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So I just built this unmanned rocket:

Screenshot of Kerbal Engineer Redux 1.1.1.0 rocket

Although the center of mass is in the center of the rocket it is "drifting" north when I launch it.
Since I play in career mode and I'm still very early in the game I only have access to the basic Sputnik Command Pod which does not support SAS. I tried using the WASD keys to hold against it but the rocket doesn't react to it.

  • Does the drifting happen at any particular moment? Or during the whole ascent? – Wrigglenite Jun 12 '16 at 18:33
  • It happens 4-5 seconds after the start and it makes an arc until it crashes into the ground. – Michael Pittino Jun 12 '16 at 19:01
  • What I meant to say is, does it happen when you do anything in particular? Like turning? – Wrigglenite Jun 12 '16 at 19:03
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    I think it might simply be regular irregularities that simply aren't compensated for because the Stayputnik is not outfitted with any sort of SAS, so the computer won't be able to stabilize your trajectory. In addition to that, I can't tell if this rocket is equipped with torque wheels, or if it relies entirely on its engine for any kind of movement. – Wrigglenite Jun 12 '16 at 19:49
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    As I said, you have no torque wheels. Now, I can't tell which engine you're using, but if it's one without any gimbaling, there's no way for you to turn at all. – Wrigglenite Jun 12 '16 at 20:06
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Your rocket is uncontrollable due to lack of aerodynamic control surfaces, no gimbaling in first stage, triple symmetry, excessive (non-throttlable) thrust and horrible aerodynamics of payload.

TLDR: Put that Goo and KER inside of service bay! Putting unbalanced Goo on side of rocket is a neat trick for gravity turn without any control input. And look! Your Goo is roughly on north of rocket ;)


I'll keep this answer rather short, because I wrote quite a bit about rocket designs already: Low tech rockets and Very big rockets.

(I will presume equatorial prograde launch)

Symmetry of side boosters:

  • no boosters: Keep it tail heavy and put winglets low in quad-symmetry.
  • single boosters: That won't work.
  • twin boosters: Put them on north/south axis, so it will be self-stabilizing during gravity turn (flat side toward wind, just like airplanes)
  • triple boosters: Try putting one of boosters on west so rocket will look symmetrical against air flow during early gravity turn.
  • quad boosters: Worse than twin in surfing on airflow, but offers control in four cardinal directions (unless you ride on on stack of SRB's, then you mostly go up, or explode).
  • penta boosters: Stop. Don't add more. Or add. Its KSP. But have in mind that you will leave region of sane rocketry.

Booster stage: You went with trio of SRB's, and it look its not aligned well against airflow. It also is made out of uncontrollable parts. Once it goes out of control it will only gets worse. High, and quickly rising, thrust of boosters won't let rocket stabilize on its own with aero forces. With force of 7g it might even rip apart or crush upper stages (You know rocket is too strong when it burns on ascent). Off to drawing board with that stage.

Tip: You can tweak thrust of SRB's in their context menu to lower values.

Hint: Winglets on top give you high control authority but it can be oversensitive, winglets on bottom give you stability and moderate control.

Note: Winglets on stage with gimbal capability are usually unnecessary. If you need them to fly straight, you might have design problem. For stack of SRB's winglets however are advised.

Payload: Its aerodynamic hell. Put that Goo and KER module in that service bay. Coupled with uncontrollable first stage it will make rocket fail. Also I do not see antenna nor parachutes. You won't be able to transmit science back to base nor land to recover it.

Tip: Put Science Jr. above Service Bay. When parachuting to surface Heatshield+Service Bay will easily swallow impact while Science Jr. just above Heatshield will often be crushed.

Hack: Service Bay doors can be used as powerful landing legs. Example.

Hint: Use part-offset gizmo (gizmos are those four buttons in top left corner of preview window) and put parts into nose cones. Its not cheating. Its engineering. Be a man and build your own parts ;)

Note: Stayputnik have no reaction wheel capability. Without it you can only turn it with engine power. Pack small reaction wheel and some (a lot) batteries (Swivel can recharge them).

Tricks to save that rocket:

  • Spin stabilization. Give winglets a little angle to side. (rotate with shift for change of 5° instead of 90°)
  • Start Swivel at low thrust together with boosters (SRB's are unaffected by throttle) to make use of its gimbal and electric generation capabilities.
  • Use Tail Fin or Delta-Deluxe Winglet instead of static ones. They have control surfaces.
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    Question: Do you have to start every paragraph like that? ducks&runs – vwegert Jun 14 '16 at 5:31
  • @vwegert I am unsure. I started adding hints/Notes after writing answers while editing/proofreading as a bonus (usually easily Googlable) information. No one complained so far so I kept doing it, but feel free to slap me with a trout/guideline if any exists :) – PTwr Jun 14 '16 at 5:44
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    I like it! And if you write such an extensive answer for me you may start your paragraphes with whatever you want! – Michael Pittino Jun 14 '16 at 6:04
  • "Put that Goo and KER module in that service bay." @PTwr What is "KER module"? – Mike Harris Jul 6 '16 at 13:42
  • @MikeHarris That tape recorder thing on side of Service Bay , its from KER mod (it gives you that table with numbers) . – PTwr Jul 6 '16 at 13:47

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