The 100 year starship program has been completed within the last decade - around 2110. Earth's closest star system is finally within reach and none too soon. A comet the size of the state of Alaska has been spotted by deep space monitoring satellites and it is on a collision course with our planet.
We have less than a year to prepare to leave the cradle of humankind. Earth is doomed and we must leave her if we are to survive. Two starships have been completed and they will become arks to transport our race to another star system in the hope of finding a new planet, a new home and a new life.
With only two starships completed, we will have to make some tough choices about who will get to go on the mission to find a new exoplanetary system in the star system of Alpha Centauri, over 4 light years away. Those who stay behind will have to go underground into the the deep cave systems built by the various governments of the world for just such an apocalyptic event - a collision with a planet-buster comet.
You are one of the lucky ones you believe. Under the age of forty, way above average intelligence, a PhD in Astrophysics and Biochemistry, much needed skills aboard a starship and no immediate family to leave behind and perhaps most importantly, you are a fertile female with a positive gnome map. Your jobs, besides that of Astrophysicist and Biochemist, will be to produce healthy progeny, who will in turn also be capable of producing another additional generation of children to continue your mission. It is a little disconcerting to realize your second most important job requirement is being a baby-factory; both bearing them and providing eggs to freeze-dry for later. But you understand the urgency of your mission and accept this vital role as female crew aboard the ark.
It's a one-way journey for you however. You will never see Earth again. Nor will you ever see the sunrise of a new sun. Your children's children might. They will hopefully become the future colonists for a new home for mankind. But you will spend the rest of your life, the next seventy-plus years in the blackness of interstellar space.
As you join your shipmates, lined up in front of the various entry ports to one of the two space-arks, you reflect on the design and layout of the ship - your new home. The ship will house over ten thousand voyagers, who will live, work, play and eventually die aboard her. None of the body parts will go to waste. They will contribute DNA, blood, bone and tissue to culture cloned body parts. Human waste will be reprocessed into fertilizers for the hydroponic farms.
There is several tiers of redundancy in the organizational chart aboard each ship. Everyone will know at least 10 other crew members jobs and can perform them flawlessly should the need arise. There is no turning back. Every possible scenario that might befall the ships and their crews has been simulated, programmed and drilled. You are as ready as you'll ever be.
But as you walk toward the first familiar face among your crew mates, the weight of the challenge and a paralyzing fear of the unknown falls over you like a shroud. You've been trained to handle the psychology of the mission as well. You shake off the feeling of doom and stride forward confidently again. There is no greater, or nobler cause you could undertake for the fate of mankind. It is your destiny.
The ships are large; over 100,000 tons. They are impossible to launch from Earth with conventional propulsion. They will each ride a lev-rail system over 10 miles long that will slowly move the ship from a dead-stop to almost 4 kilometers per second, gradually angling up to over 60 degrees in order to hit pre-orbital velocity. After leaving the lev-rail, huge solid rocket boosters ignite and increase acceleration to the 8 km per second needed to achieve orbital velocity. Once in orbit the solid rocket boosters will be jettisoned and the ships powerful first stage engines will kick in driving each ship along Earth's orbital plane to increase speed to escape velocity.
Read more about it at: NASA's 100-Year Starship Project Sets Sights on Interstellar Travel