Being at the Icarus Interstellar conference along with many people who have spent their careers designing and building spaceships, and the slogan of which is "Build a Starship," it is appropriate to reflect on the problems of spacecraft design.
There is an amusing list of forty "laws of spacecraft design" that is readily available, and which includes as its final "law" this observation:
"Space is a completely unforgiving environment. If you screw up the engineering, somebody dies (and there's no partial credit because most of the analysis was right...)"
Recently I watched "How to build a nuclear submarine" and I realized that this might possibly be a helpful analogy to understand building spaceships, i.e., to think of building spacecraft of the future as we think today of building a nuclear-powered submarine.
For starters, a spacecraft is going to have significant power demands, and the most compact way to address this with our current technology is what we do with your biggest submarines: nuclear power. These compact reactors on submarines (and aircraft carriers, which typically have two reactors) have proved themselves to be safe and serviceable, and they have keep generating power for 25-30 years without refueling.
Like a nuclear submarine, an SSTO (single stage to orbit) spacecraft will be one of the most technically difficult and demanding engineering tasks ever attempted; it will involve parts suppliers from all over the world; it will involve millions of individual parts that each have to fitted in place by a human hand, and the assembly itself is likely to require many years of painstaking construction.
When we are able to build spacecraft that take off directly from the earth and fly into orbit (HOTOL -- horizontal take off and landing), perhaps beyond earth orbit after that -- i.e., the kind of spacecraft we see in every science fiction film, and which we call an SSTO -- and as our technology for doing so improves, we will be faced with a choice: do we build spacecraft on Earth and send them into space, or do we build them in orbit? It would seem to be obvious that we would build a spacecraft in orbit, because there we need not concern ourselves with aerodynamics and we can build a spacecraft as large as we like without it having to go through the stresses of transiting the Earth's atmosphere.
But there is a problem with the obviousness of this vision. For the next few decades at least, and perhaps for longer, there will be no machine tools and no industrial plant in space. All the facilities we need to build a large and complex engineering project that is likely to occupy many years of painstaking effort, are earth-bound.
At the Icarus Interstellar Starship Congress today, a member of the audience asked a question of Kelvin Long in which the questioner used the phrase, "the infrastructure problem," which strikes me as the perfect formulation for talking about the difficulties sketched above.
There are advantages to constructing spacecraft in orbit, but the world's most advanced industrial plant and best construction teams are on the earth and will be for some time, so that there remain compelling reasons for continuing to construct spacecraft on Earth, despite being at the bottom of a gravity well (which someone else today called "the minimum of a gravitational potential"). This, in a nutshell, is the infrastructure problem.┬а
