There are many things that humanity must overcome before starting a return trip to Mars.
The two main players are NASA and SpaceX, who work closely together on missions to the International Space Station, but have competing ideas about what a manned Mars mission would look like.
Size matters
The biggest challenge (or limitation) is the mass of the payload (spacecraft, people, fuel, supplies, etc.) required to make 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 launch vehicle.
For example, the Saturn V rocket that launched Apollo 11 to the moon weighed 3,000 tons.
But it could only launch 140 tons (5% of its initial launch mass) to low Earth orbit 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 carried into space with the spacecraft.
SpaceX’s plan is for its manned Starship vehicle to be refueled in space by a separately launched fuel tanker. That means that much more fuel can be put into orbit than with a single launch.
Time is important
Another challenge, closely related to fuel, is time.
Missions that send spacecraft to the outer planets without a crew often travel complex trajectories around the sun. They use so-called gravity assist maneuvers to swing effectively around different planets in order to gain enough momentum to reach their target.
This saves a lot of fuel, but can result in missions that take years to reach their destination. Obviously, this is something people wouldn’t want to do.
Both Earth and Mars have (nearly) circular orbits, and a maneuver known as the Hohmann transfer is the most fuel-efficient way to travel between two planets. Basically, without going into too much detail, this is where a spacecraft fires once or twice in an elliptical 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 of the Sun of Earth and Mars.
A spacecraft could reach Mars in a shorter time (SpaceX claims six months) but – you guessed it – it would take more fuel to do it that way.
Safe landing
Suppose our spacecraft and crew go to Mars. The next challenge is landing.
A spacecraft entering Earth can use the drag generated by interacting with the atmosphere to slow down. This allows the craft 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 Earth’s. That means less chance of resistance, so it’s not possible to land safely without some kind of help.
Some missions have landed on airbags (like NASA’s Pathfinder mission), while others have used thrusters (NASA’s Phoenix mission). The latter again requires more fuel.
A thruster landing on Mars.
Life on Mars
A March day lasts 24 hours and 37 minutes, but the similarities with Earth end there.
The rarefied atmosphere on Mars means that it cannot retain heat as well as Earth, so life on Mars is characterized by wide variations in temperature during the day / night cycle.
Mars has a maximum temperature of 30 ℃, which sounds 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 at night.
Gravity on Mars is 38% that of Earth (so you feel lighter), but the air is mostly carbon dioxide (CO₂) with a few percent of nitrogen, so it’s completely inhale. We should build a climate-controlled place 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 facility for return missions to Earth.
Life on Mars would be possible and several simulation tests have already been done on Earth to see how humans would cope with such an existence.
Return to Earth
The final challenge is the return journey and the safe return of people to Earth.
Apollo 11 entered the Earth’s atmosphere at approximately 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.
They could slow down in low Earth orbit to about 28,800 km / h before entering our atmosphere, but – you guessed it – they need extra fuel for that.
If they just shoot into the atmosphere, it will do all the delay for them. We just need to make sure we don’t kill the astronauts with G-forces or burn them from overheating.
These are just some of the challenges facing a Mars mission and all the technological building blocks to achieve them are in place. We just have to spend the time and money and put it all together.
This article was originally published on The Conversation by Chris James of The University of Queensland. Read the original article here.