So, unless there's a good reason, you always want to launch with as little orbital inclination as you can. The maximum orbital inclination (unless you have money to throw out the window) is then 90 degree and that would put your ship in a polar orbit, which is the most expensive one. By doing so you lose some of the earth initial speed and your launch would cost more money or you would have to compromise on weight to accelerate faster. If you need to fly over land that is half way toward the North Pole you would then have an orbital inclination of 45 degrees. Logically we want to fly above more than a single strip of land and that's where the roll is used. That would obviously put your ship in an orbit that fly strait above the equator. Why is that? Well, at the equator the rotation speed (relative to a fix point in space) is at its maximum and that is free speed that your ship will not have to generate. The cheapest way to put something in space (satellite or shuttle) is at the equator while launching due East with an orbital inclination of zero degree (relative to the plane that cuts the earth at the equator). This is what I understand about the roll manoeuvre. Even unmanned rockets have roll and pitch programs including today.įrom: St-Jean Chrysostome, Quebec, Canada I believe antennas are involved in all of the rolls to some degree. I believe it was to orientate the crew cabin to view the horizon during launch. The costs to add such a feature to the crawlerway are so high that it was much cheaper to turn the shuttle in the air than it was to turn it on the ground.īegs the question, why did Apollo also have a roll program? It was after all a symmetrical tube. So, whatever leaves the VAB for the pads ends up facing the same direction as when it left. The crawlerways are specially constructed to handle the immense weight of the crawler, mobile launch pad, and the shuttle stack but they have no place to turn around. We mate the shuttle with its tank and boosters in the Vehicle Assembly Building, and then it is transported to the launch pads along the crawlerway by the crawler/transporters, some of the largest tracked vehicles ever made. While there are antennas on the lower side of the vehicle, they are blocked by the external tank and the solid rocket boosters.Īs for the second part of your question, why not start out in this position in the first place? The answer stems from the fact that we are reusing facilities built for the Apollo program. More about the roll program from Ask The Expert: The shuttle rolls to an inverted position just after launch so that it can point antennas on the top surface of the vehicle at ground tracking stations. With the shuttle on the bottom, it is "pushing" on the other components, with the resulting compressive forces being easier to design for, with regards to the interface. With the shuttle (and its SSMEs) on top, it would essentially be "pulling" on the ET, putting a lot of stress (tension) on the mounts. If I remember (and can translate!) correctly what one of the NASA engineers told me, the difference this makes has to do with the position of the orbiter and the rest of the stack.
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