Angled Engines on the STS-One man asks...why?

[Fortunateson1969]

Okay-quick clarification-simply because I spent all day braining in one area and now I can't brain in another.

The SSME's on the American Space Shuttle (and possibly Buran I don't know) were angled away from CoG to counter the off-center CoG caused by the ET and the thrust caused by the SRB's right? Theoretically, the CoT vector in Kerbal Space Program would anti-point right at the CoG marker? Was that true all the way throughout the launch or were they adjusted after stagings?

I'm trying to work on a little plugin that will automatically gimbal engines to adjust the CoT to wherever it needs to be with a constantly changing CoG, and I'm trying to figure out what variables I have to account for. A quick rundown (or a super-technical webpage) would be much appreciated!

-Thankya!

[SinPistones]

The engines don't have enough gimbal range in KSP. That being said, what game me some decent results was using damned robotics and use the servos to point the engines to where I needded... It *almost* worked

Oh, and Buran didn't have main engines per se, the Energia launcher did almost all the work.

[Fortunateson1969]

The engines don't have enough gimbal range in KSP. That being said, what game me some decent results was using damned robotics and use the servos to point the engines to where I needded... It *almost* worked

I didn't say I was going to use DR, but that is my plan.

[numerobis]

EndlessWaves has already written that plugin; might want to send a PM.

[Fortunateson1969]

EndlessWaves has already written that plugin; might want to send a PM.

Yeah, if I code myself into a corner I might hit him up, but this is more a project aimed at keeping me "in shape" during the code offseason. Throw myself into an unknown codebase, using a (previously unused) language, and wa-hey at the end of it I get a nifty little doodad that makes my KSP more enjoyable.

Can anyone answer my question? I'm thinking that the thrust vector needs to intersect the CoG right in the center for controlled, straight flight. If that's the case, it should be a simple matter of drawing a triangle from the angle of the engines now, to the center of gravity at (0,0,0) and then to the "ground leg" of this triangle (let's call it the z-axis for ease).

Anyone?

[EndlessWaves]

Can anyone answer my question? I'm thinking that the thrust vector needs to intersect the CoG right in the center for controlled, straight flight. If that's the case, it should be a simple matter of drawing a triangle from the angle of the engines now, to the center of gravity at (0,0,0) and then to the "ground leg" of this triangle (let's call it the z-axis for ease).

Your approach isn't quite clear, but the combined thrust vector does need to point directly towards the center of mass to have a spacecraft that doesn't rotate. If you're doing it with all engines (including or post-SRBs) then as you say it's a simple job to rotate them to point through the CoM.

If you're trying to get the SSMEs to compensate for fixed SRBs then you can't point the SSME through the CoM as the SRBs will be generating torque to roll you but you need to find the point where they provide equal counter torque/where the combined CoT points through the CoM.

[Fortunateson1969]

If you're trying to get the SSMEs to compensate for fixed SRBs then you can't point the SSME through the CoM as the SRBs will be generating torque to roll you but you need to find the point where they provide equal counter torque/where the combined CoT points through the CoM.

I appreciate that torque will also factor into this, but only if a force is applied a distance from the center of mass (i.e. the lever arm). At least I think. In theory, my program will modify the total Thrust Vector to point through the CoG by only manipulating the gimbal (using the DR hinges) on the SSMEs-the thrust vector of any solids or asparagus stages will be taken into account by the CoT calculation already done by the game and is then included in the total Thrust Vector.

I don't know. I'm not super awesome at moment of inertia stuff and free body diagrams (especially when the CoM and the CoT aren't aligned). Darn it Jim, I'm a Computer Scientist-not an Aeronautical Engineer.

Endless-what did this plugin that was brought up earlier do? I would like mine to be able to have modes for automatic CoM/CoT compensaton, "Stowed" and manual control. I'd like it to have a graphic depicting CoM, CoT and CoL (mostly for debugging purposes), and I'd like it to not add a lot of lag to the game (my shuttles are insane, and they don't need any help in the lag department). You can PM if you want to. Thanks for your answer!

[EndlessWaves]

In theory, my program will modify the total Thrust Vector to point through the CoG by only manipulating the gimbal (using the DR hinges) on the SSMEs-the thrust vector of any solids or asparagus stages will be taken into account by the CoT calculation already done by the game and is then included in the total Thrust Vector.

I haven't investigated the game's built in CoT calculation but you do need a magnitude to compare to the thrust of the SSMEs so it may not be that useful if you only get a unit vector for direction.

Endless-what did this plugin that was brought up earlier do? I would like mine to be able to have modes for automatic CoM/CoT compensaton, "Stowed" and manual control. I'd like it to have a graphic depicting CoM, CoT and CoL (mostly for debugging purposes), and I'd like it to not add a lot of lag to the game (my shuttles are insane, and they don't need any help in the lag department). You can PM if you want to. Thanks for your answer!

Mine only did the basics, I wrote it for Tiberion for his tiberdyne shuttles. It just sits in the background and angles one engine (the SSME/OMS)to ensure net thrust for the vehicle doesn't cause any rotation (lines the CoT up with the CoM effectively). It works 'behind' the standard gimbal (feeding it the current position as it's default position), so you still get a couple of degrees of steering gimbal on top of that. The only option is to disable it.

If you don't want additional lag then I'd advise not using the DR hinges as they do use physics joints so they can rotate other parts attached to them. As you presumably won't be attaching other parts to your engine thrustVectorTransform I'd just rotate it directly (transform.rotation).