| ET differences The first two ET's were painted white. After that, they have been the natural color of the foam insulation. The color of the foam varies a lot. The foam originally is much lighter in color. Both age, and especially exposure to sunlight, causes it to darken. Due to slips in launch schedules, some ET's sat in storage for a very long time, so they got even darker. Also, in some photographs the color may vary due to the exposure or lighting. The only truly realyl useful color comes from photos on the day of launch and even then it depends on the lighting, exposure, and film color sensitivity. On tanks that look dark orange or rust, but also have lighter orange or yellow-orange places on them, what is that about? Two causes. One, where new foam was applied in places for various reasons. Such as building up the foam ramps that are along the right sides of the conduit lines. The other, where old foam was ground down or cut into for some reason. Only the outer part gets dark, like a "rind", so when the rind is cut away the exposed old foam is lighter in color. More recent ET's, "Super Lightweight Tanks", first flown in June 1998, are even lighter. I do not know if the foam itself is any different, or if the ET's are being produced closer to the time of launch rather than being stored for a very long time. In any case, the tanks can have an almost butter-yellow color to them when they arrive, as seen below. When rolled out, they might look a little darker, but not much. The big thing is that being exposed to sunlight for weeks on the pad, the foam gets significantly darker. But the RSS covers a lot of the tank from direct sunlight. So when the RSS is rotated back for launch, the ET has a sort of a "sunburned look", the exposed areas are darker than the areas protected by the RSS. The SLT's have other differences than color. The ET nose is graphite composite, as is the intertank access door and Lox line fairing. As well, the intertank region shows a webbed stringer pattern that was completely filled-in flight with foam ever since some of the early shuttle flights.But unlike the early ET's there are some horizontal portions that are flush. See the first photo below left for a great view of this. |
