"filth" falling off rockets after lift-off

[KSK]

Make me wonder why they keep the open structure instead of covering during launch if as it must create drag?

Pure speculation but if the Long March relies on hot firing during staging (starting the second stage engine before the first stage has detached), you would want the open structure to relieve pressure in the interstage and stop things exploding. There was a fairly recent thread on this.

[K^2]

Looks like ice to me, probably due to the propellants, since Proton doesn't have one...

Correct. Proton does not use cryo-fuels, so there is no ice formation. Falcon 9 does. Cryogenic oxidizer, LOX, to be specific.

Even with hypergolics, shouldn't there be a small tank with neutral gas, like helium, to "fill the void" made by spent fuel in fuel tanks? Probably, also liquid and cold?

Hypergolic fuels are self-igniting. It has nothing to do with them being cryogenic or not.

As for gas used to maintain tank pressure, it can be LN2 generated, but there are a number of other alternatives. There are many gas generators that are non-cryogenic as well.

Edited May 14, 2014 by K^2

[Kryten]

As for gas used to maintain tank pressure, it can be LN2 generated, but there are a number of other alternatives. There are many gas generators that are non-cryogenic as well.

The design is ultimately a stretched ballistic missile, so I highly doubt it'd have any cryogenics, particularly something as hard to deal with as liquid helium.

[jjwb22101]

Yeah, the Falcon one is ice. Apparently, before launches of the Saturn V, they would sometimes get small snowstorms near the launchpad due to the cryogenic fuels, which I think is really cool! No clue as to what would be falling off the Chinese rocket, might be some sort of a sheath to make sure the hypergolic fuels don't leak (that stuff is REALLY nasty).

[Alchemist]

Make me wonder why they keep the open structure instead of covering during launch if as it must create drag?

Maybe they decided to not carry extra weight of additional fairings that would be dropped before stage separation. The thing has to be open because the next stage is ignited before previous stage cutoff - 'hot separation' as a solution to the ullage problem. Dates back to R-9 ICBM, second stage of which was later adapted as third stage of Luna/Vostok launch vehicle.

BTW, third stage of Soyuz still has droppable fairings above the interstage, but these are primarily structural fairings around the engine and are dropped when you don't have to transmit force from the bottom stages (that is after stage separation). 2nd and 3rd stages of N1 had these, too.

[deadshot462]

One reason why ice didn't really form on the Space Shuttle or its external tank was because it was covered in that thick insulation (painted in orange).