Today, we are speaking about space tourism, or sending men to Mars. What about longer, much longer journeys, out of our solar system? Of course, the question has been around for quite some time, and it seems that space agencies are more and more interested in the idea. When reading about the dangers of radiation during pregnancy in space (here), I couldn’t stop thinking that this might actually be the smallest of our problems…

Indeed, for any civilization who would attempt such long journeys, there are many things to take into account. The question of pregnancy on a spacecraft was raised in relation to the possibility of long journeys (and, if you want to push the idea further, transgenerational journeys out of our solar system). When considering the eventuality of interstellar travel, transgenerational journeys seem to be the most plausible solution: technically, traveling to another star is simply impossible in a lifetime. The solution to send people who would then have children during the journey, and this for several generations appears to be the solution.
Unfortunately, cosmic radiation would probably make any pregnancy on a spaceship impossible without appropriate shielding. Even if we assume that this shielding problem was solved, we would then be facing other issues…
Proxima Centauri, the nearest star to the Sun, is located 4.24 light-years away from us (it takes approximately 4 years and 3 months for its light to reach us). The highest speed ever reached by a spacecraft was 250,000 kilometers per hour (the Helios probes), i.e. about 4320 times slower than light. At that speed, it would take more than 18,000 years to reach Proxima Centauri… Assuming there would be a new generation every 30 years on average, it would take a bit more than 610 generations to get there, and as many to come back… Of course, the population on the spaceship would have to be numerous enough to avoid inbreeding; you can then imagine that the number of people required for such a long mission is simply unrealistic, so would be the spaceship, the budget and the amount of energy required (this is probably the biggest problem)…
You could assume that the technology will improve and allow faster speeds, yet the problem remains the same unless you reach relativistic speeds (which is currently impossible to achieve, here the only purpose is to show the problems raised by interstellar flights). If you imagine a spaceship accelerating at 9.81 m/s² (the crew would experience the equivalent of the Earth’s gravitational field), according to special relativity, and considering the ship will have to slow down to stop when reaching Proxima, you have the following results:

  • For the crew, approximately 3 years and 7 months will have passed;
  • On Earth, approximately 5 years and 10 months will have passed.

If this hypothetical spaceship was to come back, you can easily see the problem: the amount of time that passed is not the same – and we are here only considering a journey to the nearest star (and once again, this would require an outrageous amount of fuel, as well as extremely strong shielding – even the cosmic microwave background, after a few years traveling at a speed near that of light, would melt absolutely anything); in the case of much longer journeys, the difference would be so significant that the crew would come back to a world they would not know, where their families would have aged much more than them.

There are many other elements you might consider obstacles to traveling to other stars, but these seemed to me the most important ones.

Finally, these are many assumptions, most of which may never come true. I wouldn’t like to sound too pessimistic, but it seems that traveling to other stars is something we might never achieve, or at least not anytime soon…

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