I am not exactly sure what the delta v difference between the barest once around orbit and a depot might be, but I suspect it is significant. Perhaps a tug to make up the difference and do the docking. Maybe even often only bringing the payload to the depot and leaving the RLV to reenter – saving the RLV deorbiting delta v.

3 – depots next – what would be the next steps to make this a reality. especially if we wern’t willing to wait until Boeing to do something on their own.

I hope Masten’s success doesn’t keep you from exploring these options.

4,5

Pete’s #6 “low cost workshops” sounds worthwhile as well.

As for #5 you could include an idea (from Alan Stern?) of firing chunks of ice to the moon (if no indigenous ice could be found) with astronauts excavating some fraction that would wind up embedded in the lunar regolith. Outrageous, but seems more reasonable than firing extracted oxygen at an approaching spacecraft to generate aerobraking in the lunar vacuum.

Only Bigelow seems to be working in this area, though they do not seem to be working on developing workshops and they also seem trapped somewhere between old and new space.

Not being able to develop stuff in space leads to the when failure is not an option success becomes very expensive paradigm, this is not the new space way. Space workshops must come before #4. and #5 at least. Developing space infrastructure without a usable workshop is really asking for trouble. It would be like developing a lunar lander challenge vehicle without a workshop…

With regard to #1, I have started playing with the idea of electric VTVL air launch. Similar to lunar lander challenge vehicles but using lithium batteries and electric ducted fans.

Practical air launch altitude is about 10-15km, and increasing every year as batteries improve, one could go higher with staging. This is sufficient to design rocket vehicles without altitude compensating engines, significant aero drag losses (small scale limitations) or even cryogenic tank insulation (shroud the rocket vehicle until release).

Development costs (similar to an electric car), fuel costs, utilization rates and general operating costs appear to be orders of magnitude less than for traditional air launch – this has by far become my favored method of air launch and changes the design and economics significantly. This is far cheaper than any alternative for the atmospheric delta v section of launch, as far as I can see.

The glide forward trajectories are still possible, though range is limited. For fast pick up and return of stages landed down range is also possible – without the need for runways.

Such electric aircraft could also be used to test or replicate many of the challenges associated with #1, at much lower cost and far greater convenience. I suspect a fully reusable CATS vehicle as per #1 could thus be developed at the scales so far used for the lunar lander challenge. $10 million might go a long way, perhaps even all the way to orbit, definitely high enough to start testing reentry systems (I am ignoring regulatory costs here).

An electric aircraft capable of launching a one ton rocket vehicle at 10-15km might cost a few hundred thousand dollars to develeop, can be capable of many thousands of flights with little maintenance and cost perhaps $10 per flight to recharge. Turnaround time could be as little as ten minutes with some battery types. Interestingly, this is fairly scalable, up and down.