idobox wrote:The thing is you need factories in space to build habitats, and you need habitats to build factories.
At first all habs will be built on earth and lifted from earth's gravity well. We will not have the infrastructure in space to do this sort of challenging manufacturing for some time to come.
However In Situ Resource Utilization can reduce hab mass. At the lunar poles there is water. Which can be used for radiation shielding and drinking. You can split it to hydrogen and oxygen. Oxygen is useful for breathing. Hydrogen and oxygen is useful for propellant. A propellant source high on the slopes of our planet's gravity well could be immensely useful in enabling space transportation.
Further, the moon is close enough that much of the work can be accomplished with telerobots. Not so for NEOs or Mars.
idobox wrote:At one point, someone will have to invest an absurd amount of money, time and effort to build the first step.
It's my contention that building lunar infrastructure is plausible while NEO and Martian infrastructure much less so.
Let's review the metrics:
Frequency of launch windows
Communication light lag
Delta V has a huge impact on vehicle size, complexity and reusability. Local propellant resources can break the delta V budget into several parts. In terms of delta V and trip time, lunar propellant is quite close to EML1, EML2, GEO, LEO as well as other orbits in the earth-moon neighborhood.
Lunar propellant has the potential for enabling transportation to all parts of our solar system as well as within the earth moon neighborhood. Martian propellant has the potential to enable trips from Mars to earth, but little else.
Most of the metallic asteroids likely have no exploitable volatiles that could be used for ISRU propellant. If their platinum takes a 20 km/sec round trip for delivery to earth market, they will never be profitable.