ODE for Space Physics

[{MSX}]

The engines are fixed on the hull, not rotating (although that's an interesting idea... ).

Ok, then fixed should do the job.

Now when I call dBodyAddRelForce (becuause it needs to be relative to the body's current orientation) the engines all move off together, but the hull lags behind and does not keep up with the engines although the joint is still active as it does response to new inputs. Any ideas on how to ensure that the hull and the engines stay together?

I didn't understand the problem. Is the hull "late" in moving with respect to the engines, but still following them; or is it completely detached as if the joins wasn't there ?

In the first case, you have to adjust the joints ERP and CFM parameters. (error reduction parameter and constraint force mixing). The combination of this two values define how "loose" and how bouncy the joint is. You define them where you create the joint.
The ode guide has some nice chapter on this settings, i suggest strongly to read them (it's not a hard read), then you can experiment with values to find a model that fits your needs. I think your joints should be as fixed as possible, so it should be easy to find out.

If the hull competely detached, than probably you have some problem in your sources.. Compare it with some working project or demo.

I can post a exe to demo the problem if that will help.

I'd like to see how things are coming out
Does it work on linux too ?