Wednesday, November 17, 2010
A One-Way Trip To Mars?
Every now and then there is a flurry of news stories about a mission to Mars and what it might look like. A few scientists, or a former astronaut perhaps, will come out with an opinion and the debate is rejuvenated in the mainstream media for a couple of news cycles. Well, yesterday seemed like one of those times, with another suggestion that perhaps we ought to send astronauts on a one-way trip to the Red Planet, so that they could build a small colony and live out the rest of their days as the first pioneers on that barren world. (Make sure you also check out this article from New Scientist on the major obstacles that will complicate any Mars mission plans for the foreseeable future).
A one-way trip to Mars is a provocative suggestion. It's certainly an unsettling prospect, but it's also quite imaginative. And of course there is some basis in history for making such an uncertain voyage: when the first settlers of the New World crossed the Atlantic, they had no more than a dim notion of what to expect when they reached their destination, and a return to Europe was hardly assured. The vast expanses of ocean were about as immense and inhospitable to them as interplanetary space is to us today. And then as now, there was no hope of rescue in the event of a catastrophe. Still, there are some problems with this analogy -- the colonists of the 15th, 16th and 17th centuries could expect there would be fresh water, flora and fauna of some kind when they landed. Life would be rough, but they would be able to live off the land sooner or later.
Though Mars is by far the most clement world in the Solar System aside from our own, it is hardly hospitable. The atmosphere is only about 1% as thick as the Earth's, and at its warmest Mars is still very cold. Mars also lacks a magnetosphere, which means dangerous radiation from the Sun is not deflected from the surface as it is on Earth (the astronauts would also have to deal with hazardous radiation on the journey itself, though perhaps their ship will be equipped with a prototype artificial magnetosphere). And liquid water on Mars' surface is impossible.
Dirk Schulze-Makuch and Paul Davies, authors of the proposal in "To Boldly Go," argue that their plan is based around preserving the health of the astronauts and kick-starting the colonization process. But from a logistical standpoint, the appeal of sending astronauts on a one-way trip would be its comparatively low cost, as just about every objective in space is weighed against the costs. The cost of sending astronauts to land on the surface and return them to Earth is prohibitive. You'd need enough propellant to get there -- and back -- and food supplies for the several-month journey each way. In space travel, weight is money. Every little bit costs something, and quite a lot in fact. On the space shuttle it costs thousands of dollars per pound of payload. And when you consider that a gallon of water weighs about 8 pounds, you can start to understand why NASA has invented a device so that astronauts aboard the International Space Station can recycle their own urine for drinking water. But for a trip to Mars we need to get this spacecraft much farther than low-Earth orbit, so you can imagine how costs will multiply.
But maintaining the health of the astronauts is still a major hurdle. In addition to the solar radiation bombardment, astronauts on a mission to Mars will endure long periods without gravity, and their bodies will deteriorate significantly. Their bones will wither, their muscles will atrophy, and when they return to gravity their weakened hearts will pump less blood into their brains. Astronauts aboard the ISS experience these same problems, but when those astronauts come back to Earth after months in space, they have a team of physicians caring for them and they get to take it easy for a while. Our first astronauts on Mars won't be so lucky. Sure, Mars' surface gravity is only about one third of Earth's, but this still poses a serious problem. What about a spinning spacecraft to create artificial gravity, you say? Well, the physics dictate that such a spacecraft, simulating a 1g environment, would have to have a very large diameter, or it would have to spin at a rate that would be uncomfortable for its passengers. How large? Well, try some calculations on your own. Such a spacecraft would have to be assembled in space, and given our current rate of assembly on the ISS, that would take years. And then we'd have to actually launch the thing towards Mars. At this point it's an unreasonable option. So we can expect our astronauts to have a tough time setting up a base and preparing for a permanent stay.
As we have to contend with weight restrictions, one intriguing suggestion is to send the bulk of our astronauts' supplies ahead of time. Why not? There's no reason they have to carry anything other than supplies for the initial journey with them as they fly to Mars. In this scenario, a return to Earth is more feasible. Perhaps the astronauts could rendezvous with an unmanned supply ship in orbit before descending to the surface. Perhaps the ascent stage, necessary for getting off Mars again, is attached to this orbiting fuel and supply station. And either this, or another spacecraft, contains everything necessary for getting home. If we launch them early enough, we could give these unmanned craft years to reach Mars, so they could use less fuel. Perhaps they could be equipped with enormous solar sails, as that technology will hopefully come into its own over the next few decades. Though we are building two or possibly three spacecraft for this job, it's better than trying to launch one ship with everything necessary for the round trip. And only one craft need have life support systems.
In this case, then, it seems like finding a way for these astronauts to get home should be easier, and more affordable, than marooning them on Mars and committing ourselves to an indefinite stream of re-supply missions. We can't simply send them there and have them fend for themselves. Even if they are growing their own food, we can hardly expect to simply forget about them, and it's unlikely they will be able to build anything substantial on the surface without significant support from Earth. And besides, let us not forget that an off-world colony has yet to be tried anywhere yet. Perhaps we would be well advised to try a Moon base first, where astronauts could get home in a matter of days should something go wrong. A Moon base would have its own challenges, of course... 14 days of light and 14 days of dark (which complicates the use of solar power), extreme temperature fluctuations, and possible meteorite punctures. But there would be no dust storms, and it would be anywhere from 93 to 650 times closer to Earth. Among other advantages, inhabitants of a Moon base could enjoy virtually instantaneous communication with Earth. This is not to say that a Moon base should precede a mission to Mars, but that we would probably be well advised to try it before talking about a Martian colony.
As for the health of the astronauts, these problems aren't going away, and the authors of "To Boldy Go" are right to consider it seriously. But hopefully the medical advances of the next few decades will be able to solve some of these issues. We can imagine better exercise equipment and routines, improved dietary supplements and medicines, and who knows what we might be able to do with stem cells in the future. To me, these sorts of advancements are a more reasonable solution than simply avoiding the return trip to Earth. One day, hundreds or thousands of years from now, when humanity may be venturing out into interstellar space, we may well have to send astronauts on a one-way trip. But today, we have the capacity to navigate the inner Solar System with relative ease, and we should not let comparatively minor obstacles stop us from landing a man on Mars and returning him safely to the Earth.
You can see why it's a controversial subject when you get down to the details. Some people want us to get to Mars as soon as possible, while others think we need a Moon base to get ourselves in shape before making more daring journeys into the abyss. President Obama's proposal calls for a manned mission to an asteroid as a precursor to a Mars mission. This will be an extraordinary challenge in its own right, but it may prove to be an important middle step. A rendezvous with an asteroid will not be very different from a spacewalk, as the asteroid's surface gravity will be very low. The trip may take as long as a trip to Mars, but we would not need to contend with Mars' gravity when we try to come home (some scientists have suggested that a mission to one of Mars' two small moons would be a good idea for the same reason).
This much is clear, though: sooner or later we will send our first human emissaries to Mars, and that will be a voyage for the ages. But we have much to do before we take that historic step. I hope I'll be around to see it.
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