88 Years

The Orion pulsed-fission starship will be able to attain and maintain speeds of 5% of the speed of light, or about 15,000 kilometers per second. This is the fastest speed which a crewed or uncrewed vessel may be propelled with current technology and resources (it is theoretically possible for a vessel which constantly accelerates throughout an interstellar journey to go much faster, but there isn't enough fissionable material in the solar system to sustain this). More, it may well prove to be the fastest speed practical regardless of any advances in propulsion technology. For example, a grain of sand striking an object traveling at 12% of the speed of light will release the energy of a hydrogen bomb. Which would, in the words of Han Solo, "end your trip real quick".

So, 5% of the speed of light. From earth to Alpha Centauri in a mere 88 years. 88 years is a long time, in the scale of a human lifetime. Current human life expectancy world-wide is 67 years, but varies greatly by region. The longest national life expectancy on earth right now is nearly 90 years, in the Principality of Monaco, which speaks well to my retirement plans. In the extreme, the actual human lifespan is constrained by the Hayflick Limit of about 50 cycles of cellular mitosis, which translates to about 121 years. Jeanne Calment of France lived to be 122 years and 164 days old, but she is definitely the upper bracket.

Let us assume, for the sake of argument, that through a combination of eugenics, medicine, and rigorously controlled diet, regimen and environment, that we can guarantee that an entire crew will live to an age of 120 years. Let us also assume that, through an extraordinary but not inconceivable training regimen, all of the crew could be trained to complete the first part of their mission by the age of 14, and then would launch at this time. 102 years from the moment of their births the crew would reach Alpha Centauri, old but spry with another good 18 years left in them to explore the star system.

This seems pretty far-fetched for a number of reasons. But it does demonstrate that it is theoretically possible, with existing technology, for a single generation of humans to reach and explore the three nearest stars, including Proxima.

The next nearest star, Barnard's Star, at 118 years is just beyond the reach of a human generation. The next star beyond that, Wolf 359, is 156 years.

But, still, three stars, two of which are pretty decent candidates for habitable (or at least terraformable) planets, and a third which is at least possible, isn't a bad dice roll. If there was only going to be one other star system within our relatively easy reach, we could have done a helluva lot worse.

In point of fact, unless we choose to use some form of suspended animation (several of which are already possible, more on this in an upcoming post, soon), the first generation or generations of crew will get busy creating the next generations of crew rather soon into the flight. We don't need to make elaborate plans to create "generation ships"; nature will take care of that part all by itself. Because the ship will be a completely closed ecosystem for the entirety of the journey, populations of all species on board will need to be closely regulated. But in the end, there will be plenty of young people to colonize any worlds found around the Alpha Centauri stars.

This method could also be used to reach Barnard's Star, if there were compelling evidence of habitable planets or moons there. But that seems fairly unlikely.

It is not, however, reasonable to expect entire generations to live out their lives and die in a tin can in hopes that their descendants might one day colonize a distant star. To go further than Alpha Centauri or Barnard's Star, a different method is needed. The next post will explore possibilities of suspended animation.