The space shuttle TVC controller included an acceleration term which kicked in above 547 ft/s to alleviate side loads caused by wind shear, etc. The acceleration term basically allowed the shuttle to fly into the wind to reduce angle of attack, and this would be done even if it took the shuttle off course (until velocity hit Mach 2.2, at which point the shuttle would go back to tracking its attitude schedule).

My question: what was the lateral load limit on the shuttle? I’ve seen charts of Falcon 9 showing a 1g limit along one of the lateral axes, I believe. How much lateral acceleration (e.g. from wind gusts) would have been acceptable in the space shuttle?


Operationally there was no such limit. The limits that were managed to in the yaw channel were "q-beta" limits, the product of dynamic pressure and sideslip angle. A "stack" of q-beta vs q-alpha limit planes, indexed by Mach number, was produced preflight and the trajectory was calculated to keep the vehicle "in the funnel".

enter image description here

See this answer for more info Upper stage structural loads on ascent? as well as a link to the source of the image.

Also, load relief in the yaw channel didn't take the vehicle "off course" - the roll channel would roll the vehicle to point it back into the correct plane.

enter image description here

Source: Ascent Guidance Workbook

  • $\begingroup$ Ah! I've been staring at that second picture for a whole day now. I can't make sense of it! Say a side wind produces a Y acceleration, causing the acceleration term of the TVC controller to yaw out of the target orbital plane, so as to reduce angle of attack in the presence of that wind. If the thrust line passes through the centerline of the shuttle, then rolling would do nothing. If the thrust line is at an angle to the shuttle centerline, then rolling about the centerline would bring the thrust line back into the orbital plane---but even then, wouldn't you have to roll 90 deg? $\endgroup$ – user39728 May 23 at 16:42
  • $\begingroup$ The illustration does suggest that the thrust line is at angle to the shuttle's centerline, but sadly... I actually don't know for sure if that's the case? I think the engine nozzles are angled at some 10 deg to the centerline when in their relaxed "centered" position? But even if so, the only I can visualize roll correction is with the shuttle rolling a full 90 deg to get the thrust vector back on the orbital plane... even for the slightest out-of-plane yaw correction... No? $\endgroup$ – user39728 May 23 at 16:47
  • $\begingroup$ See space.stackexchange.com/a/23139/6944 for the first part. $\endgroup$ – Organic Marble May 23 at 16:49
  • $\begingroup$ Perfect! So my suspicion is that load-relief in the roll-control channel was very specific to the space shuttle, as it seems to assume that the thrust vector would be at an angle to the X axis. In a rocket like Falcon 9, the thrust line would pass straight through the X axis (in the null position), so no amount of rolling would bring the thrust vector back into the orbital plane... It seems? $\endgroup$ – user39728 May 23 at 16:58
  • $\begingroup$ I've been ignoring the roll-channel load-relief term in my controller for this reason. I keep wondering if maybe I'm just misunderstanding that term and if maybe it would be useful in my model, but... it doesn't seem it could work without an offset thrust vector like the space shuttle had? $\endgroup$ – user39728 May 23 at 17:00

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