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...from common observation, I can easily conclude there is a lot of infrared (from burning, superheated fuel), ending somewhere near yellow of visible spectrum; there should be next to none of UV and higher. But how far up does it reach? Do the engines emit a considerable amount of microwaves?

This question is motivated by "How does a Falcon 9 booster know how far away the ground is?", and relevant available options.

The obvious solution is "reflected waves", but they must be in a spectrum not obscured by the engines. Ultrasound, or anything audio is right off, with the enormous level of audible noise. A laser (visible or IR) distance measurement will have the dot lost in the bright flame. I wonder how viable microwaves are, though - essentially, a radar.

For example, during a spacecraft reentry, the communicational blackout is caused by the plasma of superheated air and ablator, radiating on a spectrum broad enough to flood both long waves and x-rays with enough noisy energy to make them not viable for communication. Rocket exhaust is much less energetic, but it's still one of most energetic large-scale emissions achieved by technology and I wouldn't be surprised if it exceeds the standard "visible+infrared" range of "burning stuff".

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    $\begingroup$ I think the spectrum of a rocket flame is going to vary a lot depending on the type. (Kerosene, Hydrogen, various solids, hybrid etc.) A quick example here. $\endgroup$ – Andy Jun 20 '16 at 13:55
  • $\begingroup$ @Andy: The best answer would contain a full overview. A good one will give the brackets. An acceptable one will give a typical example. $\endgroup$ – SF. Jun 20 '16 at 14:07
  • $\begingroup$ @Andy: The problem with the paper you linked is that it cuts the graphs off way early, the highest going to 800nm and it seems the cut-off point is the limit of their equipment rather than end of the emission band. Only the calcium graph is "extinguished" reasonably on both ends, but does anyone seriously use calcium in rocket fuel? I mean, I know you can load up any crap into the hybrid engine and it will still work, but does any calcium compound contribute anything? $\endgroup$ – SF. Jun 20 '16 at 14:20
  • $\begingroup$ By the way I wouldn't expect the article I linked to be acceptable as an answer - just an example of the sort of research that has been done previously (yes that one's only around the visible range). It has one item in the references mentioning IR and UV for example; if someone can find a copy of that that it might make an answer. $\endgroup$ – Andy Jun 20 '16 at 14:36
  • $\begingroup$ @Andy: Definitely so. I'm most interested in the upper bond of the spectrum: how much interference does the engine cause to microwaves=radar. $\endgroup$ – SF. Jun 20 '16 at 19:21

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