Inserting into orbit, descending, ascending, and departing the Moon was originally accomplished with pressure-fed hypergolic engines. No turbopumps, no regenerative cooling, with only the descent engine on the lander even having a variable thrust mode. The 20,000 pound thrust of the service module (actually twice as powerful as necessary), the 10,000 pound thrust descent engine, and the 3500 pound thrust ascent engine required no ignition systems or cryogenic management and used high pressure helium bottles to pressurize the fuel tanks. Not much could go wrong and these engines were not even test fired before actual use.

However simple does not mean cheap. The absolute reliability required meant a phenomenal amount of work went into these systems. The ascent engine in particular had no failure mode- no back-up. It had to work. Armstrong actually suggested a manual lever to actuate the ascent engine to get rid of the electrical system. Making these engines “reusable” would have made them more expensive and far more complicated- and increased the possibility of failure. Using cryogenic propellants and regenerative cooling for a longer service life would again make them much more complicated. This kind of craft would require a pressurived and radiation shielded (underground) hangar, mechanics, spare parts, and support equipment to keep flying- there is no way around it.

The rocket equation is merciless and imposes severe limitations not only on performance but on “reusability.” Future developments in beam propulsion, which would use a monopropellant in a much different fashion than conventional rocket engines, might reduce complexity and increase reliability- but require a Moon base of course.

I completely blame the NewSpace movement for this.

It is now set in the public awareness that “space must be cheap” and billionaire hobbyists are much smarter than NASA engineers. In reality the basic requirements were all worked out in the 60’s and the laws of physics and materials science have not and are not going to change.

This “corrupted paradigm” and endless marketing of dollar sign hyperbole has found it’s way into all discussions about space. No one dares to stand up for the idea that some things do cost money and you get what you pay for.

Sadly, it now causes the majority of people with a fair amount of common sense and some technical knowledge to err on the side of the fairy tale instead of the slide rule.

The ISS already produces oxygen through the electrolysis of water, simply throwing away the hydrogen produced. Propellant depots on the Moon and in orbit will simply liquefy the H2 using cryocooler technology already invented by NASA. Cryocoolers can also eliminate the boil-off of ullage gasses.

Heavy lift vehicles will enable NASA to deploy water/propellant depots and large reusable LOX/LH2 interplanetary vehicles capable of transporting hundreds of tonnes of cargo and crew to Mars orbit.

A reusable crew lander that is also capable of being utilized as an– unmanned– transport to deploy multiple small mobile robots, each perhaps weighing 100 kilograms or less, would be quite useful, IMO. Such a vehicle could be used to retrieve as much as a tonne of regolith samples from the lunar poles and other interesting regions on the Moon and return those samples to EML1 for human return to Earth via the Orion or other vehicles capable of traveling between LEO and the Lagrange points.

Performing maintenance duties on the ISS or, in the future, on the surfaces of the Moon and Mars will be just part of the essential pioneering experience.

Marcel

Also gives insight into the history of the Ranger probes that I wasn’t aware of.

A human-rated reusable lander is an entirely different proposition than a semi-expendable robot lander so we do not really agree Marcel. Any conveyance that is going to descend into and out of the lunar gravity well with humans will be much more difficult to maintain than any type of terrestrial aircraft. Performing maintenance and fueling will require a pressurized underground hangar and unless we find some lava tubes to move into that may take awhile. I consider Mars and LEO to be dead ends.

The fuel depot miracle has never been anything more than an argument to justify smaller, nearly useless inferior lift hobby rockets and an excuse to cancel any Super Heavy Lift Vehicle. It is a transparent marketing ploy and has never been considered seriously in 40 years of LEO operations. There is a reason for that- it is a hopelessly complicated mess. The only place there will ever be any large fuel farms is under the surface of the Moon.

The ULA plan to use a piston engine to manage cryogenic boil-off is very clever but it will not solve any of the major technical obstacles concerning propellant depots. It can manage LOX and methane well enough on the way to the Moon and for limited duration missions in lunar orbit but it will not work to re-liquify hydrogen.

Such a vehicle could be deployed to EML1 by the SLS. At EML1 the ETLV could transport crews or multiple small mobile vehicles from EML1 to the lunar surface and back on a single fueling of LOX/LH2.

With the RL-10 engine’s ability to throttle to as low as 8% of maximum thrust, an ETLV could also be used to land humans and mobile robots on the tiny moons of Mars.

With NASA’s future ADEPT deceleration shield, a lunar ETLV could also be used to land crews or mobile vehicles on Mars and transport astronauts or the mobile vehicles back to low Mars orbit.

With SLS deployed propellant depots at LEO and EML1, an ETLV could also be used as an orbital transfer vehicle, transporting crews between LEO and EML1 and then on to the lunar surface. So such a vehicle, with propellant depots, could also give Commercial Crew passengers access to the lunar surface. You could even derive the propellant depots from the ETLV vehicle architecture.

If full funding for an ETLV started in 2017 then Extraterrestrial Landing Vehicles could be transporting humans to the lunar surface well before 2025.

Marcel

As I have commented in the past, partially filling spent upper SLS stages in lunar orbit turns them into near-sea-level radiation sanctuaries proof against the worst possible solar events and cosmic radiation. A tether system attached to two such workshops would provide Earth gravity. The hundreds of tons of water in each shield would serve as a medium for a closed loop life support system. These true space stations would allow long duration human habitation Beyond Earth Orbit with no ill effects.

No radiation exposure, no hypo-gravity debilitation, and by mating the station with a nuclear propulsion system it becomes……a spaceship.