellow we are used to seeing with LOX/Kerosene?
Yes, hypergolic propellants produce a characteristically faint plume even at sea level. See also videos of Gemini/Titan II launches, and of the early (pre-SRB) models of ESA's Ariane. You'll often see a tinge of red or orange from unreacted N2O4 during ignition.

Offline ka9q

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Re: Long March
« Reply #9 on: February 14, 2017, 02:47:27 AM »
If you have a look at this video, there is a slight delay; perhaps I just didn't notice it in the clip I originally saw?
I see a hold-down delay in both clips: short, but definite. The engines probably reach "mainstage" (steady state operation) as soon as the transient ignition clouds disappear from under their nozzles, but there's still a definite pause before liftoff.

You want the hold-down to be long enough to allow all engines to reach operating pressure, but not so long that you just waste propellant.

Offline Obviousman

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Re: Long March
« Reply #10 on: February 14, 2017, 06:13:13 PM »
Many thanks!