October 2, 2014 – The scene of the rotating space station from 2001: A Space Odyssey reminds me of just how much further we need to go in 2014 to achieve that science fiction dream. What’s holding us back from building a spinning station that creates artificial gravity, like the one envisioned by Arthur C. Clarke and by the builder of America’s Saturn V rocket, Wernher von Braun?
Rotating a human habitat in space takes away some of the medical conditions human spacefarers suffer from while in near-Earth orbit. Microgravity is tough on us. It causes decalcification in our bones. It weakens our heart and fools with our circulatory system. It causes us to lose muscle mass. It affects our vision. And it prematurely ages us.
So why not spin the International Space Station (ISS)? The solar panels would lose their ability to produce energy because they would no longer be in optimal position to gather the energy from sunlight. To create and maintain the spin we would need extra propellant and we would have to do frequent refueling. But the most obvious reason is we didn’t design the ISS to be spun. If we rotate it we put stress on its many modular components and rip it apart.
So why didn’t we design it to look like the station in 2001? For a number of reasons. The ISS is largely composed of thin-walled aluminum modules, from 1.27 millimeters (0.05 inches) to 7 millimeters (0.27 inches) thick. The air pressure from within exerts the force to keep the walls rigid. Windows on the station are thicker but not by much. To build a rotating station the materials used and thickness would have to be far greater. And when you consider current payload capacity of the rockets we have deployed in building the station, a more rigid, artificial gravity station, would have taken much longer to construct and would have been astronomically higher in cost. Consider that the partnering nations of the world spent $100 billion on building ISS, how would a higher price tag have been justified?
Payload consideration limits, however, can be overcome if we start using materials in space, rather than bringing them up from the gravity well that is Earth. That’s why future space stations may feature the space wheel design. Captured asteroids could provide ideal building materials. 3D printers in space could produce much of the component parts.
A way to get around building a rigid space wheel involves tethering two spacecraft together and rotating them around a central point along the tether. This would provide Earth equivalent gravity to the occupants of both spacecraft. Such an experiment has recently been proposed for a future crewed mission to the ISS aboard a Soyuz.
But a rotating space wheel would have considerable advantages. It could feature a central microgravity hub where humans could conduct experiments. Along each spoke radiating to the outer rim human crews could use variable gravity conditions for other forms of experiments, or even condition themselves to lower gravity in anticipation of landing on a lower gravity world like Mars.
Changing the rate of spin could also alter the gravity environment. For instance, if a spacecraft were to be built to fly to Mars and were designed to spin creating artificial gravity, at the beginning of the trip the voyagers could experience Earth gravity conditions with a higher spin rate and as the craft moved closer to its destination the spin would slow to reduce the gravity to conditions found on Mars.
Of course spinning a spacecraft also means we have to consider its size. A small spinning craft will create artificial gravity but the force and frequency of rotations will have a negative impact on those aboard. Human crews will experience disruptive changes to the fluids in the inner ear leading to disorientation and nausea. A near disaster in the flight of Gemini 8, when it rendezvoused and docked with an Atlas-Agena target, and shortly thereafter because of a stuck thruster experienced rapid spin. The spin rate was so high it almost caused the human crew to lose consciousness. If it had we would have lost Neil Armstrong, the first human to set foot on the Moon.
The other aspect of a spinning spacecraft is the strange side affect of Coriolis Force. First described by Gaspard-Gustave Coriolis in an 1835 paper, Coriolis Force is the explanation for the spinning observed in cyclonic storms like hurricanes, and in the motion of water as it drains from a sink. It is the rotation of our Earth that creates the spin effect. If Earth didn’t rotate, then storms wouldn’t spin.
Now apply this to astronaut on a spinning spaceship. Coriolis Force would act in the same way. So if the astronaut reached to press a key or icon on a screen his or her hand would be deflected and miss. It would take some getting used to on the part of a space crew to adjust to this peculiar byproduct of a spinning spacecraft.
And despite all this spinning spacecraft remain on the drawing boards at NASA. That’s because for long duration spaceflight humans are going to need artificial gravity in some form to ensure that they survive the journey. So maybe that 2001 space wheel will come about but unfortunately not on the timetable first divined by Arthur C. Clarke. My best guess is we will see artificial gravity deployed on spacecraft in the 2020s and become integrally a part of spaceship and space station design in the 2030s and beyond.
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