The image you see is an artist's rendering, of course. The Shuttle main engines used to be painted white (this is the big central tank supplying liquid hydroge

The image you see is an artist's rendering, of course. The Shuttle main engines used to be painted white (this is the big central tank supplying liquid hydrogen and oxygen to the engine). But it turned out to save about 600lb to leave it unpainted, so that's what they did for all later launches. The tank already has an insulator. You can see both versions in Shuttle launch imagery. From wiki (http://en.wikipedia.org/wiki/Space_Shuttle_external_tank http://en.wikipedia.org/wiki/Space_Shuttle_external_tank): "The original ET is informally known as the Standard Weight Tank (SWT) and is fabricated from 2219 - a high strength aluminium-copper alloy used for many aerospace applications. The first two, used for STS-1 and STS-2, were painted white to protect the tanks from ultraviolet light during the extended time that the shuttle spends on the launch pad prior to launch.[4] Because this did not turn out to be a problem and in order to reduce weight, Lockheed Martin ceased painting the external tanks beginning with STS-3, leaving the rust-colored spray-on insulation bare, saving approximately 272 kg (600 lb) of weight."