[X] My Assistant

[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.

[tasp]

The many protuberences of the shuttle (wings, OMS pods, rudder) all contribute to the multiple complex shock waves coming off the vehicle.



If I may be permitted (if this isn't too far off the topic), it seems about every launch I have watched closely, I will see a 'flare' or two in the shuttle main engine exhaust.

IIRC, they were even looked into during the Challenger accident investigation and were deemed 'acceptable' or some such thing.

But I have never seen anywhere, just what is it that causes them.

Tiny bits of turbine or bearings working there way through the plumbing? That sounds too scary to me to be correct.

It doesn't seem possible for there to be impurities in the fuel or oxidizer.

So does anyone know what makes the flares?

(incinerated pigeons caught in the exhaust? - that one is a joke)

[ugordan]

So does anyone know what makes the flares?

I'm not sure what flares you have in mind, but I remember a recent study that announced that every shuttle launch brought a significant amount of water vapor over the south pole or something like that. I also clearly remember iron dust being mentioned as an additional exhaust product, apart from H2O.
Supposedly, the engine wears itself out ever so slowly, but enough to detect these trace amounts.
Is there a flare visible in the specific clip I linked above? If so, at what time?

While we're off-topic, there is a Proton launch (just about the only one I have in my collection) that also exhibited a flare at an early stage of liftoff. It gave out a red flash to an otherwise blue exhaust plume.

Also off-topic, notice how the bottom of the fuel tank insulation gradually gets charred. Is this due to infrared radiation from the engines or do some of the exhaust gases actually make it all the way up there and burn the foam?
The burn pattern looks pretty sharply defined so I'd bet on gas circulation. Which puzzles me - how can gas come back up when the whole vehicle is going supersonic and the air is dragging everything downwards? Must be one hell of a turbulence!

[tty]

Also off-topic, notice how the bottom of the fuel tank insulation gradually gets charred. Is this due to infrared radiation from the engines or do some of the exhaust gases actually make it all the way up there and burn the foam?
The burn pattern looks pretty sharply defined so I'd bet on gas circulation. Which puzzles me - how can gas come back up when the whole vehicle is going supersonic and the air is dragging everything downwards? Must be one hell of a turbulence!

There is certain to be an area of flow separation and turbulent flow behind the fuel tank and with this very complex geometry and pressure distribution I wouldn't be in the least surprised by some "wrong-way" flow. Stranger things happen. There have even been cases where dropped bombs simply refuse to leave and fly along with the aircraft until the speed drops below a certain point!

tty

[GregM]

There is certain to be an area of flow separation and turbulent flow behind the fuel tank and with this very complex geometry and pressure distribution I wouldn't be in the least surprised by some "wrong-way" flow.

Wrong way flow? Were's a good example:

http://www.hq.nasa.gov/alsj/a11/ap11-KSC-69PC-413HR.jpg