How to get people from Earth to Mars and safely back again

phys.org ^ | December 21, 2020 | Chris James

[BenLurkin]

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

The payload mass is usually just 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 launch only 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 constrains the size of a Mars spacecraft and what it can do in space. Every maneuver costs fuel to fire rocket motors, and this fuel must currently be carried into space on the spacecraft.

SpaceX's plan is for its crewed Starship vehicle to be refueled in space by a separately launched fuel tanker. That means much more fuel can be carried into orbit than could be carried on a single launch.

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 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 does a single burn into an elliptical transfer orbit from one planet to the other.

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.

A spacecraft could reach Mars in a shorter time (SpaceX is claiming six months) but—you guessed it—it would cost more fuel to do it that way.

[Doc91678]

That’s basically how the new lands of North/South America and Australia were “settled”.

Those who came to the “New World” never returned to whence they came.