Multiplier of Producing Fuel on Planets

Robert Zubrin describes the multiplier of producing fuel on the moon or Mars.

Producing oxygen on the moon and with hydrogen (that you brought) would be a 7X multiplier for what you brought. There is also water on the moon which can produce fuel directly. This means a 450 ISP engine with oxygen on the moon would be like a 3000 ISP vehicle.

Producing methane-oxygen fuel on Mars with hydrogen (that you brought) would be a 18X multiplier. A 350 ISP engine would be like a 7000 ISP engine. Mars again can have all of the fuel produced from in situ resources. The weight cost is the weight of the simple systems that would generate fuel.

Zubrin again argues for the mini-starship that would go on top of a SpaceX Falcon 9. A mini-starship could also be carried inside a larger starship.

Zubrin indicates that landing the first Starship on the moon will cause a crater and a lot of debris that could reach lunar and even earth orbit. We need a smaller lunar lander that will first make the landing pads.

73 thoughts on “Multiplier of Producing Fuel on Planets”

  1. If spotting a site from high altitude isn’t a problem, then there’s no problem to begin with, because they can adjust the landing site during the main descent.

  2. High altitude shouldn’t be that much of a problem if they have good optics. Might even be an advantage, since it gives a wider field of view. They can pick a few potential spots from high altitude, then take a closer look as they come down.

    Anyway, depending on the Raptors configuration and assuming they only need one at a time during Lunar landing, they could possibly cycle them. That may still not be rapid enough, but closer.

  3. It’s a good question about Raptor restarts. I’d guess that there’s a minimum interval between shutdown and restart, even if there’s an unlimited number of restarts per mission. (The limitation with Merlins was the number of TEA/TEB charges you had to start combustion, but Raptors are supposed to have spark igniters.)

    Off the top of my head, you may have to purge a shut-down engine, which takes a bit of time. That time may be enough for combustion heat to leak back into the turbopump and feed line assemblies, requiring a new chill-in procedure. That would make the interval at least multiple tens of seconds, which means that, if you’re going to pogo up and down looking for a good spot, you’re likely pogoing really high, which makes looking kinda difficult.

  4. It is possible for hydrogen to be in the soil of the Moon from solar winds. It is also possible that there is water deep underground. I don’t think the Moon is bone dry.

    The only way to be sure is to go there and find out. First thing I would do is send some low flying Prospecting Satellites to map the moon surface. Once I have done I will be send some Sampling Rovers.

  5. If you’ve been there long enough to place such infrastructure, it’s simpler to level some ground, and place a tarp on it (or sintered/compacted blocks, or maybe lunacrete). The bigger issue is the early landings, when you don’t have any infrastructure in place.

  6. On the off chance that they do need to look around before landing, can’t they do a series of short ballistic mid-“air” hops? Or is there a problem with multiple short burns? I guess the Raptors aren’t designed for that?

  7. Space X charges NASA more cause NASA demands much more. And that costs money. Space X is still much cheaper than its NASA competition. S[ace X is not a country so it is a profit centered organization that makes money.

  8. put a large pole off from ground and have large electromagnet couple too the landing ship. fire this pole at moon too say 50 foot depth. or could land on rails

  9. As long as you can keep the Starship upright during the fall after the engines shut down, there’s a pretty straightforward way of dealing with sloped and rough surfaces: Extend the landing struts to maximum for landing, then let them retract freely until they’re all on the ground. Then apply linear braking to absorb the landing energy.

    It makes for more mass in the landing struts, and longer (more massive) housings to retract the struts, but it also lets you tailor your strut length to the slope, roughness, and landing energy for your payload and destination.

    My biggest concern with hoverslam on the Moon is the inability to have T/W<=1 when throttled all the way down. If you can’t hover, you can’t manually search for a smoother landing site if there’s a big honkin’ rock or big honkin’ hole where you’d otherwise set down. But I’ve sorta convinced myself that, with modern imaging and navigation tools at your disposal, the odds of that happening are pretty low.

  10. This is a topic of fairly hot debate in the space nerd community. A lot of it comes down to landing gear design.

    If your guidance and navigation is good enough to avoid landing in a field of giant boulders, then you can hoverslam (i.e., have a thrust-to-weight ratio greater than one, but still satisfy the condition height=velocity=0) on the Moon. But instead of setting your hoverslam height to zero, you set the point where velocity reaches zero to, say, 10-30m above the surface. Then you shut down the engines and fall.

    If you know the mass of the Starship (dry mass + payload + prop needed for returning to Earth), and you know the shutdown height, then you know how much energy your landing gear have to absorb. The shutdown height scales linearly with gravity, so you can shut down 6x higher on the Moon than you can on Earth.

    With linear brakes in long enough housings, Starship landing gear should be able to shut down on Earth at heights of 4-5 meters, which would translate on the Moon to 24-30m. That’s high enough that plume effects are going to be fairly modest.

    Another possibility: If Starship really does have 10 tonne-force thrusters, as Musk as tweeted, then using 8 of those thrusters generates 784 kN of upward thrust fairly high up on the vehicle. That can further retard the acceleration on the Moon, raising the Raptor shutdown height even more.

  11. There is much less mass in contact with particles at lower air pressures, even if there are higher speeds.
    On Mars, for example, you could stand in a 300mph wind and you would barely feel it. You might not even feel it at all.

  12. This may be saying the same thing in different words, but basically, Isp is defined as “impulse per fuel”. If you can refuel along the way, you need less fuel at the start point to achieve the same total impulse. If you get the same total impulse from 1/x as much starting fuel, then supposedly you get x times more Isp. But that ignores the refuling fuel in the Isp calculation.

    The problem here is that the usual rocket equation that uses those Isp figures assumes that the rocket gets consistently lighter as fuel is burned up. But with refueling that’s no longer true. So you’ll get less total delta-v with “3000 Isp” per the above accounting (with refueling), than you’d get with an actual 3000 Isp rocket without refueling. That is because the refueled rocket is heavier, so you get less delta-v for the same impulse.

  13. Colloquial English often uses hyperbole and isn’t meant to be taken precisely and literally and certainly not out of context. Attempting to do that is the sort of thing a lawyer might do.

    There’s plenty of evidence in the transcripts that quite a bit of regolith got blown outward as dust during the landings, including a comment about the landing being IFR for Apollo 12.

  14. Zubrin has this to say about Apollo debris

    For exhaust plume debris, Apollo style landings on the Moon showed ejecta occurred but did not threaten the LEM which was ~18 MT. However, examining the Surveyor lander after the Apollo 12 LEM landed showed that plume debris did strike the Surveyor III[6].

    In his video he says that the amount of debris kicked up is a greater than linear function of the landing craft mass.

    So when he is comparing the scattering from Apollo to the effect from a ship 10x the mass, he is expecting the result to be squared (100x) or cubed (1000x) or something. (I can’t be bothered sitting through the whole thing again to find the exact equation).

  15. I see you’re trying to lawyer it up. Poorly, due to the poor material at your disposal.
    There is no ambiguity in what the astronauts said. There was no ‘crater of any size’; just like Neil’s, no ‘crater at all’. The context does not change the meaning of their words at all.

    It’s just that you cannot accept what they clearly said, for whatever reason. Which is strictly your problem.

  16. I think you’re mis-interpreting their words, because you aren’t consdering their context. They’d been concerned that they *would* dig a substantial crater that might make landing hazardous. What they actually observed was negligible relative to what they worried they would see. The mere fact that they even talked about this is an indication of this concern.

    Hence “no crater of any size” meant “the erosion is very small compared to what we were fearing”. Same goes for the slightly hyperbolic “didn’t dig any crater at all”. Note that he also says “Just like Neil’s”, meaning he was visually verifying that digging a crater was not a concern.

    You can also pick up on this context by listening to the chatter of the first landing, with a lot of emphasis on how little dust they were seeing, even though the video does show a fair amount of dust obscuring the view for a while. They were very concerned they might be landing on a thick layer of dust only lightly bound together.

  17. Certainly after you can prepare stuff, you would not land in tube skylights. Rubble should be the same anywhere on Moon, seems like? Anyway, landing there to avoid damage early may work if the cargo is to be used to build in the tube. Or, I may be overestimating how hard it is to contain the blowout. Crater may suffice.

  18. The tube skylights will have rubble piles directly underneath them, the former ceiling. They might make good landing sites after some work to remove it, but as much work or less would make simple flat ground a good landing site.

    I tend to think that if you have a lava tube, you’re going to want to use it for purposes that aren’t compatible with periodically being flooded with hot rocket exhaust.

  19. Eh, debris thrown in one direction would be precluded from hitting the launch site, (Wonky mascon effects aside.) debris thrown in the other certainly could.

    But this is largely a non-issue; A Starship landing is only going to launch a small amount of material into long trajectories, and far less on takeoff, the loose stuff having already been moved. Keep in mind that as you’re coming down, the gas flow on the landing site starts out diffuse and ramps up; This is a recipe for moving things a minimal distance, not efficiently launching them into orbit.

    And once you’re out a substantial distance from the landing site, that small amount is distributed over a rather large area.

    It’s estimated that the Moon gets hit by about 3 tons of meteors a day. Unless you’re fairly close to the landing site, the thrown debris isn’t going to substantially elevate that.

    The first landing at any site should just bring some equipment/materials to build a debris screen, if further landings at that site are anticipated.

  20. Musk’s all purpose vehicle is a rational response to scarcity of engineering resources. Sure, a bespoke vehicle for every mission would be ideal for that mission, except for the fact that you’d find yourself unable to afford the missions.

    Musk isn’t building different rockets for each purpose, for the same reason you don’t have a car for grocery shopping, and a car for long vacations, and a car for going fishing, and a car for… Finite resources!

    Are there missions that the Starship isn’t ideal for? Sure. But the ship you actually HAVE is in some sense always superior to the hypothetical ship you couldn’t afford.

  21. Mindbreaker, what exactly do you mean by “Not much blows away because there is no atmosphere to carry it away.”?

    Objects move because they have momentum, NOT because the atmosphere carries them.

  22. Hrm…

    Now that I think on it, the rotation of the Moon during the at least 2 hour orbit of the debris would cause it to miss the launch point.

  23. Mercury has almost double the escape velocity of the Moon, and barely less than the exhaust velocity of a liquid hydrogen rocket engine. I don’t think it would be an issue.

  24. Odds against returning to the same exact spot seems small, but yes could happen. Seems like something that would happen to Wile E. Coyote

  25. ~10+ tons on landing makes it a heavy lander, Brett. Did we ever land something heavier on another world?

    And, if ~10+ tons made no crater in the fine moon dust, the ~100+ tons Starship should make a rather timid crater upon landing. Landing a few 10s of meters from the settlement should be enough to negate any possible problems.

    I’m curious how R. Zubrin reconciles his predictions about the crater that Starship should make with the Apollo record. He is a moon landing enthusiast, after all. And yet, not a peep from him on the subject.

  26. I bet you that Starship ends up with a small set of orbital maneuvering engines, to supplement the Raptors. That might greatly ease the problem of landing on the Moon.

    Hoverslam recovery might be fine for landing an empty Falcon 9 1st stage on a prepared landing site, but for landing a fully equipped Starship on an unprepared natural lunar surface? That sounds dubious to me.

  27. When that surface debris at lunar orbital velocity returns to hit the lunar surface at the end of one orbit, what is waiting there on the surface, about to get hit at periapsis?


  28. Tom, let us read the transcripts from the moon landings.

    Apollo 11 first step transcript:
    “109:26:16 Armstrong: Okay. The descent engine did not leave a crater of any size. It has about one foot clearance on the ground. We’re essentially on a very level place here. I can see some evidence of rays emanating from the descent engine, but a very insignificant amount.”
    So – no crater of any size; few insignificant rays. This, despite the fact that Neil Armstrong’s footprints made clear indentations in the fine moon dust.

    Apollo 12 transcript:
    “115:28:06 Bean: I’ll tell you, your boots are digging in the soil quite a bit. If you don’t pick up your feet, you really kick a load of dirt ahead of you. Your left foot’s got a big mound ahead of it right now that it’s just pushing along. (…)
    115:29:53 Conrad: The descent engine, it’s just like Neil’s. I didn’t dig any crater at all!”
    Again – no crater at all. Despite the fact that the astronaut’s boots dug a clear path in the moon dust.

    You’ll probably find similar comments in the other transcripts.
    Watch the footage/pictures from the landings. You will never see a crater that was not a feature of the local terrain.

  29. Re: mini-Starship

    Zubrin makes an interesting case for a mini-Starship. I think he’s half right.

    As far as a mini-Starship in combination with a Falcon 9 1st stage creating a fully reusable launch vehicle, I think Zubrin is dead wrong. It might be reusable, but it would have zero payload to LEO. Yeah, a crew of a few people might get to orbit that way, but at the risk of launching crew with no means of launch abort.

    If you used mini-Starship in combination with the lower stages of Falcon Heavy, you might get a payload of 15,000 kg to LEO with a fully reusable system. But recovery of the core booster is probably going to fail at a high rate. If losing the core booster is the normal cost of doing business with Falcon Heavy, then using mini-Starship makes less economic sense than a conventional Falcon Heavy.

    On the other hand, the idea of a mini-Starship as a smaller Earth Return Vehicle from Mars or as a smaller exploration vehicle launched into LEO fully fueled (as cargo carried by the full sized Starship), those ideas have a lot more merit.

    I don’t know if many people appreciate the astounding engineering challenges facing the Starship beyond the simpler initial goal of a fully reusable vehicle lifting 150 tonnes payload to LEO. Zubrin pointed out one of the more minor problems with the exhaust plume problem when landing on the Moon. What about the thermal heating when a Starship returns from Mars and hits the atmosphere at around a velocity of 14 km/s?!

  30. My understanding of orbital mechanics, while limited, was that a ballistic orbit which begins on the ground ends on the ground. In other words, rocks thrown into space around the moon will either be at escape velocity or will orbit exactly once and then hit the lunar ground. There is no sideways force to circularize the orbits of the rocks.

  31. Musk has said that his plan for landing safely on the moon is “Aim for zero velocity just above surface & fall. You won’t fall fast.”

  32. LEM didn’t make a big deep crater but I don’t know that it didn’t make ANY crater. Take a close look at the area directly under the rocket bell in the image of the LEM at this site:×554.jpg

    Looks like there’s a bit of a shallow pit and some color variation in exactly the right place for dust to have been blown away by rocket exhaust, and it looks deeper than the surface dust in which the astronauts’ footprints were made. Also notice the subtle striations in the dust, radiating from that area, in front of the right footpad.

    It COULD just be a pre-existing surface feature that just happens to be in exactly the right spot, of course.

  33. Might also want to worry about ricochettes. Seems unlikely the debris will be fast and dense enough to get through stainless steel tanks, but might do other damage.

  34. Unless SpaceX finds a way to throttle the Raptors back enough to land on the moon without sending debris into orbit, they’ll be blocked by NASA.

    (NASA *might* approve them to do a few uncrewed Mars landings early on – with high risk that the Starship will tip over after landing in a crater it just dug (or be punctured by debris bouncing back) – but expect them to build safe landing pads before attempting to land crew with Starship.)

    Maybe SpaceX could make the Raptors run very lean. Oxygen would be most of the reaction mass at a much lower exhaust velocity, while burning a much smaller amount of methane – enough to run the turbo-pumps and heat the LOX to a gas.

    That sounds “wasteful” of oxygen, but it’d only be for early landings and later on landing away from established bases with hardened landing pads. Oxygen can be produced pretty much anywhere on the surface of Mars or the moon, if refueling is needed for re-launching.

  35. No, there no need for a mini-starship. I think the large ship is the best way to to go to Mars. I think Zubrin is thinking of old style rockets that cost in the billions and could be only be used once. His Hopper created dust when it took off at Broca Chica. Going on a 7 month trip to Mars in something the size of lunar module would drive people crazy. A mini rocket would be a waste of money and waste of time. In any case his first trips will be automated and deliver supplies not people. We`ll soon find out if there is any problems soon enough. Many of his large rockets will serve as habitats anyway until proper accommodation is built. Even though they are there many people may want to go back to earth soon after they land. There will be a strong erg to lie down in a grassy field look up at a blue sky. I`m guessing the only people who will want to stay there for long periods of time will be scientists. People want to search evidence of life past and present. Geologist who want to look into the past history of Mars and what changes happened there. Scientist who want to find out about if it geologically active. Scientist will want to find out what caused the traces of methane detected. Some will want to find out if there ever was an ocean on Mars and will want to study the dry river beds. There will want to find out if it is possible to terraform Mars. It is going to take a long time for to find people who want to live there.

  36. Russia’s state space corporation has retained its competitive edge after it reduced prices for its services by 39%, despite the sanctions, Roscosmos CEO Dmitry Rogozin said on Sunday.

    According to the Roscosmos chief, Russian and American experts believe that only ten-fold use of reentry modules can yield profits. “SpaceX does not demonstrate such results,” he said, adding that SpaceX is secretive about the economic aspects of its launches.

    In Russia’s view, of course, SpaceX is coming by all of this business dishonestly, undercharging commercial customers for their rocket launches (SpaceX’s base price for a Falcon 9 launch hasn’t budged since it raised it to $62 million in 2016), but charging NASA as much as four times more for government launches to make up the difference. In essence, says Rogozin, SpaceX is “price dumping” its commercial space launch services — selling them below cost — in order to “force Russia out of the market for space launch.”

    Can SpaceX maintain prices without 10x reuse and higher margin govt launches?

  37. I think the calculation is:
    A ship that takes off from Earth, flies to orbit, then transfers to luna orbit, then lands on the moon, then takes off and flies back, needs A plus B plus C plus…. = X total delta V.

    If you assume it was taking all the fuel from the original takeoff, with Y assumed fuel ratio (90%??) then you need an ISP of 3000 for the maths to let you do the entire flight profile.

    But if you assume that it can refuel on the surface of the moon, then you only need a 450 second ISP.

    Think about how fuel efficient your car would have to be if you couldn’t refuel it after it left the dealership, but still wanted to drive just as much.

  38. It probably MSc in AeroAstro simple.

    Zubrin has done actual work on such systems. I recall seeing a video long ago of when Zubrin was at Marietta/Lockheed, there was a picture of him with equipment said to be experimental propellant production system. When i was a kid, I had expected “rocket scientists” to work on building rockets and not on boring ancillary integrated systems, he was a big disappointment.

    Integrated Mars In Situ Propellant Production System

    doi: 10.1061/(ASCE)AS.1943-5525.0000201


    Zubrin, R., S. Price, L. Mason, L. Clark, 1995: “Phase III Final Report: An End-to-End Demonstration of a full scale Mars In-Situ Propellant Production Unit” Contract NAS 9-19145 Martin Marietta Astronautics, Denver, CO.

    The projected cost for a cornucopia machine that produces 0.14 kg of methane per day ~$10M(1997)

  39. Mercury’s orbital distance is about 60 million km if we approximate it as a circle (not close to true, but for this sort of calculation it’s OK).
    So the total circumference is about 190 million km.

    Mercury itself is 3.285 × 10^23 kg, let’s say 1 × 10^23 cubic metres.

    If we break it into chunks 1 m in size (big enough that the solar wind won’t just blow it away) and spread that out over the full orbit we get a band 530 000 km wide.

    That’s nearly half the width of the entire sun, so it would produce a big shadow out by Earth.

    So yes, there is enough material in Mercury to block significant amounts of sunlight from Earth.

    But surely you’d have a much easier time just blowing the material off the moon? The orbit of the moon around the Earth is much, much smaller, you’d need much, much less material to block the sunlight, and the moon is closer anyway.

  40. We can check for tubes before landing big things. We can spread tarps around the bottom of the tube hole and let the landing/leaving rockets excavate ldirt onto the tarps. Then simple cable lift will put it in furnace for smelting.

  41. I would dispute the idea that the LEM could by any stretch of the imagination be described as a “heavy lander”. Fully fueled it was about 16-17 tons, considerably less on landing. The Starship is almost ten times that empty without payload.

  42. Wow, never thought of exhaust blowing debris into lunar orbit. I guess that’s why we need geniuses.

    Thinking out loud: If we landed something big enough on Mercury and often enough, could we blow enough debris into solar orbit to significantly reduce solar radiation to Earth?

  43. Yes. Sounds rather pie in the sky. We may want simple, easy, and fast. Getting what we want quickly is unlikely…and probably will not be cheap.
    If they make hydrogen, they have to make it much faster than it makes its way out of the container. A hydrogen tank in a rocket is not generally designed to hold hydrogen very long. They have weight limitations, so they likely leak pretty fast. That means you have to combine the hydrogen into something other than hydrogen, like methane. That is not likely not be cheap, light, easy, simple or fast.
    Perhaps they can use some lithium alloy to make hydrogen rocket tanks that will hold the hydrogen well enough…put them in the shade were it is cooler, and use nuclear or solar to power a cooling system to keep it liquid. Maybe that really is the best option…hard to say.
    Any way you cut it, we will need many rockets to build the facilities to mine and process stuff into fuel at a scale that can make enough fuel to fill rockets in a reasonable time…say a large rocket in a week or less.
    I like mass drivers for launching stuff from the Moon. Give them some fuel, but as much as possible, use electricity from PV or nuclear. We need to conserve the water we find.
    If we really need a lot of water, I would suggest finding a small comet, building a radiation shield surrounding it and put it in lunar orbit. Make hydrogen and oxygen there, refuel there, deliver water to the Moon as needed for growing food and whatnot.

  44. Not to support Zubrin too much, but here he was comparing to powerful ion engine, quite complex!. And he was following Ehricke, not a bad thing to do. The weight was the key, as it can gradually build up reserve fuel, not itself part of rocket. And having support for ISRU is good.

  45. Gravity and vibration can make rocks roll under the feet if you land in craters (mostly stuff on the crater rim coming down). It is a bowling ally. It also could make moving cargo to the base more difficult.
    Using a boulder between your base and your landing area? That should be fine. You don’t want to be too far away. But as everything can be planned in advance and an ideal site chosen, these things can be taken into consideration. Obviously, all the best sites are still available. Like all the best natural bays available for the taking 10,000 years ago. Choose well, and your base will have a great future.

  46. Not conducive to moving people or cargo. Better to land near your base. Also, if lava tubes are in the area, that makes it a bad landing area initially as you don’t want to land where there may be a lava tube beneath as it may break and your rocket take a tumble.

  47. If you have a flat landing pad the only stuff that will move fast is at an angle that is almost level with the ground. So all you need is a fire-pit ring maybe half a meter high. Maybe 2m to be sure. Easy to just cut some rock and make a ring. In a pinch, just place several uncut rocks in a ring.
    I don’t think much will be thrown at a higher angle, but if it is and it is moving fast, it should go over your base, and if it is slow enough to arc down and hit, it would not have much momentum, and wouldn’t hurt anything.
    your landing grid should work just fine, of course. Just more cargo.

  48. Maybe landing the rockets on big enough hard rock areas if there are any on the moon and after a proper big enough cement landing base will be built on the moon the dust is not going to be so much of an issue.

  49. Not much blows away because there is no atmosphere to carry it away. It becomes a question of how much gas pressure there is near the ground…how quickly the pressure from the nozzles dissipate in space with distance. Spaceship is much larger than an Apollo lander, and the first landings will certainly require substantial fuel weight so some could be blown.
    Best might just be sensing if there is a loose rock that a foot is going to land on and just rotating the craft a few degrees to miss it. A more primitive approach would be to have explosives under the feet that detonate 6 inches from touchdown to remove anything loose and insure solid contact. That should work, but would not be a great choice once there is stuff on the surface that could be damaged. Explosives to relese things have been used in space for a long time, using the same sort of thing under the feet would not be difficult, and any lift created should be trivial.
    Once stuff is well established on the Moon landing pads will probably have a small wall like a fire pit, so any particle that is propelled is stopped rather than flying thousands of feet and potentially hitting someone or something. The wall would not need to be tall, 1/2m would probably be sufficient.

  50. My opinion can be wrapped up in criticism of a single quote from above, “The weight cost is the weight of the simple systems that would generate fuel.”

    Simple?  Great! Then please someone send me a linkie to where I can see one of these simple systems in action. 

    I mean, they’re simple, right?
    High-school Science-Fair simple?


    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  51. Yes. The dust is very thin. It is made by micrometeorites which can’t penetrate very deeply. There are certainly regularities and craters, but they won’t be made by landing Starships.
    Before anything landed on the Moon, the experts believed that there was dust several meters thick, and astronauts probably would not be able to leave landing spacecraft. Very nice that, that was not true.
    Spaceship itself should already be level when landing. You just have to avoid tilting as the struts take the weight.
    What Spaceship needs for the Moon is struts that adjust for nonlevel surfaces.
    The simplest is to just have vertical hydraulic cylinders on the ends of the struts that are 1-1.5m long which can extend downward with the feet on the bottom to accomplish the absorption until the third (last) foot touches, at which time, the cylinders lock firmly.

  52. We do not need to calculate from theory what happens when a heavy lander lands on the Moon. The experiment was performed with the Apollo Moon landings.

    The result – the small dust, rocks small and large were not blown away to any discernible degree.

  53. What you want to do is land inside a small crater or behind a hill or large rock. They will protect your lunar base by deflecting the thrown dust and rocks upwards

    Later on you can build paved landing fields. But to start with use the natural features already there.

  54. What a lander’s engine does is blow away all the small dust and rocks, leaving the larger ones behind. How big a rock needs to be to not get moved can be calculated from straightforward fluid dynamics.

  55. I would say the heavy lifter is needed for Mars because at least for the first decade or so any base or even bases on Mars is going to require crew rotation to negate the health effects until facilities can be hardened and enlarged enough to solve those issues on Mars/Moon. Also I would imagine we will find lots of stuff if nothing but rocks ores etc… that we will want to ship back to Earth for more detailed study that will just not be possible on site for decades. If you are producing the fuel on site so not taking the added payload hit for the fuel needed for a larger ship vs smaller the value or security of having a larger ship with more payload would seem better.

  56. Not sure if there is overlap between O’Neill and Ehricke, but Krafft’s analogy that the Moon should be considered a *continent* of the Earth is highly informative. Everything else, except TCOs, is WAY further away. The Moon is a stable part of our starting place, our cradle.

  57. “Starship in the original idea by Musk, should be able to go “anywere” in solar system, this is a crazy statement, each planet has it own properies/challange and it needs specialized vehicles” Actually, this is a crazy statement. It assumes without stating that we will be landing on planets for most Space activities. We need ISRU robots and useful (Space Solar such as LSP) manufacturing in Space, eventually building settlements. None of this involves planets, just asteroids and airless Moon, where launch is not needed, just mass driver. Getting off Earth is the solution. Being on a planet, even Earth, is the problem.

  58. The Apollo Lunar Modules landed on the moon without making any visible craters, as can be confirmed from the footage/pictures. Neil Armstrong said it directly, after setting foot on the Moon.
    This, despite the fact that the astronauts’ boots made clear impressions on the Moon, near the landing areas.

    R. Zubrin greatly exaggerates the “Starship’s landing on the Moon will make a big crater” problem.

  59. While orbital velocity around the Moon is about 1.67 kps, and the exhaust velocity of Musk’s rockets is on the order of 3.8 kps, you have to keep in mind that a lot of the kinetic energy of the gas is going to be rethermalized (Changed from organized unidirectional motion to random thermal motion.) when it hits the surface and has to make a 90 degree turn. Then you have to account for inefficient momentum transfer.

    Which is a long winded way of saying that only the smallest particles would make orbit, if even they could.

    That’s not to say there isn’t a real problem here, because you don’t have to make orbit to be thrown many kilometers. You can do the first landing at any isolated site without a prepared surface, but once you have anything else on site already or even nearby, you’re going to need some way to minimize thrown debris. A mat, hanging curtains, a grid with a big hole underneath it.

  60. “This means a 450 ISP engine with oxygen on the moon would be like a 3000 ISP vehicle.”

    That’s a pretty bad analogy, which would only work in the absence of gravity.

  61. I think that Musk’s vision of one for all purpose vehicle is really poor, StarShip is too huge to have safe landing on the Moon or Mars, a flat area should be built before the first landing, with an automated unit. Starship in the original idea by Musk, should be able to go “anywere” in solar system, this is a crazy statement, each planet has it own properies/challange and it needs specialized vehicles

  62. I think Musk’s answer is to try to mitigate debris at the landing site issues as much as possible but otherwise just go ahead and try it. Starships will be cheap enough he can afford to fail.

  63. All makes Blue Origin vehicle more proper for moon travel, the way it is designed to, than SpaceX’s, both for size and the choice of hydrogen fuel. Blue Origin should still work on reusability for the later stages and fueling in orbit. To some extent this arguments also are somewhat true for Mars. The Musk with all his qualifications has bombastic tendencies.

  64. “We need a smaller lunar lander that will first make the landing pads” As I mentioned before, Bezos will make the pads for Musk.

  65. Happy to see that Zubrin has realized that the Moon is the place to start, as O’Neill pointed out almost 50 years ago. Then we can do other things useful to the Earth, and even go to Mars if any reason to do so is discovered.

  66. What about the Starship coming down to the Moon’s surface very slowly so that the debris are blown away but not with enough force to go into orbit?

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