4 ms·

Can someone do the math to calculate the energy needed for a ship like this to accelerate near the speed of light? I suspect the amount of energy may exceed wha

by soheil 5y ago

Can someone do the math to calculate the energy needed for a ship like this to accelerate near the speed of light? I suspect the amount of energy may exceed what's available even if we were to capture all energy generated from the sun.

jandrese 5y ago
It's not even the energy that is a problem, it is the mass. The rocket equation is a harsh mistress.
- soheil 5y ago
  But more energy is the only thing that is needed when mass is increased, so not sure why it wouldn't all boil down to energy? Unless you're talking about escaping Earth specific gravitation.
  - jandrese 5y ago
    Are you talking about kicking your reactant so hard that it picks up significant amounts of relativistic mass?
    - soheil 5y ago
      Haha no but I'm not assuming the rocket equation is applied in Earth's gravitation, but maybe the spacecraft could be built far enough from any plants to be impacted by an initial gravitational field. If nuclear energy is used, it can be increased in less than linear change in mass.
    - jandrese 5y ago
      Regardless of what you use for power a rocket has to eject mass from the rear to propel you forward. Newton's second law. The problem is that as you increase burn times (like years at 1G), you need to increase the amount of mass you are pushing out the back. But to do this you increase the mass of your rocket which means you need to push even more mass out and it becomes a vicious circle of exponentially increasing rocket mass. The idea of accelerating at 1G for the entire trip only works if you have a source of propulsion that doesn't obey Newton's second law. Otherwise there literally isn't enough mass in the galaxy to make it work. The caveat being that if you can somehow exploit relativistic mass to effectively multiply your fuel it might be possible, but my math isn't good enough to work it out. My gut feeling is that it would require an unreasonable amount of power however, even for an extremely powerful nuclear power plant.

by soheil 5y ago

jandrese 5y ago

It's not even the energy that is a problem, it is the mass. The rocket equation is a harsh mistress.

soheil 5y ago
But more energy is the only thing that is needed when mass is increased, so not sure why it wouldn't all boil down to energy? Unless you're talking about escaping Earth specific gravitation.
- jandrese 5y ago
  Are you talking about kicking your reactant so hard that it picks up significant amounts of relativistic mass?
  - soheil 5y ago
    Haha no but I'm not assuming the rocket equation is applied in Earth's gravitation, but maybe the spacecraft could be built far enough from any plants to be impacted by an initial gravitational field. If nuclear energy is used, it can be increased in less than linear change in mass.
  - jandrese 5y ago
    Regardless of what you use for power a rocket has to eject mass from the rear to propel you forward. Newton's second law. The problem is that as you increase burn times (like years at 1G), you need to increase the amount of mass you are pushing out the back. But to do this you increase the mass of your rocket which means you need to push even more mass out and it becomes a vicious circle of exponentially increasing rocket mass. The idea of accelerating at 1G for the entire trip only works if you have a source of propulsion that doesn't obey Newton's second law. Otherwise there literally isn't enough mass in the galaxy to make it work. The caveat being that if you can somehow exploit relativistic mass to effectively multiply your fuel it might be possible, but my math isn't good enough to work it out. My gut feeling is that it would require an unreasonable amount of power however, even for an extremely powerful nuclear power plant.