Permanent Human Settlement of the Earth, Space and Ocean Frontiers

Monday, July 17, 2006

The Dangers of Artificial Gravity

Ralph Buttigieg

Sydney NSW
Rotating centrifuge from the movie Mission to Mars

Artificial gravity was discussed in depth here by Dennis. It can be achieved by spinning the spacecraft (centrifugal force) but , like a lot of things, the devil is in the details. I'll spare everybody the maths and instead refer you to a gravity calculator. Run a few numbers through. You will see the way to increase the gravity level is by increasing the radius of the spaceship or by increasing the spin rate. Now you don't want to make the craft too big so the RPM is important. Experiments were done years ago in a centrifuge to see what spin rate humans can handle. Its been generally agreed that just about everyone suffers no ill effects at 1-2 RPM and most people will adapt to 3 RPM. However even 3 RPM can take a while to adapt, a bit like sea sickness. After that the number of people who can acclimatised rapidly drop off. Hardly anyone can handle 6RPM + . The trouble is severe nausea and dizziness caused by the Coriolis effect. An explanation of the Coriolis Effect can be found here but is I understand it, the problem is that your head will be traveling faster then your feet and head movements will cause illness. This meant that the internal centrifuge on 2001 Space Odyssey's Discovery , Dennis's favorite fictional spaceship, couldn't be used as it rotated at 6 RPM.

Engineers have tried to get around this problem by designing large space habitats. The main advantage of the Stanford Torus habitat design of the 1970's was that the RPM could be kept down to one. Others had spaceships spinning from lengthy cables attached to a counterweight.

Well, recent studies indicate people are more adaptable then previously thought. Previous experiments have taken test subjects from zero to full rotation in one go. The new tests had the subjects taken up in steps and had them preform exercises at each stage. It now appears people can adapt to well over 6 RPM, perhaps over ten.

Theres experiments have produced some interesting results:

Other discoveries surprised the researchers, too. For example, after rotating for a while, people in their study no longer perceived the Coriolis effect. The veering pull on their arms and legs seemed to vanish. Their brains had compensated for it, so their minds no longer took notice of it.

Even stranger, when test-subjects first return to a non-rotating environment, they report feeling a Coriolis-pull in the opposite direction. It's just a trick of the mind, notes DiZio. After another 10 to 20 attempts at a goal-oriented motion, their brains readjust to the non-rotating world, and the phantom effect goes away.

DiZio and Lackner have found that people can adapt to rotational speeds as fast as a carnival-ride-like 25 rpm. That's about as fast as people turn their bodies during day-to-day life. For comparison, a spinning spaceship would likely rotate more slowly, perhaps 10 rpm, depending on the size and design of the craft.

It looks like Arthur C Clarke may have been right after all.