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On all of the launch videos and recordings for the Space Shuttle, the mention is made from Houston (after getting through Max-Q) of "go at throttle up", indicating that the launch is ok for going back to full thrust. Is there something that the astronauts on the shuttle needed to do manually at this point, or is this just courtesy information from the ground to let the on-board astronauts know what's going on (similar to other information from the ground later in the launch in regards to being able to make it to orbit if an engine fails, etc.)?

I'd always been under the impression that for launch that the astronauts were pretty much just along for the ride and computers controlled everything in regards to controls and actions until at least the main tank is released (assuming there are no issues). So, I'm curious the purpose of this instruction from the ground.

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  • $\begingroup$ I'm going to edit the title; as correctly noted in the body of the question, the call is "go at throttle-up", not "go for throttle-up", which bears on the answer. $\endgroup$
    – Russell Borogove
    Jul 13, 2017 at 20:32

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The only source I could find on the issue was a forum post, which itself did not provide any references. It seems that there is nothing the astronauts actually need to do, it is just a status check between the crew and mission control.

“throttle up” is usually complete by about 56 (for station trajectories) seconds into the flight…the call made by Houston, “Go At Throttle Up” is not a command but rather a status check/comm check performed at that point…think of it as “you are go at (this point in time)”…The engines are already throttled back up and Houston has looked at all of the data an they like what they see.

The text is a little ways down, a search "Go at throttle up" in your browser should quickly pin point its location.

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    $\begingroup$ On that forum, Jim is a reference in and of himself. His posts nowadays tend to be short (I think he mentioned a hand surgery, which would explain the brevity these days), but his early posts are full of war stories that make for a great read. $\endgroup$
    – Tristan
    Jul 14, 2017 at 16:36
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    $\begingroup$ Keep in mind that, at the time of the "Go at throttle up" transmission by Mission Control, it had been almost a minute since the last time the crew had heard from them (at the "Roger roll..." transmission). $\endgroup$
    – Digger
    Jul 14, 2017 at 20:16
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So far as I understand it, that throttle up is a significant event during launch; as the Shuttle (or other rockets) accelerate toward the speed of sound, aerodynamic forces increase toward a peak (Max Q). Engines are throttled down as the vehicle approaches this point to reduce stresses. Since the vehicle is ascending while this is happening, it is passing through progressively thinning atmosphere, which will generate progressively less aerodynamic forces for any given speed. Once the vehicle has safely passed through Max Q (and aerodynamic forces decrease), the engines can be throttled back up again. The "go at throttle up" would be an indication that everything is still good at this point in the flight.

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    $\begingroup$ You imply that Max Q is at the speed of sound, but it is really the point where the increasing speed of the rocket is outweighed by the decreasing density of the atmosphere as the rocket climbs higher and the dynamic pressure decreases from that point on. $\endgroup$
    – user8269
    Apr 5, 2018 at 17:12
  • $\begingroup$ @PhilipNgai fair point. I just assumed they would coincide. $\endgroup$
    – Anthony X
    Apr 6, 2018 at 23:40
  • $\begingroup$ For the Saturn V, max Q was about 15 seconds after mach 1. i.stack.imgur.com/RWzJt.gif $\endgroup$
    – user8269
    Apr 16, 2018 at 6:33

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