Perhaps the most critical part of the Shuttle's flight is the communications blackout phase of reentry, when atmospheric plasma is directly interacting with the vehicle's heat shield. As I understand it, they had to maintain a 40 degree angle of attack during this phase of the flight, and I'm curious how this was actually achieved through the design of the control surfaces.

  • Were they hydraulically controlled?
  • What were the specifications?
  • How did they prevent plasma from entering through the hinges of the control surfaces?

I'm assuming this phase of the flight required some level of active control here, though it's possible that's incorrect. In this video, they mention "closed-loop guidance" during this phase of the flight.

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    $\begingroup$ All phases of flight had active control. Did you mean manual control? $\endgroup$ Commented Feb 7 at 21:57
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    $\begingroup$ This question is pretty broad, but the answer gives a good overview of all the sub-questions. $\endgroup$ Commented Feb 7 at 22:01
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    $\begingroup$ @ijustlovemath, as far as I know, every capsule has used attitude jets rather than mechanical control surfaces, though I've seen proposals for weight-shift control (which turns the entire capsule into a control surface). $\endgroup$
    – Mark
    Commented Feb 8 at 23:46
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    $\begingroup$ Am I correct in my impression that, during the period of high reentry heating, the actual forces are comparatively low? $\endgroup$
    – ikrase
    Commented Feb 9 at 12:01
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    $\begingroup$ @ijustlovemath - if a capsule comes in with a slight off-axis angle it will generate lift. By controlling the angle of attack they can increase or decrease lift, giving them quite a bit of control over downrange landing distance, as well as a little bit of cross-range capability. As Mark said they did not use control surfaces to change the angle. However using RCS alone would have used too much to hold an angle. The trick is that the capsule's center of gravity is purposely off-center, causing the capsule to tilt. Using small amounts of RCS to roll the capsule they can change the pitch angle. $\endgroup$ Commented Feb 10 at 3:33

2 Answers 2

  1. A NASA report says that "Three independent hydraulic systems (APU's) supply power to the surface actuators." The elevons and body flap controlled pitch and thus AoA.

  2. A full list of specifications of these control surfaces might run to hundreds of pages.

  3. Fairings and cove seals "successfully prevented the entry of 1200F hot gases into the wing/elevon joint." That NASA report has more details, and diagrams of the hinges.

  4. https://space.stackexchange.com/a/39136/1235 quotes from and links to a few mission reports, which mention manual flying or autopilot at various stages of descent.

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    $\begingroup$ Re: question 2, I'm mostly interested in the broad specifications, eg, maximum force it can reject, material choices, etc. I'm certainly not intending to build one of these in my garage! $\endgroup$ Commented Feb 7 at 22:34

Supplementary answer regarding the "specifications".

re: Material Choices

The two-segment elevons are of conventional aluminum multirib and beam construction with aluminum honeycomb skins. Each segment is supported by three hinges. Flight control systems are attached along the forward extremity of the elevons. The upper leading edge of each elevon incorporates rub strips. The rub strips are of titanium / Inconel honeycomb construction and are not covered with the thermal protection system. The rub strips provide the sealing surface for the elevon seal panels.

Space Shuttle Press Reference Manual p. 3-21


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