Space 15: Doing the Boldly Go Thing and Infesting the Universe
(continued from here)
How exploration will work
First: the explorer probes will need to be slow. This is a side-effect of how stupid rockets are. Because in the case where you're arriving at a system for the first time, rockets will be the only alternative for slowing down, you'll need exponential amounts of fuel for that, and since the explorer has to carry all of its deceleration fuel with it, you then have to accelerate all of that fuel at the start of the trip,... so there'll actually be this doubled exponential factor in there.
But if we don't try to get anywhere near lightspeed it won't be too bad. Since all of the terraforming is taking thousands of years anyway, nobody's going to care about the explorers being slow.
Numbers for this:
If we do all of our acceleration within the solar system (hint: if the probe only carries deceleration fuel, then all acceleration has to be externally applied, i.e., that part will be all lasers and lightsails, and there's a reason for doing as much of that as we can from planet/asteroid based lasers), say, within 10 AU (Saturn orbit radius) and we keep it to 1g, that gets us to 1.8% of lightspeed with a 3.7% mass cost. That is, we'll need 37 kg in the antimatter cell for every metric ton we send, or 14 months worth of our entire civilization's energy production if we want to send an explorer massing 1 million metric tons (10 Enterprise-class aircraft carriers)…
… an entirely-out-of-my-ass number which you might think is really quite small for something that's supposed to be eventually starting a terraforming operation, … but, since what we're really talking about here is not the Thing That'll Do The Terraforming itself, but rather The Thing to Build The Facilities to Build The Facilities to Build The Facilities to Build The Things to Do The Terraforming, I'm pretty sure small will be doable.
And it's getting to Tau Ceti in 600 years. If you're still fantasizing about putting humans on this ship, keep in mind they'll have to be total sociopath nutjobs who will need to raise their great¹⁸-grandkids to do the work at the far end, and,… yeah, I'm not seeing that part ending very well.
Also, not having a return trip simplifies a whole lot of things. On general principles we were always going to need to be careful what, if anything, we brought back to Earth.
Alsoalso, without humans on board, we're not actually limited to 1g acceleration, though this is not as much of a win as you might think. If we do, say, 10g acceleration, in which case we get up to 5.7% lightspeed, spend 121 kg of energy per metric ton, then we're devoting 46 months worth of our hypothetical civilization's energy output to getting this thing launched and showing up at Tau Ceti in a mere 175 years.
Which will really be kind of a waste if it needs n000 years to get the terraforming done. Never mind the small matter that high acceleration implies a larger chance of things getting broken, which would be stupid.
We probably get a better bang for the buck sticking with a 1g acceleration plan and sending 3 times as much stuff.
To be sure, we do want to splurge a bit on these exploration missions, because we won't need to launch that many. Once we have a probe design with a good enough reproduction rate that a single launch is guaranteed at least 3 successful repros -- and for this we just need star systems that are viable for mining and manufacturing, the terraforming part won't matter -- we're done; we won't need to launch anything else, ever again. Our existing probes and their descendants will just spread out everywhere and exponential growth will do the rest for us.
If every probe has 3 child probes, then five or six generations will be enough to hit all the 100-some-odd systems within 15 light years, and from then on, if we stick to the 1.8% lightspeed plan, and, say, it takes 400 years to build enough infrastructure to get to the point of launching the child probes (400 years being enough time to exchange messages with the neighboring systems to work out who's going to do which systems next), that plus 600 years to get to the next system, if we're going in 10 light-year hops, means 1000 years per hop and a radius of explored space expanding at a rate of 1/100 lightspeed for as long as we keep encountering systems that are good for building stuff.
And in 10 million years, we will have hit every system in the Milky Way.
But, more to the point, within the space of 2500 years, we can have a presence in every single system within 15 light-years of us, meaning if there are any planets near us that are worth terraforming, we will not only find them, we'll be concurrently working on all of them at the same time.
Environmental Impact Statement
Meanwhile, our explorers will be like cockroaches; they will be fucking everywhere.
Which presents some command and control issues that are,… interesting to say the least.
- Clearly, given the expense, nothing like this is going to get built/launched unless a substantial percentage of our civilization -- or at least a substantial percentage of the wealth of our civilization, which may, unfortunately, be a different thing -- is agreed that it should happen. As I've said before, there are political problems we will need to have completely solved before we're, say, even getting to build a solar-conveyer satellite energy scheme creating and distributing millions of kg of antimatter cells everywhere. We kind of have to assume there's some kind of rational decision-making in place as to what it's all going to get used for
- (or more to the point, if we somehow haven't progressed beyond needing to fight stupid wars, this shit is going to kill us faster and more thoroughly than nuclear weapons could ever even dream)
- But we may want to be careful, all the same. What degree of control should Earth have over these things? How much will we want to trust Future Politics?
Figure the secret key for the root certificate for all of the cockroaches -- if there's going to be such a thing (note that there's going to have to be some kind of security on these things) -- may well turn out to be the most valuable secret in the entire history of the galaxy, in which case, what the hell do we do to protect it? (This is probably a good argument for not having such a thing.)
- If we instead decide to make them truly autonomous, then what principles are we going to have them follow? (there are some gimmes, e.g., "Only terraform bare rocks," and "Stay the hell away from anything that looks like life," may well cover most of the problematic situations.)
- The software will, of course, have bugs in it. How are we going to manage the updates?
- Encountering other intelligent life will be an insanely rare scenario, but we might still want a plan for it ("Drop asteroids on them until they're not there anymore." Yeah okay, I had to get that out of my system…)
- Somewhat more likely, I suspect, will be Encountering Somebody Else's Cockroaches. We may well want to arrange our explorer trajectories to obfuscate where Core Human Space actually is (e.g., skew the directions we explore so that the center of explored space is offset from Earth by some number of lightyears that can keep getting larger, so that if anybody tries to infer where we are, they will lose…)
Meanwhile, while the exploration boundary is expanding, there's going to be stuff happening in the human-settled volume. Which finally brings us to:
(making colonization and commerce work)
This entry was originally posted at https://wrog.dreamwidth.org/65615.html. Please comment there using OpenID.