Long Duration Spaceflight II

I earlier discussed some design ideas for the design of a long duration spacecraft in this post, but MS Paint wasn't quite the tool to use to illustrate what I was suggesting.

Another difficult problem in spaceflight is radiation shielding, whether aluminum or water or some other material. During solar events protons with energies of over 1000 MeV can come streaming through, which is enough energy for the little solid object to not only shoot through the walls of a spacecraft, through some plants, and then through you, but to do so at a rate that is fatal in just half an hour. The greater the energy of these particles the longer it takes to stop them, and thus the thicker the shielding. The Earth's Van Allen belts shield our Shuttle and ISS crews from most of these particles, but venturing further out presents some very serious radiation hazards. During our Apollo Lunar missions we basically winged it, and stood ready to turn the astronauts around at the first sign of an impending solar storm. That won't be an option on a Mars mission.

Some have suggested that they use the water for hydroponically grown plants as the radiation shielding, but for a serious event it would make sense to pack the shielding into as small an area around the crew as possible. For a given mass of shielding material, as you try to encircle more volume, the shielding per square foot drops off, just like inflating a balloon. However, for a given shield thickness the shield mass goes up roughly with the square of the radius, though with the square root of the relative volume. What would be nice is if a large area could be moderately shielded for periods of normal particle energies, but be collapsed down to a small core encompassing just the crew during a major, once in a decade type solar storm.

There are several ways to make collapsing shielding, and with water you could pump everything into the volume held in a set of nested spheres, with the astronauts sitting out the event for a couple days surrounded by a thick jacket of water. However, during normal operations you still have a set of otherwise poorly used space taken up by such spheres, kind of like having an elephant in the living room. An water inflatable set of spheres might work, but such waterbeds can cause trouble. If leakage is a risk I suppose you could add lots and lots of Jello to the water. Of course, if the plants all died from the radiation then the astronauts would have plenty of Jello to eat, though they'd probably never touch the stuff for the rest of their natural lives.

Another method would be to provide a small central cylinder four stories tall, normally serving as crew cabins. The walls on each level would have moderate shield thickness, say a foot or so of aluminum. But you make the shielding as four telescoping segments, like a car antenna. That way the crew is normally fairly well protected and not packed in like sardines. But during a massive solar event where you need increased shield thickness, you have everyone drop into the bottom cabin and slide all the telescoping shielding down to the bottom level, providing protection four times as thick. You've then flood the basement of the bottom level with water, giving extra shielding to the floor. If you've already got a pretty thick ceiling for the bottom level cabin, then you can also exploit the fact that the room's ceiling is aimed right up the central airshaft to the hub, so radiation coming down at steep angles is blocked by the long path length through the rest of the ship. You ride out the serious storm for a few days, then telescope the shields and expand back to normal.

While I'm off thinking about how to geometrically move radiation shielding around in a more efficient and spherical fashion, here's an improved drawing of my concept featuring the habitation sphere and the air ducts leading to the thermal radiators, along with the mylar shade for the radiators.

Better Rendering of the Ship