<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Correct; those are steam, as pointed out by others.The plume from the engines is actually white as well, as you can see by looking at the base of the plume after the vehicle has ascended a fair ways. It's only "brownish" near the vehicle, and I think this is actually an optical illusion. The very topmost bit is very bright, and glowing somewhat yellow. This makes the top of the plume appear yellowish or brownish on video, even though it's really white. <br />Posted by CalliArcale</DIV></p><p>Right. The plume from the solids, near the exhaust plane of the nozzle contains quite a bit of white hot aluminum oxide that is very luminous, and cools down fairly rapidly as the plume gasses expand aft of the nozzle. The light from those particles is reflected from the remainder of the plume and may account for some redish light near the vehicle. But once radiation from the plume has diminished the basic color of the plume is white. Hydrogen chloride, formed due to the ammonium perchlorate oxidizer, in the exhaust tends to form nucleation sites for condensation of water vapor, creating a vapor trail.</p><p>Some tactical missiles, in order to minimize a visible trail, eliminate both metals and ammonium perchlorate from the propellant formulation. Such formulations are called "min smoke" propellants. They are used to both to make the source of a rocket launch less detectable and to make it more difficult for aircraft to detect the missile and take evasive action. <br /></p> <div class="Discussion_UserSignature"> </div>