Dreamcatchers. Circles of thin webbing hung by your bed to ward off bad dreams. In space it’s not bad dreams that you have to worry about as much as space itself. And not so much the utter emptiness and cold of the vacuum, but rather what is constantly streaming through that vacuum. Spacecraft outside the Earth’s protective magnetic fields are constantly bombarded by a rain of ionizing radiation—protons, neutrons, cosmic rays, and other exotic stuff. It’s not the big rocks in the asteroid belt, or comets from the Oort Cloud that threaten long-range spaceflight. It is the tiny, indeed the subatomic, that pose the greatest threat.
The Earth’s molten iron core spinning along with the rest of the planet generates a huge magnetic field that extends far out into space. That magnetic field shields the Earth and all life on it from the harsh radiation streaming from the sun and from stars, supernovae, and black holes throughout the universe. Without it, that radiation would shatter and scramble complex organic molecules like our DNA, effectively keeping life from evolving or perhaps even getting started. Humans placed unprotected outside Earth’s magnetosphere will most likely have shortened, cancer-ridden lives.
This is a problem that most science fiction writers just seem to ignore, which is fine for space opera or far future stories with lots of unexplained technologies. But, for near-future and very hard science fiction, writers ignore the problem at their peril.
So, imagine you’re spending years on a mission in an L-4 ship to a nearby star. What methods might help? Well, you could sheath the spaceship in a thick layer of lead, but adding that much mass just makes the whole propulsion problem that much worse. You could posit a lighter, as-yet undiscovered material for the ship’s hull. Or, advances in medical science could allow the crew to continually repair any damage done by the radiation. There are lots of solutions we could think up out of the blue with no basis in reality, but as the great science fiction writer Larry Niven said, a little bit of the element Ballonium is OK, but too much is a poison.
So, what advancements in known technology could solve this problem? You could, for instance, generate your own magnetic field around the spaceship. It would have to be extremely powerful, extending far enough out from the ship to divert the incoming charged particles around it rather than through it. Putting your stores of water just inside the hull would help slow down or stop the neutron flux, as well. Of course, generating a magnetic field strong enough to protect the crew without screwing up all of the instruments and equipment on board would take some pretty interesting engineering—the advancements in known technology I mentioned above—and a lot of electrical power. We need power to run the ship, power for the L-4 drive, and lots of power for the magnetic shield. Where can we get it.
Back to Mr. Niven. In many of his Known Space stories, he used a magnetic “ramscoop” to draw in those alpha particles, which are actually hydrogen nuclei, or just plain protons and slam them together so they fuse into helium nuclei and release enormous energy. The fusion reaction sped up the resultant helium enormously, which served as rocket exhaust. In effect, the ramscoop pulled the fusion rocket’s fuel from the surrounding space. Very clever.
We don’t need the complexity and danger of a fusion rocket, though. We have the L-4 drive, after all. What we need is the fusion-produced energy to be converted to electricity. We sort of know how to do that today based on experimental fusion power generators, and scientists are hopeful that the engineering problems they face will eventually be overcome. Our ramscoop power plant has a different set of challenges, of course, but in general it’s OK to assume engineering problems will be solved, rather than assume the invention of new science (which we’ll get to in future articles).
A reactionless thruster, the L-4 drive; a magnetic shield to protect the crew from the onslaught of radiation; and a live-off-the-land power source. That’s all we need to get people to the stars, assuming they’re willing to make it their life’s work spending years or decades getting there. I’m ignoring issues like self-sustaining, closed-cycle spaceship designs, crew hibernation technology, and a whole host of other “engineering” problems, of course. But, at least we know how to get people out there at less than c—the speed of light. Starting with tomorrow’s article, we’ll get very theoretical as we delve into FTL—Faster Than Light—drives. That’ll take not just engineering, but new science, as well.
May 23, 2020