A human mission to Mars is technologically feasible, but hugely expensive requiring enormous financial and political commitments. A creative solution to this dilemma would be a one-way human mission to Mars in place of the manned return mission that remains stuck on the drawing board. Our proposal would cut the costs several fold but ensure at the same time a continuous commitment to the exploration of Mars in particular and space in general. It would also obviate the need for years of rehabilitation for returning astronauts, which would not be an issue if the astronauts were to remain in the low-gravity environment of Mars. We envision that Mars exploration would begin and proceed for a long time on the basis of outbound journeys only. A mission to Mars could use some of the hardware that has been developed for the Moon program. One approach could be to send four astronauts initially, two on each of two space craft, each with a lander and sufficient supplies, to stake a single outpost on Mars. A one-way human mission to Mars would not be a fixed duration project as in the Apollo program, but the first step in establishing a permanent human presence on the planet. The astronauts would be re-supplied on a periodic basis from Earth with basic necessities, but otherwise would be expected to become increasingly proficient at harvesting and utilizing resources available on Mars. Eventually the outpost would reach self-sufficiency, and then it could serve as a hub for a greatly expanded colonization program. There are many reasons why a human colony on Mars is a desirable goal, scientifically and politically. The strategy of one-way missions brings this goal within technological and financial feasibility. Nevertheless, to attain it would require not only major international cooperation, but a return to the exploration spirit and risk-taking ethos of the great period of Earth exploration, from Columbus to Amundsen, but which has nowadays been replaced with a culture of safety and political correctness.

Key Words: Mars exploration, Human exploration, Manned Mission, Human Mission, Mars, exploration, lander, bold, risk

1. Introduction

The exploration of Mars has been a priority for the space programs of several nations for decades, yet the prospect of a manned expedition continually recedes in the face of daunting and well-recognized challenges. The long travel time to Mars in zero gravity and high radiation conditions would impose a serious health burden on the astronauts. The costs of developing the launch vehicle and assembling the large amount of equipment needed for the astronauts to survive the journey and their long sojourn on the Martian surface, together with a need to send all the fuel and supplies for a return journey make a manned Mars expedition at least an order of magnitude more expensive than the Apollo program.

In our view, however, many of these human and financial problems would be ameliorated by a one-way mission. It is important to realize that this is not a "suicide mission." The astronauts would go to Mars with the intention of staying for the rest of their lives, as trailblazers of a permanent human Mars colony. They would be resupplied periodically from Earth, and eventually develop some "home grown" industry such as food production and mineral/chemical processing (Zubrin and Baker 1992; Zubrin and Wagner 1997). Their role would be to establish a "base camp" to which more colonists would eventually be sent, and to carry out important scientific and technological projects meanwhile. Of course, the life expectancy of the astronauts would be substantially reduced, but that would also be the case for a return mission. The riskiest part of space exploration is take-off and landing, followed by the exposure to space conditions. Both risk factors would be halved in a one-way mission, and traded for the rigors of life in a cramped and hostile environment away from sophisticated medical equipment. On the financial front, abandoning the need to send the fuel and supplies for the return journey would cut costs dramatically, arguably by about 80 percent. Furthermore, once a Mars base has been established, it would be politically much easier to find the funding for sustaining it over the long term than to mount a hugely expensive return mission.

There are several reasons that motivate the establishment of a permanent Mars colony. We are a vulnerable species living in a part of the galaxy where cosmic events such as major asteroid and comet impacts and supernova explosions pose a significant threat to life on Earth, especially to human life. There are also more immediate threats to our culture, if not our survival as a species. These include global pandemics, nuclear or biological warfare, runaway global warming, sudden ecological collapse and supervolcanoes (Rees 2004). Thus, the colonization of other worlds is a must if the human species is to survive for the long term. The first potential colonization targets would be asteroids, the Moon and Mars. The Moon is the closest object and does provide some shelter (e.g., lava tube caves), but in all other respects falls short compared to the variety of resources available on Mars. The latter is true for asteroids as well. Mars is by far the most promising for sustained colonization and development, because it is similar in many respects to Earth and, crucially, possesses a moderate surface gravity, an atmosphere, abundant water and carbon dioxide, together with a range of essential minerals. Mars is our second closest planetary neighbor (after Venus) and a trip to Mars at the most favorable launch option takes about six months with current chemical rocket technology.

In addition to offering humanity a "lifeboat" in the event of a mega-catastrophe, a Mars colony is attractive for other reasons. Astrobiologists agree that there is a fair probability that Mars hosts, or once hosted, microbial life, perhaps deep beneath the surface (Lederberg and Sagan 1962; Levin 2010; Levin and Straat 1977, 1981; McKay and Stoker 1989; McKay et al. 1996; Baker et al. 2005; Schulze-Makuch et al. 2005, 2008, Darling and Schulze-Makuch 2010; Wierzchos et al. 2010; Mahaney and Dohm 2010). A scientific facility on Mars might therefore be a unique opportunity to study an alien life form and a second evolutionary record, and to develop novel biotechnology therefrom. At the very least, an intensive study of ancient and modern Mars will cast important light on the origin of life on Earth. Mars also conceals a wealth of geological and astronomical data that is almost impossible to access from Earth using robotic probes. A permanent human presence on Mars would open the way to comparative planetology on a scale unimagined by any former generation. In the fullness of time, a Mars base would offer a springboard for human/robotic exploration of the outer solar system and the asteroid belt. Finally, establishing a permanent multicultural and multinational human presence on another world would have major beneficial political and social implications for Earth, and serve as a strong unifying and uplifting theme for all humanity.

2. The Concept of a One-Way Mission to Mars

A human mission to Mars is undoubtedly technologically feasible, but unlikely to lift off in the very near future, because of the enormous financial and political commitments associated with it. As remarked, however, much of the costs and payload of the mission are associated with bringing the astronauts back to Earth. Furthermore, the returning astronauts would have to go through an intense rehabilitation program after being exposed for at least one year to zero gravity and an extended period to reduced gravity on the surface of Mars. Eliminating the need for returning early colonists would cut the costs several fold and at the same time ensure a continuous commitment to the exploration of Mars and space in general.

The first colonists to Mars wouldn’t go in "cold." Robotic probes sent on ahead would establish necessities such as an energy source (such as a small nuclear reactor augmented by solar panels), enough food for two years, the basics for creating home-grown agriculture, one or more rover vehicles and a tool-kit for carrying out essential engineering and maintenance work. In addition, the scientific equipment needed for the colonists to do important research work should be part of the preceding unmanned mission. All this equipment could easily be put into place using current technology before the astronauts set out. The first human contingent would rely heavily on resources that can be produced from Mars such as water, nutrients, and shelter (such as in form of lava tube caves). They also would be continuously resupplied from Earth with necessities that could not be produced from the resources available on Mars. This semi-autonomous phase might last for decades, perhaps even centuries before the size and sophistication of the Mars colony enabled it to be self-sustaining.

The first human contingent would consist of a crew of four, ideally (and if the budget permits) distributed between two two-man space craft to allow for some mission redundancy such as in the Viking mission or for the Mars Exploration Rovers. Also, if any technical malfunction occurs on one space craft, the other craft could come to the rescue. Further, any critical part of equipment after landing would be available in duplicate in case of an emergency.

A one-way human mission to Mars would not be a one-time commitment as was the case with the Apollo program. More than 40 years after the last Apollo mission, no human has set foot on a planetary body beyond Earth. Such a hiatus cannot be afforded if humanity is to commit to a grander vision of space exploration (Davies and Schulze-Makuch 2008; Schulze-Makuch and Irwin 2008). No base on the Moon is needed to launch a one-way human mission to Mars. Given the broad variety of resources available on Mars, the long-term survival of the first colonists is much more feasible than it would be on the Moon.

While the pragmatic advantages of this approach are clear, we anticipate that some ethical considerations may be raised against it. Some in the space agencies or public might feel that the astronauts are being abandoned on Mars, or sacrificed for the sake of the project. However, the situation these first Martian settlers are in, who would of course be volunteers, would really be little different from the first white settlers of the North American continent, who left Europe with little expectation of return. Explorers such as Columbus, Frobisher, Scott and Amundsen, while not embarking on their voyages with the intention of staying at their destination, nevertheless took huge personal risks to explore new lands, in the knowledge that there was a significant likelihood that they would perish in the attempt. A volunteer signing up for a one-way mission to Mars would do so in the full understanding that he or she would not return to Earth. Nevertheless, informal surveys conducted after lectures and conference presentations on our proposal, have repeatedly shown that many people are willing to volunteer for a one-way mission, both for reasons of scientific curiosity and in a spirit of adventure and human destiny. Others may raise objections based on planetary protection considerations, depending on whether indigenous life exists on Mars or not. However, any Martian biota is almost certainly restricted to microbes that would be adapted to the natural environment of that planet, and would therefore almost certainly not pose a safety concern for the colonists due to their presumably different biochemical make-up (e.g., Houtkooper and Schulze-Makuch 2007). Nevertheless, caution has to be urged since we do not know the biochemistry of the putative Martian biota at this time. Thus, it might be prudent to launch a life detection mission or even a sample return mission prior to a one-way human mission to Mars. On the other hand, if Martian organisms really do pose a hazard to human health, it may be preferable to limit the exposure to the crew of a one-way mission rather than place at risk the entire human population from a botched sample return mission (Rummel et al. 2002).

A much more likely problem is the reverse: that the human habitation would pose a threat to any indigenous Martian micro-organisms, even if all possible precautions would be employed to protect it. Sadly, the battle to protect putative Martian biota from terrestrial organisms has already been compromised by the fact that several unsterilized, or inadequately sterilized, spacecraft have already been sent to Mars. In addition, terrestrial impact ejecta may have conveyed viable Earth microbes to Mars repeatedly over geological time scales (Melosh and Tonks 1993; Davies 1996, 2008; Kirschvink and Weiss 2001). Nor is it clear that terrestrial microbes would be better adapted to life on Mars that they would spread uncontrollably in a way that would completely displace the indigenous organisms. Furthermore, the colonists would likely only affect a small portion of the planet and "nature parks" could be designated with special precautions enforced in respect to human interference. Again, such issues could be addressed by a prior life detection or sample return mission to inform us about any risks to Martian biota and the type of precautions that could be taken to protect it. And while we agree that all reasonable precautions should be taken, we do not think their presence should be an over-riding reason to forever resist sending humans to Mars. Indeed, our presence there would allow us to study indigenous life in detail, further our knowledge about essential characteristics of life, and design methods to actually enhance the prospects of Martian biota (McKay 1982; McKay and Marinova 2001).

3. First Steps in the Human Colonization of Mars

The success of the project we are proposing would hinge on the quality of preparation. We envisage three stages: careful site selection using existing and future probes to gather relevant data, the establishment of an unmanned base with minimum resources necessary for human habitation, and the dispatch of the first astronauts. We shall not dwell here on the astronautics of the mission, as these have been thoroughly discussed elsewhere (e.g., Zubrin and Wagner 1997).

3.1 Site selection The final determination of a suitable settlement location would require advance scouting missions that could use geophysical exploration tools like ground penetrating radar to locate subsurface voids from aerial or buoyant platforms. Numerous igneous flow features, including lava tubes (large cave structures formed by rivulets of molten lava) have already been identified on Mars (Boston 2003; Figure 1). Lava tube caves on Mars appear to be much larger than on Earth probably due to the lower gravity on Mars (0.38g compared to 1g on Earth). They are natural caves, and some of them are located at a low elevation in close proximity to the former northern ocean, which means that they could harbor ice deposits inside similar to many ice-containing caves on Earth. Ice caves would go a long way to solving the needs of a settlement for water and oxygen. Mars has a thin but substantial atmosphere mostly consisting of carbon dioxide (95%), but it is approximately 1/100^th the density of Earth’s atmosphere, has no ozone shield and no magnetospheric shielding; thus some natural or artificial shielding to protect from ionizing and ultraviolet radiation will be required. Ice caves would also provide shelter from this radiation. After a candidate cave is located, its interior would need to be robotically explored before selecting it for the colony’s first home.

3.2. Establishing an unmanned base After a suitable location is identified, preferentially associated with some natural shelter (e.g., lava tube caves as discussed above) and other nearby resources (water, minerals, nutrients), a base should be established using unmanned probes and robots, including small rover vehicles, to prepare for the arrival of the first human contingent. The base would also be equipped to allow for a more thorough investigation of specific localities of interest. The base would not have to be very sophisticated, but could simply consist of a communication relay and a power generator, perhaps together with a remotely operated telescope (Schulze-Makuch and Irwin 2008). The lander craft should be designed to double as a permanent station, in modular form, to allow later expansion following further one-way missions.

3.3. The first colonists Crew selection for the initial manned mission would have to take into account several factors. Initially, colonists may be preferred who are beyond their reproductive age, because their life expectancy is likely to be 20 years or less, and secondly, the first settlers will endure some radiation damage to their reproductive organs, both during the trip to Mars and on the Martian surface. One feasible approach for the initial one-way mission would be to send two space probes with two astronauts each. Ideally, one should be a trained physician, and all should have advanced scientific and technical know-how, and show a strong commitment to scientific research and exploration.

Once the humans arrived at the base, their task would be not unlike that of the early settlers in North America – only the underlying technology and utilized tools would be much more sophisticated. Plants could be grown outside of the caves in an enriched soil underneath a robotically constructed dome, thus providing the inhabitants of the outpost with food and an additional supply of oxygen. Microbes could be used to break down and recycle wastes, thus the human base would constitute its own independent biosphere with some additional resources provided by the Martian environment. Certainly, the first colonists would be exposed to multiple challenges, from physical rigor to psychological strains due to isolation and uncertainties. However, the astronauts will have undergone psychological profiling and training before embarking on the mission, and would remain in constant contact with Earth via normal channels such as email, radio and video links. In the era of modern communications they would in fact feel more connected to home than the early Antarctic explorers (who had no systematic psychological training either). Over time, the human contingent on Mars would slowly increase with follow-up missions. Several cave-centered biospheres would be created, each being in constant communication with other cave-centered biospheres to share experiences on which approaches are working best. At some later time, probably several decades after the first human mission, the colony’s population might have expanded to about 150 individuals, which would constitute a viable gene pool to allow the possibility of a successful long-term reproduction program. New arrivees and possibly the use of genetic engineering would further enhance genetic variety and contribute to the health and longevity of the colonists.

While it would undoubtedly take a tremendous effort over many years to establish multiple settlements on Mars, we see no fundamental reason why this plan is not technologically implementable. Some of the heavy lifting hardware has been developed or is in an advanced stage from the recently cancelled Moon program. Work on the permanent unmanned base could be initiated right away, while the human mission and colonization details could be worked out later. We estimate that a reasonable time line for establishing a permanent unmanned base with robots would be 20 years, with the first human contingent arriving shortly thereafter. The main impediment is the narrow vision and the culture of political caution that now pervades the space programs of most nations.

4. Conclusions

Self-preservation considerations in a dangerous universe and the human exploratory spirit compel us to explore space and colonize other planets. Mars is the planet in our solar system, which is reasonably close and provides an abundance of resources and shelter for such a colonization effort. Nevertheless, the first step for the colonization of Mars will be the most difficult. Here, we propose that the most pragmatic approach to achieve this goal is by establishing a small permanent robotic base followed by a series of one-way missions to Mars. The advantages of a one-way human mission are many-fold including a dramatic reduction of costs, the long-term commitment by the space agency, the public, and the crew, and that no rehabilitation program is needed for crew members when remaining on the low-gravity surface of Mars. The challenges are still monumental, though, foremost because political and financial long-term commitments have to be secured.

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