I had a reader ask me what I thought of humanity’s chances of reaching and living on other worlds, and thus we have this post. For most people, the idea of interplanetary travel seems like a pipe dream. The obstacles seem to be insurmountable. However, I would assert that the only obstacle preventing us from reaching, say, Mars, is cost, not technology.
Let’s start with some of the problems that need to be overcome. The first of which is there is no gravity in space, and the effects of zero g on the human body are, to say the least, undesirable. Muscle and bone atrophy are huge problems. Your heart is a muscle, so imagine the atrophy that would take place in zero gravity for an extended period of time. Now imagine that you’re suddenly standing on the surface of a planet with earth-like gravity. Your weakened heart would have difficulty adjusting, if it could adjust at all. The same could be said of your bones. Our bone density is dependent upon gravity. Less gravity, less bone density. Depending on how long your travel through zero g took, your legs might snap like twigs the moment you stepped out of the ship and back into normal gravity. These two phenomena are why astronauts on the ISS spend a good chunk of every day exercising.
Another problem that long term deep space travel poses is radiation. Without the magnetosphere of the earth to shield them, the astronauts on any sort of deep space mission would be exposed to all sorts of cosmic radiation, constantly. And no, it wouldn’t give them sweet superpowers a la the fantastic four. It would give them cancer, and probably a lot of it.
There are several ideas for combating these two effects, and they’re all very feasible. The first idea would be to create a spinning capsule of some sort, a habitat ring for the astronauts, that would simulate earth gravity or a close approximation thereof. This is a sound principle, and mechanically there’s nothing beyond our technology required for it (think of those carnival rides that spin around, gluing you to the wall). One idea for shielding astronauts from the effects of radiation would be to simply increase material shielding, although that would require sending much heavier payloads into space, which would dramatically increases the cost. A more promising idea is using plasma to recreate the effects of the earth’s magnetic field. Sounds too sci-fi, but this is a reality: a team at the Rutherford Appleton Lab (RAL) has created a working model. I don’t know what it cost, but the fact remains that the technology exists.
There is a much simpler solution to these two hurdles, though, and it involves speed. With current rocket propulsion technology, it would take about fifty weeks to reach Mars. But what if it only took four weeks? Well, practically speaking you’d only be exposed to 1/12 of the radiation. You’d also only experience 1/12 the muscular and bone atrophy. Another added benefit of traveling at higher speeds would be the simulation of gravity. If you could reach high enough velocities, the thrust that a ship generates might be able to create “weight” for the astronauts on board. And since “up” and “down” don’t technically exist in space, you could essentially design a ship that would allow you to walk around while under thrust.
So how do we travel that fast? Well, there are two technologies currently available that could realistically deliver those kinds of a results. The first is the solar sail. Photons, the packets of energy that make up light, hit a reflective surface and push the sail forward, just like the wind on a conventional sail. The materials for this exist, and there have been successful tests of small probes that use solar sails. There are two disadvantages to using solar sails. The mass of a photon is almost negligible, ergo the acceleration of a craft using a solar sail would be small, probably measures in millimeters per second–although the upper limit of your speed could theoretically be up to 20% the speed of light, so solar sails are theoretically better for much longer ranged mission. Another obstacle is space debris. The material for the sail would have to be very thin, and the sail would have to be very large to collect enough light to generate any appreciable thrust. All it would take is one spec of dust to put a hole in the sail once you got up to speed. One advantage to the solar sail, though, is that there’s no need to carry fuel (the sun is your fuel!) and the acceleration is constant. It would take several years to reach Jupiter with a solar sail, but if you could use a plasma shield like the RAL lab has developed, you wouldn’t have to worry about radiation, and if you constructed a spinning crew module, you could potentially mitigate the ill effects of zero g upon the body. Here’s an artist’s rendering.
And here’s a real life solar sail:
A much more promising and feasible idea is nuclear pulse propulsion (NPP). NPP is a very simple premise: a ship is constructed with a concave pusher plate in the aft section; a nuclear bomb is denoted some distance from the ship, and the energy is captured by the pusher plate and the ship is propelled forward. The beauty of this idea is that a) we have pretty huge stockpile of nuclear weapons on earth essentially just sitting around doing nothing, and b) you can reach high velocities much faster than you could with a solar sail. Like 8-10% the speed of light. At speeds attainable by NPP the travel time to Mars is, you guess it, four weeks. And, amazingly, the materials for this have existed since the 1960’s. The US government developed a project to create a NPP powered spacecraft called Orion, with plans drawn up by none other than Freeman Dyson (of Dyson sphere fame). Materials that could withstand repeated nuclear blasts were tested successfully (I believe they were steel spheres covered in graphite). So what stopped this promising technology? The Limited Test Ban Treaty of 1963, which prohibited the detonation of nuclear weapons in space (actually, it prohibited testing and detonation of nuclear weapons anywhere except underground, but this precludes detonation in space). And I know what you’re thinking: nuclear bomb = radiation. But you’re forgetting shielding and the plasma field! Let’s take a look at another artist’s rendering and some plans drafted for the Orion project:
So I believe that the hurdles preventing us from traveling to another planet are all entirely surmountable, right now with our current level of technology. We already know how to recycle air and water, and hydroponics could supply food. There are a lot of planets in our solar system that have ice that could be used for water and agriculture. In fact, it was recently announced that Saturn’s moon, Enceladus, has an ocean of liquid water beneath it’s frozen surface. So actually living on another planet is the relatively easy part; it’s the getting there part that poses the greatest hazards and complications. But, as I believe scientists have shown, it’s not nearly as hazardous and complicated as we think it is, and it’s only getting more feasible and less dangerous every year as technology improves.
What is holding us back, as usual, is money. Obviously these projects would cost money. But they wouldn’t cost an insane amount of money. For the amount of money we poured into the Iraq war would probably could have already constructed and launched a NPP powered spacecraft. It’s simply a matter of priority. In 2011, NASA’s budget was $18.4 billion dollars, or about 0.5% of the federal budget. And even that number is 35% of the total spending we did on scientific research. By comparison, the defense budget for that year was $683.7 billion dollars, or 18% federal spending–37x that of NASA. By 2008, we’d spent $900 billion on the Iraq war, which would be enough to double NASA’s funding for 25 years. As of June 2011, we’d spent 3.7 TRILLION to fight the wars in Iraq and Afghanistan, meaning we could have effectively quadrupled NASA’s budget for the next 25 years. So yes, there is enough money out there to fund these scientific and exploratory endeavors. It just seems that as a country, we’d rather make war than explore the universe. We obviously have a lot of growing up to do as a species.