In the distant future, assuming mankind eventually takes to the stars, how big will starships be and how many crewmembers will man them? I have pondered these questions before as a GM for various space-based games. There seem to be two schools of thought on this in space movies, the "Star Trek" model and the "Alien" model.
In the "Star Trek" model, starships are like navy ships today. They come in a variety of sizes, but they all have large crews. It's not entirely clear why this should be. After all, a modern warship needs lots of crewmen to man guns, to repair battle damage and to replace casualties. In Star Trek, and most other space shows and movies that follow a similar model, many of these responsibilities seem to be handled by a small number of people. Weapon batteries aren't manned individually, rather, they are controlled from a single gunnery station on the bridge. Likewise, most engineering functions seem to be controlled from a single location manned by only a handful of people. Many of the people on board "Star Trek" type ships seem to serve no major purpose except to repel an occasional boarding party and to serve as casualties so the major characters don't have to.
The "Alien" model envisions enormous ships with tiny crew complements, typically fewer than 10. This is similar to modern freighters and tankers, which have small crews since they don't need much in the way of skillset redundancy or security. A small bridge crew, a cook and a couple of deckhands are sufficient. A giant freighter in space would probably need a few more crewmembers than a present-day ship because help is far away. A couple of people with technical skills would be required as would someone with medical knowledge. Still, that adds up to no more than a dozen at most.
My current thinking tends toward the "Alien" model for a couple of reasons. First of all, humans require a huge amount of resources for life. Food, water, air, living space, recreational activities all take up valuable space and cargo capacity on a ship. Many activities on a spaceship can be performed as well or better by robots and computers, so I'm guessing these will be used whenever possible to reduce the number of humans required. Secondly, I expect the drive systems needed to propel spaceships will be friggin' huge. Consider this, according to E=mc2, it would take 900 petaJoules (quadrillion) to accelerate 1,000 kilograms of matter to 0.1 lightspeed. If we took a year to get to 0.1 c, it would require 28.5 GW of continuous power output. The most advanced nuclear fission reactors today produce about 0.6 to 1.2 GW and they are, themselves, heavier than 1,000 kg. When you add in fuel, radiation shielding and reaction mass, a fission drive will be orders of magnitude larger. Of course, fusion or other more speculative technologies might come into play, but we're still talking about pretty large propulsion systems. For this reason, I suspect space within starships will be at a premium, much as it is now on the space shuttle.
So, I envision massive starships, kilometers in length, with most of the bulk being drive systems. Of course, the question then becomes, why are we going into space at all? If it is just for exploration, why send people at all? Robots fulfil that role right now and they do it a heck of a lot cheaper. On the other hand, if we want to exploit the natural resources of the asteroids and comets, we will need huge cargo holds (probably in the form of detachable modules) and even more drive capacity to transport these massive amounts of material. This seems enormously inefficient, so perhaps factory ships will be the way to go. Process the raw materials where they are and then transport the refined material or finished products. Again, it seems like most of this could be done a lot cheaper by robotic systems. It seems the only reason to send people into space is colonization. That changes the calculus a lot. Now you need large numbers to create viable colonies. Depending on how livable the colonized worlds are and how much support they can expect from Earth, we could be talking a hundred or several thousand. Any less would seriously threaten the viability of the colony.
I'm not really going anywhere with this, hence the title of the post. I'm just looking to generate discussion and get ideas from the rest of you nerds.