Mars Direct — the Plan
How we can reach Red Planet with the technology we already have
We have always thought of Mars as the next thing after landing on the Moon. Where else? Venus is hellish, Europa lethally irradiated, … Even more, Mars was the planet that cemented itself in Sci-Fi. Werner von Braun, the chief engineer behind the Apollo program, described his vision for a journey to Mars in his book “Das Marsprojekt.” However, Space Shuttle became the next focus of NASA’s human spaceflight and with it the construction of the International Space Station, which allowed the permanent human presence in low Earth orbit.
Over the years, several plans were proposed for manned missions to Mars, including NASA’s “90-day study” that described the vision of Space Exploration Initiative. It considered the construction of space transport and habitation infrastructure, ranging from the construction of space station, over permanent Moon base, to mission to Mars. Yet, as the NASA leadership changed, it canceled this ambitious program. The project spread over (at least) two-decades and was perceived as too costly ($450 billion in 1989). Taken together, this created a void that creative engineers aimed to fill. Then, Robert Zubrin and David Baker of Martin Marietta drafted a plan that later became Mars Direct.
The concept
The chief objectives of the mission to Mars were clear:
- Simplicity and robustness necessarily require the least amount of cross-dependencies between different missions (e.g., basing the mission to Mars on Space Station) and technologies.
- Low-cost spurs from highly versatile launch systems that can be used for missions to Moon, Mars, and elsewhere. It also requires that missions make use of the most efficient trajectories.
- High effectiveness frames the mission such that it maximizes useful time on Mars. It facilitates the exploration with mobility and provides the astronauts with sufficient energy sources to power the equipment and surface vehicles.
As Baker and Zubrin tried to find the mission profile fulfilling these criteria, they also realized that the mission must not use any technologies that are out of reach. Programs that are longer than a decade have a lower rate of success as political forces might cut programs short. Therefore, they tried to shape the mission around the well-understood technologies (such as chemical rather than more exotic nuclear rockets).
They came across the research work of J. French, who proposed in situ (“in place”) production of propellant. How can you make fuel on Mars? Martian atmosphere is 95% carbon dioxide, which can be converted into methane by the means of Sabatier reaction. When the mixture of carbon dioxide and hydrogen is at 300–400ºC in the presence of the catalyst, then water and methane are produced.
Methane serves as a fuel, while oxygen (obtained by the electrolysis of water) serves as an oxidizer. By using Martian resources (carbon dioxide) only a relatively small amount of hydrogen would need to be brought from Earth. The propellant production plant would convert every tonne of hydrogen into twenty tonnes of propellant! This massively reduces the launch mass of the vehicle, and in turn, cheapens the launch. Methane-oxygen is the combination of choice for the SpaceX Raptor engine.
Next, Zubrin and Baker came up with the idea that shaped the whole mission profile: Mission would not consist of a single launch but two. The first launch would bring to Mars Earth Return Vehicle (ERV) with the in situ propellant plant, and the second would bring the crew and their habitat. Importantly, these two launches would be about 26 months apart (which is the time between two launch windows of the energy-efficient trajectories). This allows the plant to produce sufficient fuel for ERV — and removes the need to haul the propellant from the Earth.
The mission
The most important decision is the choice of the trajectory from Earth to Mars. It determines the travel time to Mars and back as well as the amount of time spent on the surface. Even more, it specifies how powerful booster we need and in turn constrains the amount of payload we can get to Mars. The payload fully specifies the “budget” around which we frame the mission.
The trajectory is dependent on the position of Mars relative to Earth. The most energy-efficient way to get to Mars is by using a Hohmann transfer orbit. Simply put, a spaceship boosts from Earth into an elliptical orbit with Earth (at the time of launch) on one side of the ellipse and Mars (as the spaceship arrives) on the other. As the spaceship flies further away from the Earth, Mars slowly approaches from behind and “catches” the spaceship.
This most efficient trajectory results in roughly nine months of space flight before reaching Mars. The time can be reduced to around 150 days with an extra boost. While it took three days for Apollo missions to reach the Moon, it would take fifty-times longer to get to Mars. While certainly long, this is still manageable.
Taking the Saturn V as the heavy-lift booster of choice (and as a tried-and-proven rocket), we can send 140 tonnes to the low Earth orbit. From there, a hydrogen-oxygen engine can propel the vehicle towards Mars — around 25 tonnes can be delivered to the Martian surface using modern rocket engines (e.g., Space Shuttle’s RS-25) and on the slightly accelerated trajectory. We can send cargo (which does not get bored on the fight and can thus travel longer) using ideal Hohmann transfer orbit, which allows sending an additional three tonnes.
Energy-efficient orbits dictate the schedule — the crew would need to wait for the appropriate window to return for around 550 days. While a long time, it allows the team to explore the planet: plenty of time to conduct scientific experiments, collect specimens (and souvenirs) as well as provides insights into how humans can operate on another planet for extended periods. With the help of rovers, the crew can cover large areas around the landing site.
At the landing site, fully-fueled ERV would await the crew. It is reassuring as the mission planners know in advance how the ERV and propellant production are performing. First delivery brings a part of supplies and the crewed mission tops-them off. With a total mass of more than fifty tonnes of equipment and supplies, exciting and — importantly — livable experience for the crew can begin.
The promise
This type of mission design — based on cost-efficient and robust approaches and proven technologies — is likelier to succeed. The tandem of large space agencies and private companies appears today even more fruitful than it has before. NASA has always outsourced a vast majority of rocket-building — nowadays, the incentive of companies to establish an efficient infrastructure for space exploration further facilitates this collaboration.
The motivation could arise from a proof-of-concept mission, that would demonstrate the crucial principle behind the presented concept: in situ propellant production. A sample-return mission could fit this scope. A probe that would produce the propellant on the surface of the Mars, collect the samples and return to Earth would demonstrate the soundness of the principles. Even more importantly, it would identify issues we need to address.
Imagine waking up and seeing the red mountains of Mars. You note the row of dusty solar panels and the rocket close-by that towers into the still-dark sky. Rovers are parked next to the refueling stations, and the small flags flicker in the morning Martian breeze. Wouldn’t it be exciting?
Going to Mars is as much of an adventure as it is a challenge. It requires a lasting international commitment of governments and private sectors and strong political support that will stand behind the program. It will take courage, resources, and a need to keep the desire for exploration alive. It will not be easy — our civilization is facing numerous challenges, both spurring from our society, as well as due to the changes in the environment. These are serious challenges, and we have to dedicate our efforts to solve those for the next generations. But space exploration and human space flight are not a distraction. As Ernst Stuhlinger put it brilliantly in his remarkable letter:
Although our space program seems to lead us away from our earth and out toward the moon, the sun, the planets, and the stars, I believe that none of these celestial objects will find as much attention and study by space scientists as our earth.
I firmly believe that it can be the next thing that unites us, and progress spurring from the research can benefit everyone on this pale blue dot amid nothingness.
Sources:
Zubrin R. & Wagner R., The Case for Mars, [Free Press (2011)]
Davenport C., The Space Barons, [PublicAffairs (2018)]
