Last fall Elon Musk delivered his highly anticipated “Making Humans a Multiplanetary Species,” keynote talk at the 67th International Astronautical Congress in Guadalajara, Mexico, providing an overview of his plan for a Martian settlement sufficiently large to be self-sustaining (he mentioned the figure of a million persons moving to Mars in a fleet of 1,000 spacecraft leaving Earth en masse), and with this plan now public the detailed analysis of Mars mission architecture can begin. Musk said in his talk that he thought it was a good idea that there should be many different approaches, so he clearly was not making any claim that his plan was the one and only workable mission architecture.
As both public space agencies and private space companies go beyond the talking phase and begin the design, testing, and construction of a Mars mission (or missions), these designs will embody assumptions about the best way to get to Mars with contemporary technology (there are many ways to do this). The assumptions, as usual, aren’t often explicitly discussed, because assumptions are foundational, and you have to have a community of individuals who share the same or similar assumptions even to begin designing something as complex as a human mission to Mars. Foundational assumptions may be challenged in initial “brainstorming” sessions, but once we get to sketches and calculations, the assumptions are already built into the design.
One of the most important assumptions about Mars mission design is whether that mission should be slow or fast. In this context. “slow” means following one of the well-established gravitational transfer trajectories (Hohmann Transfer Orbits) that many uncrewed missions to Mars have followed, which require a minimum of fuel use and little or no braking upon arrival, but instead requires time.
A Hohmann transfer orbit to Mars would require many months (six months or more; cf. Flight to Mars: How Long? Along what Path?, which gives a figure of 8.5 months), the window to make the journey only occurs every 25 months, and during a long voyage such as this the crew would have to be maintained in good health, protected from radiation, and have enough personal space onboard to keep from going stir crazy. A Mars cycler configuration would involve travel times on the order of years. This is definitely a “slow” option, but also an option that minimizes propellant use.
The Mars Design Reference Mission (which I recently quoted in A Distinctive Signature of an Early Spacefaring Civilization), a design document produced by NASA in July 2009 (the full title is Human Exploration of Mars: Design Reference Architecture 5.0), characterizes their mission architecture as “fast” (the document repeatedly cites “fast transit trajectory”), but involves a one-way transit time of 6 to 7.5 months:
“…the flight crew would be injected on the appropriate fast-transit trajectory towards Mars. The length of this outbound transfer to Mars is dependent on the mission date, and ranges from 175 to 225 days.”
A “slow” mission to Mars such as this (which NASA calls a “fast” mission) ought to be designed about a large, rotating habitat that can simulate gravity (this has featured in films, such as The Martian). No one wants to spend six months in a “capsule.” An additional benefit of a large and slow Mars mission is that the rotating habitat sent to Mars could be maintained in Mars orbit as a Martian space station (such as I wrote about in A Martian Space Station and A Passage to Mars) and subsequent missions could add to this Martian space station.
Alternatively, instead of a large and comfortable habitat in which to travel, a slow mission to Mars might involve induced torpor in the crew (effectively, human hibernation), and while this would require far less food and water for the journey, this option, too, might be best achieved with simulated gravity. Human bodies evolved in a gravity field, and don’t do well outside that gravity field (cf. Hibernation for Long-term Manned Space Exploration by Shen Ge, which includes many links to resources on induced torpor).
A “fast” mission to Mars I will identify as anything faster that the six months or so required for a Hohmann transfer orbit. Fast journeys could be anything from a gentle ion thrust, using very little propellant and only cutting a little time off the trip, to powering half way to Mars (preferably at 1.0 g acceleration in order to again simulate gravity) and then decelerating for the second half of the trip. Musk’s mission design as presented in his IAC talk called for initial transfer times “as low as” 80 days (i.e., less than three months; his graphic for this section of the talk showed transit durations from 80–150 days), perhaps improving to as little as 30 days further in the future, but little detail was offered on this part of the mission architecture.
The quickest “fast” trips to Mars contemplated with contemporary technology would be about two weeks. A nuclear-powered ion engine might make the trip in three months, which is a lot better than six months, and might be considered “fast,” but Musk’s 30–80 day transit times are all designed around well-known chemical rocket technology, which makes the effort much closer to being practical in the near term. If you have enough rocket engines, big enough engines, and enough fuel, you can make the trip to Mars more quickly with chemical rockets than is usually contemplated, and that seems to be the SpaceX approach; much of Musk’s IAC talk was taken up with concerns of propellant, fuel transfer in Earth orbit, and producing fuel on Mars.
It is important to point out that most of the technologies I have mentioned above — rotating spacecraft, induced torpor, nuclear rockets, and so on — have been the object of much study, but little practical experience. (An early version of the Nerva nuclear rocket was built and tested, but it wasn’t flown into space; cf. Secrecy and the STEM Cycle.) However, we have a pretty good grasp of the science involved in these technologies, so building actual spacecraft incorporating them is primarily an engineering challenge, not a science challenge (except in so far as there is a science of technology design and engineering application; cf. Testing Technology as a Scientific Research Program: A Practical Exercise in the Philosophy of Technology). In other words, we don’t need any scientific breakthroughs for a mission to Mars, but we need a lot of technological development and engineering solutions.
Hearing a presentation such as Elon Musk gave on SpaceX’s Mars mission architecture at the IAC is exciting, and definitely communicates that this project can be done, that it can be done soon, and even that it can be done on a grand scale. This is invigorating, and stokes what Keynes called our “animal spirits” for a voyage to Mars. If the momentum can be maintained, the development of a spacefaring civilization can be a practical reality within decades rather then centuries. Musk discussed the “forcing function” of having a settlement on Mars, and he is correct that this human outpost away from Earth would entail continual improvements in space transportation, and moreover it would extend human consciousness to include Mars as a human concern. Human habitation of Mars would not only change the distribution and destiny of our species, it would change the way we understand ourselves; it would present an intellectual challenge that will be met with differing responses accordingly as different human beings experience this challenge.
It is difficult to discuss human habitation of Mars scientifically because Mars has for so long played an disproportionate role in fantasy and fiction, and any future human habitation of Mars will take place against this imaginative background. Future human inhabitants of Mars will themselves read this cultural legacy of fiction centered on Mars, and while some of it will be laughable, there are also likely to be passages that start heads nodding, however dated and inaccurate the portrayal of human life on Mars. And this human future on Mars is seeming increasingly likely as private space enterprises vie with national space agencies, and both public and private space programs are publicly discussing the possibility of sending human beings to Mars.
A human population on Mars would eventually come to identify as Martians, even though entirely human — Ray Bradbury already said as much decades ago — and it would be expected that the Martian perspective would be different in detail from the terrestrial perspective, though scientifically literate persons in both communities would share the Copernican perspective. There would be countless small differences — Martians would come to number their lives both in Terrestrial years and Martian years, for example — that would cumulatively and over time come to constitute a distinctively Martian way of looking at the world. There would also be unavoidably important differences — being separated from the bulk of humanity, having no large cities at first, not being able to go outside without protective gear, and so on — that would define the lives of Martian human beings.
At what point will Martians come to understand themselves as Martians? At what point will Mars become a homeworld? There will be a first human being to set foot on Mars, a first human being born on Mars, a first human being to die on Mars and be buried in its red soil, a first crime committed on Mars, and so on. Any of these “firsts” might come to be identified as a crucial turning point, the moment at which a distinctively Martian consciousness emerges among Mars residents, but any such symbolic turning point can only come about against the background of the countless small differences that accumulate over time. Given human settlement on Mars, this Martian consciousness will surely emerge in time, but the Martian consciousness that perceives Mars as a homeworld will differ from the sense in which Earth is perceived as our homeworld.
Human beings lived on Earth for more than a hundred thousand years without knowing that we lived on a planet among planets. We have only known ourselves as a planetary species for two or three thousand years, and it is only in the past century that we have learned what it means, in a scientific sense, to be a planet among countless planets in the universe. A consequence of our terrestrial endemism is that we as a species can only transcend our homeworld once. Once and once only can we ascend into the cosmos at large; every other celestial body we visit thereafter we will see first from afar, and we will descend to its surface after having first seen that celestial body as a planet among planets. Thus when we arrive at Mars, we will arrive at Mars knowing that we arrive at a planet, and knowing that, if we settle there, we settle on a planet among planets — and not even the most hospitable planet for life in our planetary system. In the case of Mars, our knowledge of our circumstances will precede our experience, whereas on Earth our experience of our circumstances preceded our knowledge. This reversal in the order of experience and knowledge follows from planetary endemism — that civilizations during the Stelliferous Era emerge on planetary surfaces, and only if they become spacefaring civilizations do they leave these planetary surfaces to visit other celestial bodies.
What is it like, or what will it be like, to be a Martian? The question immediately reminds us of Thomas Nagel’s well known paper, “What is it like to be a bat?” (I have previously discussed this famous philosophical paper in What is it like to be a serpent? and Computational Omniscience, inter alia.) Nagel holds that, “…the fact that an organism has conscious experience at all means, basically, that there is something it is like to be that organism.” A generalization of Nagel’s contention that there is something that it is like to be a bat suggests that there is something that it is like to be a conscious being that perceives the world. If we narrow our conception somewhat from this pure generalization, we arrive at level of generality at which there is something that it is like to be a Terrestrial being. That there is something that it is like to be a bat, or a human being, are further constrictions on the conception of being a consciousness being that perceives the world. But at the same level of generality that there is something that it is like to be a Terrestrial being, there is also something that it is like to be a Martian. Let us call this the Martian standpoint.
To stand on the surface of Mars would be to experience the Martian standpoint. I am here adopting the term “standpoint” to refer to the actual physical point of view of an intelligent being capable of looking out into the world and understanding themselves as a part of the world in which they find themselves. Every intelligent being emergent from life as we know it has such a standpoint as a consequence of being embodied. Being an embodied mind that acquires knowledge through particular senses means that our evolutionary history has furnished us with the particular sensory endowments with which we view the world. Being an embodied intelligence also means having a particular spatio-temporal location and having a perspective on the world determined by this location and the sensory locus of embodiment. The perspective we have in virtue of being a being on the surface of a planet at the bottom of a gravity well might be understood as a yet deeper level of cosmological evolution than the terrestrial evolutionary process that resulted in our particular suite of sensory endowments, because all life as we know it during the Stelliferous Era originates on planetary surfaces, and this precedes in evolutionary order the evolution of particular senses.
Mars, like Earth, will offer a planetary perspective. Someday there may be great cities and extensive industries on the moon, supporting a burgeoning population, but, even with cities and industries, the moon will not be a world like Earth, with an atmosphere, and therefore a sky and a landscape in which a human being can feel at home. For those native to Mars — for eventually there will be human beings native to Mars — Mars will be their homeworld. As such, Mars will have a certain homeworld effect, though limited in comparison to Earth. Even those born on Mars will carry a genome that is the result of natural selection on Earth; they will have a body created by the selection pressures of Earth, and their minds will function according to an inherited evolutionary psychology formed on Earth. Mars will be a homeworld, then, but it will not produce a homeworld effect — or, at least, no homeworld effect equivalent to that experienced due to the origins of humanity on Earth. The homeworld effect of Mars, then, will be ontogenic and not phylogenic.
If, however, human beings were to reside on Mars for an evolutionarily significant period of time, the ontogenic homeworld effect of individual development on Mars would be transformed into a phylogenic homeworld effect as Mars became an environment of evolutionary adaptedness. As the idea of million-year-old or even billion-year-old civilizations is a familiar theme of SETI, we should not reject this possibility out of hand. If human civilization comes to maturity within our planetary system and conforms to the SETI paradigm (i.e., that civilizations are trapped within their planetary systems and communicate rather than travel), we should expect such an eventuality, though over these time scales we will probably change Mars more than Mars will change us. At this point, Mars would become a homeworld among homeworlds — one of many for humanity. But it would still be a homeworld absent the homeworld effect specific to human origins on Earth — unless human beings settled Mars, civilization utterly collapsed, resulting in a total ellipsis of knowledge, and humanity had to rediscover itself as a species living on a planetary surface. For this to happen, Mars would have to be Terraformed in order for human beings to live on Mars without the preservation of knowledge sufficient to maintain an advanced technology, and this, too, is possible over time scales of a million years or more. Thus Mars could eventually be a homeworld for humanity in a sense parallel to Earth being a homeworld, though for civilization to continue its development based on cumulative knowledge implies consciousness of only a single homeworld, which we might call the singular homeworld thesis.
Once humanity begins to make itself a home on Mars, and human beings can, perhaps even with a certain sense of pride, call themselves “Martians” (because by this time there will be something that it is like to be a Martian) and adopt a genuinely Martian standpoint, humanity will be a multiplanetary species, a multiplanetary human civilization will begin to emerge, and this multiplanetary civilization will be distinct from our planetary civilization of today. Mars, in this scenario, would be a point of bifurcation, the origin of a new kind of civilization, localized in the same way that the industrial revolution can be localized to England.