Why We Need Artificial Gravity for Long Space Missions

In a very real sense, this type of rotation produces gravity — artificial gravity to be precise. It provides weight to your body — weight that your bones and muscles cannot distinguish from the weight that Earth, or another planet, provides on account of its sheer mass.

Consequently, for decades, science fiction writers have envisioned rotating spaceships that produce artificial gravity for astronauts during the longest phases of space missions. These phases are when they are not extra-heavy due to the ship accelerating to build up speed, or decelerating in the atmosphere, but weightless due to the craft coasting, negating the effects of gravity. For example, the International Space Station relies on its microgravity environment in low Earth orbit to have a similar effect.

Two examples of such artificial gravity in science fiction are the 2015 film "The Martian" and the 1968 epic "2001: A Space Odyssey". "The Martian" features an interplanetary craft, the Hermes, with a large, wheel-shaped section that rotates on its journey between Earth and Mars. As the camera zooms in, you notice that "up" for astronauts inside the Hermes is always toward the center of the wheel, while "down," the "floor," is the rim. This notion of centrifugal force and constant acceleration is also applied to Space Station V in "2001: A Space Odyssey", which is a spinning space station that generates artificial gravity equal to that of the moon's gravity.

Apart from mere comfort, there are good reasons why we need artificial gravity on long distance space missions. For one, in weightlessness our bodies change in ways that could be harmful when astronauts arrive at their destinations — such as Mars — or return to Earth.

Bones lose mineral content, essentially softening and becoming vulnerable to fracture. Muscles also shrink and weaken. Fluids shift toward the head and are also excreted from the body, causing changes in the cardiovascular system and lungs. Meanwhile, the nervous system is thrown out of whack.

In recent years, space medicine researchers have found what could be permanent eye damage in some astronauts. Additionally, research suggests that gravity may be required for humans to have a normal pregnancy in space. So, it almost seems like a no-brainer that any spacecraft carrying humans around the solar system either should rotate, or have some part of the ship that does.

Are NASA and others researching the possibility of creating artificial gravity? The answer is yes. Since the 1960s, NASA scientists have been considering the prospect of artificial gravity by way of rotation. However, the effort, funding and overall enthusiasm has waxed and waned through the decades. There was a surge in research in the 1960s when NASA was working on sending man to the moon. (Note: the budget for NASA at that time was nearly 5 percent of the entire federal government —10 times what it is today.)

While NASA has not emphasized research on artificial gravity over the past half-century, scientists both inside and outside of the space agency are studying a range of situations. For instance, mice spinning in a small centrifuge aboard the International Space Station survived with no problem.

Meanwhile, Earth-bound humans are learning how to adapt to zero gravity in spinning rooms. There's one at the Ashton Graybiel Spatial Orientation Laboratory at Brandeis University, while the DLR Institute of Aerospace Medicine in Cologne, Germany, is home to the DLR Short-Arm Centrifuge, Module 1. It's researching the effects of altered gravity on the human body, especially as it pertains to health risks that occur in microgravity.

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 with centrifugal force, 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, whether you're in a rotating spacecraft or a lousy carnival ride.

Plus, the 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. We basically need a faster rotation rate than we can handle.

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. While barely meeting the requirements for Coriolis force, it's slow enough that scientists are very sure nobody would get nauseous or disoriented.

Other than the floor being a little bit curved, things aboard such a rotating vehicle 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 gravity, a faster rotation (more RPMs) — or both.

A laboratory on the moon, where the lunar gravity is about 16 percent that of Earth's surface, would be a great place to research the effects of low gravity, as opposed to weightlessness. Unfortunately, that laboratory doesn't exist. Plus, there simply isn't enough data to know how much gravity humans may need for long duration missions or space colonies. Such data is needed, as is data on how much rotation humans can reasonably tolerate, and that's the rationale to continue researching how to generate artificial gravity.