See also parts one, three and four.
How will we get to the stars? With extreme difficulty. We have enough trouble getting to Mars and it’s right next door. The time it takes light to get from Earth to Mars is measured in minutes. The closest extrasolar star is over four light years away. A ship with people on board will take months to get to Mars using current technology. At that rate it would take over a hundred thousand years to reach the nearest star. Obviously we’re not going to get there in chemical rockets, even forgetting about the impossibility of carrying enough fuel to do it.
As any engineer worth their salt would say, there must be a better way. And there are a few. We’ll look at some that are theoretically possible using currently known technology.
Nuclear power is more efficient than chemical power. It still only releases about one tenth of one percent of its fuel as energy, though. It could be used to force something, steam maybe, through rocket nozzles to drive the ship in a traditional way. Another option is to detonate a series of atomic bombs behind the ship to push it along. These would require carrying less fuel than chemical rockets, but they’re still pretty bad.
The best method of propulsion that we could use now, with physics that we understand and technology that we can build, is the light sail. Four hundred years ago Johannes Kepler, an astronomer, noticed that something was blowing long tails off comets. He speculated that someday we might be able to use that wind to sail in space. These days Freeman Dyson, the legendary scientist, is saying the same thing. It’s been tried and it works. Light really does push on a reflective surface. One could simply use sunlight, but it gets weaker very rapidly with distance. A better way is to use a powerful laser, whose beam doesn’t scatter too quickly and which can provide plenty of power to the sail as it speeds away. Calculations show that such a ship could reach one tenth of the speed of light, and wouldn’t have to carry all that heavy fuel.
At that speed it would still take about five decades to reach the nearest stars, so it would be best to send robots first. With enough intelligence built in they could explore, set up a base, extract resources to build more robots, look for suitable destinations and prepare the way for us. Fifty years is still too long, though. The original crew would grow old on the way. The current best solution for that is the generation ship, carrying a clan of families to continually replenish the crew. Analyses show that a minimum of eighty people is needed for sufficient genetic diversity, but 150 would be a better number.
Next time we’ll look at methods that aren’t possible now, but could be soon.
rjb
