OK. *Space Cowboys *is on TNT right now. I’m glad I’m watching ‘cause the launch footage reminded me of a question I have been meaning to post for a year or so. I know a fair deal about aerodynamics and physics, and in the wake of Columbia’s destruction I read a great deal about the shuttle.
But one thing has me mystified. Why does the shuttle after clearing the tower go through what is known as “the roll program”? To explain, the shuttle rolls to the right around 90 degrees until it is oriented with its upper surfaces facing east, or downrange. Eventually, this results in the shuttle flying upside-down into orbit. As for flying in this manner into orbit I have heard a couple of explanations from NASA’s websites. Flying inverted reduces the lift generated by the shuttle’s wings to near zero to minimize induced drag and lower total dynamic forces on the structure. The attitude also puts the emergency landing sites in Africa into view through the windscreen, though this seems minor to me.
All well and good. My question is why the heck isn’t the shuttle launched with the topside facing downrange while it’s on the tower, obviating the need for the roll program. A friend of mine tried to convince me that the roll program allows them to test out their flight control systems. I think this is malarkey. If the flight control systems weren’t working properly the shuttle would not be stable at all. (Model rocket enthusiasts know what I am talking about here.)
My only guess is that NASA as stuck with the orientation of the Vehicle Assembly Building from the Apollo days. Rather erect a new building or rework the whole infrastructure of the somewhat massive highway leading out to Launch Complex 34 they said, “Screw it. Roll it out there the way it’s aligned and we’ll just roll to the proper attitude after launch.
Anyone got the dope? In sixteen years of shuttle following I’ve never heard the real story.
It could be that they like to have the orbiter ‘underneath’ to improve communications with the ground - telemetry and so forth.
Later in the journey to space (at about T+6 minutes) the shuttle rolls back so that it is ‘on top’, so that communications with orbiting satellites are improved.
Exactly. Not just the VAB and roadway orientation, but the shape of the launch pad and the placement of the flame trenches were dictated by the needs of the Saturn V rockets. The shuttle rolls on takeoff because having it take off in the correct roll attitude for ascent would require ripping up and rebuilding the entire launch pad.