By the 2300s, the Solar System was held together by fusion-driven spacecraft like this passenger ferry, the Vagabond Saint. Ships of its class use a specialized fusion method known as sheared-flow stabilized Z-pinch fusion, in which a bolt of electricity is dumped into the plasma, squeezing it until it fuses. Rather than attempting to confine it, the plasma is allowed to flow axially to mute the various instabilities that arise in other Z-pinch devices. This also makes it a very convenient rocket engine.
When the planets are at their closest, trips between Earth and Mars can take only a few weeks, and the outer planets can be reached in only a few months. Passengers will be in freefall for the majority of the flight, except during departure and arrival burns which can generate a small amount of thrust gravity, typically between only 0.1 - 0.2 gees.