People have lived in space stations for decades now, but something is wrong with them. Where are the big rotating wheels? You know the ones. They show up in old paintings of the future and, perhaps most memorably, in 2001: A Space Odyssey. Spin a great wheel in space, and people can stroll around inside with something that feels suspiciously like gravity. It seems like an obvious idea.

It is also an old idea. Much older than actual spaceflight, in fact. But to find the beginning of the space station, we have to go back to a time when powered aircraft were still several decades in the future.

A Moon Made of Bricks

In 1869, Edward Everett Hale published The Brick Moon in The Atlantic Monthly. The moon in question wasn’t natural. Hale imagined building a 200-foot-diameter sphere made from bricks and putting it into orbit as a navigation aid. Sailors could sight it and use its known orbit to determine their longitude. There was only one small problem: the thing was accidentally launched with people aboard.

That makes The Brick Moon generally regarded as not only the first fictional artificial satellite, but also the first fictional space station. Hale followed it in 1870 with Life on the Brick Moon, describing how the accidental colonists got along up there.

Hale didn’t have rockets. He proposed flinging the thing into the sky with giant flywheels, but, then again, it was 1869, so we’re inclined to cut him some slack. As the 19th century turned into the 20th, however, people started doing the math.

Konstantin Tsiolkovsky is best remembered for putting rocket flight on a sound theoretical footing. The Russian schoolteacher wrote extensively about orbital flight and space habitation, envisioning people living in orbit long before anyone had demonstrated that a liquid-fueled rocket actually worked. His ideas included rotating habitats to provide artificial gravity.

Hermann Oberth’s 1923 book Die Rakete zu den Planetenräumen — The Rocket into Planetary Space — Oberth went beyond fiction and seriously considered a permanently inhabited station. He envisioned it being periodically supplied by smaller rockets, serving as an observation and communications platform, and even acting as a jumping-off point for trips farther into space. He also suggested spinning the station to give the crew artificial gravity.

Enter The Wheel

But the space station that looks like the space station in your head probably comes from a different Hermann. Herman Potočnik was an Austro-Hungarian army officer and engineer who wrote under the name Hermann Noordung. In 1929, he published Das Problem der Befahrung des Weltraums, translated by NASA many years later as The Problem of Space Travel: The Rocket Motor.

Noordung didn’t merely say, “We should have a space station.” He drew one. His station consisted of several components, but the memorable one was the Wohnrad — literally the habitation wheel. Living quarters occupied a rotating ring connected to a central hub. Rotation provided artificial gravity, while other portions of the complex could remain weightless. He considered power, communications, observing Earth, astronomy, docking, and the practical business of living in orbit. NASA calls his work one of the first detailed technical designs for a space station.

If you have seen Wernher von Braun’s famous wheel station from the 1950s, you may notice something. Von Braun certainly knew Noordung’s work — he had cited it years earlier — and the family resemblance between Noordung’s 1929 Wohnrad and the wheel station that von Braun and Willy Ley presented to American readers in Collier’s in 1952 is hard to miss. The only place we have found the articles is the reprints in Horizons, by the AIAA (start with page 46).

Whatever the exact family tree, von Braun was the man who put the wheel-shaped station into American popular culture. In 1952 he described a 250-foot-class rotating station in Collier’s, accompanied by some gorgeous Chesley Bonestell artwork. A few years later he took the idea to television with Walt Disney.

If you’ve never seen these, they are worth your time. Disney’s 1955 Man in Space and Man and the Moon let von Braun explain a remarkably detailed vision of rockets, orbital stations, and trips to the Moon to a mass television audience. A generation of kids grew up expecting this stuff. What happened?

Gravity, More Or Less

The attraction of the wheel is simple. You can’t really make gravity, at least not without bringing along a planet-sized lump of mass, but acceleration will do nicely. Stand on the inside of a rotating ring, and the floor keeps accelerating you toward the axis. In your rotating frame, it feels as though something is pushing you outward against the floor.

The acceleration is a=ω²r where (r) is the radius and (ω) is the angular velocity. Sadly, the numbers explain part of the problem.

If you want one Earth gravity at the floor, you need to either spin fast or have a large ring. For example, at 1 RPM the ring has to be 1.79 km in diameter. Speed up to 2 RPM, and you can get away with 447 meters. At 4 RPM, you are down to 112 meters.

Seems like you could just keep going faster, but there’s a problem. Four RPM doesn’t sound very fast until you are inside the thing moving your head around.

Humans can adapt to rotation, but increasing the speed makes Coriolis effects increasingly noticeable. Move your head, climb a ladder toward the hub, throw something, or even walk spinward instead of anti-spinward, and the results aren’t quite what your inner ear expects. NASA artificial-gravity studies have often used approximately four RPM as an important practical region for human tolerance, although this isn’t a hard physical limit and training matters.

There’s also a gravity gradient. Your feet are farther from the axis than your head, so they weigh slightly more. Make the radius large enough, and you won’t notice. Make the station small enough, and things get strange quickly. So bigger is better except when it comes to cost, of course.

There is another oddity that movies sometimes get wrong. The outside circumference of the wheel is the floor. “Down” is away from the hub. Imagine a tire in space. You aren’t walking around on one of the flat sidewalls with the axle beside you. You are walking around the inside of the tread. So when a movie gives you a nice conventional room with a picture window on what looks like the outer wall, stop and think about where gravity ought to be pointing. Depending on the geometry, that window would probably be underfoot.

Stanley Kubrick got this wonderfully right in 2001: A Space Odyssey. Both Space Station V and the rotating centrifuge aboard Discovery make “down” follow the rotation. The famous jogging sequence works precisely because the circular wall of the set becomes the floor as the camera watches.

Next Time

Next time, I’ll look at early attempts to make a space station ranging from TASSEL, MTSS, and MARS to real Soviet and U.S. stations that had varying degrees of success. Spoiler alert: none of them are going to rotate for gravity.

Of course, people didn’t just imagine space stations. They also imagined moon bases, both fictional and actual.