In 1990, a couple of engineers from Martin Marietta, one of NASA’s contractors, proposed a new scenario for going to Mars.
Robert Zubrin and David Baker posed the question “why take everything with you”? Specifically, they asked “why do you need to take all of your fuel for the return trip with you”?
Their alternative mission architecture, called Mars Direct, involved making the rocket fuel for the return trip on the surface of Mars. Here’s how it would work.
You’d take a relatively small amount of hydrogen with you on your outbound spaceship. 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 you and your vehicle. This would provide all your power. You’d then react a small amount of liquid hydrogen you brought with you with the carbon dioxide in the Martian atmosphere to make methane. That’s rocket fuel. Enough to get you home, and some left over to run your Mars rovers so you can visit places once you’ve got there.
The chemical process is tried and tested, technology that’s been used for over a century. But it’s never been tried on Mars. What if something went wrong with the chemical plant or your power plant and you can’t make your rocket fuel? You’d be stuck on Mars.
Here’s the second innovation 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 on the Martian surface and happily makes the fuel by itself, and the crew don’t set off to Mars 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 Habitation 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 spaceship in orbit, you have two vehicles that could be launched by separate rockets of the size we may have in the next few years.
At the same time as the crew are launched, the ERV for the next mission is launched and landed within rover range of the first mission (or, later on, in the same place, to start building a base). If anything went wrong with the Crews return vehicle, they could wait for the vehicle that came out at the same time as them to fuel up, drive over in their Mars Rover, and hitch a ride home on it.
Mars Direct provides a lower cost, lower risk approach to sending humans to Mars. Zubrin continues to lobby NASA and the American government to adopt and implement it, forming the Mars Society to further these aims. Zubrin and Baker also wrote The Case for Mars, which goes into detail of how missions would work – technology has moved on in some areas since it was written, but it’s premise is still good and it’s a useful read.
NASA thinking does seem to be leaning in this direction nowadays, and hopefully the new entrepreneurs now joining the game will follow the same thinking.