Our visions about the possibilities for living in space have been derailed by two unfortunate influences: the frequent resort of lazy science fiction writers to the fantasy of faster-than-light (FTL) travel, and an excessive focus on planets. This has led to a vision of life in space as a series of (hopefully faster than light) trips between planets. Both ideas are worse than wrong -- the first because it is impossible, the second because it is wildly improbable.
There is only one earth-like planet in this solar system, and its inhabitants are engaged in a large-scale project to reduce that number to zero as quickly as possible. The number goes to zero in any case in a timescale of a few billion years. Thus any travel to earthlike planets is necessarily interstellar.
If we consider the requirements of interstellar space travel in a non-fantasy world without FTL drive, wormholes, or other paraphernalia of lazy science fiction writers, it is clear that we would need systems for living in space for extended periods of time. Assuming lifespans similar to what we currently enjoy (or endure) these trips would last many generations. Those generations that live and die en route would not experience their lifetimes as a journey between planets (assuming a planet was the ultimate destination): they would be living in space. If we cannot construct an environment that makes multigenerational human(ish) life in space bearable, we might as well accept that we are doomed to live and die with our home planet (in which case we might want to consider taking better care of it). On the other hand, if our descendants could live in space on a multigenerational voyage, why bother going anywhere? They are already there. "Whereever you go, there you are." The beauty of adapting to life in space is that there is so much of it: no longer confined to the limited habitable real estate of Earth, or the (apparently) very limited supply of Earth-like planets, the 3-and 4-dimensional horizon of the entire universe beckons invitingly.
One might argue that while Earthlike planets may be in short supply, planets are nonetheless necessary for creatures such as ourselves, and that uninhabitable, un-terraformable rocky planets such as the moon, Mars, Mercury, maybe Venus, or the larger moons of Jupiter and Saturn would be better homes than space itself. At least we would have gravity. And some raw materials.
This view may have some merit, and I certainly wouldn't argue against colonizing these places where possible. However, any such colonization would have to occur in conjunction with the development of space-based transit networks -- orbiting space-stations and long-voyage ships -- which would require substantial adaptation to life in space.
Rockets require enormous amounts of propellant to accelerate payloads, most of which is spent accelerating the propellant itself. A round trip to anywhere requires enough fuel to accelerate towards the destination, decelerate on arrival, reaccelerate for the return, and decelerate again for the final landing. The rocket equation imposes an exponential dependence of the ratio of final to initial mass on the change in velocity; this would be compounded by the 4 legs of the roundtrip journey. The obvious conclusion is that rockets are no good in the long term. Solar sails may provide a promising alternative for moving about the solar system. Like sails from the age of sail, they use ambient energy sources to accelerate without the need to carry (or accelerate) fuel or propellant. Whether the same approach can be adapted for interstellar sailing is unclear; most current proposals depend on laser beams pointed bythe sender, so are not sustainable over large distances or times. Another approach, the Bussard ramjet, would use interstellar matter either as fuel or propellant, but it is not clear if it would work.
Is living in space possible? By that I don't mean the 6 month visits of today's space tourism, but living one's entire life there, birth to death, for open-ended numbers of generations. Could it ever be desirable? What technologies would be required? What would it do to us -- what would we become -- if we chose to live there? Is space fit only for our silicon creations or could carbon-based life make a home there? Would space-adapted humans become cyborgs, or squid, or something else? Could carbon-based life become endemic, infecting portions of space currently considered incompatible with life?
- Gerard O'Neill was one of the first people to argue that space may be a better place for a technological civilization than Earth's surface.
- Beyond by Chris Impey
- Solar sails may represent the best way to traverse the solar system -- no fuel needed!