There are many things that humanity must overcome before any return trip to Mars is launched.
The two main players are NASA and SpaceX, which work closely together on missions to the International Space Station, but have competing ideas about what a Mars mission with crew would look like.
Size matters
The biggest challenge (or constraint) is the mass of the payload (spacecraft, people, fuel, supplies, etc.) needed to undertake the journey.
We’re still talking about launching something into space, like launching its weight in gold.
The payload mass is usually only a small percentage of the total mass of the launcher.
The Saturn V rocket that launched Apollo 11 to the moon, for example, weighed 3,000 tons.
But it can send only 140 tons (5% of its initial launch mass) to a low orbit around the Earth, and 50 tons (less than 2% of its initial launch mass) to the Moon.
Mass limits the size of a Mars spacecraft and what it can do in space. Each maneuver costs fuel to fire rocket engines, and this fuel must currently be fed on the spacecraft in space.
SpaceX’s plan is to have its Starship vehicle with space crews powered by a separate fuel tank. This means that much more fuel can be transported in one lane than can be transported with a single launch.
Time matters
Another challenge, closely linked to fuel, is time.
Missions that send spacecraft without crew to the outer planets often travel complex trajectories around the sun. They use the so-called gravity maneuvers to swing effectively on different planets to gain enough momentum to reach their target.
It saves a lot of fuel, but can lead to missions that take years to reach their destinations. Clearly, people do not want to do anything.
Both Earth and Mars have (almost) circular orbits and a maneuver known as the Hohmann transmission is the most fuel efficient way to travel between two planets. Actually, without going into too much detail, this is where a spacecraft burns a single in an elliptical orbit from one planet to another.
A Hohmann transfer between Earth and Mars lasts about 259 days (between eight and nine months) and is only possible about every two years due to the different orbits around the Sun of Earth and Mars.
A spacecraft could reach Mars in less time (SpaceX claims six months), but – you guessed it – it would cost more fuel to do so.
Safe landing
Suppose our spacecraft and crew come to Mars. The next challenge is the landing.
A spacecraft penetrating the earth is capable of slowing down the resistance generated by interaction with the atmosphere. This allows the craft to land safely on the earth’s surface (provided it can survive the related warming).
But the atmosphere on Mars is about 100 times thinner than Earth. This means less potential for resistance, so it is not possible to land safely without some help.
Some missions ended up on airbags (like NASA’s Pathfinder mission), while others used drivers (NASA’s Phoenix mission). The latter once again requires more fuel.
A propeller that lands on Mars.
Life on Mars
A Martian day lasts 24 hours and 37 minutes, but the similarities with the earth end there.
The thin atmosphere on Mars means that it can not retain heat as well as the earth, and therefore life on Mars is characterized by high extreme temperatures during the day / night cycle.
Mars has a maximum temperature of 30 ℃, which sounds very pleasant, but the minimum temperature is -140 ℃ and the 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 want to live on Mars and how we manage the temperature during the night.
Gravity on Mars is 38% of Earth (so you will feel lighter), but the air is mainly carbon dioxide (CO₂) with a few percent nitrogen, so it is completely unattractive. We will have to 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 fuel production plant for missions to Earth.
Life on Mars would be possible and there have been several simulation tests done on Earth to see how humans can handle such an existence.
Return to Earth
The last challenge is the return journey and bringing 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 the Earth’s orbit.
Spacecraft returning from Mars will travel again from 47,000 km / h to 54,000 km / h, depending on the orbit they use to reach Earth.
They can slow down to a low orbit around the earth to about 28,800 km / h before entering our atmosphere, but – you guessed it – they need extra fuel to do so.
If they just enter the atmosphere, it will do all the delay for them. We just need to make sure we do not kill or burn the astronauts with G-forces due to excess heating.
These are just some of the challenges facing a Mars mission, and all the technological building blocks to achieve them are there. We just have to spend the time and the money and bring everything together.
This article was originally published on The Conversation by Chris James at the University of Queensland. Read the original article here.