Mars has been a destination even before humanity walked on the Moon. Since the cancellation of the Apollo moon program plans for human Mars exploration have remained somewhat in the periphery and always a few decades away. There are a number of proposed Mars architectures that could bring humans to Mars, each with their own unique challenges. Before detailing these architectures, the objectives of a Mars mission must be understood as it directly impacts the mission design and requirements. The objective could simply be one to plant a flag and gain prestige. It could also entail a permanent human presence on Mars in the form of a research outpost or perhaps a larger scale colonisation effort. While these objectives differ in scale they all share two common challenges, the cost of the mission and keeping the humans involved alive. Humans have maintained a continuous presence in space since 2000 with the construction of the International Space Station (ISS), all the time conducting research on how to keep astronauts alive and healthy. Rocketry has only recently begun progressing after a long period of stagnation with costs only just starting to fall. The balancing of the cost and acceptable risk, while mostly political, is the biggest challenge and in order to effectively balance these there must be an answer to the simple question, ‘Why Mars?’.
Mars is a planet similar to Earth. It is a small rocky planet with a surface area slightly less than Earth’s land area and surface gravity roughly a third of Earth’s. Billions of years ago Mars also had liquid surface oceans and perhaps even harboured life. The scientific exploration of Mars gives insight into how the solar system formed and builds a greater understanding of the geophysical processes occurring on Earth. Additionally, finding evidence of past or current life would be a monumental discovery. Robotic exploration in the form of rovers, landers and satellites has been ongoing since the first successful flyby by Mariner 4 in 1965. With communication times for Mars between 3 and 20 minutes science missions progress slowly. The Opportunity rover, which holds the record for distance travelled on Mars, has only explored 40km. It has been operating since 2004 which far exceeded its prime mission time of 92.5 days. With humans on the surface of Mars, or on orbit, the time delay would be in the milliseconds enabling a lot more science to be done. Of course, humans could also perform sampling and other experiments directly which could speed up discovery even more.
Mars is not just a scientific destination. Mars has the potential to play a much larger role in the future of humanity than just as a scientific outpost. It could host the first attempts of human colonisation of another planet. Any crewed mission would not be a simple task; however, Mars has a number of resources that increases the viability of missions. Firstly, Mars has water ice just under the surface that could be used for humans directly as well as for food and fuel production. This works if the fuel is hydrogen and liquid oxygen (LOX). However, if the fuel of choice is methane then carbon dioxide from the atmosphere can be used as well. Even with a mean atmospheric pressure around 0.6% of Earth’s, the radiation could be up to 2.5 times higher than astronauts on the ISS are exposed to. For further protection caves and lava tubes, remainders of Mars’ volcanic past, could be used. Moving habitats underground also protects against meteorites and the rock could be used to help hold the pressure in. At the surface the intensity of sunlight is only around 50% that of on Earth which, while reducing the effectiveness of photovoltaics, still leaves solar power a viable solution to begin with. Mars is still a radically inhospitable environment but with the right technological development it is within reach.
The biggest challenge to putting humans on the surface of Mars is cost. Missions that are particularly costly could occur but would lead to only a limited number and no permanent presence. In a similar vein, humanity has not sent anyone back to the moon for almost half a century. For a similar fate to befall Mars would be incredibly disappointing. Unfortunately, the high cost, small team style mission has been the preferred mission style from NASA and its more established contractors such as Boeing and Lockheed Martin. The most concrete plan of this style is the ‘Mars Base Camp’ missions proposed by Lockheed Martin. This would require a number of launches of the Space Launch System (SLS), the new heavy lift rocket developed for NASA with Boeing as a prime contractor. SLS is not expected to have a launch cadence of more than two a year with an estimated yearly operating and production costs of US$1.5 billion. ‘Mars Base Camp’ would require the launch of two space capsules, a habitation module, supplies and a small crew complement. The ‘Mars Base Camp’ would then travel to Mars orbit where the astronauts would be able to directly control rovers on the surface. Martian landers would then be developed for future missions. This plan would not put humans on the surface before the 2030s but realistically it could be closer to the 2050s. This ‘legacy’ approach has drawn significant criticism as alternatives would achieve the same objectives for a reduced cost and time frame.
The ‘Mars Direct’ mission, proposed by Dr Robert Zubrin in 1991 and championed by him to this day, is one of the most influential alternate architectures proposed. Mars Direct would still require a number of launches but would use existing cheaper rockets such as the Falcon Heavy with the cost of each in the US$90 million range. The crew and supplies would be launched directly to the surface of Mars without on-orbit assembly required. Even more radical than Mars Direct are the plans of newer, private launch companies. SpaceX, which was founded in 2002, has the explicit goal of enabling Mars colonisation in the form of a self-sustaining colony. Blue Origin has the goal of “millions of people living and working in space” with the eventual ambition to move all heavy industry of Earth, essentially leaving Earth as a residential and light industry zone. While Blue Origin has yet to demonstrate an orbital rocket flight it is expected that it will invest US$1 billion in this capability in 2019. SpaceX currently flies the Falcon 9 and Falcon Heavy which are both low cost, capable, reusable rockets. The Falcon rocket family first stages land vertically under the power of their engines. This method of reuse has been proven over the last two years with SpaceX successfully landing 23 boosters out of 34 successful missions and reusing 15 boosters.
The main elements of Martian surface infrastructure to consider are habitats, fuel production, food production and surface travel. All these elements have been under investigation by various space agencies and private companies. The continuous human presence in Low Earth Orbit (LEO) on the ISS since 2000 has been vital in developing the necessary technology to keep humans alive and healthy. The exercise equipment and regimes on the ISS have improved to the point where there is only about a 1% per month degradation of bone density. These results are from astronauts spending as much as a year in a micro-gravity environment, a trip to Mars could see the time period as short as three months. The ISS has also hosted an inflatable habitat module from Bigelow Aerospace for over two years, this could be a precursor to habitats on the surface of Mars. Experiments have also been conducted on growing vegetables and flowers in space, a precursor to some food production on Mars. The Sabatier reaction for fuel production is known and an experiment on the Mars 2020 rover will demonstrate the extraction of oxygen from Mars’ atmosphere. NASA has also been prototyping space suits and rovers for the Martian surface. The technology for enabling human survival on the surface of Mars is not complete but there is a solid base of understanding and development that agencies and private companies alike can build off. The major problem has been a lack of a viable transportation method to deliver payloads to the Martian surface.
The plans of SpaceX to make humanity a multi-planetary species are perhaps the boldest public plans. The latest iteration of their plans calls for a booster and spaceship which would stand at a combined 118 metres tall with a diameter of 9 metres. The booster would start out with 31 engines with the potential addition of 11 engines in later revisions. The spaceship would have a pressurised cargo space of 1000 cubic metres. With orbital refuelling, which has never been demonstrated at the scale required, the Big Falcon Rocket (BFR) could enable the transport of up to 100 tons to the surface of Mars. The BFR uses a methane and liquid oxygen fuel mix which could be produced with the resources present on Mars. This means that the BFR will not need to carry fuel for a return trip, further increasing the useful payload to the surface of Mars. Due to the fully reusable nature of the BFR architecture SpaceX hopes to, over time, reduce the launch cost to be in the order of tens of millions of dollars. SpaceX is publicly aiming for the first humans on Mars in 2024, a goal even Elon Musk the CEO and Lead Designer admits is aspirational. Musk estimates the development cost to be in the $2-10 billion range. Even with the near inevitable delays, the BFR could be one of the most revolutionary developments in space exploration.
Crewed missions to Mars must be the result of a collaboration between space agencies and private companies. Without the sharing of resources and costs, the timeline for humans landing on the surface is at least 20 years. The significant investment required is not so large as to prevent improving the situation on Earth either. Indeed, NASA’s yearly budget of US$20.7 billion is only about 0.5% of the US federal budget and an initial investment of that magnitude could be sufficient to at least begin missions. Additionally, the technology required, especially regarding food production and life support, will not only enable human spaceflight to Mars but will have real impacts back on the surface of Earth. Cheap access to space will also allow a greater number of beneficial scientific missions enabling better monitoring of the Earth’s climate, oceans and vegetation. It would also allow better commercial services such as global gigabit internet coverage. While it is hard to quantify the economic returns of the Apollo program the improvements in computing, aerospace and other areas are certainly extensive. The benefit of crewed Mars missions could be just as far reaching.
Human missions to Mars have been seriously considered in various forms for over sixty years. Humanity is at the intersection of deep space technology development and improvements in rocketry. The window for human Mars missions could stay open for some time or, through some disaster, could slip away and might never return. If that were to happen humanity would be doomed to live and die on Earth with no prospects of humanity extending out to other planets and perhaps other stars. The opportunity must be seized and perhaps the missions might just provide a reminder of how incredibly unique and important Earth is. Humanity must choose to go to Mars, not because it is easy, but because it is hard.