10 Things You Didn't Know About The Expanse
4. The Spin
The OPAS Behemoth is by far the most distinctive ship in The Expanse. Immense, lumbering and utterly dwarfing everything that isn't a planet or made from protomolecule, the Behemoth (formerly Nauvoo) is instantly recognisable thanks to its huge rotating drum.
This apparatus is called an O'Neill cylinder, a speculative design for human habitation in space proposed by Gerard O'Neill in 1976. Using spin gravity, the force of momentum pulls individuals onto the walls of the drum, capable of exerting close to 1G of constant force so long as the drum spins.
It is the only vessel in The Expanse we see use this technology for precisely the same reason that we also never see the Behemoth engage in combat: it really isn't made for it. When it was the Nauvoo it was a colony ship, designed to carry generations of Mormons over to Tau-Ceti, a course that would have taken hundreds of years and see virtually no shift in the flight plan.
With the combat of The Expanse relying so much on evasive maneuvres, sharp accelerations and brake-burns, the extra gravitational forces of having a spinning drum would only be a liability. The Behemoth, like everything else in the OPA Fleet, was salvaged and repurposed for war, and its constant power failures and maintenance needs indicates this.