SpaceX Super Heavy Starship Will Also Be Space Tugs and Cycler

Many space plans propose different space vehicles for different roles and activities. There is a launcher that goes from Earth to low earth orbit or the launcher goes directly to higher orbits with lower mass. The SpaceX Super Heavy Starship should be flying to orbit by 2020 with a fully reusable rocket. It will be 2-4 more years before it is fully developed for commercial flights.

If it is flying with minimal maintenance for 100 trips then it will bring the cost of each space launch down to about $5 million per launch.

It appears to make sense for 5-10 years after the development of the commercial SpaceX Super Heavy Starship that various slightly modified versions are used in the role of orbital space tugs, fuel stations and orbit to moon and orbit to Mars vehicles.

It is similar to the old ideas about using the Space Shuttle fuel tanks back in the 1980s for space stations.

The SpaceX Super Heavy Starship can land back on Earth and would be able to act as a giant lander for the moon as well.

The Space Super Heavy Starship can bring mining equipment to the moon and make lunar fuel. This will drop costs throughout Cis-lunar system.

Fuel Costs and Fuel Requirements to Move Beyond Earth Orbit

Philip Metzger had an analysis for United Launch Alliance for commercial lunar fuel.

Elon Musk has talked about the SpaceX Super Heavy Starship transferring fuel between vehicles. This was to allow many loads of fuel to be brought from Earth so that a fully fueled mission could be sent to Mars.

This also means that SpaceX Super Heavy Starships could be placed into Low Earth Orbit, High Earth Orbit, at Lagrange points, Cycler Orbits, and on the moon. They could be transferring fuel between vehicles and store fuel for other missions. Having vehicles and vehicles acting as refueling stations will greatly reduce the cost of moving around from space and not just to low earth orbit.

Going from low earth orbit to the surface of the moon takes about half of the fuel going from Earth to low earth orbit.

There could be SpaceX Super Heavy Starships placed into Lunar Cycling and Mars Cycling orbits.

Simplifying to have modifications of one vehicle for all of the roles in Space would reduce the development costs. Refueling at different points would allow for more cargo to be moved and to lower fuel costs.

121 thoughts on “SpaceX Super Heavy Starship Will Also Be Space Tugs and Cycler”

  1. We think the tragedy of two world wars is behind us.

    Nevertheless, we can look ahead for World War III which may start as a nuclear bomb accident or just a local skirmish in the Middle East or between India and Pakistan.

    Fifty megaton nuclear weapons can obliterate big cities like Moscow, London, New York and Beijing for a long, long time. Even for a thousand year.

    I am an optimist. I think we can put our monkey behavior behind us and be intelligent about our future! The first step is setting up the United Nations of Nuclear Nations near the UN building in New York City. All nuclear-armed nations should be in it including Israel and North Korea.

  2. How do you dig holes? Mine? With shovels? Even sending a hammer to Mars costs millions of dollars.

    Before we send humans, habitat must be built on Mars by robots. Food, water, medicine. Cost: trillion dollars.

    At a steep cost, we can start populating the Mars. But no country will pay the price. We have more important problems to solve on Earth, like overpopulation and nuclear disarmament, creating an Earth government, eliminating the threat of high IQ robots taking over and putting humans to zoos.

    Who would want to live on Mars? How about Alaska? Sahara? Siberia? Greenland? Montana?

    How about sending ten couples, 2 sheriffs with wives (and guns) and 1 judge with wife on a round trip mission to Mars for one hundred billion dollars? What if one of the sheriffs goes crazy and kills everybody?

  3. We can send robots to Mars at a fraction of the cost of sending humans.

    Which one is more important: money saving nuclear disarmament or very expensive suicide missions to Mars?

    The biggest threats to humanity:

    1. Nuclear war
    2. Overpopulation – 1 billion humans are sufficient
    3. High IQ robots killing every human
  4. They dig holes, mine water, and set up electrical grids. What do you think they do? Supply ships will land first and your robots will have at it for several years. Then when the return vehicle(s) are refueled from the atmosphere, and preliminary tunnels are dug we send people. Your $6 Billion figure is being ignored by the Elon. Have faith young Padawan.

  5. Not long ago, people piled into ships much smaller and took months to get to a new land. Why Mars? Why not? If we want to exploit the Asteroid Belt, Mars is a logical processing station. It is literally a fixer-upper planet that we could make habitable for our great-grandchildren. That used to mean something. However that was back when people were willing to travel to new lands and ignored the people saying “why? For what purpose?”

  6. I hate to drone on about this, but you’re making a crucial mistake: Musk didn’t dream this thing into existence. He simply saw that some things had changed, and then he did the math based on how they’d changed.

    It’s one thing to shoot for where you think the numbers will be sometime in the near future, and plan accordingly. Sometimes people go out of business if their judgment was off, but at least they were being rational. SpaceX may or may not get to Mars, but the numbers say it’s not impossible.

    It’s quite another thing just to assume that a miracle will happen and something fundamental will change with the system that you yourself designed. That’s flat-out crazy. “Dreamers” like this do exist–but none of them are in business for very long.

    If you could get SuperHeavy/Starship launch costs down to about $3.7M a launch, then Starship has better cost/mass than any of the tug alternatives I’ve looked at. If you assume that SpaceX will need a gross margin of at least 30% (which is way low, BTW), that makes your cost $2.8M a launch.

    But the cost of propellant alone for SuperHeavy/Starship looks like about $1.5M. If you think that you can do all the turnaround, inspection, refurbishment, payload integration, and launch operations for $1.3M, then by all means, dream on.

  7. The digits were yelling at Musk to put away his silly dreams of shiny 1950’s rockets.

    “Flying back from Mars and landing at home base, all ready and raring to go again?!”

    “Dream on!”

  8. Nope, the future always lies with the digits. The trick is to get the dream to overlap the same space as the digits.

  9. Superheavy Starship going to Mars in 2024!? With astronauts!?

    70% chance that Elon himself going to Mars!? He is 47. Hopefully, he can take the g-forces.

    These are like titles from supermarket tabloid magazines. But they are not! They are from regular news publications. Many people believe that the extremely successful entrepreneur can actually accomplish this! Humans to Mars! On private money! Billions & billions of dollars!

    I doubt that Mars trip can be accomplished so fast. Suicide trip yes. But any kind of socially responsible trip, no. But even a suicide trip has two big unanswered questioned: why and who pays the huge price?

    There is no immediate urgency for humans to go to Mars. Robots will do the decades or centuries. Fifty times cheaper to send a robot than a human.

    Would there be any benefits from a manned Mars mission? Probably many. Such as cancer X does not happen during space flight. How to do radiation protection in spacecrafts? To go to orbit around the Venus would be a cinch after the Mars trip.

    Here is the psychological aspect of the Mars trip. Put twenty people together into confined space for months or years, and see if they stay sane?

    As far as human colonization of Mars? Fun topic! Fun movies! It may happen in the year 3000.

    Kalman Toth, Puzzlebook Author
    M.A. Physics & Computer Science, Columbia University, Private Pilot, Flew surplus DC-8 (almost died), personally knows Charles Simonyi (space tourist twice from Kazakstan)

  10. The V-1 wasn’t a rocket. The V-2 was, but it used ethanol as its fuel.

    I’d love to see an NTR spacecraft, but you’re dreaming if you think one is ever going to provide propulsion in Earth’s atmosphere. And, while NTRs can at least reject some heat through their exhaust, they can’t reject all the heat. The reason that nukes are so hard in space is because there’s no conductive or convective cooling, and radiators are big and heavy.

  11. Can’t argue with that, except to say that your head can do math, and the math and your mental movie are a bit at odds with one another.

    BTW, I’m not talking about mission-optimized spacecraft here; the tugs are 60%-70% the cost/mass of the Starship, for any of the cis-lunar orbits.

  12. If you’re talking about cost+ spacecraft, hand-built to near-zero tolerance, optimally designed for a very specific mission profile, OK.

    And, when you’re selling your lightly used, well maintained mandated-for-replacement tug on Musklist.mars, I will gladly buy a few units from you for 3 cents on the dollar.

    Then, I will strip them down for reconfiguration into a medium haul asteroid shuttle with one re-purposed propellent tank fitted out in the style of a 19th century Pullman car. Extra crushed red velvet padding on the ceiling.

    ‘Caus, this is all happening in MY head.

  13. SLS main engines burn hydrogen/oxygen for water exhaust. The solid boosters are “sick-sticks” puking out chlorine and aluminium garbage. Doesn’t matter; won’t fly.

    The Starships burn methane to produce water and CO2, mostly, exhaust – plus a bit of soot.

    Jets in America alone burn over 300 million pounds of fuel per day. One launch of a Starship would burn, (more efficiently) about 500,000 lbs of much cleaner methane.


    If you have a rocket company, and you want to feel better about its’ environmental impact, you could start a company to build electric vehicles to replace all of the fossil-fuel burners. And, you could start a company to build solar power units to replace fossil-fuelled electric plants.

    Nuclear isn’t going to fly; not Earth-to-orbit. Simple folk just won’t let that happen. No time soon, anyhow.

    Space-based use is far more likely.

    Everything is going to be OK. Earth is going to be better off in the long run if Starships replace a significant number of the passenger jets currently fouling the air.

    Not sure how “THEY” will replace jets for distributing their Chem-trails, though.

  14. A quick update to this: There’s one thing that causes an ordinary Starship to have a little less than 100 t of prop in the tanks when it gets to LEO: The lighter the load lifted by SuperHeavy, the faster it’s going at burnout, which requires SuperHeavy to reserve more prop for entry and landing burns.

    So adding some extra prop in the payload area does help a bit. If I were doing this, I’d design a payload with special methalox tanks, which could be mounted on the Starship payload adapter whenever needed. No need for a separate Starship design, though.

  15. I’ve got the numbers down-thread somewhere, but a Starship isn’t even close to hitting the same kind of cost/mass numbers that can be obtained using a special-purpose tug launched to LEO inside the Starship fairing.

    So it’s unlikely to be the one-size-fits all craft that the DC-3 was for a while. You really do need specialized spacecraft to fit specific economic niches. At the very least, you need a heavy launcher (SuperHeavy/Starship works great) and a tug. If the tug can also double as a lunar lander/ascender, so much the better, but that’s not an easy design.

    Starship started out life as a way to get to Mars, and it’s still a pretty good design for that. But it’s pretty marginal for cis-lunar applications, because it’s too heavy, and requires too many refueling launches.

  16. Yes, there were many aircraft flying before the DC-3. None of them are in any way still in service, except as historical exhibits infrequently taking to the air for shows or special events/commemorations.

    Right now you can still book a chartered or scheduled flight on a DC-3, if you so wish.

    I doubt the present design for the Starship will fly as is, and did mention the surpluses as being those that come from any eventual mass produced iteration.

    The biggest reason the DC-3, (military designation C-47) survives, beyond its’ physical durability, is that it was built in such huge numbers during WWII. After the war, nations all over the world wanted, needed reliable commercial air transport, and cheap, surplus “Dakotas” fit the bill, there having been ~16,000 built by the time production shut down in 1946. Plenty available, and easily obtained spare parts .

    Musk has talked about a 1000 ships being in service at any one time when full-on Martian colonial transport begins. After all, considering the trip windows, you’ll be looking at fleets of Starships all leaving for Mars in waves. Puts me in mind of WWII bombing waves, the sky full of dark shapes in singular motion.

    Breaking down a Starship to construct something designed to a specific purpose is to me much the same as reconfiguring a paratrooper version of a C-47 to carry passengers. Kind of.

    There’s a rural genius for reuse here on Earth that will still hold true in a maturing system-wide culture.

  17. Or they can kick red rocks in the red sand in spacesuits….. Mars colonization? Starting in ten years? Dutch con artists sending people to Mars suicide mission in five years?

    Cost estimate for Mars colony: 100,000 people * $1 billion = $100 trillion

    A much cheaper colonization trial: move 10,000 people to artificial habitat in Greenland without using the air for oxygen…. Movie to watch for colonization dreamers: Mars Needs Moms

  18. It is purely scientific … there is no economic reason. The main reason to send people to Mars (or at least Mars orbit) is so they can drive around Mars rovers with sub-second latency … much more productive than what we do today. If Elon can make a go of colonization with his own money – great. But the taxpayer should not be leading this effort.

  19. Can you give one good reason for humans to go to Mars? I give you one. China or India wants to show off! There is no other reason for humans to go to Mars. Robots yes. We should send more robots!

    Dutch con artists conned thousands of people believing that a human Mars trip is imminent.

    The cost of sending 20 humans with supplies may cost $50 billion. Before humans can go, habitat has to be established. Temporary habitat may cost $100 billion. Permanent habitat may cost $500 billion.

    The only reasonable Mars mission is NASA’s plan of sending 3 astronauts for a few weeks and bringing them back. Even that costs $20+ billion.

    My prediction: China may send a few astronauts to Mars by 2100 to show off.

    There is some scientific merit researching how humans can take long space trips with exposure to radiation and live on Mars long term. However, the cost of such a venture is enormous. Cheaper to produce humans on Mars movies!

    As far as populating the Mars with hundred thousand people in the coming decades? Come on you guys? Are you smoking something?

    How about getting the Earth in order first? Like nuclear disarmament? Decrease Earth’s population to 3 billions?

  20. How Much Air Pollution Is Produced by Rockets?
    With economic activity poised to surge in space, scientists are reexamining how rockets might harm Earth’s atmosphere

    Nuclear thermal rocket
    The overall gross lift-off mass of a nuclear rocket is about half that of a chemical rocket, and hence when used as an upper stage it roughly doubles or triples the payload carried to orbit.

  21. Thrust has nothing to do with it. The mass ratio is worse, which means you get much less delta-v.

    If you want to stick an SEP system on the Starship instead of a bunch of Raptors… sure. But now the thrust (or more accurately, the mass flow) does matter, because it takes forever to use the delta-v you have available to you. SEP does much better moving fairly modest payloads around than moving gigantic ones.

  22. It’s kind of an irritant that they renamed things in the first place. BFB, BFS, and BFR (or BFR, BFS, and BFR/BFS) were pretty unambiguous–and took less time to type.

  23. The tanker version doesn’t help as much as you think. If you launch a Starship with no payload, it shouldn’t surprise you that there’s about 100 t of prop left in the tanks when it makes LEO. The tanker lets you reduce the dry mass a little bit, possibly by making a shorter Starship without a cargo bay and fairing, but we’re only talking about reducing the dry mass by a few percent. So maybe you get 105 t of prop to LEO instead of 100 t. Nothing to sneeze at, but it’s a fair amount of work for a modest payoff.

  24. Short answer: not on the Moon.

    Longer answer: It’s not terrible having to bring LCH4 up from Earth, because it’s only 21% of the total propellant mass. Making LOX goes a long way.

    Even longer answer: Starship is not a great architecture for lunar operations; it’s too big. Even if you had methalox available on the lunar surface, it still takes something like 14 SuperHeavy launches to provide enough prop for Starship to land a full 100 t payload on the lunar surface.

    If you have to go somewhere where the economics don’t militate toward specialized spacecraft for each segment of a trip, Starship is a nice way of doing a one-size-sorta-fits-all architecture, but it’s not super-cheap. And of course it’s awesome at getting stuff to LEO for very low prices. But the moment you have an established logistical tail to a destination like the Moon, it makes more sense to launch a tug with a smaller payload to LLO, rendezvous with a reusable lander/ascender, and then perhaps return the tug to Earth for reuse. The lander/ascender will definitely be hydrolox, and SpaceX would have to decide whether the tug would be methalox or hydrolox, based on how they feel about loading LH2 on payloads.

    BTW: I get about 21 tonnes of payload to LLO using a reusable methalox tug, which would basically be a mini-Starship, launched as cargo inside the SuperHeavy/Starship’s fairing. And that’s one launch. To get the same payload to LLO with Starship alone requires 8 launches with the refueling.

  25. Hythane isn’t typically liquefied. And if it were, I’d suspect that the LH2 would have the same boiling point as pure LH2.

    I kinda wonder where the point is where the specific power of solar panels becomes high enough that you can store water on your spacecraft and electrolyze enough of it to provide prop for your next burn. It would make the LH2 and LOX tanks smaller, and the water would be easier to use for radiation shielding than hydrolox.

  26. There were an awful lot of aircraft before the DC-3. It seems unlikely that Starship is going to be the thing that hits the sweet spot the first time out.

    I’ll be happy if it’s moderately reusable, can get 100 t to LEO and refuel on-orbit. We can leave the DC-3 of space for another decade.

  27. Nope. But you have two different things conflated here:

    1) The cost of the moon base, which you presumably want for more reasons than just mining water.

    2) The cost of mining water and (maybe) turning it into hydrolox at that moon base.

    If your business case is only “let’s sell prop on-orbit”, then water mining is a hard sell, or at least requires a project lifetime that will be unacceptable to most investors. But if the business case is “let’s lower the cost of a moon base”, then water mining looks really, really good. And then the “let’s sell prop on-orbit” business case gets enabled a few years down the road.

  28. The table in Brian’s post assumes the cost of transport. And there’s no “net loss”, there’s only the cost to a particular orbit, from a particular launch site. To make a profit, you mark the cost up by an appropriate amount.

  29. You need to look at the economics more closely. Starship requires a lot of refueling launches to go anywhere BEO, and the cost of those launches, even if it’s only $10M/launch, rapidly swamps the economics of the one-size-fits-all Starship.

    I’ve got something down-thread that looks at a couple of payload+tug systems that would fit in the Starship fairing to LEO. They handily outperform Starship in most cases. Also, it’s hard to envision any near-term uses for a 100 t payload to any cis-lunar destinations. Starship does best when it’s fully loaded. If you need to get 30 t somewhere, tugs work a lot better.

  30. The problem with microgravity isn’t that you aren’t stuck to the floor; it’s that your body isn’t mechanically loaded. Magnetic boots don’t do anything, because your bones are still losing mass and your eyes are still floating in microgravity.

    On the other hand, rotating the spacecraft to produce centrifugal force on the crew loads their bodies quite nicely–as long as it can spin slow enough that they don’t get motion sickness. That implies that paired spacecraft attached to long tethers might do well.

    The problem with radiation shielding is that you still need a certain number of centimeters of shielding, no matter how big or small the thing being shielded is. A spacesuit that’s surrounded by a meter of water on all sides isn’t very practical, either outside or inside your spacecraft.

    If your spacecraft needs lots of propellant, you can arrange the tanks around the living area and do pretty well–at least until the prop is exhausted. The other possibility is active shielding, where you put either an electric or magnetic field around the living area to deflect charged particles. That’ll work well for solar protons, but galactic cosmic radiation is incredibly high-energy. Pretty much nothing will stop it unless you’re willing to put several meters of water between the crew and space, in all directions.

  31. I’ve got the numbers down-thread somewhere, but just putting a reusable mini-Starship (same structural coefficient, same reentry profile, but everything is smaller) in Starship’s fairing and starting the mission from LEO handily outperforms Starship. When you actually run the numbers, the refueling that’s needed for Starship to do decent BEO missions rapidly swamps the advantages of having a single one-size-fits-all spacecraft.

    One quibble with what you have here: The big difference between vacuum-only spacecraft and those that go through atmosphere is the lack of fairings. For now, since spacecraft need to be launched from Earth, the structural loads are still fairly high. Until we can manufacture spacecraft on-orbit, the spindly things from science fiction stories will remain just that. The smaller form-factor is a bigger deal.

  32. SuperHeavy/Starship is a great way of getting stuff to LEO, and it’s a great way of landing on things with atmospheres, but it can’t be overstated how important it is not to go lugging needless dry mass around in vacuum.

    Below is a spreadsheet that looks at missions to EM-L2, NRHO, LLO, and the lunar surface for three types of tugs:

    1) An expendable tug that fits into the Starship fairing and launches from LEO.

    2) A reusable tug, similar to the first one, but capable of reentering and landing back on Earth once its mission is finished. This is essentially a mini-Starship within a Starship.

    3) A DearMoon-vintage Starship, with a payload to LEO of 100 tonnes. Note that the 8% structural coefficient, which makes the dry mass higher than the Adelaide numbers.

    All tugs use the same Raptor. I’m assuming that the expendable tug is $20M, the reusable tug costs $5M a trip, and the Starship is free for the cost of its SuperHeavy launch. All launches cost $10M a pop.

    While Starship modestly outperforms the expendable tug, it isn’t even close to the reusable one, except in landing cargo on the lunar surface, where you simply can’t do an EOR-style mission with a 100 t tug. The reason is that you need a lot of refueling for Starship because it’s so big.

  33. I’m the kind of person who prefers to respond to others comments with a belief that they are serious in their desire to contribute to the discussion, and without attacking or insulting someone who may be sincere in their efforts to contribute to the dialogue.

    However, in this instance, it appears to me that you’ve come here primarily to sell your puzzle books.

    That doesn’t mean I think you should be ignored, but the purely factual inaccuracies contained in your comments seem to betray a lack of prior engagement with the subjects at hand.

    Therefore, in response to your resistance to those here who voice support for human expansion into off-world environs, a resistance seemingly based on mis-understood dangers, and incorrectly calculated costs , I will quote, out of context, a certain 19th century poet…

    “We hear unnumbered voices shake the sky
    And “Forward!” still is their inspired cry.”

  34. > Must be cheaper to process on the asteroid and just ship the carbon

    The processing plant is generally more massive than the mining tug, so you don’t want to move it around much. Also, we have uses for the other 80% of the asteroid that isn’t carbon.

    The simplest “product” is radiation shielding, for which we don’t have to do anything to the ore except stuff it in lockers around our habitats. But this asteroid type typically contains silicates, oxides, and sulfides, including the minerals Olivine [ (Mg, Fe)2SiO4 ] and Sepentine [ ((Mg, Fe)3Si2O5(OH)4) ]. The OH in the formula of Serpentine makes it a “hydrated” mineral, from which you can drive off water by heating.

  35. The problem is making those stages “habitable”. You need to do so much work that is probably cheaper and far lower risk to just make your space station with inflatable concepts and loft it as a payload. As a historic ref, with the Shuttle some wanted to keep those expendable big fuel tanks in orbit and convert them to space stations … your are talking SpaceX Starship volumes there.

  36. The future of space travel is clean nuclear propulsion!

    Fossil fuel rockets add to the destruction of the Earth’s environment.

    Almost 100 years later we still use the same fossil fuel propulsion as Hitler’s V1 rockets.

    Kalman Toth, Puzzle Author

    (My wife was a nuclear engineer at Indian Point Nuclear Power Plant.)

  37. Must be cheaper to process on the astroid and just ship the carbon – unless the carbon is bound to something useful. However, I still think hydrolox makes a lot of sense in space. You get much better ISP and you can just mine water and solar power.
    Maybe Starship can use both? You don’t need much thrust in space so a hydrolox engine can be tiny. If they bring a nuclear power source they can fuel up with water and make the hydrolox on the fly.

  38. Spacecraft to Mars with 16 people in an extremely confined space…. Assume they don’t kill each other…. assume radiation does not kill them…. they arrive at Mars after 8 months….. What happens next? If there is no underground tunnel habitat prepared for them ($$$$$), they have to stay in the spacecraft, cramped for months, for years, until they run out from food or other supplies. What do they do there? This is the question nobody answering. ‘They do research!’ What kind of research? Robots can do all the research we need. Elon says they start working. How? With picks and shovels?
    A supply ship launch from Kazakhstan to the Space Station may cost $30 million. A supply ship launch to Mars may cost $6 billion. Who is paying for it? For what purpose? Just to have a human footprint on Mars? Like on the Moon?

    Kalman Toth, Puzzle Author

  39. “What can happen if we manufacture 1 million robots with IQ 250? IQ 1000? IQ 1000000?”
    AI doesn’t work like human intelligence. We can train it to do certain types of tasks (like Watson doing a web search and regurgitating facts on Jeopardy), but we still don’t have a clue how to add ambition, purpose, or real emotion of any kind. Without that, you just have a tool that can be turned on and off as you desire, it won’t care. Eight years after appearing on Jeopardy, the Watson software is being applied to cancer research, with mixed results. It’s useful, but it’s not going to take over the world.

    Nuclear weapons are indeed a concern, as is a coronal mass ejection from the Sun that hits the Earth straight on and knocks out all of our electronics and electrical grid. And who knows if somebody evil engineers some kind of destructive bio-weapon.

    For those and other cases (even the smart robot case) I would think you would want a self-supporting colony off of Earth. Maybe not at Mars, but someplace removed from the surface of Earth. Eventually build it up to be an ark of plants and animals we want to protect from extinction if something goes wrong on Earth. Yeah, 8 people aren’t going to save civilization from extinction, but it’s a start. A few years after that it will be twenty, then 100 then a true self-supporting city with pets and crops and flowers and butterflies to feel like a new version of home. And the 8 original colonists will still be there.

  40. The reference I have shows at 200 km the dominant species are monatomic oxygen and diatomic nitrogen. Once collected and cooled, the monatomic atoms would combine with something. I’m not sure if you get entirely O2, or some mix with nitrogen oxides.

    Collecting higher up doesn’t work well, because there simply aren’t enough molecules to collect at a reasonable rate. Your scoop has to work at an altitude between where the density is high enough to be worthwhile, and where drag becomes too great to overcome. It’s a fairly narrow range, due to the exponential change in pressure with height.

  41. Some of the rotating houses can get way above 0.1 rpm when being deliberately positioned.

    Just pointing out that we’re not totally without data. Could use more, though, I wouldn’t dispute that.

    And, yes, it is an issue that the spin axis on these buildings is aligned with the acceleration vector, while for a spun up habitat it would be normal to it. Rather hard to test that on Earth.

    I’m on record advocating an orbital research lab to do these tests. But I estimate doing it properly might cost a quarter billion dollars.

  42. That’s because you’re wedged in between strangers and can’t even move your shoulders or stretch your legs without bumping into them. If the flight was half-full it would be a much different story. Given the time, I’d much rather take an all-day Amtrak ride than a 3-hour flight, the difference is night and day!

  43. Tom, please share some of that research then. Like I said, I’ve done a little investigation and it seems like most tests have been small scale and small duration, and the results vary quite a bit.

    Check out section 4 of this document:
    The limits described here are definitely no more than 6 rpm, and may be as low as 0.1 rpm for optimum comfort. But can a person adapt over a few days to a higher level? And does the total artificial G force play a part in that (what happens at simulated Mars gravity, for instance).

  44. A rotating restaurant is not at all the same thing. At all.

    A full rotation is measured in many tens of minutes, the vast majority of “gravitational force” is due to Earth’s gravity. Show me a restaurant or house that rotates anything above 0.1 rpm, let alone 1 rpm.

  45. Why don’t we experiment with magnetic boots and a radiation shielding space suit that provides resistance in all directions, on the space station. See how it works. Maybe it would help but not solve some of the problems caused by no gravity. And don’t forget about kilopower to replace solar?

  46. Mat… Yes fuel or water for shielding. Plus already have submitted another option to nasa for shielding.

  47. Depending on altitude, the thermosphere has differing composition. Towards the lower end of it you’d mostly be collecting atomic Oxygen, higher up you’d be collecting Hydrogen. So I suppose you could get all your propellant from the thermosphere, if you wanted to go with hydrogen/oxygen.

  48. ” If one ship has to accelerate 7 other ships it will end up using 8 times as much fuel. ”

    Which at 1/100th gee just to aggregate propellant at one end of the tank will still be a trivial amount of fuel. Also, if it is one of the tankers the departing vessel still has a full fuel load, so who cares?

  49. Take a 14-hour flight from JFK to Tokyo. You can hardly wait to land after multiple meals and multiple movies. Take an 8-month trip to Mars from Earth. If you are still alive, land in a red sand desert with underground bunker habitat waiting for you with a few boring people!

    Who would finance a very expensive human Mars trip? Who would pay for the underground habitat preparation? You need to be underground on Mars due to radiation. For what purpose? Robots will do all the exploration we need. Much cheaper than humans.

    Kalman Toth, Puzzle Author

  50. What is the reality?

    USA is using Russian rockets in Kazakhstan to send astronauts to the Spacestation.

    USA can send robots to Mars.

    $100+ billion funding for human suicide Mars trip is a fantasy. It would never pass Congress.

    Even a no-human radiation exposure measuring trip may cost billions of dollars.

  51. Wife-swapping the easy part! Or hard! What if your wife does not like the next rotation?

    Imagine bringing up children in a tunnel on Mars!

    Glass dome habitat would make Martian living more tolerable. However, we don’t know if sufficient radiation protection can be provided with glass.

  52. Pick your role on Elon’s Starship. You can also be the Sheriff to bring space travel murderers to justice! You cannot do hanging though in weightlessness.

    James T. Kirk
    Christopher Pike
    Leonard McCoy
    Montgomery Scott
    Nyota Uhura
    Hikaru Sulu
    Pavel Chekov
    Christine Chapel
    Jean-Luc Picard
    William Riker
    Geordi La Forge
    Tasha Yar
    Beverly Crusher
    Deanna Troi

  53. Yes! You can be the 9th couple. If you are ready for a suicide mission! Death by radiation! Living in a tunnel on Mars! Going crazy! Plot to kill each other! You can live longer if you kill the others! Who is going to arrest you for murder?

    It would cost an extra $5 billion to put you on. How about crowdfunding? Who said suicide is cheap?

    Much cheaper and more fun to watch The Martian movie!

  54. Great idea, but which way is ‘up’ in those things? Where would we want gravity? Because a couple of strong cables connected to the right spots on the Starships and we could have 1g facing out nearly any direction we want.

  55. That Mars journey looks more and more exciting, maybe you should inform Elon about partner exchange so he can redesign Starship back to BFR.

    Paul Toth
    Now a wannabe Marsonaut

  56. I can really see a post-SpaceX entrepreneurial life for whatever iteration of the Starship that emerges. One that parallels the post-WWII utilization of thousands of cheap, surplus DC-3s’.

    What a creature that old bird is!

    Even though they stopped making them in 1946, there are at least a hundred of them still in service, delivering cargo and passengers into and out of remote locals every day.

    Pilots would buy them on the cheap, then set-up their own island hopping passenger service, or make fuel and cargo runs in and out of isolated communities.

    I can see stripped-down Starships, “island hopping” from asteroid to asteroid, dropping off parts and goodies, topping off their tanks, then moving on to ferry rotating crews back to a Martian moon. Rinse. Repeat.

    Or, a retired long-haul space pilot kicking in with two or three others to buy a surplus Starship, then going into business servicing tiny science outposts, mining camps and tourist resort-domes scattered around the Martian surface.

    Seriously, the surplus DC-3s changed the world. The Starship could end up doing the same, system wide.

  57. For either the Mars or artificial Moons around Venus, we need smart robots to prepare human habitats. Robots can take radiation much better, and basically they operate on solar energy.

    What can happen if we manufacture 1 million robots with IQ 250? IQ 1000? IQ 1000000?

    There are two immediate dangers to humanity currently, neither can be solved by putting a few humans on the Mars: total nuclear war and smart robots taking over and killing us.

    We became so smart that we represent the greatest danger to ourselves.

  58. One estimate ( is $20 billion for 3 astronauts for two months on the Mars. That makes my $50 billion estimates for 8 couple suicide mission quite reasonable.

    Are there laws in Netherlands against conning millions from thousands of people using a fake Mars project?

    The Dutch con artists’ project is nothing but pure fiction. Just take a look at their qualifications. Zero space travel experience.

    An unknown factor is what kind of shielding would be required to protect humans from radiation. Shielding adds to the weight of the spacecraft, that can double the cost of the transport.

    How much does it cost to prepare an underground bunker habitat for 16 people? I do hope you don’t expect the 8 love couples to do the digging?

  59. An idea that has been floated around is to use water in the walls for shielding. The water can be used for fuel and for human/crop usage. And the whole thing need not be shielded, just the the sleeping quarters and maybe the main control center for instance. They can monitor the sun for any solar radiation outbursts, and retreat to the shielded areas when needed. Cosmic radiation would still affect them while outside of the shelter.

  60. Did you see the delta-v costs (essentially, fuel costs) going to Venus? From Earth intercept, it’s about 5x more cost to get to Venus compared to Mars. (That’s a cool map, I’ll have to bookmark that.)

    Once at Venus you could build a floating city to stay high up in the atmosphere, where conveniently both the air pressure and temperature are comparable to Earth (unfortunately, not the oxygen levels). Of course, the gravity is equivalent to Earth as well. But the problem there is you can never descend to the surface, so you have no access to metals, minerals, or regalith. Only the elements you can pull out of the air. Plenty of solar power, but even on Mars the sun is as strong as an overcast day on Earth. Use some low-cost mirrors and you’re good to go. If we can capture some asteroids (for mining & supplies) and put them in orbit around Venus, then it might be a worthwhile target.

  61. You seem to like the number 50. I’m guessing that’s a number you just pulled out of the air.

    I’m not saying this number is any better justified, but Mars One estimated it would cost $6 billion to bring 4 people to Mars. And that’s with growing their own crops for much of their food needs, indefinitely. Part of the reason they have a lower number than some others is that they don’t cover anything for bringing the colonists back home.

    Construction, science, exploration, new sports will keep them plenty busy for quite a while, no need for planned partner swapping on such a frequent basis, not sure why that notion appeals to you so much.

    Just for reference, a modern sports stadium in the U.S. can cost $500 million to build. The new World Trade Center in New York is about $4 billion. Boston’s Big Dig was nearly $15 billion.

  62. The thing of it is, we really don’t know what the limits are for sure. It likely varies from one person to the next, but we haven’t done large-scale or long-term tests. Most have been done in room-size (big rooms) centrifuges here on Earth. Some say we can handle several RPM, others say it should be less than 1 RPM. We really need to put something in space, like two capsules connected by a cable, and see what the effects are on people as they move and do normal things.

  63. Heh, I drew the scoop in the image above, it was an illustration for my Space Systems Engineering book ( )

    The reason the scoop is so long and narrow is molecules at 200 km altitude average 1 km/s. In order to not bounce them back out of the scoop, it needs a shallow angled wall. At the back of the funnel you reach sufficient density for fluid flow to take over from free molecular flow (where the molecules are acting individually). At that point you form a stagnation shock, behind which the temperature and pressure rises. Then a vacuum pump sucks off that higher pressure area to put the collected gas in a tank.

    Since the drag on your scoop is based on the size of the front opening, you want to put the solar panels behind it, so as not to add to drag. You have a plasma engine at the back that kicks out part of the collected gas to make up for drag (about 20%). When your tanks are full, you increase the duty cycle of the engine to climb higher than 200 km, and offload the full tanks to whoever needs it.

  64. There is about 5 million cubic km of water on Mars, concentrated in the polar regions, including major polar ice caps. But even equatorial regions, where the Curiosity rover is working, have about 2% water in the soil. You just need some heat to bake it out.

  65. Many Near Earth Asteroids, of which more than 19,000 are known so far, are of the “carbonaceous” type (carbon-bearing). That includes the two being visited by probes right now, Bennu and Ryugu.

    Since these NEAs don’t have significant gravity wells, they can be mined and loads of “ore” returned to high orbits near the Moon, where 24 hour sunlight is available for processing.

    The mass return ratio for an electric asteroid tug is 200:1 over its life. Since carbon compounds make up to 20% of the asteroid by mass, your fuel return ratio is 40:1.

  66. Titan is the mother of all methane and hydrocarbon sources, plus it has high atm pressure and Moon like gravity. But its cryogenic temperatures may make it harder to build a refueling station there (the rockets aren’t made for it).

    But AFAIK there are plenty of other sources of carbon, like carbonaceous asteroids and comets out there. Gee, even the other frozen Moons in the outer solar system must have it, buried in the ground.

  67. The starship would be over designed for any non-atmospheric aplications. Just the extra mass from the re-entry shielding would be a huge disadvantage when compared to tugs or stations developed as purse space ships. A few key issues:

    1) Space craft experience much lower loads than atmosperic craft that experience extreme aero loading, especially on re-entry. Space craft can have much more delicate and light structural parts.
    2) You don’t need a high thrust to weight ratio in space, so you can use much higher impulse engines, which means more delta v for the same fuel mass. Ion propulsion today has x10 specific impulse over the raptor.
    3) Spacecraft do not need any aerodynamic systems, so the weight of fairing, wings and cowlings is not needed. This includes the shielding mentioned above.

    If the Starship is used as a tug, it will be quickly surpassed by 100% pure spacecraft. The Starship might be used for Mars missions if its can be used for re-entry there. In that case, its added structure and airfoils are what’s needed, although in all fairness, the Martian thin atmosphere is substantially different with regards aero requirements than Earth. Once more, once some critical mass of Mars demand would be reached, there would be an optimized shuttle for cycling material to and low Martian orbit at some point, optimized for Martian atmospheric condictions, not Earth’s.

  68. The future first space liner humanity ever built will certainly have a place in the history of spaceflight.

    And being probably built in more numerous amounts than the costly spendable rockets of yore, there certainly will be a few ending up in funny places, like collectors’s hands and scrapyards of the future.

  69. According to this, Hydrogen is fairly insoluble in liquid methane, to the point where it’s actually usable as a pressurizing gas without need of an isolating membrane.

    The problem is that their boiling points are too far apart, and they’re both non-polar, so they’re not really interacting. You get about as much hydrogen in the tank as though the methane weren’t there, which is not much at that temperature and any feasible pressure.

  70. Business Models: Initially: science and exploration, government supported. There are various agencies and (some) universities that would fund initial exploration. For all the work the rovers and landers have done on Mars, one human could’ve done it all in a week. So, land a team and take 6 months to do a serious amount of research and exploration. Tourism will play a small part as hyper-rich spend $$ to experience spaceflight and (some) time on Mars. Technologies will be developed and refined from these early efforts to make transport to/from and life on Mars “doable”. Then: colonization and manufacturing. Getting something out of Mars’ gravity well is much cheaper than Earth’s (assuming the research and exploration turn up minerals/ores/resources to manufacture with). Mars will be the manufacturing site and launch base for future Solar system exploration and habitation, not Earth or the Moon.

  71. It approaches being indistinguishable as the radius increases and the rate of rotation drops. Once you get down to just a few RPM, low enough to avoid disorienting people when they turn their heads, it’s likely good enough.

  72. The technology is great, but what is the business model?

    Earth orbit is big business. Maybe producing fuel on the moon instead of lifting from Earth also makes sense for moving satellites within Earth orbit.

    What is the business model for sending humans to Mars or anywhere else in the solar system?

  73. Elon’s ultimate Cargo Cult business. Spend all available money so we can be like 2000 A Space Odyssey.

    1. We won’t be
    2. What then?

    Nanu nanu.

  74. Kalman, just hang around here and start a wife-swapping club or something. No charge – bring your own Cheetos and beer.

  75. Real gravity. If your swing arm (distance between the two ships) is too short or your spin speed is too fast, you’ll get inner ear effects on your balance.

  76. If one ship has to accelerate 7 other ships it will end up using 8 times as much fuel.

    You can sometimes get what looks like “free” energy by doing clever things in space, sometimes even by tying your spaceships together with long tethers. But just tying together ships that are all going to the same location will not work.

  77. There’s quite a bit embedded into the rigolith. Its’ a mystery to a degree where it all came from. Much, but not all, comes from the Solar wind. Some, but not all, comes from Earth.

  78. See my answer elsewhere here: bring the Carbon from Earth – the overall fuel bill using lunar water will still be about 1/4th as high.

  79. By my calculations using the above cost of fuel table, if you take Carbon to GTO and bring water from the moon to GTO, the cost of methane/LOX fuel is about $1833/kg.

    (That assumes excess hydrogen is discarded – you could reduce that a bit more by sending some LOX from the moon to use with the excess hydrogen.)

    So assuming you want to send your spaceship beyond GTO, fuel made that way in GTO costs about 1/4th as much as launching it from Earth to GTO. (This ignores the added cost of the fuel factory at GTO.)

  80. Propellant stored in space has to get there. That makes that propellant to be the cost of the propellant in addition to the cost of getting it there. Making it a net loss. Making propellant on the Moon, perhaps, but there is no methane on the Moon and you have to the the hardware there and NOBODY is designing any of that currently. It’s a long way off.

  81. There is absolutely no valid reason to go to Mars. Besides it would be very expensive. We should be satisfied with movies about Mars trips.

    For around $50 billion we could send 8 couples to Mars. To make the 8 months journey bearable, they would switch partners every month. Assume they survive the radiation exposure and don’t kill each other!

    $50 billion is the price of 2.5 million Honda Civic or Toyota Corolla automobiles!

    After arrival to Mars, they would live in underground bunkers until they die, switching partners every month to beat depression and boredom.

    For another $50 billion we could send supplies so they live a few years longer.

    Tractors? Another $50 billion. Building equipment? Another $50 billion. Return to Earth. Another $50 billion.

    Are you willing to finance it? For what purpose?

    It is 50 times more expensive to send a human than a robot to Mars. Robots can do all the explorations we need for centuries to come.

    If we need an alternate planet for a living, Venus is a much better choice. We can have artificial moons orbiting Venus with a capacity for one million people each. Plenty of solar energy available for the operation of the artificial moons, unlike Mars with very limited solar energy. 1,000 artificial Venus moons can provide habitat for 1 billion humans.

    Kalman Toth, Puzzle Author

  82. You’ll want them attached at the nose with a 500 meter cable and then spin it. If you want 1/3 G (no idea why you chose that other than The Expanse. Mars is 0.38 g’s), you don’t want to spin too fast, twice per minute at most or your people will get rather sick. Spin gravity is not at all the same.

  83. Nitrogen in the Lunar regolith can be combined with the hydrogen to form ammonia.

    Ammonia is easy to store, is a very good rocket fuel, acts as an effective radiation barrier, can be used for thermal management, and will be needed as a fertilizer.

    It can also be cracked on stations to release the nitrogen for atmosphere, and to provide hydrogen for all your hydrogen needs.

    For your icon, may I suggest…

    EDIT: Absolutely meant in jest, not as an insult.

  84. The Starship is a tool. So was/is the DC-3. And they shine the same, both in utility and their mirrored surfaces. So beautiful!

    There was a reverent respect given by most dirt strip pilots to Mr.Donald W. Douglas. They felt it when they dropped His DC-3, a hold full of diesel, beer and nails, into a jungle clearing, its’ balloon tires pogo-ing down a poor village “main street” doubling as an airstrip.

    I know someday a retired SpaceX pilot, in the surplus Starship he and his brother refurbished, will drop down hard, a little too close to the craters rim than he knows he should.

    And in the relative quiet that follows, sitting over a cargo of methane, beer and coils of CNT fibre, that pad duster will feel something of the same reverence for Mr. Elon Musk.

  85. Couple of thoughts:

    Could Raptors use hythane (hydrogen/methane mix)? Or would it separate under high-G acceleration? If it worked, it might be a way to make better use of lunar hydrogen.

    Might air circulation be poor enough in a tight-packed pressurized cargo bay to allow cold spots , letting ice accumulate? Pretty easy to fix with some spacers that maintain a continuous air gap around the outside.

    Are these dumb questions? Because my default icon appears to be “purple dumbell”… 🙂 gonna have to upload a file…

  86. Although I generally respect Elon, I’d like to understand where will the Mars inhabitants get the water needed to sustain life? Haul it from Earth?

  87. Kind of an irritant in this article is the use of
    “SpaceX Super Heavy Starship” term speaking of the Starship. The Super Heavy is the booster or first stage. It will not go to space and will land to be re-used to launch another Starship or the same Starship after it lands. Please correct your terminology.

  88. Just look at all the Soyuz spacecraft wasted as disposable garbage scows. Re-use of spacecraft, re-purposing existing spacecraft with modifications in space is problematic. Sure, we can train an astro/cosmonaut to change batteries and whatnot, but we lack a space dock.
    A space dock would require a big container of breathable proper pressure atmosphere into which broken craft could be inserted for repair. Some gravity would be nice, so opposing ballast would be necessary, too. Repurposable scaffolding, and a nice less than atmospheric pressure exterior buffer with self-sealing for dock defense. Bigelow! Bigelow! Big a low!

  89. would it be possible to put half a dozen or more star ships together in space in octoweb design and use center ship for the engine as others coast as there is no drag in space i wonder if Elon and his team has thought of this way to have one ship spend fuel ? then separate at there destination like mars to land use the star ship like a convoy why take one to mars when you can take 6-8 star ships with spending only one star ships fuel

  90. The 2017 presentation indicated plans for a cargo version, tanker version, and crew version. They were presented in that order, and I see that as meaningful.

    The cargo version was shown with a large, split payload door that looked to be the majority of the length of the payload section. I would guess that it would be first to facilitate making money as early as possible launching satellites.

    The tanker version would then allow for higher orbit, lunar, and interplanetary trips for the cargo version – again for early revenue production as well as being able to deliver on those first cargo missions to Mars.

    The manned version would follow simply because it takes the longest to develop and it is nice to prove most of its functionality with many launches of the unmanned versions.

  91. I wonder if Musk and his team has ever thought of making a second stage that Just delivers cargo. Nothing really returns.

  92. Mat… If they can send it to mars mainly fueled an idea to help shield against radiation might be to have longer fuel tank inside and habitat partially recesed inside the fuel tank to use the fuel inside to help shield the crew from solar radiation.

  93. Yep. Fairly common that people have trouble understanding that these rockets and ships can perform very different roles with relatively minor modifications. Orbital cargo carriers with a retractable fairing, tankers, point to point passenger carriers, lunar transports, early planetary settlements, orbital labs, etc.

    BFR/Starship will be more like a platform, a family of spaceships with different applications than a single kind of application one.

    There will be some designs being produced sort of in series (like the tankers and satellite launchers), others will be more customized, for example, any interplanetary crewed ones.

    It’s more like the birth of airliners than the creation of any single kind of airplane.

  94. I would think that it will also be possible in the near future to build a hydrogen/Oxygen production station for space refueling in near orbit capturing the many ice chunks that are attracted to earth vicinity. The system could both realign the ice trajectory using lasers and adjust its own to be able to reach it and capture it.

  95. Yes! Given that Earth re-entry will probably be the most stressful part of the Starship’s missions one can see older Starships left in space to act as dedicated tugs, transfer vehicles, landers and ultimately habitats (orbital, lunar ….). We are basically talking about switching the enclosed “payloads” as needed and sometimes leaving those Staships at permanent bases … perhaps converting those big tanks to other uses over time. . The road to success: Raptor Performance & Reuse -> Space Frame Reuse -> Thermal Protection Reuse (cost driver for # of Starship Re-entries) -> On Orbit Refueling. Then specialized payloads within the same space frame. Eventually we will have a Starship payload user guide that third parties can use to create Starship compatible payloads Of course Super Heavy booster is the same for all. One final thought … if you connect two Starships (as currently speced) at the engines you can spin the pair to create 1/3 G artificial gravity with no motion sickness. Nice to have for a Mars voyage. My guesstimate here:

  96. I suspect more than a few carbonaceous chondritic asteroids have impacted the Moon, and even if not, than means what about a quarter of the needed fuel mass needs to be brought even if you use MethaLOx ?

  97. Where can one find carbon to make in situ fuel for the Raptor engines?
    It seems optimized for Mars but not for the Moon / Earth logistics. Water is the most common molecule in the universe and there is plenty on the Moon. Is there any easy carbon? Maybe a hydrolox engine is needed.

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