Spaceflight Insider

SpaceX Interplanetary Transport System: The beginning of Mars colonization

ITS Observatory

An artist’s rendering of what a person traveling inside SpaceX’s Interplanetary Transport System might see upon arriving at Mars. Image Credit: SpaceX

On Sept. 27, at the 2016 International Astronautical Congress (IAC), SpaceX outlined the design of a new spacecraft that could be used to establish a significant human presence on Mars within several decades. The key objective of this architecture, which Elon Musk had previously christened the Mars Colonial Transporter (MCT), is to deliver large quantities of equipment and passengers to Mars at costs that will be several orders of magnitude lower than any alternative. 


SpaceX's ITS vs Saturn V

ITS versus the 1960s era Saturn V. Click to enlarge. Image Credit: SpaceX

The new design, called the Interplanetary Transport System (ITS), is depicted in this animation. The foundations of this design include fully reusable vehicles, refueling in low-Earth orbit (LEO), densified methalox propellant, extensive use of lightweight carbon fiber reinforced composite structures, and application of propellant gases for tank pressurization and maneuvering thrusters.

The launch stack, slightly taller and wider than the Apollo Saturn V, consists of a first stage booster and second stage spacecraft. Both stages will use a new full-flow staged combustion Raptor engine with a chamber pressure that will be 50 percent greater than the RS-25 Space Shuttle Main Engine.

The first stage booster will employ 42 sea-level Raptor engines, only seven of which will need to be gimbaled for steering. The operation of the booster will be similar to the current Falcon 9 first stage, except that it will not have landing legs. Instead, it will land directly on the launch pad at Kennedy Space Center LC-39A, using thrusters, grid fins at the top, and small fins at the bottom to accomplish a precision landing.

The second stage spaceship will employ six vacuum Raptor engines and three sea-level Raptor engines. Above the engines and propellant tanks, it will contain an unpressurized cargo bay and a pressurized passenger compartment. Like a lifting body, it will present a maximum aerodynamic cross-section lateral profile for atmospheric re-entry, protected by a Phenolic-Impregnated Carbon Ablator (PICA) heat shield along one entire side of the spacecraft. Toward the end of the re-entry sequence, the spacecraft will rotate to a vertical orientation and the landing struts will deploy for a retro-propulsive vertical landing.

Nearly identical in external appearance to the spaceship, a second stage unmanned tanker will have larger propellant tanks instead of cargo or passenger compartments. It will rendezvous with the spaceship in LEO. SpaceX estimates that three to five tanker launches will be required to top-up the propellant tanks of each Mars-bound spaceship. Musk has noted an advantage of this approach is that additional tanker missions could be flown to mitigate the impact of any performance shortfalls.

SpaceX: Crewed Mars exploration

Other organizations, such as NASA and Boeing, are proposing on-orbit assembly of a Mars craft using multiple super-heavy lift launch vehicles. However, SpaceX’s system will require Earth-orbit rendezvous for the refueling of the second stage spaceship. Image Credit: James Vaughan / SpaceFlight Insider

Each booster will be designed to be reused up to 1,000 times, and each tanker will be designed to be reused up to 100 times. Consequently, a small number of these will be manufactured and the cost will be amortized over a large number of Mars missions.

Although the spaceships will be fully reusable, because of the years-long round trip time for each Mars mission, each spaceship will only be able to fly around 12 missions over a 30-year lifespan.  Consequently, in order to hold down the cost per kilogram, each spaceship will transport at least 300, possibly up to 450, metric tons of payload to Mars. In his IAC presentation, Musk stated that future versions of these vehicles may be even larger.

SpaceX's ITS spaceship development tank

Even though a small portion of the SpaceX workforce is being committed to the ITS system, the company was able to produce a full-scale development upper stage spaceship liquid oxygen tank. It is made of an advanced carbon fiber composite. Photo Credit: SpaceX


Although only about five percent of the SpaceX engineering workforce is currently working on this system, within two years, when Falcon Heavy and Dragon 2 development is complete, a majority of SpaceX engineers are expected to be working on this project.

Musk estimates that the total development cost may amount to $10 billion, so SpaceX is vigorously pursuing a variety of possible revenue sources to fund this development. Musk has suggested that development could be a public-private partnership with funding from NASA.


The objective of this system will be to eventually transport millions of people to Mars at a cost per person of less than $200,000. However, there are a few technical issues that will first need to be resolved. It is possible that there will be a need for astrobiologists to determine if there are any native microorganisms on Mars. If so, human activity on the surface of Mars could be restricted. Furthermore, all the long-term effects of low gravity on the health of passengers will need to be studied and taken into consideration.

There are also open questions about how to best mitigate human exposure to radiation both on the way and on the surface of Mars. It should be possible to use the fuel to partially shield passengers from solar particles during brief solar flares and coronal mass ejection (CME) events by pointing the spaceship engines toward the Sun. Additional shielding may be possible by temporarily positioning passengers near strategically located water storage tanks.

In addition, future colonists will need cities where they can safely work and live. Those cities will not be possible without electric power, transportation, agriculture, and other infrastructures. All of this will require significant amounts of time and money to develop. The new spacecraft that SpaceX has designed is just the first step in making it all possible.


SpaceX: Crewed spacecraft in orbit above the Red Planet

For Mars colonization, a lot of hardware will need to be sent toward the Red Planet to support colonization, regardless of whether the Hawthorne, California-based company is successful in developing the ITS. Elon Musk has stated SpaceX is a transportation company. Infrastructure beyond the NewSpace firm’s ITS architecture will need to be created by other organizations. Lockheed Martin, for example, is working on a concept called Mars Base Camp. If developed, it would see a space station placed into orbit around the Red Planet by 2030. Image Credit: James Vaughan / SpaceFlight Insider

In order to survive on Mars, the first occupants will need to bring along a substantial quantity of equipment and supplies. Unlike later passengers, these first pioneers will have a much higher cargo mass to passenger ratio. Consequently, camping out on Mars will be very expensive.

Because of this high initial expense, SpaceX will need to find “anchor” tenants who have the funding and technical capabilities needed to set up small outposts on Mars. Preferred candidates are members of the scientific community, particularly scientists from NASA or other space agencies. This new SpaceX architecture has the potential to easily support scientific efforts such as more expansive rover fleets, heavy rigs for geological and astrobiological deep drilling, larger geological samples for Earth labs, and manned surface outposts.

Over the years, as the first manned scientific outposts begin to materialize, a need will also arise for supporting infrastructure, which will create a demand for commercial services and goods on Mars. These commercial operators, in turn, will create a demand for other supporting services. Then the long colonization process will begin.

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

I am dubious about the ITS spaceship having nine Raptors; the three sea-level Raptors seem entirely wasted except for returning to the surface of Terra — which is not necessary, and might be an unwanted source of extra risk.

I think creating a pure passengers-to-LEO-then-land version might be a better approach; it would do a minimal (LEO @ 110 km, for example) second stage burn, then transfer passengers, cargo, and propellant to the spaceship. The spaceship is already doing rendezvous with the automated tankers to load propellant, so one more doesn’t seem onerous. Do the loading at very low LEO to save launch thrust; none of these craft are going to be hanging around long enough to worry about orbital decay.

The Mars crewed lander and the tanker versions of the upper stage are supposed to share a common design. Since the tanker must return to earth it needs to have sea-level thrust Raptor engines. Additionally, the crewed lander needs to have a launch escape system. This includes low-altitude capability. Therefore, the crewed lander vehicle needs to have sea-level thrust Raptor engines also.

BTW: Both versions of the Raptor engine use all the same components except that the vacuum version has an addition bell extension. This is the same design philosophy used in the current Merlin engines.

The sea level Raptors are used for landing on Earth and Mars. They are kinda important when you consider that you’re talking about a reusable craft designed to ferry between the surface of the Earth and the surface of Mars. And since the tanker version needs to land back on Earth every time, I think it is safe to say that you’re very wrong about the need for sea level Raptors.


Every version add a billion. Or two. It is important to keep the development costs down, since there will be no revenue at that point This is expected to be at least partially privately funded after all.

Musk mentioned the Union Pacific several times during the talk. He wants to create a space railroad and get paid for getting people and supplies there.

But, the Union Pacific and Central Pacific that built the transcontinental railroad connected two parts of a country poorly served by other transportation options. And they helped to open up all the land between those two spots for settlement. With Mars you have to build everything up from scratch on a planet that combines the worst of Antarctica, the desert and a vacuum chamber.

The infrastructure needed to support the numbers of people he wants to send to Mars will not be cheap to build, expand and maintain. This is something I think space advocates don’t appreciate because they come from advanced societies where infrastructure is taken for granted. Infrastructure is typically left to governments. What governments are going to pay for that?

Building a city in the desert or even Antarctica is not impossible, there is just no drive to do so. Once everything has been established, Mars will actually be easier than Antarctica to colonize. Antarctica’s biggest weaknesses are its ice, which both creates and hides hazards, and its 6 month day and night. The hard things about Mars have always been getting the first outposts established and the extreme costs, both of these issues are made a hundred times easier with the ITS. Still very difficult nonetheless, but no longer an unmanageable problem.

Yes, you could engineer and build a city on Mars. But, who is going to pay for it? The cost is not included in Musk’s $10 billion estimate.


Musk mentions a public private partnership. If this works, then every gov. will want to be part of it. Just in case there is an edge. Don’t forget 10 billion is spare change, compared to military spending. So if people believe this will add to their safety, there will be money for it.

This is why we must develop fusion propulsion before sacrificing space travelers:
Mars-bound astronauts face chronic dementia risk from galactic cosmic ray exposure
UCI study raises questions about long-term brain health after extended spaceflights–maf100716.php

Oh please. A 3 month journey one way, or six months both ways, covered in water shielding and newer materials is not going to ‘sacrifice’ these people. Fusion tech is 20, 30, 40 years off; while Chemical rockets can get people to Mars in 3 months, or we can dust off NERVA and get them to Mars in around 2. Fusion is more of a pipedream than the SEI at this point!

I have several questions about the proposed design:
1) Is there harmonic vibration concerns with using so many engines on ITS?
2) In the variant where ITS is lifting a fuel tanker, would the launch site be sufficiently clear of population if it was to explode close to sea level? That’s a whole lot of fuel in one stack.
3) Since the Raptor engine is similar size to the Merlin, are there plans to swap out Merlin for Raptor on Falcon?

I don’t think they can pull this without using some type of landing legs. Why risk such an important mission and a very expensive spacecraft in such method. $10B, is not like they will have several boosters to choose from. If something goes wrong that’s it. No mission and they will miss the open window.


The booster costs about 200 millions each, so they can build a few. It will be used hundreds of times. The return without legs is the ideal, if they can’T manage it, they will add legs. Watch the last return to a barge of Falcon 9 and think about how precise it is, even with a moving target. Then think how this will be 6 to 10 years from now.

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