But if the need for artificial gravity is so clear, why bother with research in space, or on Earth? Why don't engineers simply get to work designing spinning ships, like the Hermes?
The answer is that artificial gravity requires a trade-off, because all that spinning creates problems. As on the Rotor Ride, moving your head while you're spinning that fast causes nausea. Spinning also impacts the fluid in your inner ear and any other body parts that you move while you're in a rotating environment.
And that nausea, disorientation and movement problems worsen the faster you rotate (the number of revolutions per minute [RPMs]). But the amount of artificial gravity that can be produced depends both on the RPMs and the size of whatever is rotating.
To experience a given amount of gravity — for example one-half the usual amount that you feel on Earth — the length of the radius of rotation (the distance from you standing on the floor to the center of whatever is spinning) determines how fast you need to spin. Build a wheel-shaped craft with a radius of 738 feet (225 meters) and you'll produce full Earth gravity (known as 1G) rotating at just 1 RPM. That's slow enough that scientists are very sure that nobody would get nauseous or disoriented.
Other than the floor being a little bit curved, things aboard such a craft would feel pretty normal. But building and flying such an enormous structure in space would entail numerous engineering challenges.
This means that NASA and any other space agencies or organizations likely to send people around the solar system in the future must settle for a lower amount of gravity, a faster rotation (more RPMs) — or both. Since there is no laboratory on the moon where the surface gravity is about 16 percent that of Earth's surface, making it a great place to research the effects of low gravity, as opposed to weightlessness, there simply isn't not enough data to know how much gravity humans may need for long-term space missions or space colonies. Such data is needed, as is data on how much rotation humans can reasonably tolerate, and that's the rationale for ongoing artificial gravity research.