eeergo - 19/12/2006 5:06 PMWhile feeling wordlessly amazed by the images, I was thinking...How does this maneuver work? Still learning orbital mechanics... I figured that maybe they caused some extra velocity in the zenith direction by firing the thrusters, along with some velocity in the aft direction... and because of not having enough orbital velocity to achieve a higher orbit, they fall slowly again. Or do they continously fire the thrusters to control the maneuver? I didn't see any plume though... What I can't grasp is why the shuttle is always properly oriented with respect to their movement...
Flightstar - 19/12/2006 10:30 PMI don't question the skills of astronauts, but the general misconception is they are holding on to a joystick and flying the vehicle.
This is simply not acceptable to the engineers that build look after these vehicles. It's astronaut corp propoganda. Sure they are punching in commands, but its the vehicle that's carrying it out through its engineering.
Jorge - 19/12/2006 11:29 PMI'll have to take some exception to the earlier statements that orbital mechanics are not significant during flyaround... they are, and PLTs spend considerable simulator time during training learning to use this to their advantage. The flyaround can be segmented into quadrants, two within +/-45 degrees of the +/-Vbar, and two within +/-45 degrees of the +/-Rbar.
Jorge - 19/12/2006 10:50 PM Next time you're lurking around OPF2, poke your head into one of those orbiters and check out the hand controllers in the aft flight deck. They aren't just there for decoration.-- JRF
ZeeNL - 19/12/2006 8:43 PMNice stitch work, Avron! And I think at the end of next year, the ISS will be unbalanced again due to the moving of P6 to P5?
The flyaround is indeed initiated with a thrust in the zenith direction. Prior to this, the orbiter is separating along the +Vbar (i.e. along the ISS velocity vector) in a tail-to-Earth, belly-forward attitude. During the initial separation, the PLT uses the translational hand controller (THC) to maintain the ISS docking target within an 8 degree corridor on the centerline (C/L) docking camera. The flyaround is actually initiated with two actions. First, the crew commands the orbiter to point the payload bay at the Earth. This causes the orbiter to pitch nose-up, and causes the ISS docking target to rise in the C/L camera. The PLT reacts to this by pulsing the THC "up" to gradually null the motion until ISS once again appears motionless in the C/L camera. So while an outside observer sees the orbiter thrusting in the zenith direction, to the PLT it's just a matter of keeping the target centered. That probably also answers your question about how the orbiter is always properly oriented with respect to movement.Now, if the crew does nothing else, in about eleven minutes the orbiter will reach the payload-bay-to-Earth attitude and stop rotating. To keep the flyaround going, the crew next commands the orbiter to point the nose at the Earth, then 90 degrees later, the belly, then 90 degrees later, the tail. And the PLT just keeps performing THC pulses to keep ISS in the C/L camera field of view, and maintain range between 600 and 700 ft.I'll have to take some exception to the earlier statements that orbital mechanics are not significant during flyaround... they are, and PLTs spend considerable simulator time during training learning to use this to their advantage. The flyaround can be segmented into quadrants, two within +/-45 degrees of the +/-Vbar, and two within +/-45 degrees of the +/-Rbar.In the Rbar quadrants, the predominant orbital mechanics effect is a tidal effect caused by the orbiter and ISS being different distances from the Earth. This tends to pull the two vehicles apart. It's commonly called, oddly enough, the "Rbar effect". In these quadrants, the PLT mostly has to use THC "in" pulses to keep from drifting outside 700 ft, and "down" pulses (especially when moving toward the Rbar) to keep ISS in the C/L camera.In the Vbar quadrants, the predominant orbital mechanics effect is a coriolis effect due to the orbiter's radial velocity that causes the trajectory to "curl in" toward ISS. This could be countered by using THC "out" pulses, but since the orbiter DAP is in Low Z (see earlier posts for explanation), braking uses a lot of propellant and is avoided by all right-thinking PLTs. The preferred PLT technique is to "power through" the Vbar using THC "up" pulses... while this actually increases the orbiter's radial velocity, it delays the "curl in" until the orbiter is past the Vbar and once again heading toward the Rbar, when the Rbar effect takes over again.
northanger - 20/12/2006 3:46 AMHope this is OT. Somebody got a list of all possible Shuttle landing locations? Not just for STS-116, but all of them? And the list of TALs too if you got em.
northanger - 20/12/2006 8:48 AMfound this.....DoD Support to STS-116 (Discovery)http://www.norad.mil/newsroom/news_releases/2006/120606_e.html
rdale - 20/12/2006 4:22 AMQuotenorthanger - 20/12/2006 3:46 AMHope this is OT. Somebody got a list of all possible Shuttle landing locations? Not just for STS-116, but all of them? And the list of TALs too if you got em.Check the shuttle Q&A thread, I'm pretty sure it's in there, and the full manual with runway markings / pictures / etc is on L2.
