{"id":279330,"date":"2020-12-21T04:35:40","date_gmt":"2020-12-21T09:35:40","guid":{"rendered":"https:\/\/canadianinquirer.net\/v1\/?p=279330"},"modified":"2020-12-21T04:35:40","modified_gmt":"2020-12-21T09:35:40","slug":"how-to-get-people-from-earth-to-mars-and-safely-back-again","status":"publish","type":"post","link":"https:\/\/canadianinquirer.net\/v1\/2020\/12\/21\/how-to-get-people-from-earth-to-mars-and-safely-back-again\/","title":{"rendered":"How to get people from Earth to Mars and safely back again"},"content":{"rendered":"
NASA<\/a>, CC BY-NC-ND<\/a><\/span><\/p>\n<\/figcaption><\/figure>\n

There are many things humanity must overcome before any return journey to Mars is launched.<\/p>\n

The two major players are NASA and SpaceX, which work together intimately on missions to the International Space Station but have competing ideas of what a crewed Mars mission would look like.<\/p>\n

Size matters<\/h2>\n

The biggest challenge (or constraint) is the mass of the payload (spacecraft, people, fuel, supplies etc) needed to make the journey.<\/p>\n

We still talk about launching something into space being like launching its weight in gold.<\/p>\n

The payload mass is usually just a small percentage of the total mass of the launch vehicle.<\/p>\n

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For example, the Saturn V<\/a> rocket that launched Apollo 11<\/a> to the Moon weighed 3,000 tonnes.<\/p>\n

But it could launch only 140 tonnes (5% of its initial launch mass) to low Earth orbit, and 50 tonnes (less than 2% of its initial launch mass) to the Moon.<\/p>\n

Mass constrains the size of a Mars spacecraft and what it can do in space. Every manoeuvre costs fuel to fire rocket motors, and this fuel must currently be carried into space on the spacecraft.<\/p>\n

SpaceX\u2019s plan is for its crewed Starship<\/a> vehicle to be refuelled in space<\/a> by a separately launched fuel tanker. That means much more fuel can be carried into orbit than could be carried on a single launch.<\/p>\n

\"A<\/a>
Concept art of SpaceX\u2019s Dragon landing on Mars.<\/span>
\nOfficial SpaceX Photos\/Flickr<\/a>, CC BY-NC<\/a><\/span><\/figcaption><\/figure>\n

Time matters<\/h2>\n

Another challenge, intimately connected with fuel, is time.<\/p>\n

Missions that send spacecraft with no crew to the outer planets often travel complex trajectories around the Sun. They use what are called gravity assist manoeuvres<\/a> to effectively slingshot around different planets to gain enough momentum to reach their target.<\/p>\n

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.<\/p>\n

Both Earth and Mars have (almost) circular orbits and a manoeuvre known as the Hohmann transfer<\/a> is the most fuel-efficient way to travel between two planets. Basically, without going into too much detail, this is where a spacecraft does a single burn into an elliptical transfer orbit from one planet to the other.<\/p>\n

A Hohmann transfer between Earth and Mars takes around 259 days (between eight and nine months) and is only possible approximately every two years due to the different orbits around the Sun of Earth and Mars.<\/p>\n

A spacecraft could reach Mars in a shorter time (SpaceX is claiming six months<\/a>) but \u2014 you guessed it \u2014 it would cost more fuel to do it that way.<\/p>\n

\"Mars,<\/a>
Mars and Earth have few similarities.<\/span>
\nNASA\/JPL-Caltech<\/a><\/span><\/figcaption><\/figure>\n

Safe landing<\/h2>\n

Suppose our spacecraft and crew get to Mars. The next challenge is landing.<\/p>\n

A spacecraft entering Earth is able to use the drag generated by interaction with the atmosphere to slow down. This allows the craft to land safely on the Earth\u2019s surface (provided it can survive the related heating).<\/p>\n

But the atmosphere on Mars is about 100 times thinner than Earth\u2019s. That means less potential for drag, so it isn\u2019t possible to land safely without some kind of aid.<\/p>\n

Some missions have landed on airbags (such as NASA\u2019s Pathfider<\/a> mission) while others have used thrusters (NASA\u2019s Phoenix<\/a> mission). The latter, once again, requires more fuel.<\/p>\n