The problem with beamed power over that kind of distance is beam divergeance (yes, even laser beams do diverge). Even very low wavelength beams, starting with very wide aperture emitters, end up with a beam many times the diameter of the solar system over these kinds of ranges. Good luck trying to capture that energy for your spaceship.
The problem with picking up reaction mass along the way is, you need to lose energy to accelerate it up to your own current speed first before you can consume it as reaction mass to speed yourself up. As you get closer to lightspeed, even with perfect, lossless conversion, e.g. at 0.9c you lose 90% of the energy of the reaction mass bringing it up to your own velocity and get only 10% of it for beneficial thrust. The total of required reaction mass, which was already ludicrously huge for any practical payload, balloons massively.
If you do actualy have energy conversion losses, those limit your maximum possible speed. If you lose e.g. 1% of the energy you convert, then once you're at 99% lightspeed, the energy you gain from burning the reaction mass is the same as the energy you expended bringing it upto your own velocity. So there's no net gain.
A top speed of 0.99C only gives you a time dilation factor of about x2.3 or so.
And of course all of that is assuming magic fantasy tech with unbelievably high efficiencies and negligibly sized engines and mass storage.
Ok, true about the divergence, but how installing lasers along your flight path? In principle that should work, right?
Or alternatively instead of placing stationary fuel pellets in your flight path, have them accelerated by an external accelerator to as high a speed as possible.
You'd end up spending hundreds of thousands of years, and expending the combined resources of many solar systems, just to deliver one guy in a space capsule. What is the point of this journey anyway?
Comments
The problem with beamed power over that kind of distance is beam divergeance (yes, even laser beams do diverge). Even very low wavelength beams, starting with very wide aperture emitters, end up with a beam many times the diameter of the solar system over these kinds of ranges. Good luck trying to capture that energy for your spaceship.
The problem with picking up reaction mass along the way is, you need to lose energy to accelerate it up to your own current speed first before you can consume it as reaction mass to speed yourself up. As you get closer to lightspeed, even with perfect, lossless conversion, e.g. at 0.9c you lose 90% of the energy of the reaction mass bringing it up to your own velocity and get only 10% of it for beneficial thrust. The total of required reaction mass, which was already ludicrously huge for any practical payload, balloons massively.
If you do actualy have energy conversion losses, those limit your maximum possible speed. If you lose e.g. 1% of the energy you convert, then once you're at 99% lightspeed, the energy you gain from burning the reaction mass is the same as the energy you expended bringing it upto your own velocity. So there's no net gain.
A top speed of 0.99C only gives you a time dilation factor of about x2.3 or so.
And of course all of that is assuming magic fantasy tech with unbelievably high efficiencies and negligibly sized engines and mass storage.
Ok, true about the divergence, but how installing lasers along your flight path? In principle that should work, right?
Or alternatively instead of placing stationary fuel pellets in your flight path, have them accelerated by an external accelerator to as high a speed as possible.
You'd end up spending hundreds of thousands of years, and expending the combined resources of many solar systems, just to deliver one guy in a space capsule. What is the point of this journey anyway?
I was thinking you were saying it was physically impossible. But you're right it's more of a cost issue.