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There are questions on this site about minimal sound in space. But I was very surprised by Russell Borogove's answer to "Why did the Saturn V stage faring appear to burn after separation?" that "hydrogen-oxygen exhaust is essentially clear".

Without visible and audible evidence...is spacecraft exhaust even observable in space? I suspect it still has an infrared heat signature or something. This paints a very different picture than most movie depictions of spacecraft maneuvering in space.

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  • $\begingroup$ See also space.stackexchange.com/q/20268/195 $\endgroup$ May 4 '18 at 4:16
  • $\begingroup$ "The Expanse" and some other modern visual media actually do a fair job of this -- the main engines give off a blue glow suggestive of hydrogen combustion and the attitude thrusters give off white puffs similar to what's seen when e.g. the space shuttle manuevers. youtube.com/watch?v=2ewbD2Pv5ag $\endgroup$ May 4 '18 at 4:22
  • $\begingroup$ While the question may overlap with Organic Marble's question, the answer in Russell Borogove's link was more satisfactory to my misunderstanding. Both were useful. Thank you. $\endgroup$ May 4 '18 at 4:41
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    $\begingroup$ Most exhaust from upper stages is (more or less by coincidence) clear. Additional the big clouds of smoke and steam at the beginning of a launch is usually from SRBs and water to protect the pads, both of which are usually not used in space (except as kick motors for satellites). However RCS thruster exhaust is clearly visible while docking and very prominent in ISS cargo and crew launches. $\endgroup$
    – Hans
    May 4 '18 at 8:07