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There are many things that humanity must overcome before embarking on any journey back to Mars.
The two main players are NASA and SpaceX, who work closely together on missions to the International Space Station, but have conflicting ideas about what a manned mission to Mars would look like.
Size Matters
The biggest challenge (or limitation) is the mass of payload (spacecraft, people, fuel, supplies, etc.) required to make the trip.
We keep talking about throwing something into space is like throwing its weight in gold.
The mass of the payload is usually only a small percentage of the total mass of the launch vehicle.
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For example, the Saturn V rocket that launched Apollo 11 to the Moon weighed 3,000 tons.
But it was only able to launch 140 tons (5% of its initial launch mass) into low Earth orbit and 50 tons (less than 2% of its initial launch mass) to the Moon.
Mass limits the size of a spacecraft from Mars and what it can do in space. Each maneuver costs fuel to start the rocket engines, and this fuel must currently be transported into space on the spacecraft.
SpaceX’s plan is for its Starship manned vehicle to be refueled in space by a separately launched fuel tanker. That means that much more fuel can be brought into orbit than could be carried in a single launch.
Official photos from SpaceX / Flickr, CC BY-NC
Time matters
Another challenge, closely related to fuel, is time.
Missions that send unmanned spacecraft to the outer planets often travel complex trajectories around the Sun. They use what are called gravity assist maneuvers to launch effectively around different planets to gain enough momentum to hit their target.
This saves a lot of fuel, but can result in missions that take years to reach their destinations. Clearly, this is something humans would not want to do.
Both Earth and Mars have (almost) circular orbits, and a maneuver known as a Hohmann transfer is the cheapest way to travel between two planets. Basically, without going into too much detail, this is where a spacecraft makes a single combustion in an elliptical transfer orbit from one planet to another.
A Hohmann transfer between Earth and Mars takes around 259 days (between eight and nine months) and is only possible about every two years due to Earth and Mars’ different orbits around the Sun.
A spacecraft could get to Mars in less time (SpaceX claims six months) but, you guessed it, it would cost more fuel to do it that way.
NASA / JPL-Caltech
Safe landing
Suppose our spacecraft and crew arrive on Mars. The next challenge is landing.
A spacecraft entering Earth can use drag generated by interaction with the atmosphere to slow down. This allows the spacecraft to land safely on the Earth’s surface (provided it can survive related warming).
But the atmosphere of Mars is about 100 times thinner than that of Earth. That means less potential to drag, so it is not possible to land safely without some help.
Some missions have landed in airbags (like NASA’s Pathfider mission) while others have 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 similarities to Earth stop there.
Mars’ thin atmosphere means that it cannot retain heat as well as Earth can, which is why life on Mars is characterized by extreme temperatures during the day / night cycle.
Mars has a maximum temperature of 30 ℃, which sounds nice enough, 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 ℃.
Therefore, we must be very selective about where we choose to live on Mars and how we handle the temperature at night.
The gravity on Mars is 38% that of Earth (so you would feel lighter) but the air is mostly carbon dioxide (CO₂) with several percent nitrogen, making it completely unbreathable. We would need to build a climate controlled place just to live there.
SpaceX plans to launch several cargo flights, including critical infrastructure like greenhouses, solar panels, and, you guessed it, a fuel production facility for missions back to Earth.
Life on Mars would be possible and several simulation tests have already been carried out on Earth to see how people would cope with such an existence.
Return to earth
The final challenge is the return journey and getting the people back safely to Earth.
Apollo 11 entered Earth’s atmosphere at about 40,000 km / h, which is just below the speed required to escape Earth’s orbit.
Spaceships returning from Mars will have reentry speeds of 47,000 km / h to 54,000 km / h, depending on the orbit they use to reach Earth.
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They could slow down to a low orbit around the Earth at around 28,800 km / h before entering our atmosphere, but, you guessed it, they would need additional fuel to do that.
If they are simply released into the atmosphere, it will do all the deceleration for them. We just need to make sure that we don’t kill the astronauts with G forces or burn them due to excess heat.
These are just some of the challenges facing a mission to Mars and all the technological components to achieve it are there. We just need to spend the time and money and put it all together.
POT
