Doug Plata has done some detailed comments on the suggestions, ideas, and differences from his ideas that my posts laid out in minimal form. His comments deserve better than I can do in a little comment window. Probably better than I can do in a post, but I won’t admit that part in public. It is my opinion that these technologies would speed up Lunar development, expand the possible scope of operations, and cut the cost in the process. They do carry risk though, which is Dougs’ objection, along with getting permission to use them in the first place.
I did a post on my views on the Lunar hoverslam landings. This one is how I see the depot and rotovator getting underway. I think initial proof of concepts and bringing the TRL up to snuff should be done on company internal resources without fighting the Federal funding battles.
The only real reason depots are not in use now is that there is no real demand for them. A comment on one post noted that propellant in orbit was as valuable as dirt. A bitingly true statement as long as there are limited missions beyond LEO, and few satellites share orbits that would make depots useful. A constant flow of material to and from Lunar orbit changes the situation with many vehicles taking the same path.
I see the initial depot flights as secondary payload technology demonstrators. Often flights to LEO are at less than payload capacity of the launcher. Either the upper stage carries a small second spacecraft, or it makes a rendezvous with another vehicle. The upper stage docks(berths?) with another vehicle and transfers propellant to it. They separate for a while and then hook up and transfer propellant back. Operating as a secondary payload on a stage that is expendable anyway should have the possibility of being a fairly economical mission. This would give a chance to solve propellant settling and transfer in (off?) the real world. Several missions could be flown for relatively low operating costs until the company is comfortable with the transfer techniques and has the boil off data for a few configurations. Then start flying more ambitious missions that do need some help until it is an accepted practice. There is too much information out there on depots to justify me going long on the subject.
Rotovators are far more risky. The payoff is also very high. The Lunar rotovator alone would offer major savings to a serious development operation. The ability to return material from the Lunar surface to an Earth bound trajectory without propellant, engines, or tanks would make it attractive even without the ability to intercept cargos from Earth for a soft landing without fuel. The TRL is very low for tethers of any kind in space with rotovators having no test data at all.
I suggest the rotovator demonstration unit be a secondary payload with the minimum mass that can demonstrate the principles. This mission would be the rotovator itself, whatever auxiliary equipment is needed to make it work, and a bunch of expendable small spacecraft with the only function being thrown and caught.
The rotovator is lightly spun up when orbit is reached testing deployment and system dynamics. The initial target velocity is that which brings the tip thrown vehicles to a 15 orbit per day instead of 16 of the base vehicle. This brings the small vehicle back to rendezvous in one day if all the calculations and results work out. It is to be expected that most of the little test spacecraft will be missed and lost early on. Perigee would be kept low enough that missed ships would reenter in a matter of days to avoid creating more orbital debris. It would be a risk that there would not be enough of the little ships to establish success and possibly no captures at all on the first rotovator mission. Further rotovators would be sent out as secondaries until accurate slinging and reliable captures were expected instead of experimental.
After initial proficiency is reached at the 15/16 orbits, velocities are increased to 14/16 and 13/16 until the 1,600 m/s target is reached that would validate a Lunar rotovator. Then one is sent to Lunar orbit as a working system. If the 1,600 /s units were successful enough in Earth orbit some would remain to pick up suborbital ships to sling them most of the way to GTO or TLI with the rockets relighting after the rotovator boost.