2

The space shuttle used quaternions for navigation, guidance, and control which don't suffer from the singularities that affect euler angle sequences.

Yet, the attitude indicator had a digital readout with roll-pitch-yaw numbers relative to a chosen frame---LVLH, Inertial, or Reference, being the choices available to the crew.

And that roll-pitch-yaw is an Euler angle sequence which would have suffered from mathematical gimbal lock (singularities when two axes became aligned).

And two of those angles would have been limited to +-180 degrees while one of those angles would have been limited to +-90 degrees (relative whatever frame the crew had selected at the time).

So I'm curious: what would the digital roll-pitch-yaw readouts have shown when the space shuttle did a flipover of 180 degrees about the axis limited to +-90 degrees (pitch for a roll-pitch-yaw sequence)?

Or did they simply avoid flipovers about that most restricted of axes?

  • 1
    Oh wow, super cool! @OrganicMarble: is that a 180-degree pitcharound? Are you pitching up or down? I think I see the pitch angle go down while the pitch rate is positive at first? And then the pitch angle creeps up while the pitch rate goes negative? Is the pitch angle going opposite the pitch rate because you've flipped over? –  Jan 25 '21 at 01:34
  • 2
    Note that one of the few nominal switch throws during ascent was because the ADI would have been in a singularity if selected to LVLH while the shuttle was on the pad. https://space.stackexchange.com/q/36028/6944 – Organic Marble Jan 25 '21 at 01:35
  • 1
    Yes! LVLH would have been in singularity! OK, I got one thing right, then. Thanks for mentioning it, @OrganicMarble! So then that means you wouldn't use LVLH until you'd pitched over at least some? Would you ever have used LVLH during launch (before orbital insertion)? If so, what is the earliest you would have used it? –  Jan 25 '21 at 01:40
  • 2
    They went to LVLH right at the famous "roll program" since the orbiter was pitching and rolling then. – Organic Marble Jan 25 '21 at 01:42
  • 1
    Ahhhh... Any reason they didn't stick with the inertial frame? Also, am I right that the LVLH reading would have indicated zero roll and zero yaw (and variable pitch) during launch, so that zero would have meant aligned with the launch azimuth? @OrganicMarble –  Jan 25 '21 at 01:50
  • 1
    Give my answer in that linked question a read; I think it answers a lot of that. – Organic Marble Jan 25 '21 at 01:51
  • 2
    This all answers so many things. This is great. I've been wondering about this and figuring I'd just have to make blind guesses and get half of them dead wrong. Thanks again for sharing. –  Jan 25 '21 at 01:58
  • 1
    In answer to your first comment, powered pitcharound on a RTLS is pitching down - but remember you start out upside down, so your vehicle's aft with the engines is rotating down, the engines point at the Earth, then you keep pitching down, finally the engines are pointing away from KSC so you can start slowing down. Ass-backwards into the unknown! – Organic Marble Jan 25 '21 at 21:26
  • Getting here late (again)! Unsure as to what exactly the OP is referring to wrt "flipover." One such maneuver that was performed during all missions that reached orbit was the pitch change of ~220 degrees which took place directly after the deorbit burn (OMS powered) to get the Orbiter into a 40 degrees "nose high, upright" attitude prior to Entry Interface. Anecdotal embellishment: For STS-109, said maneuver took place right over Australia and the view from the front seats on the flight deck were unbelievable...never to be forgotten! – Digger Feb 25 '21 at 17:31

0 Answers0