Instead of the old concept of nuclear thermal steam rocket, could we use spin in a pill shaped rocket to provide structural integrity, flight stability, energy storage, artificial gravity, and improved shielding?
Structural integrity. Spin could pull outward stiffening ultra low weight fibers with high tensile strength. It's much cheaper, lighter, and stronger to use materials of high tensile and use spin to convert the tensile to compression strength.
Flight Stability. It doesn't take much spin velocity to weight ratio to force extreme stability in the way of a frisbee. Water as propellant has high mass making this even better.
Energy Storage. If the spin is also used to generate electrical power through magnets and coils and the water is preheated, you should have plenty of potential to convert the hot water to steam, I'd think.
Artificial Gravity. Remaining spin once orbital velocity and altitude are reached could be used as spin gravity. The large pill shaped vessel now with far less water inside, could be easily habitable since water is not toxic.
Improved Shielding. Of course, any remaining water can be used as shielding under the floor. However, a rate of spin should also provide an angle to micrometeor impacts, increasing the material it has to go through a bit.
I would probably use a thin aluminum cavity under the floors wrapped with kevlar, some insulation, and then more kevlar... Use cables to the center, like a bicycle wheel.
This is a concept for launching as premade space station or deep space voyager ..