If I were going to build a launch vehicle from scratch, up until a few years ago I would have used a pair of pressure-fed boosters parachuted into the ocean as originally specified for the space shuttle. As much as I detest a certain company as the worst thing that has ever happened to space exploration it must be given credit for now routinely landing back the first stage of their otherwise mediocre launch vehicle. But not as much credit as they claim, as original work on the concept was done in the early 60’s by Philip Bono. https://en.wikipedia.org/wiki/Philip_Bono . The Vertical Take-off Vertical Landing (VTVL) concept was also incorporated into several proposed vehicles such as the Chrysler Serv from the 1960’s.
Landing back was done in the 90’s with the Delta Clipper and so, like almost all of SpaceX supposed innovation, much of what they claim as their own is just reuse of old NASA taxpayer funded technology. Landing a first stage on a ship downrange may or may not be as efficient as pressure-feds parachuted into the ocean, but it must be admitted applying the technique to a Saturn V sized first stage (with further refinements) is an attractive concept.
The problem with the hobby rocket is it has little practical use for Human Space Flight. LEO stopped being “space” in 1968 with Apollo 8. Space should be redefined as beginning at GEO and cislunar space being the main theater of operations. The Saturn V was the bare minimum and only adequate due to Lunar Orbit Rendezvous (LOR). The original Nova rocket would have been far more useful but of course more expensive due to using nearly twice as many engines. The fewer engines the better and roughly doubling the thrust of the F-1 type engine to close to 3 million pounds of thrust would allow 4 such engines to approach the Nova’s lift-off thrust. With a steering/landing engine in the center with roughly half a million pounds of thrust I would guess this is the most efficient configuration for a reusable Super Heavy Lift Vehicle (SHLV) first stage.
The goal of the SHLV should logically be to send a “Fat Workshop” to the Moon. The SHLV/Fat Workshop concept is, in my view, the fundamental building block of a cislunar infrastructure. The Fat Workshop is a minimum of 50 ft. in diameter (60 ft. would be much better) with a double hull to facilitate a 15 ft. cosmic ray water shield, this size upper stage is what the SHLV must be capable of sending on a lunar trajectory, along with a useful payload. The second stage, due to the laws of physics, can get away with landing back the engine module but the stage itself, as with the external tank of the shuttle, may have to be expended. The most efficient configuration of the second stage would be a single main engine with 3 smaller steering/landing engines. One method of returning the stages to the launch point without transporting them on the ships they land on might be to refuel them and fly them back, perhaps fitted with aerodynamic nose fairings. The second stage engine module would also be within the weight range to be lifted by helicopter and/or returned to the launch site by long range transport aircraft.
One of my favorite concepts for funding a cislunar infrastructure is to move the nuclear deterrent into deep space on human-crewed “space boomers.” The path to building such a fleet of spaceships could begin with monthly SHLV launches of lunar fat workshops carrying robot landers. The function of the semi-expendable Landers would be to alight on the ice deposits at the lunar south pole, derive water and propellants and repeatedly carry the water up to fat workshops in frozen lunar orbits. Once the workshop cosmic ray shield is full the second step would be to attach a tether system to another workshop and spin the pair to provide near sea level radiation and artificial Earth gravity crew compartments.
Once a number of these stations are in a frozen Low Lunar Orbit (LLO) a fleet of Lunar Cyclers providing an Earth-Moon transportation system would be the next goal. After the Lunar Platforms and Lunar Cycler fleets would come GEO platforms and finally the spaceships themselves. A monthly launch schedule would provide for 6 such platforms, Cyclers, or spaceships per year with 60 going into operation in the first decade. Such an effort would be partially funded by the well over one trillion dollars needed for new terrestrial nuclear delivery systems. Besides ratcheting down the over half century launch-on-warning conditions to a far less dangerous situation, the superpower space boomer fleets would defend the Earth from comet and asteroid impacts.
Ice on the Moon 