Let's say we absolutely found another advanced civilization, and in fact somewhat close, reachable in just 500 years. Let's assume we can build a rather large spaceship, say the size of the Empire State Building, and can fill it with enough food and fuel for the journey.

My question, what are the ethics of sending humans on such a trip? It would take 15 to 20 generations of human beings, living their entire lives confined to a prison, to complete this journey. An absolute nightmare of an existence, to be entirely disposable except to procreate in order to produce more prisoners like themselves for a few hundred more years. And when the ship did arrive, the living passengers would not be Earthlings, in the sense they would have little idea about the Earth, none would have ever been there or know anyone who had. We could provide them with every book, movie, etc that ever existed but they would still have no Earth-bound experiences. And it would likely depress them greatly, seeing and hearing things they will never experience. And finally, why would we expect anyone to ever return, to "complete" the mission? Their choice would be to make the best of life on their new planet or to once again volunteer for this bleak, suicidal journey to get back to Earth.

Some may say that future tech, or ultra-advanced VR, or cryogenics, or "downloading" brains and sending inert bodies, may make such a journey possible, but no answers sound very convincing, in my opinion.