SpaceX’s Mars Colonial Transporter: Rumors and Realities
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.
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?
- 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.
- A booster will launch a second “tanker” spaceship towards Earth orbit and then return to the launch site.
- The tanker will rendezvous with and transfer fuel to the transporter.
- The tanker will undock and perform a series of reentry burns to return to the launch site.
- Steps 2–4 will be repeated 2 or more times to fully refuel the transporter.
- At the proper moment, the transporter will perform a trans-Mars injection burn that will put it on a transfer orbit toward Mars.
- As it approaches Mars, the transporter will perform a series of precision Mars entry burns to land at the desired destination.
- The transporter will offload the payload to the surface.
- The transporter will refuel from a Mars fuel production plant.
- 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.
- 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.
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.
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.
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.