A constant-acceleration flight profile would also be a lot faster for interplanetary travel, but is impractical for any known or currently plausible reaction engine: the rocket equation strikes again. Ion or Hall-effect thrusters require only electrical power and so can more or less continuously accelerate, but they produce far too little thrust to provide meaningful pseudogravity.
Classically, the way to mitigate the medical problems of long microgravity exposure is by giving the spacecraft a rotating section, which produces enough centrifugal "down" to mostly satisfy human physiology. I understand the engineering problem involved there to be fairly severe in its own right, but most likely soluble given an established orbital manufacturing industry amply supplied by heavy lift from Earthside.
Another option might be to cable a pair of spacecraft together and spin them about their common barycenter, as I believe has been done with satellites in a few cases. Perhaps this will serve to improve the economics of Martian convict labor by increasing survival rates of transportees, while the English travel first class aboard luxury liners with spin gravity and nightly zero-G cabaret.
It's really interesting/odd that spin gravity stations have not been tested out in practice yet. Everyone just wants to do zero G experiments on their station and nothing else.
I think the dual spacecraft with a long cable is really the only practical option, since you get far too much coriolis for it to be bearable otherwise. Remains to be seen if they can make it work with two spacex starships though.
New scifi story idea: two space ships tethered to spin together, Mars-bound on a multi-month trajectory, both carrying crew[1], and one of them has the cliched space horror encounter with nasty alien life -- tell the story mostly from the point of view of the other crew. What to do?
[1]: Cargo can fly cheaper & slower, not worry about radiation exposure.
Well fusion would be too exotic to be developed in this century unless there is some unbelievable breakthrough but it is very realistic that all the micro-nuclear-reactor research & development being invested into by datacenter giants now might power a spaceship someday a decade down the road?
(the engine development would also have to advance obviously but not implausible)
It's been studied in the past (NERVA, et al.), and does seem to offer a specific-impulse advantage in the extremely high temperatures achievable by routing propellant through the reactor core. (So-called "closed-cycle" systems heat reaction mass outside a fairly conventional primary coolant loop; "open-cycle" doesn't have a coolant loop, but rather ejects hot coolant directly as reaction mass. There was also a nuclear-powered cruise missile design, I think called "Project Pluto," on this theme, although not directly related and so far as I know only studied in theory.)
It does of course still require reaction mass, but theoretical efficiency seems higher than other feasible systems; it wasn't really explored much in the old days due to the general post-Apollo builddown, and also due to the concerns of radioactive debris in case of mishap and radioactive exhaust if the system were used as a launch motor. (If not used to launch, it would need some orbital assembly and a lot of heavy lift, given not least the massive shielding required for remotely survivable crewed use.)
Another fission-based propulsion system, not relying on a steady-state reaction, was also studied under the name "Project Orion." I'll leave that one as a diversion for the interested reader, mainly because it seems unlikely anyone not already familiar would believe a word of any description I could give.
Classically, the way to mitigate the medical problems of long microgravity exposure is by giving the spacecraft a rotating section, which produces enough centrifugal "down" to mostly satisfy human physiology. I understand the engineering problem involved there to be fairly severe in its own right, but most likely soluble given an established orbital manufacturing industry amply supplied by heavy lift from Earthside.
Another option might be to cable a pair of spacecraft together and spin them about their common barycenter, as I believe has been done with satellites in a few cases. Perhaps this will serve to improve the economics of Martian convict labor by increasing survival rates of transportees, while the English travel first class aboard luxury liners with spin gravity and nightly zero-G cabaret.