Spaceflight Insider

SpaceX’s Mars Colonial Transporter: Rumors and Realities

Mars Red Dragon SpaceX image posted on SpaceFlight Insider

Image Credit: SpaceX

For more than a decade, SpaceX CEO and Founder Elon Musk has been hinting at the eventual development of a super-heavy-lift launch vehicle and accompanying spacecraft that can economically transport 100 metric tons (220,462 lbs) of cargo or 100 people to the surface of Mars. 

The purpose of this ‘Mars Colonial Transporter’ (MCT) would be to establish a large city on Mars that could eventually become a self-sufficient second home for humanity.

Over the years, as the MCT concept has evolved, very few design parameters have been announced. Last year, however, Musk indicated that he will probably release MCT design details later in 2016. Until then, what do we know and what should we expect? The following are best guesses:


For a number of reasons, SpaceX has opted for cryogenic liquid methane as the MCT fuel:

  • Methane can be manufactured on Mars from subsurface ice and atmospheric CO2. This can dramatically increase the payload that can be delivered to Mars for a given launch because the fuel for the return to Earth will not need to be transported to Mars.
  • Methane is cleaner burning than kerosene (RP-1) so less engine maintenance will be required between flights.
  • Methane is denser and less technically challenging to handle than liquid hydrogen.
  • The boiling point of liquid methane and liquid oxygen are nearly the same, reducing thermal insulation requirements between the fuel and oxidizer tanks.
  • To reduce the size of the booster, liquid methane can be further “densified” by chilling it to almost the freezing point.


SpaceX's Raptor rocket engine undergoes a static test fire in this NASA image. Photo Credit: NASA / Stennis

A component of SpaceX’s Raptor rocket engine undergoes a static test fire in this NASA image. Photo Credit: NASA / Stennis

The MCT will employ a completely new rocket engine: the Raptor. Its oxygen-rich full flow staged combustion methane cycle, operates under lower temperatures and chamber pressures. This means less coking and a more benign turbine environment, which could result in less maintenance, less material fatigue, a longer lifespan, and a lower engine weight.

Parts of the Raptor engine are additively manufactured (more commonly known as 3-D printed), using titanium and Inconel alloys. 3-D printing permits greater design freedom and more rapid prototyping, compared to more conventional methods. Various Raptor engine components are currently undergoing testing at the NASA Stennis E2 test stand.

The Raptor will come in two versions: a sea-level version that will be used on the first stage of the booster and a vacuum version that will propel the second stage/spacecraft.

The most recent estimate is that the Raptor thrust will be approximately 2,300 kilonewtons—about three times the thrust of the SpaceX Merlin 1D engine and about one-third of the thrust of the Apollo Saturn F-1 engine.

A Mars Mission

A two-stage fully reusable booster plus spacecraft design has been adopted. The “Mars Colonial Transporter” will consist of a first stage booster (code name BFR) and a second stage spaceship (code name BFS). What are the elements that would comprise such a mission?

  1. A booster will launch a second stage Mars-bound “transporter” spaceship with 100 metric tons of payload towards low-Earth orbit and then return back to the launch site. The transporter will burn all of its fuel to reach orbit.
  2. A booster will launch a second “tanker” spaceship towards Earth orbit and then return to the launch site.
  3. The tanker will rendezvous with and transfer fuel to the transporter.
  4. The tanker will undock and perform a series of reentry burns to return to the launch site.
  5. Steps 2–4 will be repeated 2 or more times to fully refuel the transporter.
  6. At the proper moment, the transporter will perform a trans-Mars injection burn that will put it on a transfer orbit toward Mars.
  7. As it approaches Mars, the transporter will perform a series of precision Mars entry burns to land at the desired destination.
  8. The transporter will offload the payload to the surface.
  9. The transporter will refuel from a Mars fuel production plant.
  10. At the right moment, the transporter will launch from the Martian surface and perform a trans-Earth injection burn that will put it on a transfer orbit back toward Earth.
  11. As it approaches Earth it will perform a series of precision reentry burns to land at the launch site.

This entire mission will take more than a year because steps 6 and 10, the orbital transfers, can each take 4 or more months. Furthermore, the launch window for step 6 only happens once every 26 months.


A rendering of what the scale of the MCT might be in comparison to the Falcon 9 and Saturn V boosters. Image Credit: Reddit posted on SpaceFlight Insider

A rendering of what the scale of the MCT might be in comparison to the Falcon 9 and Saturn V boosters. Image Credit: Reddit

The single-core booster will launch and land in a similar fashion to the first stage of the SpaceX Falcon 9. However, it may require as many as 30 sea-level Raptor engines in order to generate sufficient thrust. Consequently, it could be enormous: 49 feet (15 meters) in diameter and 394 feet (120 meters) tall—taller than the Apollo Saturn V rocket, and some 50 percent wider than the launch vehicle that sent men to the Moon.


The spaceship will utilize several vacuum Raptor engines and will be large: 197 ft (60 meters) high and 49 feet (15 meters) wide. When stacked on top of the booster, the MCT will be 591 feet (180 meters) tall, more than 60 percent taller than the Saturn V.

Under this plan, there would be two versions of the spaceship: an LEO tanker and a Mars transporter.

The LEO tanker will contain additional fuel tanks that can be used to refuel transporter spaceships in low-Earth orbit. All spaceships will have docking ports to transfer fuel.

The Mars transporter would deliver up to 100 mT of cargo/passengers to Mars. For the first decade, flights will be mostly cargo, with perhaps no more than 10 passengers per mission; whereas decades later, as many as 100 or more passengers might be possible. In order to provide this versatility, the transporter will probably include a large payload bay that can be loaded with a variety of cargo and passenger modules. Individual passenger space may be less like a cruise ship and more like an SUV. At some point in the future, it might make sense for SpaceX to invest significant effort into designing truly awesome passenger transport quarters, but that may be two decades away.

For the first decade, because of the small numbers of passengers, it may be convenient to transport them in Dragon 2 capsules up to the orbiting transporter spaceship, eliminating any immediate need for a massive passenger launch escape system.

Because of the compartmentalized passenger modules, one or more modules can remain on the transporter in order to provide optional passenger transport back to Earth, whereas the offloaded passenger modules can be used as Mars surface habitation quarters.

Some type of crane may also be required to offload these modules to the Martian surface.

For Earth ascent, the spaceship will probably include a recoverable nose shroud. For Earth re-entry, it will require a large heat shield. For Mars re-entry and descent, SpaceX has not yet indicated if a ballute will be employed.

SpaceX has expressed an interest in electric propulsion in order to reduce the orbital transfer time (and consequential space radiation exposure), particularly if they can use solar or nuclear power generation gear that will be delivered to Mars.

A small radiation shelter will be needed to protect passengers from the possibility of brief solar flares. Because water provides some of the best protection from high energy solar protons, water storage tanks may provide the best shielding.

One open question is how passengers will be protected from the physiological effects of prolonged weightlessness. If it will be exercise-based, then this may impact the layout of passenger modules. On the other hand, if rotational artificial gravity will be attempted, then this may impact the design of the entire transporter spacecraft.

Launch Complex

NASA Kennedy Space Center Launch Complex 39A SpaceX Falcon 9 Heavy launch site 20 year lease photo credit Carleton Bailie SpaceFlight Insider

If the MCT booster’s dimensions are accurate – SpaceX’s Launch Complex 39A facilities will not be able to support the launch of such a large rocket. Photo Credit: Carleton Bailie / SpaceFlight Insider

The MCT will be too large for Launch Complex 39A at the Kennedy Space Center (which SpaceX has signed a 20 year lease with NASA to use). Consequently, it will need a new, larger launching pad, possibly at the new Brownsville Texas launch site.

Because the large diameter of the booster and spaceship will make it too large for road transport, the manufacturing plant will need to be near this launch site. This launch facility will also need a large vehicle assembly building, transport erector, and a liquid methane/oxygen production, storage, and distribution system.

Mars Base

At the Martian landing site, there will need to be fuel production facilities that can generate and store liquid oxygen and methane from atmospheric CO2 and ice. This facility will be powered by a compact nuclear reactor (6 meters tall and 5 meters in diameter) that will also generate heat. In order to extract the required water, some amount of exploratory drilling or digging may be required.

In order to establish this Mars base, one or more unmanned cargo missions will need to be successfully completed before manned missions to Mars can commence.

The views expressed in this article are those of the author and do not, necessarily, reflect those of SpaceFlight Insider. This article was drafted using source material from NASASpaceFlight, Reddit and elsewhere.

Video courtesy of SpaceX


Nelson Bridwell is an automation engineer with a long history of following anything that involves space exploration. He has posted editorials and content on an array of space news websites including Aviation Week and Space Technology and Space News. Bridwell, impressed by the quality level of SpaceFlight Insider's content contributes on occasion via commentaries and other postings.

Reader Comments

“The following are best guesses:” Should be re-written to “here’s a collection of things I’ve stolen off Reddit.”

Journalism at its worse.

Dear Mr. Anderson,
The author pulled from NASASpaceFlight, Reddit, SpaceX, Imgur and other sources to draft a review of speculation/what (little) is known about the MCT. Virtually all articles are drafted pulling from numerous sources. Therefore your comment about “journalism at its worse” – was uncalled for. Please review our commenting rules.
Sincerely and with kind regards, Jason Rhian – Editor, SpaceFlight Insider

Jason Rhian: The NSF and Reddit SpaceX communties have an extremely high overlap of users. It’s essentially one community for the our purposes here. So that’s one source. SpaceX Imgur == Reddit, because everything you see on Imgur that’s SpaceX based came from /r/SpaceX (imgur is the imaging site used by most subreddits). SpaceX has released nearly nothing on the MCT/BFR.

Therefore the author used exactly one source: they rewrote stuff from NSF/SpaceX Reddit. As someone that is familiar with everything on the internet based around SpaceX, claims that this is just a rewrite of /r/SpaceX and NSF’s free forum section ares not an exaggeration, they’re the literal truth.

Is such rewriting a bad thing? I’d say no, but you should own up to it.

Hi Gopher65,
Read the full statement, “…and other sources” – “ShitElonSays” (I avoided that one because of the language used) and, of course SpaceX. The author used all sources available to him. I don’t consider NSF to be Reddit, nor do I consider these other sites to be Reddit either – nor would most other journalists. Therefore, the author pulled what is known from what (little) is available – and provided a review of that. I imagine you’ll state ShitElonSays and also have a high overlap or that this is still single-sourced. In short, there are links to each of these in the article and it appears some are trying to create a problem where none exists.

And, yet again, from my earlier statement on the subject: “…draft a review of speculation/what (little) is known about the MCT.” I already did “own it.” It appears you either missed or opted not to acknowledge it.

Sorry, I’m not trying to nitpick, but this is rather petty. There is next to nothing known about this and Nelson tried to scrape what was known into one location.

Jason Rhian – Editor, SpaceFlight Insider

Nelson Bridwell


In order to write up an article like this there are 2 major challenges:

(1) identifying what has been said vs. what different SpaceX enthusiasts would like to infer. To accomplish this you need to go back to the original interviews to listen to exactly what was said, and how it was said.

(2) Making reasonable inferences about what has not been said. Again, you have to go back and read or listen to as much information as possible in order to get an idea how SpaceX operates, which is not always exactly the same as what some SpaceX fans assume.

So no, it was not as simple as just rewriting one or two posting on Reddit/SpaceX or

Can you point us to a published article on NasaSpaceFlight that clearly spells out details for the design and operation of MCT? Chris Bergen is an informative and excellent writer, but I do not recall seeing anything specific from him.

Same goes for Reddit/SpaceX.

Which is not to say that Reddit/SpaceX and NasaSpaceFlight are not good ways to keep tabs on developments, as is SpaceFlight Insider.


What is wrong with summarizing everything he thinks he knows from a variety of sources in one easy to read article? It works for me even though I have my own architecture. It saves me the trouble of having to sift through a whole bunch of scattered space cadet forums and comments where I am not particularly liked or respected.

Nelson Bridwell

Mr. Anderson:

Are you accusing me of plagiarism? Perhaps someone else wrote this exact same article previously on Reddit/SpaceX? Can you please direct me to anything that is even close?

You are entirely welcome to write a better and more informative article about MCT. I would genuinely love to read it, and we would all like to see your sources, too.

The largest challenge in writing this article has been to strip away all the enthusiastic speculation that has no realistic connection to what Musk, Mueller, and Shotwell have stated, and to try to fill in some of the blanks with semi-reasonable assumptions.

The only information that I used that came from Reddit/SpaceX alone was the size of the first and second stages. Although anonymous numbers have to be questioned, I vetted these numbers with two NASA engineers who said that they appear to be credible.

I genuinely encourage you to write up a more detailed expose on the MCT, Mr. Anderson, because I assure you that it will attract great interest.

Mr. Terry Anderson is wrong. I applaud the author. Journalism at it’s finest! Thanks for this great article and the research!

Nelson Bridwell


Thanks! I will be writing a second article about some of the financial challenges of making MCT happen. If anyone has information or ideas that might be relevant, please let me know.

Again, thanks!

Sounds like a viable architecture. The Raptor would also be useful for a return to the Moon, since CO2 ice the second most likely volatile in any cold-traps.

Nelson Bridwell

Really good point. Had not considered CO2 on the Moon, but what you say sounds quite possible. I have to will check this out with Paul Spudis.
I will be writing up a follow-on article where I will mention scientific exploration of the Moon as a possible source of initial revenue for MCT.

As noted in the text, the Mars launch vehicle will require a lot of infrastructure at and near the launch site. All of that would need to be built in Brownsville from scratch, whereas there is quite a bit already there at Kennedy. I don’t mean just stuff directly to do with rocket manufacture and integration, but stuff like housing, NASA offices, a local aerospace workforce etc. From what I understand, the Boca Chica site doesn’t even have sufficient roads to support such operation at the moment.

Mike, …you forget the sea. More specifically, you forget the intercoastal waterway. Saturn Vs could not be assembled at Canaveral, yet they were delivered. Road transport becomes a problem only when you need to move things long distances without the sea. That is why both Boca Chica and Roosevelt Roads should be still in the running. Falcon 9 was built to be cheaply brought through tunnels in the Rockies, which set their limits on its maximum stage width and stage height.

*IF* there is a BFR, then it could be built in Decataur, Alabama, or anywhere next to a river connecting to the ICW. If you demand it be built nearby, then instead of interrupting the life of Brownsville so much, you could build it at Roosevelt Roads, on Puerto Rico, more easily. It has full support facilities for Naval Fleet OPs going back 7 decades by now. Lots of options open up when you forget the width of tunnels.

BFR will be built and launched at Boca Chica. This has been confirmed by both Elon and Gwynne. While there is not anything substantial at Boca at the moment, plans are for a dramatic increase in infrastructure development over the course of the next year or two.

That is not to say that the gulf will not be used for materials shipment to Boca. The work there will be massive, so it seems reasonable that materials will arrive via road AND ship.

Nelson Bridwell

“SpaceX has indicated on several occasions that they will need more than the four launch sites currently in active use or in process. Discussions continue for future launch facility locations beyond Texas.”

Nelson Bridwell

Mike: I have to agree that a lot of work will be needed to support future launches from Brownsville. A NASA engineer pointed out exactly the same thing to me. And being so close to the Mexican border probably doesn’t help.
My impression is that the main attractions of Brownsville for SpaceX are that (1) it is cheap, (2) because it is not an Air Force site, there isn’t nearly as much red tape getting in the way, and (3) there is plenty of room for expansion.
And I have seen quotes that the manufacturing will be performed near the launch site, but I would think that major components, such as rocket motors, could still continue to be manufactured in Hawthorne.

As an Entry, Descent, and Landing person I feel like you could expand on the section “For Mars re-entry and descent, SpaceX has not yet indicated if a ballute will be employed.”
SpaceX hasn’t said ANYTHING at all about Mars re-entry and descent, but I think it is unlikely they will go with any kind of inflatable aerodynamic decelerator. My money is on some sort of lifting body vehicle with an ablative heat shield and supersonic retrorockets for descent and landing.

Nelson Bridwell

Tyler: My recollection is that Musk may be anti-wings because he considers them to be less weight-efficient. Have never seen any evidence of SpaceX interst in lifting bodies. Have you?

Purdue grad student Max Fagin on supersonic retropropulsion. Mr Fagin did intern at SpaceX for a time. Techniques such as these described may allow large multi-ton payload deliveries to the Martian surface without the exclusive use of large parachutes or heat shields, inflatable or otherwise.


As the author states, this article was sourced from SpaceX-related internet snippets. While the article’s scenario is plausible, its lacks reflect that focus. It does not mention Phobos, a resource base for Mars transport 4.5Km/sec closer to Earth than Mars surface, in terms of required Delta-vee. Having the density of a CC asteroid, Phobos will probably have water and many other resources to provide lander propellants, and propellant for transits back to Earth. It will also have materials from which later landers can be constructed, as well as energy sources such as Solar Power Satellites for beamed power to both settlements and transiting landers themselves. These lacks are examples of the simpler physical ones.

Further lacks are in the over-focus on SpaceX alone. True, this is a scenario about *SpaceX* plans for getting people to Mars but even Elon, if he hasn’t already, privately, will have to admit he cannot do and control everything in settlement himself. Trying that is the fastest way to crash and burn. There are, however, already companies focusing on extracting resources from asteroids like Phobos was before it was captured as a moon of Mars.

Planetary Resources, Deep Space Industries, Astrobotics, and others, will help explore, extract, and extrude from printers what is needed far more cheaply than bringing it along from Earth. That will mean Elon will be showing what he cannot, right now, …his high skills at extracting from a market the equipment for reaching his goals, and others. *Do*not*forget*that*market*!

Indeed, that brings in economic viability as an issue. In settling North America few isolated settlements, in communication with only the “motherland”, prospered. Only when a network of settlements existed did prosperity come to settlers and investors alike, especially since they were so often the same people. That was because their costs between each other were less than that of bringing equipment from Europe.

Focusing on just one point of settlement, …Mars, …is going to be as dysfunctional as was “Roanoke” and other isolated colonies. Planning for success in settling anywhere in the Solar System must be subtler, in that it must take account of all other settlements within reach.That includes both for physical movement and for movement of intellectual property, such as the designs to be transmitted for use by 3d printers and other “ephemeral” necessities.

Nelson Bridwell

SpaceX has not expressed interest in a Phobos mission because it has no atmosphere from which methane fuel could be manufactured.
And Musk has said that he does not consider resource extraction from asteroids to be a requirement in order to colonize Mars.
There are many enthusiastic people like you who with interesting, imaginative concepts that capture the imagination. However, just because an idea is neat does not mean that it will necessarily be pursued by SpaceX.

Nelson, my point was not that *SpaceX* would focus on Phobos, but that others would, and thus enable cheaper and faster settlements on Mars itself by selling materials to SpaceX and others. The idea of “a Phobos mission” is not productive. It assumes a stopping point. Settlement will have no stopping point. A centralized plan in *any* one person’s brain will seldom be the way to the most highly productive activity. The multitude of nodes in the network of a Solar System economy, however, have a high chance of including Phobos. It has a good chance of having the water and kerogen/carbonaceous material that CC asteroids tend to have. That will, give a small settlement there the means to make both Methane and LOX.

King of Phobos

Phobos may already be inhabited

Awesome synopsis of the reasonable speculation that’s out there; thanks for writing it up/publishing it.

Nelson Bridwell


Thanks!!! Looking forward to learning more about MCT from SpaceX in the hopefully not-so-distant future.


Can you clarify what you mean by “oxygen-rich full flow staged combustion methane cycle?” I was under the impression full flow required part of the fuel to run through an oxidizer-rich pre burner and part through a fuel-rich pre burner. I have read that fuel-rich methane combustion with oxygen would definitely produce soot, which would be a problem for this type of engine. Do you have an idea for how full-flow might be possible with this fuel combination? I’ve been wondering about it for a while, and I haven’t been able to find, or think up, any answers.

Nelson Bridwell

Not being a rocket engine expert, I used the description used by description used by Jeff Thornburg, SpaceX Senior Director of Propulsion Engineering in June 2015:
“Raptor directly contributes to the rapid advancement of oxygen-rich and full-flow staged combustion and additive manufacturing technologies for the United States, enhancing U.S. industrial capability.

And as you point out, parts are oxygen-rich while other parts of the engine are fuel-rich.

I’m with Bob. A non-full flow staged combustion engine has one pre-burner, which can either be oxygen-rich or fuel-rich.

A full flow staged combustion engine has two pre-burners, one oxygen-rich, one fuel rich. So to say it’s an oxygen-rich full flow staged combustion engine is wrong.

You quote Jeff Thornburg, but he says “Raptor directly contributes to the rapid advancement of oxygen-rich and full-flow staged combustion…” He meant they will be developing an oxygen-rich pre-burner (amongst other things) and developing full flow technology. He did not say ‘rapid advancement of an oxygen-rich, full-flow staged combustion engine’ – nor would he.

Minor quibble in an interesting article.

About mentioning financial way for MCT development. I’m not following things lastly, but long time ago there was idea to put methane upper stage on falcon heavy. This could allow to merge Mars goal design and money making design. Assuming it’s possible to put MCT upper stage on falcon heavy. This idea was from Musk, not one of enthusiast. Of course lot could change, but why not? Seems reasonable.

Nelson Bridwell

What you mention appears to be the direction that SpaceX is moving, because they have been awarded $34M from the Air Force for development of the vacuum Raptor as a higher-energy upper stage motor for the Falcon 9 and Falcon Heavy as pare of the program to free the US launch industry from dependence upon the Russian RD 180.

The above speculation about the MCT is interesting. However, and while I haven’t seen many official comments about it, in at least one I read SpaceX made mention that the MCT will not be a conventional design… which is what the rocket discussed here is. It’s a version of today’s rockets made bigger. Much bigger. Also, I cannot believe that Elon would design a rocket that requires the launch of many smaller rockets to get the passengers into orbit where they would need to dock with and board the Mars Transporter. My speculation is that the MCT will, like reusable rockets, scramble our notions of what heavy lift rockets look like. Elon Musk is not an advocate of the conventional, and I’m betting that the design for his 100-passenger MCT won’t follow it either.

Nelson Bridwell


Everything that Elon Musk has stated suggests that he, like Zubrin, doesn’t believe that anything beyond conventional chemical rocket propulsion is required in order to colonize Mars. Although his goals may appear outlandish, his methods appear very practical.

As mentioned in the article, they have expressed some interest in electric propulsion, as long as it makes a difference, and are hiring electric propulsion engineers in Seattle, but that could be for LEO-to-GEO commercial satellite tugs.

His most recent interview in Dec 2015 indicated that the MCT design is going to be BIG:

“Before we announce it, I want to make sure that we’re not gonna make really big changes to it,” he says. “Um, yeah. I think it’s gonna seem pretty crazy, no matter what. It’s really big. It’s REALLY big. There’s not been any architecture like this described that I’m aware of.”

Ernie Moore Jr.

As to the thinking that a smart person might not use ships to get to a ship…it seems as though rockets exhaust fuel and drop stages to get to outer space. There might be some economy to start the launch from space. The financial and fuel expenditure to launch at ground is perhaps offset by a LEO standing-by station with rocket set.-Ernie Moore Jr.

Payload is talked about in weight. I think we should look at shape. A colony requires structure. Structures require the building of them. Or at least the putting together of them. I presume equipment might be needed. I presume the equipment might need to be like cranes or bulldozers and dump trucks. Telescoping arms and bodies can only be done so much,and should be considered we need to build equipment that can help construct buildings. And their design except for in and under can leave unused space-reducing maximized payload area significance.-Ernie Moore Jr.

How long does a Mars fuel production plant take to be built as a sound structure? A Mars fuel production plant would have parts. Given the scheduling of 2Eyr 2Emo per Trans Mars injection burn orbital (tMibo) to Mars is four(4)tMibo in ten years; nine tMibo in twenty years…how many trips divisible by nine (remainder four) would it validly take to finish a Mars fuel production plant [excluding missed windows]. Mark:none of what goes there comes back without this part completed. and is farther off-set by sending supplies and staff or equip for just living there while building this proposed way-back-off the planet. How many scores before anyone can come back from Mars?-Ernie Moore Jr.

Mr. Bridwell, thanks for writing such an excellent summary! I’ll make this site one of my go-tos from now on for SpaceX news. Look forward to reading more of your work in the future.

All this talk new vehicles. The Space Shuttle could be reworked for Mars SRP EDL with variable double slotted flaps and RCC leading edge slats on the wings and SpaceX motors and thrusters. So doing with about 40 Earth tons of cargo onboard and put down within 10 meters of the target landing site.

This is good summary of the various speculative ideas floating around about he MCT. There is another way of working out how big a rocket the MCT will have to be and that is going back to first principles and just examine the masses. Only 4% of the mass of the take off weight makes it into low Earth orbit (LEO); the Saturn V was about 3000 tons and put 140 tons into orbit (still mind boggling all these years later). This figure is for an expendable rocket and Elon has said that for a reusable rocket the payload will be about half, so 2% to LEO. Therefore just to match the Saturn V the MCT would need to be about 6000 tons If the intention is to transfer 100 tons of stuff (methane manufacturing plant, habs, power sources, orbital booster etc) to the surface of Mars then the Mars decent stage/lander will be considerable larger probably of the order of 300 tons. It is worth considering the moon landings. About 50% of the mass of the lunar lander module was fuel. The ascent stage (the legs and decent engine were left on the surface reducing the take off mass)) was also about 50% fuel by mass. This is logically consistent since the mass/fuel ratio required for landing is matches the requirement for launching. Mars has double the gravity of the Moon (38% that of Earth as opposed to 1/6th) and a smidgin of atmosphere (about 0.6% of Earth’s at,ospheric pressure), this, and the higher Mars orbital velocity coupled with the Hohmann transfer orbit velocity will necessarily increase the fuel/mass ratio needed to effect a landing. My own quick and dirty calculations suggest a transfer mass (Earth Mars of about 450 tons). This indicates three launches of a Falcon MCT of 6000 tons (with assembly in LEO or a single launch of MCT of 18000 tons.

I simply cant see space X doing a rocket with a core of like 10Meters or even the more ridiculous suggestion of 15 meters diameter because there really is no need for it and space x will not achieve elons vision of getting to mars by bankrupting themselves.

The Sensible next step is a 9 engine raptor powered rocket with about 2.5x the lift capability of the falcon 9. The core would be about 5.8 meters diameter and this size of rocket would fit nicely into the space x commercial launch catalogue as a single core heavy lift able to replace the falcon heavy on most missions and thereby act as a workhorse for heavy commercial satellite launch market.
When and if they ever require super heavy lift they will simply make a falcon X heavy with 3 cores strapped together which would enable a super heavy lift capability of over 100T into orbit in one shot.
This methodology would be able to leverage what space x learn from their falcon heavy vehicle which essentially makes a 2 stage falcon 9 into a 3 stage heavy lifter. It also keeps the first stage rocket at a practical size for reuse that could land on a barge and survive re-entry of the first stage returning to earth etc.
And most importantly it enables spacex to develop a new vehicle and iron out the bugs as they have with the falcon 9 by servicing commercial satellite market to get the confidence in launching a larger 3 core super heavy lifter with a high chance of success whenever they need it and without having to expend huge sums retooling and developing a vehicle that will only ever be suitable for a few limited use scenarios which entails huge commercial risk and could thereby risk bankrupting the company.

If one requires more than 100T into space they would launch multiple falcon 9 or falcon X heavy and assemble something like an MCT in orbit out of several pieces just like the international space station has been assembled piece by piece.

I also seriously doubt the reliability of any rocket with a height more than 100M to get into space – there is no advantage in making a vehicle that tall as it will become structurally weaker and heavier – a shorter vehicle using 3 parallel cores is likely to be more structurally robust and capable of greater acceleration on launch than a tall one.

I’m trying to make sense of these four booster.
1. Falcon 9
2. Falcon Heavy, which 3 Falcon 9s strapped together. I’d call it the Falcon 9-3
3. Your proposed Falcon X heavy, I think from your statement would be the 9 engine Raptor first stage.
4. The Super Heavy Lift then would be, maybe, a SHL-3.

Well, that little exercise made it easier for me to put it into perspective.

Torbjörn Larsson

@Stephen: Scaling up Red Dragon’s landing technology you likely can’t land a 6 m diameter BFS directly on Mars at a 100 mt load. (Say, a 150 mt vehicle.)

The 10 m (better 12 m or 15 m) diameter heat shield is necessary to aerobrake to 2-3 Mach before the final supersonic retropropulsion burn to land.

Nelson Bridwell

It is said that at many SpaceX meetings a standard question is “How does this get us closer to Mars?”
Their primary focus appears to be Mars, whereas commercial launch is seen simply as a stepping stone to reach that goal. That is why they have chosen to bypass the reusable Falcon 9 upper stage. But there are many who agree with you that a smaller rocket makes sense for a number of reasons, and it appears that may have been their plan until about 1-2 years ago.

Nelson Bridwell

I have heard many arguments why the MCT does not need to be this large, but these are the dimensions that were leaked. The surprisingly large size also appears to conform with public comments from Elon Musk (and Chris Bergen, who has had some access to inside information).
But for all we know, the design to be announced in September could look very different.

Loved the article, thank you.

Michael J Gorman SR

Fascinating article…thanks.

Why did you conclude that the fuel facility would be powered by a nuke plant? They are expensive, heavy, and very hard to get launch permission for. Even Juno is using solar panels (although it does have very modest power requirements). Still, the Musk group of companies has core competencies in rockets, batteries, and solar panels.
What a Mars colony needs is a solar panel factory … at some point.

Nelson Bridwell

Leaked specifications for the MCT included mention of the dimensions of a compact nuclear reactor. Beyond that, we don’t have much to go on.

Is it possible that launching sunward (with appropriate shielding) might provide enough velocity to kind of sling-shot toward mars when it is out of position for closest approach transition and thus have alternatives for sending cargo mars that are not within the normal “closest approach” window?


1. Si les Réacteurs sont du type conventionnel et fonctionnent avec du carburant classique, qui est utilisé entre autre pour les fusées Ariane 5 et Ariane 6 à partir de 2020 pour cette dernière, les Réacteurs possèderont une Tuyère de Laval dont le profil sera calculé grâce aux 2 Principes de la Thermodynamique, le mélange Air Carburant sera assimilé à un Gaz Parfait Compressible, donc nous pouvons écrire les équations suivantes :
– Pv = rT (1) avec P la pression du mélange qui est variable selon le point où nous nous plaçons le long de l’axe de la tuyère, v le volume massique du mélange air carburant, r la Constante Massique du Gaz Parfait utilisé pour la combustion du mélange, et T la Température du mélange exprimée en degrés Kelvin, soient T(K) et T(C), cette dernière étant exprimée en degrés Celcius, nous pouvons écrire la seconde équation ;
– T(C) = T(K) – 273 (2)
Premier Principe de la Thermodynamique :
– dE + dK = &We + &Qe (3)
E : Energie Interne
K : Energie Cinétique
&We : Travail échangé avec le Milieu Extérieur
&Qe : Quantité de Chaleur échangée avec le Milieu Extérieur
Deuxième Principe de la Thermodynamique :
– &Qe + &We = TdS (4)
S est l’Entropie du volume considéré de gaz (mélange) brûlé
Autre hypothèse : l’évolution des gaz dans la tuyère est assimilée à une ISENTROPIQUE REVERSIBLE (pas de frottement et pas d’échange de chaleur dans la tuyère avec le milieu extérieur car la vitesse des gaz dans la tuyère est élevé).
Calcul de la poussée du Réacteur Conventionnel :
– P = QM X V avec QM = pSV (5)
P est la poussée d’un Réacteur en Newtons,
QM est le Débit Massique du mélange brulé à la sortie de la tuyère,
V est la Vitesse du mélange brulé à la sortie de la Tuyère du Réacteur. La poussée du Réacteur sera maximale quand les gaz atteindront mach 1 au Col de la Tuyère,
– P = pSV^2 (6) donc plus V est grande plus P est importante.
Théorème de la Résultante Dynamique :
– M(T) GAMMA(A) = P (7) avec GAMMA(A) l’Accélération Absolue du Vaisseau Spatial calculée dans un REPERE HELIOCENTRIQUE qui est un REPERE GALILEEN,
– M(T) = M(VS) + M(C) + M(P) (8)
M(T) : masse totale du Vaisseau Spatial carburant, personnels et voyageurs compris,
M(VS) : masse du Vaisseau Spatial vide, cad sans carburant et sans personnel ni voyageur,
M(P) : masse du personnel et des voyageurs,
M(C) : masse du carburant dans la soute,
Remarque : M(C) est variable par rapport au temps, à accélération constante le débit de carburant sera variable, car M(C) diminue avec le nombre kilomètres parcourus et a donc un impact direct sur la Poussée du Réacteur P, il faut asservir la Poussée P et la Vitesse V pour maintenir GAMMA(A) constante.
La Trajectoire Rectiligne de la Terre jusqu’à Mars est la Trajectoire Absolue du Vaisseau Spatial, La Trajectoire Relative ne nous intéresse pas.
Le Vaisseau Spatial sera équipé de 4 Réacteurs de taille acceptable assurant chacun comme poussée P/4, un seul Réacteur aurait une trop grande taille.
2. Si les Réacteurs sont du type à Fusion Nucléaire, alors les soutes à carburant permettront d’assurer le voyage aller et le voyage retour. Le principe de fonctionnement des Réacteurs à Fusion Nucléaire diffère complètement de celui des Réacteurs du type conventionnel, je rédigerai un pavé de texte spécial pour expliquer le Fonctionnement des Réacteurs à Fusion Nucléaire.

Alain Mocchetti
Ingénieur en Construction Mécanique & en Automatismes
Diplômé Bac + 5 Universitaire (1985)
UFR Sciences de Metz


Considérons que le trajet supposé rectiligne entre la Terre et Mars se décompose en 2 demi trajets de 112.500.000 km. Durant le premier le Vaisseau Spatial sera en Accélération Constante et durant le second en Décélération Constante.
GAMMA(A) est l’Accélération du Vaisseau Spatial
GAMMA(D) est la Décélération du Vaisseau Spatial
D = 112.500.000.000 m
Calcul de l’Accélération GAMMA(A) :
GAMMA(A) = (Delta V)/(Delta T) c’est l’Accélération du Vaisseau Spatial
Delta V = V(1) – V(0) avec V(0) = 30 000 km/h la vitesse initiale et V(1) = 300 000 km/h soit 10 fois la Vitesse Initiale V(0).
V(1) – V(0) = (300.000.000 – 30.000.000)/3600 m/s soit 75.000 m/s
Delta T = T(1) – T(0) avec T(0) = 0 donc T(1) = 3 X 31 X 24 X 3600 secondes, on prend comme hypothèse que les 225.000.000 km sont parcourus en 6 mois.
GAMMA(A) = 75000/(3 X 31 X 24 X 3600) = 0,01 m/s² ce qui est trop faible, remplaçons les 3 mois par 1 mois et on obtient :
GAMMA(A) = 75000/(1 X 31 X 24 X 3600) = 0,03 m/s² pour rappel G l’accélération de la pesanteur terrestre = 9,81 m/s²
Si on remplace les 1 mois par 15 jours alors GAMMA(A) = 0.06m/s², soit 1/163ème de l’Accélération de la Pesanteur Terrestre..
En phase Décélération GAMMA(D) = – GAMMA(A)
Calcul du trajet le plus économique du point de vue du carburant, ça sera indéniablement le plus long du point de vue du temps (T) : Si V(1) = V(0) = 30000 km/h = Constante tout le long du trajet, dans ce cas précis le consommation du carburant sera nulle en dehors du carburant nécessaire pour assurer la poussée des réacteurs pour échapper à l’Attraction Terrestre et pour assurer la poussée des rétrofusées pour décélérer le Vaisseau Spatial pour qu’il soit en orbite géostationnaire autour de Mars à une distance à calculer par les Scientifiques et les Ingénieurs responsables du Projet.
Pourquoi la Vitesse Initiale V(0) est égale à 30.000 km/h ?
V(0) est engendrée par la rotation de la Terre autour du Soleil, cad V(0) est la Vitesse Tangentielle du Centre de Gravité de la Terre par rapport au Centre d’Inertie du Soleil. Pour effectuer les calculs avec un maximum de précision, ceux-ci seront fait dans un REPERE HELIOCENTRIQUE ayant pour point d’origine le Centre d’Inertie ou de Gravité du Soleil et ses 3 axes orthogonaux dirigés vers 3 étoiles fixes de l’Univers (étoiles situées dans des galaxies très éloignées de la VOIE LACTEE).
Ce sont l’Accélération et la Décélération du Vaisseau Spatial qui génèrent la consommation en carburant, des Réacteurs Nucléaires à Fusion seront nécessaires pour équiper le Vaisseau Spatial et assurer la liaison Terre – Mars en un minimum de temps Delta(T).
Selon l’Accélération du Vaisseau Spatial choisie (0 ou 0.01 ou 0.03 ou 0.06 m/s²), la Trajectoire sera différente et la distance parcourue entre la Terre et Mars sera différente de 225.000.000 km, il y aura lieu de recalculer le temps T(C) (temps corrigé) par rapport à l’Accélération retenue , Ainsi Delta(T) sera égale à T(C)..

Alain Mocchetti
Ingénieur en Construction Mécanique & en Automatismes
Diplômé Bac + 5 Universitaire (1985)
UFR Sciences de Metz

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