Many people think that Mars is the primary target for off Earth settlement and development. I think that is likely to prove wrong as people start the process of moving onward. Skipping the moon to go to Mars strikes me as similar to Europeans skipping the British isles because the Americas had so many more natural resources. There is a reason the isles were inhabited for millennia before Europeans crossed the oceans. It’s called logistics. Continent to isle was a few hours in a dugout canoe with very few supplies while Europe to the Americas was months with oceangoing equipment and equivalent supplies. It’s unlikely the anyone died of scurvy during the canoe day voyages.
This is not another NASA should or Elon must post. This is a possibility of what I suspect will work out over time. Let NASA, Elon, Jeff, and others do what they think is right. Let the ones that have a reason to do things do them in their own time and their own way.
The Mars advocates point out that Mars has an atmosphere that allows for aerobraking and is a resource for oxygen and carbon. There is also considerably more known water on Mars than on the moon. The search for possible life, or even evidence of it existing previously, pretty much rounds out the advantages Mars. Except for the projected second home of humanity, which can be accomplished in a number of other ways.
There are a number of advantages that the moon has over Mars in addition to the logistics. Far side radio telescopes away from Earth spectrum noise. 3 second lag time for remote operated equipment. Lighter gravity for retirement living as suggested by Dr. Plata. The possibility of those skilled retirees still working in an environment that is not stressing their bodies with a full gravity. Fully secure location for dangerous research biological, nuclear, and anything else that requires that mistakes occur away from Earth. A third data point on gravities effects on the body.
The moon is assumed to be poor in carbon and hydrogen in particular with nitrogen and other materials close behind. It would seem arrogant to assume that a land area larger than most continents has been properly prospected by a dozen or so sample returns. I suspect that most minerals and volatiles wanted will be found in some quantity with proper searching. One impactor could supply carbon for the next several decades.
In situ propellant production is often mentioned as the Mars advantage using the atmosphere and ice to make methane and oxygen. Locate one carbon source on the moon, and mine that along with oxygen and carbon monoxide/oxygen rocket propellant becomes feasible. Give up a hundred points in Isp compared to methane/oxygen, but still would only need a mass ratio of two and a half to reach Lunar escape. Even methane/oxygen takes considerably more than that to get from the Martian surface to Earth trajectory . Getting to Mars may take a little less deltaV than getting to the moon considering aerobraking, but the round trip takes less.
The logistics and capital investments are the key advantages for the moon. A company or government with one ship would have a turnaround of over 4 years for the Martian run (assuming Hohman transfers). A single ship going to the moon could make dozens to hundreds of runs in the same timeframe. Monthly runs would have a ship delivering 52 payloads to the moon while a similar ship is delivering 1 to Mars. And if there are not 52 payloads that need to go, the ship is available for other work.
For any off Earth development to occur, it must be assumed that transportation to LEO is a solved problem. If one assumes a mass ratio of 6 from LEO to the lunar surface, then perhaps 10 tons of mass to LEO to per ton on the Lunar surface. Oddly enough, it will be a similar ratio to get a ton to the Martian surface even with the advantages of aerobraking. The heat shields and parachutes are not free mass, nor are the redundancies required for a multi-month journey. Manned flight to the moon is about 4 days which can be done with forecasting and minimal shielding while a Martian trip of months will have to use advanced cleverness to have a storm shelter available.
Anyone that has been involved in development of equipment is familiar with the problems in new systems that require troubleshooting. Several of the last lunar attempts have been by companies with relatively limited resources launching small vehicles as rideshares. Some of them in the last couple of years failed and are being retried with upgraded equipment. This is a timeframe and investment that applies to the moon by multiple small operators. As the systems mature, reliability will improve, and costs will come down. More players can be expected to join the attempts and major players will be watching them in case opportunities become evident. The search for available water and other volatiles will be enhanced by many players with various ideas and focus.
Leaving the moon is an ongoing topic featuring railguns, tether slings, cannons, and a few other exotics. Lifting off in rockets with Lunar sourced propellant is likely to be the early method. Most people seem to assume the requirement to find a hydrogen source for either H2/O2 or Methalox engines. Something I recently noticed (again) was the concept of CO/O2 rockets. Carbon Monoxide and LOX give up about a hundred points in Isp compared to Methalox and almost twice that compared to H2/O2. However, even the lower Isp could reach Lunar orbit with a mass ratio of less than two, and TEI with a mass ratio of two and a half.. Find one carbon source and use that with the known oxygen for the rocket fuels.
The reasons for being on the moon, or Mars, or a beach in Tahiti will be as varied as the entities that go. As the attempted landers have failed and retried recently, so will the surface activities. Different groups will send different landers with different capabilities and goals. With the short travel distance and time, they can break things and move fast in the current buzzwords have it. You can’t do that with Mars due to trip times and communication lags. While trying to get a billion dollar project going on Mars, many other people will be attempting to get million dollar projects going on the moon. In the history of innovation, the multiple attempts by multiple players have found a lot of solutions. The logistics of the moon favor multiple players in a way that Mars cannot for the near future.
The Starship will try flight test 8 in a couple of days. How far along would the test program be if tests were restricted once to every 26 months when a launch window opened???
johnhare
Latest posts by johnhare (see all)
- The Cost of Skipping Bases - July 12, 2026
- The Moon as a Preferred Off Earth Settlement - February 26, 2025
- SPS in the Van Allens - October 21, 2023
We don’t know the long term effect of Lunar gravity, nor Mars gravity. And lunar gravity might be better for older humans- one reason is older humans can be given shorter lifetime if they aren’t injured from falling {ie, falling down stairs}. Also lower gravity for older people could help keep older people more “physically active”. Or also make sleeping less of an issue.
It seems people living on the Moon, should be able to do more activity other than using exercise machines in some confined space. Or park like environments as compared to living in a environment such as ISS [or smaller].
It seems the cheapest way to do this, is living under ground in large Lava tubes- and the Moon is expected to have many of them.
There is another “goodie” on the Moon: it’s colossal lava tubes. Check that paper.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071588#grl55400-tbl-0001
Up to 170 km long. The Ocean of Storms underground is like Swiss cheese: full of big holes. Comparable to O’Neill cylinders, with the usual pros and cons.
Then it is all a matter of gravity.
Earth largest lava tubes : 30 m
Mars largest lava tubes: 300 m (thanks, 38% of Earth gravity)
Moon largest lava tubes: 3000 m (thanks, 16% of Earth gravity)
Numbers taken from reference papers.
What’s more: the regolith walls of these giant caves are 45% oxygen by weight. Plus Dennis Wingo PGMs brought by asteroid impacts; and some Rare Earth Elements from the Procellarum kreep terrane. Follow the thorium to find the REEs.
More generally, the Ocean of Storms if a fascinating place, with anomalies all over the place: such as the weird Reiner Gamma feature, or Aristarchus.
One business I never thought* of was caving on the moon. Robert Zimmerman over at Behind the Black is an avid caver.
*One of many I am sure. It will take many viewpoints and many attempts to get to the ones that work. Ones that work in terms of being financially self sustaining.
Well Robert Henlein once had a totally awesome idea. He calculated that, with the correct air pressure inside big lunar caves (and thanks to the 6 times lower gravity) people could fly like birds: flapping wings, taking off, the whole nine yards.
So yes, giant lunar caves with ultra low gravity could provide a lot of fun.
There are already similar business on Earth, despite the strong gravity.
https://en.wikipedia.org/wiki/Vertical_wind_tunnel
https://en.wikipedia.org/wiki/Wingsuit_flying
https://en.wikipedia.org/wiki/Jet_pack
And countless others.
I blame Kirk Sorensen for my obsession with momentum exchange tethers.
For MXers to work you need a source of up momentum as well as down momentum. I believe that could be the moon’s major commodity: up momentum.
Catching lunar PGMs, REEs and O2 from higher orbits and dropping them to lower orbits would provide up momentum.
I still believe Lunar O2 delivered to LEO could be immensely helpful in reducing re-entry velocity and thus make economical re-use of upper stages more doable.
A chain of MXers between LEO and the Lunar Hill Sphere would mitigate the gear ratio obstacle to lunar propellant.
I also see the Lunar Hill Sphere as a bay and port into the larger ocean of the solar system. EML1, NRHOs, EML2 and other loosely bound lunar orbits have similar Jacobi numbers. So delta V from one such orbit to another would be quite low. And Trans Mars Insertion from EML2 is about 1 km/s (using the Farquhar route).
In my day dreams the Lunar Hill Sphere will be a volume of immense strategic importance.
Thanks to the Moon being so huge, Earth has ten useful libration points rather than five, like Venus: EML on top of SEL. Delta-v between them are minuscule. Delta-v between them en LLO (on one “end” and GEO (on the other “end”) are very reasonable. And since then NASA has added DRO and NRHO to the list. Plenty of waypoints.
Lunar “energy of position” could be an important export via tethers or more of an impact based method. Isp in the 1,000-2,000 range for impact based. Two links.
http://www.walthelm.net/inverted-aerobraking/main.htm
http://selenianboondocks.com/2008/11/earth-launch-with-lunar-fuel/Â
Unfortunately it has become more difficult to have a reasonable discussion on most sites with various fans chanting Starship Starship. Along with claims of getting costs on orbit to single digit dollars a pound, or kilo for some. Their chant is that Starship will get costs so low that Lunar anything is a waste of time.
The problem is more fundamental than Starship fans. Demands for major infrastructure projects *on speculation* are complete non-starters. You can talk about building a bridge if there are a lot of people crossing the river but not before. You can talk about building a canal through Panama if there are a lot of ships rounding Cape Horn but not before. And you can talk about momentum exchange schemes with lunar material for launch when you have a lot of launches with a lot of mass to orbit and beyond but not before. The current launch capacity is way to small to justify such schemes.
Good point jim. The way I see it, many companies and nations will be doing small missions to the moon for many reasons. I expect some of them will find reasons to expand their operation. A century from now I expect people will be able to look back and say, “it all started with that little survey that no one thought worthwhile.” Somewhat as people are talking about the Russian snub of Elon a quarter century ago.
My main thing is pushback on the Mars focus and the Starship obsession. I think it will be more feasible to produce anything on the moon than it will be on Mars. Mining a rock on the moon with 3 second delay and 4 day travel I expect to be much earlier than mining the Martian atmosphere and ice fields. And I also don’t see Starship as the end all-be all of spaceflight. An advance almost certainly, but a step in the road rather than the whole trip.
“The problem is more fundamental…”
To have a settlement on Mars, one needs a fully reusable rocket.
One could say, to mine the Moon, one needs a fully reusable lunar rocket.
SpaceX doesn’t have a fully reusable rocket.
Blue Origin needs a fully reusable first stage rocket- and hasn’t successfully landed, it’s
first stage rocket yet, nor of course, reused one, yet.
SpaceX, according to Musk, doesn’t have a fully usable first stage falcon-9, and plans to make a rocket which does have a fully usable first and second stage rocket.
Though SpaceX has reused some of it’s first stage rockets, 25 times- which is quite impressive. One could say a first stage rocket which doesn’t have to use as much rocket fuel returning to it’s launch site, is “more” towards being fully useable, as it can deliver more payload to orbit rather using the rocket fuel to land first stage.
A lunar reusable rocket, could land it’s first stage “down range”. Or as single stage rocket it could carry enough rocket fuel, to deliver payload to lunar orbit, then return to lunar launch site, and refuel the rocket. Or it can have the rocket fuel in lunar orbit, or one component of rocket fuel, like LOX to refuel a rocket with in lunar orbit. Or it needs rocket fuel on lunar surface, or rocket fuel in lunar orbit. Or both.
Compared to reuseable Earth rocket, one might say a lunar reusable rocket is more doable. One could say something similar with a Mars reusable rocket- ie, the rocket fuel could be just on Mars surface, or Mars orbit, or both.
And if there was a Mars reusable rocket, one wouldn’t need Starship landing on Mars.
Instead one might regard a Starship as just a faster way to get from Earth to Mars- the heat shield brake one velocity. And could be fast way to get to Venus orbit
There’s plenty of hydrogen available in frozen water at the poles (and even significant CO iirc according to LCROSS mission). However, if you want an alternative propellant, aluminum/LO2 (ALLOX) monopropellant might work. Isp ~280 s and provides great thrust. Supposedly, an Al/H2/O2 tripropellant has an Isp better than H2/O2.
There is an old NSF thread that discusses the concept.
https://forum.nasaspaceflight.com/index.php?topic=14380.msg532059#msg532059
Jim Davis. The analogy with building bridges and canals is apt, but there are gradations. A rope bridge might be deployed first with the effect of increasing trade between both sides. Over time that crossing gets upgraded rather than going from a chasm to the Golden Gate in one leap. Constructing a small subsurface habitat on the moon can act as a tech demonstrator and ongoing place to test techniques. There won’t be need to build accommodations for 100 and a comprehensive research capability in one giant initial project.
National space entities can do a lot of initial work to prove concepts and identify issues so that industry can follow on with investments that have commercial applications. There needs to be that rope bridge that lets some brave adventurers make the crossing.
Jim Hare, The one critical resource that isn’t on Mars is Nitrogen. While people fixate on the need for Oxygen that people can breathe, they ignore that most of what we breathe is Nitrogen. It’s also important for plants in various bound forms which means that growing food on Mars will be very difficult. Having a containment breach and losing what little Nitrogen has been extracted could also doom a colony on Mars along with finding out that an important food crop turns out to not be viable due to various factors that didn’t show up in limited testing. Does seed growth and propagation get distorted in low G over several generations? I’m not a plant biologist so I wouldn’t know, but it might be a good question to ask since it’s the sort of research that cant be done on Earth and may have very skewed results on ISS or another orbital research station.
Warren Platts : good point about Al-LOX rocket. 280 seconds isp do not sucks on the Moon, since the escape velocity from the surface is a paltry 2400 m/s… instead of 11200 m/s for Earth.
Expendable lunar SSTOs, running on Al-LOX could lift large payloads out of the Moon.
Basic calculation : 9.81*280*ln((100+50)/(10+50)) = 2517 m/s … with 50 tons.
Make them as simple as coke cans, and you might eventually build them on the Moon – creating an industry.
This could be the lunar equivalent of Zubrin and co. Sabatier Methane / LOX process on Mars.
The problem with “retirement living” in space is that as people get older, they acquire more and more incurable medical conditions. Retirees could only live out the full term of their natural lives on the moon (or anywhere else in space) in a settlement that had the medical facilities of a large modern hospital. Towards the end of their lives, they might need full-time care.
Neither of these things is likely to be available on the moon until there are settlements that are big enough to be called towns or cities, so retirement living must follow large-scale lunar settlement instead of being an economic driver for it.
Anyone who developed medical problems that could not be treated on the moon would have to return to Earth. Presumably, retirees would be required to buy insurance to cover that eventuality. The risk is of getting too ill to survive on the moon, while also being too weak to survive the stress of returning to Earth and re-adapting to Earth gravity.
So, permanent retirement to the moon looks like a very distant prospect. What’s more plausible is lunar companies offering people with advanced technical skills the chance to work on the moon for a few years after retiring from their terrestrial jobs. The company gets the benefit of their knowledge and experience, and the worker gets one last great adventure before properly retiring on Earth.
If lunar rocket fuel is only 1000 times or less than Earth rocket fuel, we can do something with the Moon AND it would make using Mars, easier.
If Mars rocket fuel is only 10 times or less than Earth rocket fuel- you don’t need the Moon’s help, and one can have settlements on Mars. And one could use our Moon- and you would also be using the Mars moons.
Or if you can make Earth launch as cheap as Musk thinks is possible, the cost of rocket fuel on Mars and our Moon will be determined by Earth’s launch cost and/or the cost of water in Space [from places like Ceres and other space rocks or moons or dwarf planets].
Venus orbit is likely to have population levels equal or much more than Earth’s population- to use Venus orbit needs rocket fuel in Venus orbits to be about 1000 times Earth’s rocket fuel cost or less. And with Mars having rocket fuel close to only ten times Earth’s cost, it could sell Mars water in Venus orbit- and places like Ceres could ship a lot more water to Venus orbit than Mars or our Moon [and it would become far cheaper].
Living on the Moon assumes oxygen [rocket fuel] is at quite low price.
One cannot aerobrake on the moon, but for light raw materials one can lithobrake. Some light, refractory materials won’t even have enough kinetic energy to melt if they are dropped onto the moon at lunar escape velocity. One of these is carbon; another is lithium hydride. So maybe the cheapest way to get carbon on the lunar surface is to just drop it there and fish it out of the regolith.
We don’t actually need to find propellant on the moon, just use the rocks.
Spin launched, or tether launched systems are ideally suited for the moon because there is no atmosphere. They can use solar power to spin up cargoes over a number of minutes or hours. They effectively store energy so you do not need a separate storage system like electromagnetic launchers.
There are a number of papers on this but I think the best is from Baker and Zubrin in the AIAA, 1990.
https://arc.aiaa.org/doi/abs/10.2514/6.1990-2109
Though I think they miss a trick or two. Use basalt rock; it naturally forms long blocks as it cools, and is very strong.
Spin up two blocks and throw them in opposite directions. Orbital tethers can use them to accelerate or decelerate cargo even if they are not launched to orbital velocity.
Launched toward the earth the kinetic energy they develop is greater than the same mass of fuel and can be utilised by tethers to raise the delta-v of what ever cargo is required to be lifted. They can also be used as the mass for tether systems.
The alternative is to use a lunar orbital exchange tether to pick up mass from the moon and transfer to an earth orbital tether https://www.niac.usra.edu/files/studies/final_report/7Hoyt.pdf,
Basalt fibre also has the potential to make the tethers….
“We don’t actually need to find propellant on the moon,”…
If there is mineable water [and/or mineable frozen CO2] on Moon, it will allow the Moon to “develop” faster.
What needed is water in high orbit {Venus, Earth, Mars, etc. high orbit}. Venus orbit is better than Earth orbit. Venus orbit could be a large market of water from elsewhere- perhaps Moon, likely Mars- at least “in the beginning”, as in first million or so tons of water.
Mars settlements would need billions of tons of mined water per year and a small fraction of it, could be exported to Venus orbit. Using Venus orbit is “needed” for Mars settlements- and whether water comes from Lunar water. Mars. Ceres, or space rocks, a question where does Venus first get water from, the rest of solar system is where more of water will come from and once trillions of tons of water is mined, our Moon would import this cheap water. Hundreds of tons first come from Earth surface.
Anyways, bringing stuff to Earth orbit, rather Venus orbit, has risks that Earthlings might not want, so asteroid mining could ship to Venus orbit, where there is more space and more solar energy.
Anyhow, having rocket fuel at Venus orbit, helps solves Mars to Earth 2.1 year launch window. And from Venus, also makes getting to Mercury, easier.
Our moon doesn’t have to have minable water, but we should find out if it does, and should determine any errors in terms of the lunar water we think we have detected on the Moon- maybe there is a lot less [or a lot more] than the “present science” suggest there is. We will need to find mineable water somewhere in this solar system.