Curious Phenomena In Shuttle Launches Options

[ugordan]

One thing has been bugging me for a while now. There's a curious feature that appears in many shuttle launch videos (well, not only shuttle videos, but they're most prominent there). I'm talking about the following optical effects:


Now, my sort-of-educated guess would be this is a shockwave related phenomenon. Once the launch vehicle becomes supersonic, it creates a shockwave that compresses air at its front. This changes the index of refraction if the shocking is strong enough.
The same thing happens during an atmospheric nuclear detonation where the shock can be seen "breaking" the traces of the smoke rockets behind the detonation (in case you ever wondered what the smoke rockets were for )


I don't think it's related to optics in the tracker. Notice how the linear refraction is always perpendicular to the motion of the shuttle. What puzzles me is just how many of these linear features there are during the course of the liftoff. Furthermore, they seem to dance around each other exhibiting complex behavior one would not expect of a simple supersonic shock front...

Very interesting in any case, if anyone has more info about it, I'd be happy to hear it.
BTW, the launch video I took the screenshots from can be found at www.insideksc.com, specifically here.

[The Messenger]

I'm guessing that you are half right: That these are indeed pressure waves, but not from the shuttle flight surfaces - from fluctuations in the pressure waves caused by burning of the solid rocket propellant. Solid fuel burns quite chaotically -it's a rough ride. In addition, since they burn the entire length of the motor, there is a characteristic (very deep) resonant frequency. One of the reasons aluminum is used in solid rocket fuel is that the fluffly burn product - aluminum oxide - dampens the resonance which could otherwise build a pressure wave that blows off the nozzle or bursts the case.

The nozzles are also flexed-vectored during the launch, and this changes the direction and amplitude of pressure waves. Since your viewing angle is 'down wind' from the nozzle exhaust, the combination of both the natural variation in the burnrate, nozzle vectoring, and exhaust gas radiant heating of the surrounding air can all change the reflective index. This combination of factors is a likely cause of the visual artifacts you observe.

Edited to add: Looking more closely, it looks like the main liquid fuel is adding to the 'fire' too, so the expansion and radiant heat of all the exhaust gases is the most likely culprit.

[ugordan]

Edited to add: Looking more closely, it looks like the main liquid fuel is adding to the 'fire' too, so the expansion and radiant heat of all the exhaust gases is the most likely culprit.

I have a problem with that reasoning since one would expect the "vibrations" to expand concentrically away from the engines, yet in the third picture it's clear it always seems to be a line, not a feature centered around the engines. In fact, that "line" part is most puzzling to me. The refractions don't seem to be curved at all. That IMHO implies the refracting is taking place much farther from the launch vehicle where the shockwave starts to look like a flat front.
It probably has to do with changing speed of sound and temperature gradients in the atmosphere as the vehicle rockets skyward.
I just can't believe the shockwaves are due to the rocket exhaust, that would imply vibrations so strong they would invariably rip through every launch vehicle in existence.