11 ms·

Definitely a common sense step in the right direction. Humans going anywhere beyond the moon using chemical propulsion seems quite problematic due to all the un

• eddsh1994 4y ago
  How does your initial point of 1g for a few months on a heavy spacecraft lead to traveling 4.246 light years? Genuine question!
  • gpm 4y ago
    It would take 6 years to get there (earth time) or 3.6 years (spacecraft time) if you could have constant 1G acceleration (in the opposite direction for the second half of the journey). https://cosmicreflections.skythisweek.info/2019/09/04/space-travel-under-constant-1g-acceleration/ https://cosmicreflections.skythisweek.info/2019/09/04/space-...
    • geijoenr 4y ago
      With a spacecraft big enough to live in, we are talking of a time frame not too different from the one from the age of exploration by sea. I have no doubt many people would want to take such a trip even if it takes 10 years to get back to earth. Unmanned spacecrafts would be able to go much faster, sustaining more dramatic accelerations. So getting cargo and robots there for support would be way faster.
    • eddsh1994 4y ago
      This takes you to 0.99C, how feasible is that (thinking materials more than anything)
      • credit_guy 4y ago
        It's not feasible. It would require more fuel than the Earth is heavy, even if we had nuclear propulsion.
        • geijoenr 4y ago
          It depends on the mass of the ship, but yes; quite a bit. https://www.quora.com/How-much-energy-does-it-take-to-accelerate-1-gram-mass-to-99-of-the-lights-speed https://www.quora.com/How-much-energy-does-it-take-to-accele... I don't think that means is unfeasible if the energy source allows for that.
          • credit_guy 4y ago
            No, actually it does not depend. The rocket equation says that the fuel mass of a rocketship is higher than the cargo mass by exp(delta_v/v_exhaust). When the final velocity is relativistic, delta_v should be replaced with delta_rapidity. In our case this would introduce a factor of 2.65, but the results are so ridiculous that we can ignore that. So, let's simply say that delta_v is the speed of light, or 300000 km/s. The exhaust velocity for a nuclear thermal rocket is about 9 km/s. The ratio between delta_v and the exhaust velocity is about 33000. The exponential of that is roughly speaking 1 followed by 15000 zeros. There are less than 10^100 atoms in the known universe. So, even if you want to accelerate just one single atom to 99% of the speed of light, you would need more fuel than the entire universe. Many, many, many times more.
      • geijoenr 4y ago
        Yeah well, we don't really know what happens at high speeds. Probably biochemistry stops working at 0.3c? It doesn't seem structural materials would remain solid at 0.95c... who knows.
        • monkeydreams 4y ago
          I am not a physicist but I suspect that we are already moving at significant speed relative to other bodies. We have no special frame of reference that defines our "real" speed.
  • brnt 4y ago
    In fact, you could get anywhere in the universe in your lifetime/timeframe, if you could maintain the 1g acceleration.
    • mr_toad 4y ago
      Depending on the nature of the expansion of the universe, that might not be true. https://en.wikipedia.org/wiki/Cosmological_horizon https://en.wikipedia.org/wiki/Cosmological_horizon
• Kim_Bruning 4y ago
  Meanwhile, having engines that have higher specific impulse helps quite a bit as well. That is to say: a nuclear engine needs less propellant to provide the same amount of delta V (actual work). Since the majority of a rocket's mass is in the propellant, this scales non-linearly. A nuclear rocket is a big improvement over chemical rockets already.
• dmitrybrant 4y ago
  > without an action-reaction process. Just an energy source, and no propellant. Unfortunately, in our universe, momentum is conserved.
  • mr_toad 4y ago
    If you could somehow convert mass into a beam of photons then the mass loss would be tiny compared to the momentum.