While being ferried on the Shuttle Carrier Aircraft, were the shuttle orbiter's control surfaces (rudder and elevons) adjusted by controls in the SCA, to assist maneuvers? (They were, after all, fly-by-wire.) Or were the control surfaces simply locked in a neutral position?

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    $\begingroup$ It would require the Shuttle apu to be fuelled and running to provide electric and hydraulic power for the operation of the rudder and elevons. $\endgroup$
    – Uwe
    Commented Jul 14, 2019 at 14:43
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    $\begingroup$ Sorry for the error about APUs electrical power, but to use the APUs to provide hydraulic power electric power is needed. So the APUs and the fuel cells should be fuelled and running to use the shuttle orbiter's control surfaces. $\endgroup$
    – Uwe
    Commented Jul 14, 2019 at 15:06
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    $\begingroup$ related but different: This answer to ISRO's space plane on top of of a rocket - how unstable was it? suggests that its control surfaces were not operating during ascent. $\endgroup$
    – uhoh
    Commented Jul 14, 2019 at 20:13
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    $\begingroup$ I think there were several test flights with the shuttle "powered up" and using its control surfaces before it was ever released. I haven't looked for verification. $\endgroup$
    – Bit Chaser
    Commented Jul 14, 2019 at 23:55
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    $\begingroup$ @bitchaser you are correct. There was, in fact, an APU malfunction on one of these captive carry flights. $\endgroup$ Commented Jul 15, 2019 at 0:41

1 Answer 1


For the Orbiter aerosurfaces to move, hydraulic pressure must be supplied from the Orbiter's Auxiliary Power Units (APUs) (a poor name for these critical devices - the name came from the analogous devices in aircraft!).

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The APUs were not running for ferry flight, and control locks were installed to hold the elevons in a neutral position.

For the ferry flight configuration, the tail cone fairing is installed on the orbiter to decrease aerodynamic drag and buffet, and aerosurface control locks are added to the orbiter's elevons. The orbiter is unmanned and the orbiter systems inert.


Ferry locks are also referenced on p. 329 here and in step 393 (pdf page 189) here (note prior step to open the flipper doors)

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    $\begingroup$ Thank you, especially for the information about the ferry locks; that's the real answer. If they had really wanted to, they could have designed an umbilical to provide electrical and hydraulic power from the SCA. The decision to implement ferry locks meant such a measure wasn't necessary. $\endgroup$
    – DrSheldon
    Commented Jul 14, 2019 at 15:31
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    $\begingroup$ @DrSheldon it would have been hugely complicated even with your umbilical - you'd have to have the flight computers powered up and running some ferry flight mode that didn't exist to provide elevon commands, something would have had to be providing cooling to the computers and to the aerosurface servoamplifiers, etc. Lock 'em down and be done with it. $\endgroup$ Commented Jul 14, 2019 at 16:15
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    $\begingroup$ So, just not worth it? I guess locking is also safer; imagine if someone misreads the instructions, mounts the orbiter upside-down, and it ends up sending control signals in the opposite direction and crashing... $\endgroup$ Commented Jul 15, 2019 at 9:18
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    $\begingroup$ @leftaroundabout I doubt anyone seriously considered using the control surfaces of the shuttle; why would they, really? For one, the shuttle is a lifting body, not a plane - it relies on the aerodynamics of the whole thing, not just the wings. For two, the control surfaces on the shuttle are relatively small compared to the carrier plane - it's primarily designed for hypersonic flight, with just enough lift-to-weight ratio at subsonic to comfortably glide and land. Even if you ignore the complexity of linking the control surfaces and electronics to the plane (1977, don't forget), why bother? $\endgroup$
    – Luaan
    Commented Jul 16, 2019 at 6:38

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