The idea of a human mission to explore Mars has been studied repeatedly over the past 75 years. More than 1,000 piloted Mars mission studies were conducted inside and outside NASA between about 1950 and 2000. Many were the product of NASA and industry study teams, while others were the work of committed individuals or private organizations. I compiled a history of human mission studies through 2023. Essentially all of these mission design concepts were deemed impractical but now, if the SpaceX Starship proves flightworthy, new possibilities could finally emerge as the constraints on space travel change.
All of these studies were carried out in the era of constrained mass. Launch costs were high and minimizing mass sent to space was the main driver for mission design. To reduce mass, mission designs employed nuclear thermal propulsion (NTP), in-situ resource utilization (ISRU) to produce propellants for ascent from Mars and reliance on efficient recycling of gaseous and liquid wastes. Landing massive loads presented major challenges. The “initial mass in low Earth orbit” (IMLEO) was the dominant design parameter. None of these mission designs could be taken as practical and affordable, and a human mission to Mars remained a chimera of paper studies not going anywhere fast.
With the advent of reduced launch costs implemented by SpaceX, the rules of the game are changing. When the Starship becomes operational and can deliver 100 metric tons to Mars, we will have come full circle. The game is no longer to minimize mass, but rather to use large amounts of mass to reduce complexity and risk in moderate missions, and to pursue more ambitious missions than could previously be contemplated. The Starship will use chemical propulsion with a large amount of propellants. The political impediments of NTP are bypassed. It is claimed (but yet to be proven) SpaceX will be able to land huge loads on Mars.
Given the Starship, SpaceX plans a very ambitious mega mission to Mars where the crewed Starship makes the full round trip from LEO to Mars and back. This requires at least 1,200 metric tons of propellants for the return journey, produced from indigenous CO2 and H2O on Mars, which requires a crew to acquire large amounts of indigenous Mars water. To provide this water, they are considering landing sites near (an undesirable) 40°N latitude, and even at that latitude, accessible water is not proven.
SpaceX seems to have bypassed the possibility of a moderate human mission to Mars where only 40 metric tons of ascent propellants are needed. his could be provided by bringing a mere 18 metric tons of water from Earth (on a Starship) to react with 22 metric tons of Martian CO2. In addition, one could bring 60 metric tons of water for life support, thus getting rid of the headache of recycling waste which has been so problematic for the International Space Station with their massive use of “orbital replacement units”. Perhaps most important of all, the landing site could be chosen almost anywhere on Mars, including right on the equator, since Mars water is not needed. This has numerous benefits:
(1) Even though solar power is likely to be a secondary source of power, it might be an important backup and useful for outlying locations.
(2) While local air temperatures are more dependent on thermal inertia than latitude, other factors being equal, temperatures near the equator are expected to be warmer. Stress on thermal and structural design and control of habitats, rovers and other infrastructure would be less near the equator.
(3) Seeing the (weak) sun would have remarkable psychological benefits for the crew. At 40° latitude, the weak sun is only 25 degrees above the southern horizon on Dec. 21.
(4) There are several factors regarding entry, descent and landing and ascent trajectories and propellant requirements. Ascent propulsion at lower latitudes requires less propellant.
(5) The changes from season to season are less at lower latitudes, allowing thermal and energy management design to be simpler.
This moderate human mission to Mars, which I’ve described in my research, would be a first stepping stone toward more ambitious missions envisaged by SpaceX.
NASA is still living in the past, thinking small and trying to save mass by going to the relatively boring moon because they think they can’t get to Mars. Worse still, they are contemplating cockamamie plans to harvest putative ice in polar craters under unbearable conditions when it is faster, cheaper and better to just bring H2O from LEO to the moon. NASA goes to the moon to produce propellants. They produce propellants so they can go to the moon. The ultimate tautology.
The rules are changing. With the advent of the Starship, we will be able to affordably land 100 ton payloads on Mars. We are no longer mass misers. Saving mass makes no sense. The new space age empowers us to use mass to accomplish more ambitious missions. Human missions to Mars now, for the first time, seem within reach.
SpaceX now contemplates large-scale human missions to Mars with the Starship. But even with the Starship, their mission design and scale are so expansive that their requirements include at least five Starships to Mars (each requiring a dozen heavy lift launches to fuel them in LEO), a total of at least 60 heavy lift launches (or more) and finding and processing huge amounts of putative indigenous Mars water to produce at least 1,200 tons of propellants to return a Starship from Mars. That will likely restrict the landing site to about 40°N and it is far from certain they can find accessible water ice there.
Instead I propose a first human mission to Mars using the Starship with six crew members instead of 12, avoiding the need for indigenous Mars water and allowing a landing site right at the equator by having the crew ascend in a small capsule to a waiting Earth Return Vehicle in Mars orbit. Since only 40 tons of ascent propellant is needed, the crew can bring 18 tons of water from LEO and react it with 22 tons of Martian CO2 to produce 40 tons of ascent propellants. The whole mission is greatly simplified and the landing site can be at equatorial latitude.
It’s just like Goldilocks. NASA’s porridge is too cold. SpaceX is too hot. What I propose is just right.
Donald Rapp is a space scientist and engineer with a Ph.D. in chemical physics from the University of California, Berkeley. He was the co-investigator on the NASA MOXIE program from 2014 to 2023, and has been the Associate Editor of the Mars Journal since 2006.
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