While it probably won't be necessary, at least for the journey to
Mars, to apply the ultimate brute-force solution to this problem, it
still can be noted that one thing that could be done using lunar
materials is to build a world in miniature - a rotating cylinder which
provides artificial gravity not through fictional Star Trek
technology, but through centrifugal force, whose interior is covered
with soil and growing plants.

One thing that has always puzzled me is the reluctance of NASA and
commentators on the space program to even talk about creating
artificial gravity envronments in space stations and deep space
ships such as the future Mars ship. The only way we can simulate
gravity effectively is to spin the ship or station. Since it is
plain to anybody that we need simulated gravity when spending more
than a few months in space, and probably need it for more than a
few weeks to insure good health, you would think this would be
part of any design for a space station, or an interplanetary ship.
Ha! Just try to find it in NASAs near-term plans.

NASA must consider it too difficult or too expensive, but I have
yet to read a sound explanation as to why this would be the case.
I can think of designs to accomplish this myself. Arthur C. Clark
showed a couple in the ships depicted in his "2001: movie and its
sequel. The big wheel-space station design has been around for
half a century or more.

We won't be able to actually live in space without simulated
gravity. It's essential for a serious space station. Personally, I
think it's silly to even be talking about a Mars mission in a ship
that doesn't spin. By the time the astronauts reached Mars, the
poor *******s wouldn't even be able to stand up, let alone do
anything useful. All the bull**** you read about drugs to combat
the effects of weightlessness is just that, bull****. Human
biology and wightlessness don't mix. We can tolerate it for a
while, but it hurts us. Fortunately, the solution is simple. Spin
the bloody station! And spin the ship!