SpaceX Interplanetary Transport System: The beginning of Mars colonization

Nelson Bridwell

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.

Architecture

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.

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.

Development

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.

Considerations

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.

Colonization

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