The “Big Spaceship” approach was a non-starter because we just don’t have the technology or the facilities to build such a massive spaceship. And why would we? Building a thousand tonne spaceship to take six people to Mars, and throw nearly all of it away en route; a horrible waste.Even if such a mission had been built and sent, it’s hard to imagine more than one would have been sent. And then what? All the public excitement that might have driven one mission would have been expended on a mission providing two weeks on the surface. There would have been insufficient driver to build a second, so we would have stayed home, possibly forever.

Mars. Done that, been there, paid for the thousand tonne now space garbage. It might well have spelt the end of human kinds adventures in space for another century.

But could there be another way? One that could use vehicles more the size of the Apollo mooncraft, and wouldn’t cost the Earth to build?

The main reason a “Big Spaceship” would be needed would be to bring with you your return spacecraft and all its fuel. But what if you didn’t need to bring it back with you.

In 19xx, a couple of engineers from Martin Marietta, one of NASA’s contractors, proposed that very thing. Robert Zubrin and David Baker suggested making the rocket fuel for the return trip on the surface of Mars, using a the Martain atmosphere and a small nuclear power plant. That way you wouldn’t need to take the fuel with you, and you’d save a lot of mass in your out bound craft.

Here’s how it would work. You’d take a relatively small amount of hydrogen with you on your ship. When you got to Mars, you’d roll out a small nuclear reactor on a robot truck and park it behind a hill to stop it irradiating your return vehicle. You’d then use an already tried and tested chemical process to react the hydrogen with the carbon dioxide in the Martian atmosphere to make methane. That’s rocket fuel. Enough to power you home, and some left over to run your Mars rovers so you can visit places once you’ve got there.

[diagram of chemical process]

But what if something goes wrong with the chemical process and you can’t make the useless? You’re stuck on Mars.

That’s the second trick Zubrin and Baker came up with. You actually send the return craft, the Earth Return Vehicle, out to Mars two years before you send the crew out. It sits there and happily makes the fuel, and the crew don’t set off until the ERV confirms that it’s full and ready to go.

The crew then set off in a vehicle specifically designed to get you there and to live in on the surface, a xx unit. Not only do they not have to take the return leg fuel with them, the same vehicle doesn’t need to bring them home, so can be smaller. All around, less weight to send, so you don’t have to build a thousand tonne spas hip in orbit, you have two vehicles that could be launched by the same Saturn V rocket that took us to the moon (okay, we don’t have them anymore, buy America is currently building a replacement).

But you’re sending out the vehicle that will bring our brave explorers home four years before they need to use it, the first