karyn@nssdca.gsfc.nasa.gov (Karen C. Pichnarczyk) (09/15/90)
About why the shuttle turns as it launches: I haven't followed the entire discussion, but my non-scientific instincts say that if the shuttle didn't fly upside down, wouldn't the force of gravity tend to want to turn the whole shuttle (tanks and all) into the 'upside down' position? So the shuttle does it manually so that gravity won't mess with the trajectory. I would think if the angle of ascent wasn't so great, the problem wouldn't be so pronounced. Karyn Disclaimer: Remember, this is from someone who has had absolutely no physics or higher science (excluding computer science) since high school. Don't make too much fun of me.
brettvs@blake.u.washington.edu (Brett Vansteenwyk) (09/17/90)
Regarding gimbaling of the SSME's, sometimes the cameras will focus in on these just as they light up--the adjustment between quiescent and 100% (plus structural loading) you see a LOT of gimbaling. It is interesting to watch (though you only get to see 2-3 seconds). The shuttle flies "upside down" to minimize aerodynamic stress on the ENTIRE system--mostly the external tank (which, ironically enough, was originally considered one of the weakest links of the shuttle system). I think this was mentioned before, and while it would be hard for me to explain without doing a lot of drawing (I'm not good at ASCII-art), you can consider the following notion: in the "shuttle down" position, the SSME's are more underneath the c.g. of the entire vehicle, thus less of an angle of attack. The cross- sectional area of the SRB's is considerable, at least comparable to that of the wings on the shuttle, thus minimizing the angle of attack is very desirable. The tank connects the SRB's and the shuttle into the whole system--it would seem reasonable that the largest stresses are here. And to think that this remarkable piece of engineering is the only part of the shuttle system that is thrown away! --Brett Van Steenwyk
daveb@athena.mit.edu (Dave Balkwill) (09/18/90)
Thinking about things in a cylindrical coordinate reference frame fixed with the structure, it would seem (IMHO) that the aerodynamic stresses, lift vectors, and centres of stress and thrust are all the same (relative to each other) independent of the roll. The only things that seems to change is the direction of gravity, unless of course there's a real nasty cross wind. Is the effect of gravity really that stressful? Or am I missing something here? Three things that were brought up that do make immediate sense are: 1. The pilot has ground and horizon visual references. 2. ET does not block direct communications between shuttle and ground. 3. It's got to roll "upside down" sooner or later, since that's the way it orbits (if I remember correctly). What have I missed? -- ------ daveb@space.mit.edu OR wonko@athena.mit.edu --------- | "In Sweden, we play soccer in weather like this, in shorts." | | -- Bjorn Nittmo, kicker for NFL New York Giants | ----- DISCLAIMER: Of course they're only my opinions! --------