.
I saw a video recently that asserts the biggest hang-up they're having with long distance space travel (if you ignore the radiation and/or shielding problem) is that it would require the travelers to grow food in transit. So far, all the experiments to get plants to grow in a weightless environment have utterly failed, and they're thinking that there must be something about gravity that enables plants to grow, such that without it, they don't grow. Therefore, it would be necessary to have an artificial gravity embedded in the spaceship if there could be any plants growing. They said that a good portion of the space station experiments have been attempts to find edible plants that grow in space.
.