Reaction wheels IRL are used in spacecraft to adjust orientation without using thrusters or propellant. In Cosmoteer terms I'm suggesting a part be added that allows players to give their ship more turning control, without having to add external thrusters. Essentially a 1x1 and large 2x2 variant part that acts like the 4 thrusters highlighted here.

Of course, it wouldn't be able to add forward or backward thrust to the ship, and would need to be placed in the center or spread evenly around the ship to be effective, but that would be the tradeoff it has for being able to save exterior space and be able to be protected on the inside of the ship. Power and energy values would be adjusted for balance, but I think this would be a neat little part to add that would help create more ship variety.