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Thread: How does a space shuttle go straight up?

  1. #1 How does a space shuttle go straight up? 
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    From all the photos I've seen of the space shuttles, on the launchpad, their center of mass is not in the middle, but in the back, at the liquid fuel tank. Plus there are two solid thrusters.
    So on the launchpad, the shuttle should fall onto the ground, shuttle first, or if they provide enough support, once launched, it should turn and then crash, but that doesn't happen.
    Why doesn't that happen? How do they defy the laws of physics? Do they turn the thrusters to go straight up?


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    Yes, the thrusters can be direction oriented once the engines have ignited.
    Which is what they do, since each thruster is on gimbals, the thrust is properly aligned.

    Prior to engine ignition, there is a series of 8 posts that are bolted to the System to hold it upright. These are released by explosive bolts after engine ignition and the thrusters take over.

    Edit: Ok, I went ahead and googled it and found a GOOD resource here:
    http://www.interspacenews.com/Featur...t.aspx?id=2130
    You can scroll down to "Launch Sequence" and get right to the meat of your question... Or start at the top and get entranced as I did...


    Last edited by Neverfly; June 16th, 2013 at 04:56 AM.
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    Forum Professor jrmonroe's Avatar
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    Also, all sorts of surfaces of the launch vehicle produce "lift", so for example, the shuttle wings are providing "lift", which draws the launch vehicle off track. Or the vehicle may orient itself to cause the shuttle wings to produce zero or minimal lift. The connections that hold the components of the vehicle together must be able to withstand these differences in forces (that is, "lift" perpendicular to the vehicle's velocity vector, as well as "drag" and "thrust" along the velocity vector).

    Also keep in mind that rockets (here it's the solid boosters and also the combo of the liquid tank and shuttle) cannot endure large irregular perpendicular forces because they will snap in two. By "irregular", I mean irregular along its length. A rocket moving at an angle through the air produces most of its "lift" near its nose, and less elsewhere.

    Anyways, the vehicle probably doesn't fly "straight up" for very long, as it must soon angle over a bit to start accumulating its orbital speed.
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    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by dhamaniasad View Post
    From all the photos I've seen of the space shuttles, on the launchpad, their center of mass is not in the middle, but in the back, at the liquid fuel tank. Plus there are two solid thrusters.
    So on the launchpad, the shuttle should fall onto the ground, shuttle first, or if they provide enough support, once launched, it should turn and then crash, but that doesn't happen.
    Why doesn't that happen? How do they defy the laws of physics? Do they turn the thrusters to go straight up?
    One thing to realize is that looks can be deceiving. Most of the mass of the shuttle at launch is in the solid boosters and external tank. This puts the center of gravity a lot closer to being in line with the solid boosters than you might first guess. Also, while it is not always apparent, the main engines at the back of the shuttle also are providing thrust during lift-off. This means that the shuttle's weight is supported at three points. By balancing the thrust of these engines and directing them by gimbals, They can control the attitude of the shuttle.
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  6. #5  
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    Quote Originally Posted by Janus View Post
    Quote Originally Posted by dhamaniasad View Post
    From all the photos I've seen of the space shuttles, on the launchpad, their center of mass is not in the middle, but in the back, at the liquid fuel tank. Plus there are two solid thrusters.
    So on the launchpad, the shuttle should fall onto the ground, shuttle first, or if they provide enough support, once launched, it should turn and then crash, but that doesn't happen.
    Why doesn't that happen? How do they defy the laws of physics? Do they turn the thrusters to go straight up?

    One thing to realize is that looks can be deceiving. Most of the mass of the shuttle at launch is in the solid boosters and external tank. This puts the center of gravity a lot closer to being in line with the solid boosters than you might first guess. Also, while it is not always apparent, the main engines at the back of the shuttle also are providing thrust during lift-off. This means that the shuttle's weight is supported at three points. By balancing the thrust of these engines and directing them by gimbals, They can control the attitude of the shuttle.
    Yes. Presumably this must be a fairly dynamic balance, since as the fuel in the tank is consumed and it gets lighter, the CG will migrate closer to the shuttle. I notice the shuttle rolls over so that it is "under" the tank and boosters as the vehicle veers off vertical and starts accelerating horizontally to gain orbital speed. Then when the boosters run out there must be another correction in the opposite sense, since you then have the shuttle motors only, whereas the remaining weight of the fuel tank means the CG would again not be aligned with them.
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    An even trickier proposition presents itself when the shuttle is brought out of orbit: it cannot simply continue circling the Globe and be expected to achieve landing at a chosen place. Thus, it is placed into, usually, two gigantic gradually-descending "screws" of something like 400-mile radius, the exit from the last gradual bank/descent bringing it straight towards it's runway. Amazing feat, no doubt! jocular
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