I am writing about a late 21st century starship, one with most of its complement in suspended animation, and I've come up against a design issue. Either this is a real problem for the engineers of the future, or I'm missing something simple. My design is straightforward enough. It's based on a long, slender tube (I call it the "spindle") with various sections around it. Some don't move, but four of them rotate (let's call these "wheels"), causing artificial gravity of various levels. My problem is, how does a person move from a wheel to the spindle, or vice versa? They step into an elevator at the rim of a wheel, at one g, and travel inward where they lose weight. The "spoke" (of the wheel) intersects the spindle at its roof (the spoke doesn't have to aim for the centre; it could aim for a little off-centre, like a bicycle wheel, but the problem remains), so the "roof" of the elevator opens and the occupant floats into the spindle. Seems easy? Unfortunately, for the spindle (and the ship) to have structural integrity, it must effectively be continuous from nose to tail. Where the wheel intersects it, the spindle can have a door. But the elevator roof, where it meets the spindle, is orbiting it. The occupant with the open elevator roof sees the spindle door slide past each time the wheel does a rotation. He could jump through, but risks being cut in half if he's too slow. The spindle can not have a "continuous" door around its circumference - what's holding the ship together then? Potential solutions--- 1. The whole ship rotates, so there's no difference between the spindle and wheels. I don't think this is feasible as I remember reading that the direction of spin of the wheels must be balanced i.e. one clockwise, the next counter, and so on. And whoever heard of a ship spinning through space like a corkscrew? 2. Some sort of "smartdoor", that moves its position in the spindle wall, with the wheel's rotation, leaving constant access to the spindle. This would seem to require a fantastic level of tech, though. 3. Generate my gravity from the engines. I've read about potential propulsion systems where this is a proposed benefit. It would mean gravity pulls everyone towards the tail end of the ship, and everywhere on board has gravity. There are two reasons I don't want to do this. One, it doesn't seem very feasible in the 21st century. Two, it takes away the scope for zero g fighting, which would be cool. So, any suggestions? I'd be amazed if this hasn't cropped up before. Yet it’s kept me awake at night and no amount of internet searching or diagram-making has helped, so I thought I'd ask the experts.