Space Shuttle question

[kidolvski]

Hello,

I recently built this space shuttle to resupply my space station and it's working perfectly fine but I was wondering if any of you guys know a good setup for the OMS. The initial ascent goes well, then during circularisation it's not very stable, I guess due to the shifting CoM. I also find the OMS a bit lackluster as it is right now. I'd appreciate any feedback from you guys.

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Thanks already!

Edited November 13, 2014 by kidolvski

[Alshain]

There isn't really a good way to do OMS in stock at the moment. The best thing you can do is angle the engines across the center of mass of the initial rocket, then use an alternate engine, like vernors, for OMS.

If you want your shuttle to be "correct" (if there is such a thing in KSP) then there shouldn't be an engine on the primary fuel tank.

Scott Manley had a

. He used RCS, but at the time vernors didn't exist. Edited November 13, 2014 by Alshain

[RocketPilot573]

I reccomend rotating the oms engines more at the orbiters CoM. Though it looks like you already pretty much did that, so maybe add more reaction wheels? That should help keep it straight.

[kidolvski]

Thanks for all the help. I'm probably gonna try adding a ton of reaction wheels to see if that cancels out the spinning.

[Hodo]

It is because your CoT when you are doing your orbital maneuvers is above your CoM. This is causing your craft to push the nose down. If you angle the OMS engines so they push through the CoM, you will push the craft at an angle through space. This is what the real space shuttle did in space.

The other option is to move your OMS engines down inline with the CoM.

[kidolvski]

I already installed a lot of SAS and it's working perfectly fine now. I just have to decrease the max thrust on the largest engine below the tank when I get higher. That and the SAS cancels out the spinning/nose-diving. Then the OMS has enough fuel to get me to my station, allowing me to dock using RCS.

Thanks for all the help.

[Brainlord Mesomorph]

I always thought the Rokomax mark 55 radials look like the Shuttle's OMS.

[cantab]

The big challenge with stock Shuttles IMHO is that the stock engines don't gimbal enough. The real SSMEs could gimbal a full 10 degrees up or down to deal with the shifting CoM of the whole vessel, the best we have is 3 degrees.

Compensating for this is we do have excellent thrust limiters - more accurately, thrust scalers. See which way the rocket wants to turn and reducing the thrust on the "outside" of the turn to bring it in line. To make use of this technique for your OMS, replace the single engines with pairs, one above the other.

[kidolvski]

Actually the I fixed the OMS' reaction to the shifting of the CoM by using a lot of small SAS modules, it can now run on 100% thrust and not go unguided. Another problem I was having were weird motions when I was trying to get into a stable orbit using the big liquid booster and the SSME but the increased amount of SAS modules fixed that as well. It's working perfectly right now. I'm gonna try to make it fly without the big LRB, but I already know that's going to give me a headache...