|Mr. Purple Cat Esq. - 2015-10-05 |
Ooooh. That looks like plasma.
In the early orbital rocket attempts they had an issue with some systems randomly shorting out when the rocket reached a particular speed/altitude. They discovered a layer of plasma was being generated around the rocket and it was conducting electricity... Rocket-science is hard!!
*Read that in the book 'journey beyond selene' by Jeffrey Kluger which is awesome!
I think it's the exhaust or some other gasses interacting with the shockwave somehow.
Plasma doesn't last anywhere near that long.
Not gasses, meant water vapor from the propelant burn.
The expanding thing is probably from stage separation
It would be extremely cool if this were plasma but likely not the right conditions to create such an event. It's probably just the way sunlight is hitting it at altitude that allows the light to expose the behavior of the vapors in the upper atmosphere. Just gorgeous anyhow.
|The Mothership - 2015-10-05 |
That is some cool shit.
|duck&cover - 2015-10-06 |
|fedex - 2015-10-06 |
Here's another angle that helps make more sense of what we're seeing here
Boy, the Martians sure sound excited.
|Corpus Delectable - 2015-10-06 |
Because the exhaust from a rocket engine is traveling faster than the speed of sound within the exhaust gasses, ambient pressure is not communicated upstream and the exhaust gasses can therefore exit the nozzle at a static pressure higher or lower than ambient pressure. (Ever wonder why the water comes out of a hose parallel to the walls of the hose? It's because the water is traveling subsonically, so the *static* pressure of the fluid is identical to the ambient pressure of the atmosphere. I never really wondered, either, until I was told.)
Anyhow, when the exhaust gasses leave at a lower than ambient pressure, they are said to be 'overexpanded,' which causes drag since you have an area of low pressure attached to the engine nozzle. As the rocket ascends through the atmosphere, the ambient pressure drops, and the engine becomes first 'properly expanded' and then 'underexpanded.' When the engine is underexpanded, the gasses leaving the nozzle turn immediately outward and seek static pressure equilibrium with the ambient conditions, and you get this ballooning effect. As the gasses expand, they cool. For a hydrogen-oxygen engine, the exhaust products at the exit of the nozzle are mostly steam, some free oxygen and hydrogen, and a few oxygen and hydrogen ions. This pretty quickly settles down into basically steam and excess hydrogen. (Hydrolox engines are run hydrogen rich for performance reasons. It's complicated.) The Atlas V uses a hydrocarbon first stage, but you just basically add some CO2, carbon soot, and other messy stuff to the steam and hydrogen mix above. At low enough ambient pressures, the exhaust gasses can cool, in conformity with the ideal gas law, to well below the condensation point, or even the freezing point, of water. (Or even of CO2; some of what we're seeing could even be dry ice crystals.)
Et voila, the video above. The plume aborts at first stage main-engine cut-off (MECO), and you can see the second stage light up.
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