Just watched a video about the document... https://space.nss.org/nss-roadmap-to-space-settlement-3rd-edition-2018-contents/ Which is the National Space Society attempt to set out what's needed to get the whole living in space thing going. Some of their stuff seems quite logical. Like step one to lower the cost of getting into space. This I see as being like the aeroplane model. It won't quite play out the same but at the moment the companies like SpaceX, Blue Origin, Virgin Galactic and a few small players like the recent one planning to use helium balloons to take people up into space. This reminds me of the early Farnborough International Airshow days when planes were diverse and often dangerous. We have better safety, design and testing tools nowadays to back then so I expect the space version to be safer and evolve quicker than aeroplanes. Though like aeroplanes it's going to take some people to try things that are not ever going to work and eventually there will be a single best way of launching people into space like the Boeing 707 that will set the standards for decades to come. Ultimately I don't think humans will travel direct to many off world places. I think the most economical way will end up with people travelling to some orbiting space port/station and then transferring onto some ship that never lands but just ferries people around in space. This makes so much more financial sense to me as you would set up some sort of regular scheduled flights to a few low to mid earth orbit and optimise a craft for doing that. This seems to be the Blue Origin and Virgin Galactic aim and if they can get their services up and running then slowly improve on them they could get there quite quickly. I think these will end up being mostly automated and ideally you would want to get it down to under a few hours from launch to arrival at the station. From this station you will transfer onto smaller craft that go from the station to hook up with your main flight. I see these doing some sort of orbital ballet where they take you to your destination then slingshot around that body and come back to Earth, where they slingshot around Earth and shoot off to their next destination. These can then be optimised for the long trips, well beyond the Moon anyway, without needing the heat shields, landing and taking off rockets or structural integrity. Instead it can be designed just to move through space and cope with the radiation, heat and other obstacles in space. Smaller crafts dock to it at each end and load/unload the passenger as well as refilling the ships supplies of fuel, food and other essentials. Getting to your final destination will probably be the same in reverse. Their second step of Continuous Human Occupancy in Low Earth Orbit I'd argue we sort of have at the moment with the ISS. I remember back when the first crew launched it was noted that this could be the start of humans permanently having people living off planet from then on. I'd say that this should be like the first point that we just need cheaper solutions and a lot more. A likely contender for these occupied orbiting places would be the transfer stations, which can double up as hotels too for people that just want to go into space without heading out further into space. There is already a company called Axiom that is working on adding modules to the ISS and once self sufficient it can detach and become an independent space station. I can see this grow and divide model working quite well as a modular design to start with seems to make sense. Easy to repair, replace or upgrade and you can keep expanding with demand until it get to a size you can split it into two separate destinations. Maybe not that far apart like terminals at an airport. This is obviously at the very early stages and will take time to work out what sort of thing people like in these stations and what don't work. As the heavy lifters, the equivalent of the transport ships on the ocean, get cheaper and can carry more payload then this will accelerate the building of these structures. I imagine for this we need some huge rockets that most likely launch from sea a very long way away from any population. It already seem like SpaceX is considering this for their huge starship type thing. I can see both the heavy lifers enabling launching modules big enough of the initial occupants at about the same time that the likes of Blue Origin, Virgin Galactic or SpaceX will be able to safely and cheaply transport people to the orbits they will occupy. This will then kickstart the Development of a Space Tourism Industry their point number 3. So I think these first three points is really tied together into reducing the cost of getting people off the ground and into an orbiting station. After these points I think I start to deviate from what they state.... More on that later.