Long March

[Obviousman]

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?

[ka9q]

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?

[Obviousman]

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:

[smartcooky]

This rocket seems rather precariously balanced.

[bknight]

There should be some supports that retract just before liftoff otherwise it wouldn't stand long with high wind conditions.

[Dalhousie]

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.

[smartcooky]

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?

[Dalhousie]

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.

[ka9q]

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.

[ka9q]

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.

[Obviousman]

Many thanks!