2 types of nano spacecraft are planned to travel to Alpha Centauri , 4.2 light years away. One powered by an Earthbound laser, another self powered. I have loads of questions about this but here are a few - The report I read talked about an average speed of 25% of light speed. However, it is constantly accelerating during the trip won't the average be skewed as it gets towards a significant fraction of light speed? - If it does achieve this speed how long will the voyage seem to the spacecraft? From our point of view we are told 16 years, but won't it take the craft a lot less from ITS OWN point of view? - What gain in mass will it have at 25% light speed? - What will happen if it hits a planet at that relative velocity ? Most Solar System meteorites are going at only 15k or 20k on impact . What happens if 1 or 2kg hit a planet at 30million miles per hour? - Its signals back to us are expected in 20 years - 16 years for travel and 4 for the return journey of the message. I assume the frequency of the waves will need massive compensation, as it will be receding from us when it sends. (the message still arrives at light speed, of course, just a change in frequency) - The earth bound laser will need to have constant adjustment as the Earth turns and orbits the sun. HOw will it know if it is on target when the signals back are minutes, hours, days and years away? I am hoping this is not another Elon Musk spoof, and we can all have loads of fun while they try to make it happen!!