The problem that never seems to be addressed, when discussing near light speed ‘craft’ is.... how do you slow down ? You can’t just fly along at .80c and then suddenly stop when you arrive at your target.
I wonder what would happen if one of the micro spaceships failed to stop, would we drop a few grams into the middle of an alien City at .8 times the speed of light. I wonder how many megatons that would be. I wonder how long until they mailed us a package back.
Light exerts pressure on anything it hits. So one of the methods I’ve seen involves unfurling a light sail that’s hundreds of miles in diameter when you get near your destination star and the light pressure on your sail will slow you down. Don’t know about 0.80c. You might need a considerably larger sail, or you’ll just fly right on by.
It takes about a year to accelerate to near light speed at 1g, and another year to slow down again. That has to be taken into account. And of course the energy required is ridiculous.
You accelerate for the first half the trip, and decelerate thereafter. If it’s a manned interstellar flight, you’re pretty much limited to a constant G force of not much more than 1 G, but even at that you can approach light speed in less than a year. You just need the propulsion technology for constant 1 G, however you do it.
Assuming you can do it, your biggest problem would be relativistic time dilation. If you make the round trip to the nearest stars at an average speed which is a significant percentage of C, the Earth you return to is quite a bit older than your onboard clock/calendar will indicate.
If you go fast enough and far enough, you might in fact return to a far-in-the-future Earth which saw the end of your civilization in some cataclysm, followed by hundreds of thousands of years of primitive tribes surviving as hunter/gatherers, then more thousands of years as the tribes developed agriculture and trade routes and metal-working, then more centuries in which technology advanced to roughly the equivalent of what we had in 1947.
In the possibly millions of years since your departure from Earth, your species has undergone radical physical transformation to the point that the only commonality remaining is the basic form of torso, head and two arm and two legs.
Your return to your home planet would be interpreted as the arrival of aliens. No doubt about it.
Bingo!
You have to accelerate for 1/2 the trip, and then decelerate the rest of the time.