Why was the launch guidance software of the space shuttle launch between liftoff to SRB separation open loop?

  • $\begingroup$ If the questions aims for why exoatmospheric was closed loop (was it?) but endoatmospheric wasn't then the answer is likely that there are good analytical approximations for exoatmospheric flight (were you can ignore wind) but not for endoatmospheric flight and numerical solutions were too slow at that time. $\endgroup$ – Christoph Apr 5 '18 at 13:42

Closed-loop guidance combined with shifting atmospheric conditions requires a more complex set of constraints to guarantee that the launcher remains in an aerodynamically stable attitude at all times; the constraints are slightly simpler in open-loop guidance. According to a NASA study on ascent guidance, the advantage of going to closed-loop is small enough that it's not worth the added complexity.

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    $\begingroup$ This 2010 paper introduces a method of doing closed-loop ascent optimization. They simulate around only 0,5% more mass to orbit and older methods were computationally intensive (and space shuttle area computers a lot slower) so my guess is that hard- and software at that time really wasn't worth adding but that probably changed since. $\endgroup$ – Christoph Apr 5 '18 at 13:37

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