the only possible way to travel to another planet or extraterrestrial planet is to invent a transport that can travel at lightning speed
when will human be able to do that ?
even travelling at the speed of light would be slow as fuck. and imagine how long it would take to accelerate to that speed and what kind of long term effects the g's would have. we'd have to be suspended.
Robotic cloning ships. Ships travel at sub-light speed to destination. On arrival, robots terraform best location and begin printing DNA of the digital copies of humans they have on file. (If brain up/downloads are possible, they also do that.)
Repeat, von neumann style. It'd fill at least our own supercluster with humans before heat death. Dark energy might make travel beyond that impossible.
Adding to that: you can't even travel /at/ the speed of light as that would require infinite energy. You can only get close to it.
Also, time dilation would suck monkey balls even at infinitesimals of c. Pretty much everything and everybody you've ever known and loved will be dead and forgotten after less than a day on board of a vessel going that fast.