How to bring people from Earth to Mars and return safely

There are many things that mankind must overcome before launching any return trip to Mars.

The two major players are NASA and SpaceX, who work together on missions on the International Space Station, but have competing ideas about what a manned Mars mission would look like.

Size matters

The biggest challenge (or constraint) is the mass of the payload (spacecraft, people, fuel, supplies, etc.) needed to make the trip.

We’re still talking about launching something into space, like launching its weight into gold.

The mass of the payload is usually only a small percentage of the total mass of the launch vehicle.

For example, the Saturn V rocket that launched Apollo 11 on the Moon weighed 3,000 tons.

But it could launch only 140 tons (5% of the initial launch mass) in low Earth orbit and 50 tons (less than 2% of the initial launch mass) on the Moon.

The mass constrains the size of a spacecraft on Mars and what it can do in space. Each maneuver costs fuel to launch rocket engines, and this fuel must now be transported into space on the spacecraft.

SpaceX’s plan is for the manned Starship to be refueled in space by a separately launched tank. This means that much more fuel can be transported into orbit than it could be transported in a single launch.

Time matters

Another challenge, closely related to fuel, is time.

Missions that send unmanned spacecraft to outer planets often travel complex trajectories around the Sun. They use what are called gravitational assistance maneuvers to fry effectively around different planets to gain enough momentum to reach their target.

This saves a lot of fuel, but can lead to missions that take years to reach their destinations. Clearly, this is something people would not want to do.

Both Earth and Mars have (almost) circular orbits, and a maneuver known as the Hohmann transfer is the most efficient way to travel between two planets. Basically, without going into too much detail, this is where a spacecraft makes a single burn in an elliptical transfer orbit from one planet to another.

A Hohmann transfer between Earth and Mars takes about 259 days (between eight and nine months) and is only possible about every two years due to the different orbits around the Earth and Mars.

A spacecraft could reach Mars in a shorter time (SpaceX claims six months), but – you guessed it – it would cost more fuel to do so.

Safe landing

Suppose our ship and crew reach Mars. The next challenge is landing.

A spacecraft entering Earth is able to use the pull generated by the interaction with the atmosphere to slow down. This allows the boat to land safely on the Earth’s surface (provided it can survive the related heating).

But the atmosphere on Mars is about 100 times thinner than that of Earth. This means a lower firing potential, so it is not possible to land safely without some help.

Some missions landed on airbags (such as NASA’s Pathfider mission), while others used thrusters (NASA’s Phoenix mission). The latter, once again, requires more fuel.

Life on Mars

A Martian day lasts 24 hours and 37 minutes, but the resemblances to the Earth stop there.

The thin atmosphere on Mars means that it cannot retain heat as well as Earth, so life on Mars is characterized by extremely high temperatures during the day / night cycle.

Mars has a maximum temperature of 30 ℃, which sounds quite pleasant, but its minimum temperature is -140 ℃, and its average temperature is -63 ℃. The average winter temperature at the South Pole of the Earth is about -49 ℃.

So we have to be very selective about where we choose to live on Mars and how we manage the temperature during the night.

The gravity on Mars is 38% of that of Earth (so you would feel lighter), but the air is mainly carbon dioxide (CO₂) with a few percent nitrogen, so it is completely unbreathable. We should build a climate-controlled place just to live there.

SpaceX plans to launch several cargo flights, including critical infrastructure, such as greenhouses, solar panels and – you guessed it – a return fuel plant.

Life on Mars would be possible, and several attempts have already been made to simulate it on Earth to see how humans would cope with such an existence.

Return to Earth

The ultimate challenge is to return and bring people back to Earth safely.

Apollo 11 entered the Earth’s atmosphere at about 40,000 km / h, which is just below the speed required to escape Earth’s orbit.

Spacecraft returning from Mars will have re-entry speeds of 47,000 km / h to 54,000 km / h, depending on the orbit they use to reach Earth.

It could slow down in low orbit around the Earth to about 28,800 km / h before entering our atmosphere, but – you guessed it – it would need extra fuel to do so.

If they simply enter the atmosphere, it will do all the deceleration for them. We just need to make sure we don’t kill G-force astronauts or burn them because of overheating.

These are just some of the challenges facing a mission to Mars and all the technological elements to achieve this are there. We just have to spend our time and money and put it all together.

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