There are a number of milestones and challenges for mankind if we are to contemplate travelling to our nearest stars, 5-20 light years away. We must first establish a large moon-base towards mid/end of this century. This is feasible because we have discovered vast amounts of ice at the poles giving us water to drink, oxygen to breathe and hydrogen for power. Structurally, moon-base would look like a huge Eden Project with specially designed plastic interlocking blocks to resist the vacuum. Then in the early 22nd century we would have a base on Mars. This would be the nerve centre for a star mission and a suitable starship would be constructed in weightless orbit around the planet. Our mission would launch from here and use the huge gravitational pull of Jupiter to accelerate our craft. Now there are 3 key technical challenges for us to solve over the next century to make a mission lasting 20 years feasible. Firstly, we have to be able to travel at a significant fraction of the speed of light and secondly we have to develop technology for extended human hibernation by cryo or other techniques. Thirdly, and absolutely vital, we must develop artificial intelligence - computers so powerful and reliable that we can trust them to look after a starship with its precious cargo of hibernating humans throughout a 20 year voyage. I will talk in more detail about each of these in my next 3 blogs. To answer my question - I think in about 150 year’s time but I would be fascinated to hear your views. I have visualised such a journey to the stars in my book - The Blue People of Cloud Planet- available as an e-book on Amazon Kindle [eleven 5* reviews] and shortly to be available in paperback from Feedaread.