When a classmate sent me a link showing how the International Space Station (ISS) was constructed module by module it dislodged a question that has been lurking in the back of my mind for a long time. (Please note, when you click on the link, the page may take a few seconds to load. The start arrow is small, in the lower left corner.) Whatever happened to the idea that a proper space station should rotate to provide artificial gravity? That was the design pictured in the 1968 (my, has it been that long?) science fiction movie, “2001, A Space Odyssey”. The space shuttle from Earth approached the spinning station at its center, matching its rotation in the process. That scenario has some credibility because it was conceived by author and scientist Arthur C. Clarke, the same guy who first conceived the practical notion of the communications satellite.
The manned space program is probably the most glamorous and expensive single project ever undertaken by man, so most people pay attention and they probably also know that living in zero gravity is bad for your health. The ISS has been up there in one phase or another for almost 14 years now, so I know that some astronauts have stayed up there so long in zero G that they were too weak to stand up when they came back to Earth. I looked up the record and it’s held by a Russian Cosmonaut – 438 days, or more than a year plus 2 months! But anyway, zero G causes calcium to leech out of your bones, the cartilage in your joints to swell, and your muscles to weaken. The Wikipedia page for Astronauts says,
Astronauts are susceptible to a variety of health risks including decompression sickness, barotrauma, immunodeficiencies, loss of bone and muscle, orthostatic intolerance due to volume loss, sleep disturbances, and radiation injury.
Seems clear to me that a good deal of that could be alleviated by artificial gravity, so why hasn’t it been included in the design? As you can see from the construction link at the top of this post the ISS is basically a long series of cylinders of modest diameter, kind of like a man-sized version of one of those hamster habitat things and the only things they have provided to alleviate the effects of weightlessness is exercise regimes and treadmills. Why does the ISS design depend on using small cylinders? It’s a matter of well-understood engineering: pressure vessels, whether they be spacecraft or airplane fuselages, need to be small to be light in weight. Weight for a circular pressure vessel increases exponentially with diameter.
It turns out that the problem of zero G has been studied since the early twentieth century. The biological problem is laid out in a good Wikipedia page of its own under the heading, “Artificial Gravity”. The introduction says,
Without g-force, space adaptation syndrome occurs in some humans and animals. Many adaptations occur over a few days, but over a long period of time bone density decreases, and some of this decrease may be permanent. The minimum g-force required to avoid bone loss is not known—nearly all current experience is with g-forces of 1 g (on the surface of the Earth) or 0 g in orbit. There has been insufficient time spent on the Moon to determine whether lunar gravity is sufficient.
The rest of the article is thorough and interesting to anyone who likes technical detail, but the bottom line here is that while providing artificial gravity by centrifugal force is altogether practical and sensible with present-day technology, it is not economically practical. The cost of lifting weight to orbit is somewhere between $2,000 and $18,000 per pound, depending on the lifter, and just constructing the ISS the modest way it has been has run up at least $35 Billion dollars so far! Or at least until we develop and build Arthur Clarke’s space elevator.
Glamorous adventure that it is, manned space flight is wonderful stuff but when we read about NASA’s budget and follow the politics of it, I submit we need to keep in mind the impracticality of putting people up there for long periods of time, and
especially for sending them to Mars to collect rock samples. Without artificial gravity, they might be too weak to swing a rock hammer and to provide gravity would be so expensive that, well, let’s say the Tea Party would have a budgetary fit and fall in it. Or maybe not, come to think of it. They want to shrink Medicare, virtually eliminate Medicaid, and increase a Defense budget that is already half the size of the all the defense budgets of all the rest of the world put together. They might be ready to go where nobody has gone before.