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Are asteroid collisions as dangerous as they seem?

  1. Apr 12, 2017 #1
    The generation ship in my fictional story was built by aliens that know how to use these 3 things:

    • Artificial gravity to make it feel like earth throughout the ship.
    • Controlled nuclear fusion with 6 tanks. Only 1 needs to be fueled and you have fuel that will last for at least thousands if not millions of years. Going at .5c(half the speed of light), this is no problem
    • Artificial magnetic field to protect from high energy gamma ray bursts while still letting visible light through

    After they randomly select 5000 passengers that fit a certain set of criteria for being on board and in a 1:1 sex ratio with lots of genetic diversity, they use booster rockets that immediately detach once they are in space. They then use nuclear fusion. At half the speed of light, it takes them nearly 2 years to traverse the solar system. They arrive at Mars within minutes but all the planets from there take at least an hour to arrive at.

    But there is 1 main danger when going from Mars to Jupiter. That is the asteroid belt. A similar danger arises when they reach Pluto and the Oort cloud, but in this case it is comets, not asteroids.

    But there is 1 thing that puzzles me about the asteroid belt. Meteroids, some as small as a speck of dust, I have heard are more dangerous than asteroid collisions regardless of your speed.

    I get 1 factor into why meteroids are more dangerous, they are much more common than asteroid collisions with a spacecraft would be. But if the aliens were able to travel to earth, they probably ran into both of these things. Thus they would have developed technology for their ship to withstand both of these things a lot before they went to earth.

    So if the generation ship can withstand meteroids and asteroid collisions, meteroids would probably be as dangerous to them as a black hole is to us on earth, in other words, less than a 1% chance of them being dangerous, much less.

    Asteroid collisions in comparison are much more dangerous. Even though the ship is what takes most of the force of the collision, there would still be a lot of sudden force inflicted on both the aliens and the humans. Luckily, the aliens have a 2 thumbed hand with each thumb on the opposite side of their hand so their grip strength is much stronger than ours. If it breaks anything, it would likely be the eggs of which there can be 5-15 per clutch and there is 1 clutch every few years(yes, my reptilian aliens lactate).

    Anyway, for the humans, this sudden force from an asteroid collision is dangerous. Even with a very strong grip, the human hand just can't take that much force without letting go of whatever it is holding on to. Thus there would literally be a pile of humans with fractures in all sorts of places and probably some bad burns(the generation ship has a metal surface that is heated to a comfortable temperature. Since metal conducts heat, all the force from humans falling and sliding due to an asteroid collision could cause blistering burns).

    Obviously, my generation ship has a medical bay for this problem and more.

    But is my reasoning right? Is an asteroid collision with a very fast spacecraft as dangerous as I think it is? Would it really cause fractures and burns from all that force? Would humans even survive the force of an asteroid collision?
  2. jcsd
  3. Apr 12, 2017 #2
    You wouldn't be able to see one asteroid from another with the naked eye, in most cases. It's a roughly planetary size mass spread out over the entire orbit the debris.
  4. Apr 12, 2017 #3


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    A generation ship would be massive, it's very unlikely you could build such a thing on the surface of a planet and then launch it. Makes far more sense to build it in orbit.

    You're drastically underestimating how fast the speed of light is. Pluto is ~7 light hours away meaning that it takes light 7 hours to get there. Considering that as a practical edge of the solar system it would take a craft travelling at 0.5c 28 hours to cross the system. Basically a day, not two years.

    But you have a big problem here if you're trying to keep things realistic. You're not taking into account acceleration time. If they have a magic engine that can run forever and they accelerate at 1g it would still take them months to get up to 0.5c. By that point they'd be way out of the solar system.

    This is not a danger, the asteroid belt is incredibly sparse. Individual asteroids are millions of kilometers from each other, there's plenty of space. Beyond that any reasonably good network of forward facing sensors should be able to detect them.

    Anything in space is dangerous if you run into it, especially at 0.5c of the speed of light. At that speed any collision is going to release a huge amount of energy. How much? Hitting a one gram pebble at 0.5c would release over 11 terajoules of energy, which is roughly two thirds as powerful as the Hiroshima bomb. You can't protect against something like that unless you have a massive amount of mass (in which case you're not moving anywhere, see the Rocket Equation). Instead you need to build systems to avoid collisions.

    Thumb strength is the absolute least of your problems here.
  5. Apr 12, 2017 #4
    But the end of the Oort cloud is much further away, up to a light year. This is where I got my 2 years to go from the solar system to interstellar space.

    And the reason the generation ship has booster rockets that immediately detach once they reach space instead of it being in low earth orbit(like, as low as low earth orbit can be) is to avoid the side effects of microgravity in humans. Albeit it is a short time to go from the surface to low earth orbit but the humans would need spacesuits for that short time to avoid asphyxiation, swelling, and other side effects of not having a spacesuit. While some rockets including the ones recently made by SpaceX and Blue Origin are reusable, most aren't.

    With a generation ship having booster rockets built in, there are practically no side effects of microgravity since the generation ship has artificial gravity.

    And yes, I know that grip strength just isn't strong enough in humans and this is why I said that there would be a pile of humans with fractures and probably some bad burns if the generation ship did collide with an asteroid.
    Last edited: Apr 12, 2017
  6. Apr 12, 2017 #5


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    The Oort Cloud extends well into interstellar space, it is not within the solar system. There is no clear boundary between interplanetary and interstellar space but AFAIK anything beyond the heliosphere is definitely interstellar. The edge of it is 121 AU from the sun which would take 32.5 hours to cross at 0.5c.
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