Saturday, October 24, 2015

Very Cheap Interstellar Travel

It used to be, and maybe still is, possible to see the world for almost nothing. Just go down to your nearest seaport, and get a ride on a tramp cargo steamer. Get off at whatever further port you want, stay as long as you like, and then get on another one. Conditions were not lavish, but you got to go somewhere.

It seems possible to do this for star travel. Recently, Scholz’s star was re-discovered, in 2013 to be exact, by an astronomer named Scholz as a star which had come close to us very recently. It passed through our sun’s Oort cloud at about 0.8 light years from the sun approximately 70,000 years ago. It is actually a binary star, with a brown dwarf and a red dwarf as partners. Since it was traveling almost radially away from us, it had a low proper motion and so was not noticed as a nearby star. Lesson learned.

This discovery caused a tiny flurry of activity, and it was realized that there are stellar encounters at about this distance, let’s say less than one light year, on the average every 100,000 years, in rough terms. Here’s our cargo ship.

Consider the possibilities this offers. Suppose you are a citizen of an alien civilization that wants to do some interstellar colonization. Traveling to meet a star at a distance of less than a light year, which you know is coming for thousands of years, doesn’t take much fuel or much of a starship. The major costs of starships come from the fuel, which you have to carry along with you if you want to accelerate along the way and even more important, decelerate at the destination. If you are only going a light year, you don’t need much speed, therefore not much fuel for acceleration or deceleration. With a few thousand years to get ready, you could go out into the Oort Cloud of your star, assuming your star has one, and look around for some place to wait while your star is coming in. If you are interested in an interstellar probe, you can just push one out there over a period of a century or two or five or ten, and, with the patience this takes, wait until the star arrives, and then go orbit it. Most stars have planets, according to those who know, so you might be able to set up some type of base.

Hold on! You have just done an interstellar flight and established a colony on an exo-planet. It happened to be in your backyard, but still, you have just accomplished this goal at a fraction of the cost it would normally take.

If your colony on this exo-planet can last for periods in the hundreds of thousands of years, you will be passing close to other stars of the galaxy, and can get off there and set up another colony. Soon (in an astronomical sense) you will have many colonies in your neighborhood of the galaxy. You might be colonizing some real loser planets, but with some resources, you can fix up something your civilization can tolerate for a period. Recall there are some sweet spot worlds, and you would be really lucky to find one. There are also some worlds, called penumbra worlds in this blog, which have problems in habitation, but can be converted or otherwise used. Then there are worlds where the colonization has to be done in a hermetic chamber. Toxic atmosphere, too cold, or something else seriously wrong. But at least you have a place to live while you travel further out into the galaxy.

There must be exploitable resources on the planet, as carrying around enough supplies for a hundred thousand years is likely not practical. You might get energy from the sun, or scoop deuterium from a gas giant, and power your reactors, but you will still need some basic minerals. So, perhaps every planet that drifts by your own star isn’t acceptable, but some will be. Remember that most of the stars in the galaxy are red dwarfs, which are not very useful to begin with, but perhaps as we learn more about them, they will be found to have some advantages.

Another advantage of this idea of star-hopping, is that an alien civilization with a small population can pull it off. You don’t have to store up immense amounts of propellant and energy to get out to your own Oort Cloud. There is stuff out there anyway, and perhaps it could be used. Dropping down on an icy comet in the Oort Cloud might allow you to extract deuterium, and power something. You could use the protons you recover as propellant.

The obvious disadvantage of jumping on a cargo ship for seeing the world doesn’t allow you to pick your destination. You go where the ship is going. Same for a stellar encounter. You hop on and go where the star is going. Maybe it’s heading toward a sweet spot world next, but likely it’s just another red dwarf with some dismal planets circling it. You don’t get to do the seeding of life that your meme might be telling you to do, at least not nearly as fast as you could if you could afford to build a ship to cross a hundred or more light years in some understandable time, like a few millennia. You are also exploring and colonizing the galaxy at a pretty slow rate. Stars do move faster than orbital speeds, say something like .0003 c, but nothing like the speeds of 0.1 or 0.01 c that we have discussed in other posts.

If the worst Great Filter is the cost of interstellar travel, this is a solution to that problem. Assuredly, every alien civilization recognizes this possibility as soon as they develop a robust astronomical observation program. If it is actually the accepted way of dispersing an alien civilization through the galaxy, it means that looking for aliens needs to take a very different tack. Instead of looking for planets with biosignatures, we should be closely examining every star with us as a destination for any signs of unusual activity there. Examining stars that are within, say ten light years of us, is much easier than searching a radius of a thousand light years. It also means that learning more about the Oort Cloud and what assets it possesses might be very interesting for exploring the details of this possible cheap star travel method.

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