I've been looking at of the STS-94 skylab launch and other launching involving asymmetrical rocket launch vehicles, mostly because I've never been able to design something similar in KSP with perfectly balanced thrust for an asymmetrical rocket. How did they balance the thrust for the first and second stages?

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In this picture of the STS-94 it seems as if the shuttle thrusters are firing to maintain the center of thrust, is this the case? How much fuel did the shuttle expend to maintain thrust balance? How would/could they have built the rocket to not require the firing of the shuttle engines in this asymmetrical design?

  • 3
    $\begingroup$ no, the engines weren't fired to maintain the centre of thrust, but they were angled so their thrust went through the centre of mass. This angle causes the horizontal component of the motion seen at launch. While the majority of the thrust is used to lift the craft, due to the divergence of the jets there is some thrust wasted, at about 10 degrees, for the first quarter of the flight (after which the boosters separate) you're looking at about a twentieth wasted. This wastage occurs at the start of the flight, where it experiences least rocket equation tyranny. $\endgroup$
    – user20636
    Commented Oct 17, 2018 at 15:44
  • $\begingroup$ Can you point out where you see thrusters firing in the picture (or any other picture or video for that matter). $\endgroup$
    – JohnHoltz
    Commented Oct 17, 2018 at 16:25
  • $\begingroup$ @johnholtz the 3 shuttle thrusters have flames coming out of them. $\endgroup$ Commented Oct 17, 2018 at 16:47
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    $\begingroup$ Ok. I misunderstood your use of the word "thruster" and was thinking of the reaction control system (RCS) in the nose and tail. The items your are referring to are the 3 main engines (SSME). As others have indicated, the angle and ability to swivel (gimbal) the engines were designed to keep the net thrust pointed in the proper direction. JCRM's comment of "about 10 degrees" implies the answer you are asking. Sine(10)=0.17, so 17% of the thrust was in the horizontal direction, cosine(10)=98% was in the vertical direction. $\endgroup$
    – JohnHoltz
    Commented Oct 17, 2018 at 17:20
  • $\begingroup$ @johnholtz thank you for the diction clarification. Ill keep that in mind for clarification on future questions. And thanks for the 17% number. The other answer does a great job of explaining that- I just didnt know it existed. $\endgroup$ Commented Oct 17, 2018 at 17:30


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