Even if we are capable of interstellar travel some day, there is another problem. Those vessels must support gravity for the crew. In order to be able to maintain the ship, space travellers must have gravity pull that is close to Earth’s. As a species we are not supposed to spend long periods of time in weightlessness.
Today’s astronauts must go over special zero gravity training. This problem has many different solutions in Sci-Fi literature. Some of the technologies, providing the fictional characters with artificial gravity are explained in detail and have very sound logic, which makes them possible in the near future.
How could we achieve that?
Artificial gravity is something scientists and Sci-Fi fans desire for a long time. So there are a lot of theories about how can that be achieved. The most popular ways to provide ships with gravity are: by rotation and by field generators.
Rotational gravity is a technique you have probably seen in 2001: A Space Odyssey (1968) first. The concept is simple. Space stations and ships use the centrifugal force in the farthest ends of the big-diameter rotating ring, containing compartments.
This example is the closest science has by now. However, there are some fundamental differences between ‘normal’ gravity and the centrifugal one. Normal gravity attracts objects to each other, while the rotation effect pushes them away from the center.
Besides, if the radius of the rotating element is relatively small, each object would feel different amount of force on its ends. In other words, your head will feel greater force, compared to your feet.
This problem, however, can be reduced to minimum be building rotating rings with large radius. Another problem with this concept is the need to build the rotating element from very strong materials since centrifugal forces would be huge.
Another favourite Sci-Fi hypothesis suggests Gravity field generators/plates. They would not require neither rotation or acceleration to apply the gravitational effect required. According to Star Trek’s lore, ships use “gravity plates” installed in the decks’ floors.
Those plates generate gravitational field imitating the effect of mass that does not exist. Gravity plating could be constructed from “Duranium“ sheeting. (VOY: “Alice“). The gravity force levels of those plates can also be regulated according to various species preferences (DS9: “Melora“).
There are some speculations about discovering devices that resemble the Sci-Fi gravity plates. Yevgeny Podkletnov, a Russian engineer, has claimed in a telephone interview in 1996 that he have made such a device using a rotating superconductor producing gravitomagnetic field, but there has been no official verification and the proof was very controversial.
In 2006, researchers funded by ESA stated that they have created a similar device that demonstrated positive results for the production of gravitomagnetism, although it produced only 100 millionths of a g.
Another speculative theory is the String theory, which predicts that gravity and electromagnetism unify in hidden dimensions and that extremely short photons can enter those dimensions.
The need for longer space flights by providing spaceships with artificial gravity is obvious. There are already such proposals for manned missions, based on rotational gravity: Discovery II, Multi-Mission Space Exploration Vehicle (MMSEV), ISS Centrifuge Demo, Mars Direct. Hopefully, someday our grandchildren might be walking on the floors of space stations and spaceships, the same way we do it on Earth.