7. Ion propulsion
In the movie, Watney’s crewmates, who thought he was dead, evacuated the planet without him, traveling in a spacecraft that uses ion propulsion to move back and forth between Earth and Mars.
That too is not science fiction.
Ion propulsion works by electrically charging a gas, like argon or xenon. Once charged, the gas becomes an ion. Voltage is then added to the ions, which causes them to shoot out of the engine at high velocity, pushing the spacecraft in the opposite direction.
Ion propulsion has 10 times the efficiency of conventional propulsion. However, it doesn’t have the great power and initial speed that conventional rockets do.
The advantage of ion-based systems is that they don’t demand the great amounts of fuel that traditional gas systems do.
Ion propulsion is a technology for spacecraft that are traveling long distances. NASA’s Dawn spacecraft (artist's image shown above), which earlier this year became the first spacecraft to orbit a dwarf planet, used ion propulsion to travel 3.1 billion miles.
"We’ve got to put a lot of tonnage on Mars. We’re going to have to land something the size of a two-story house on Mars -- the habitation system and the life support system. And the crew vehicle is going to be very large if you’re going to put three people on Mars for a year," said Jeff Sheehy, the senior technical officer for NASA's Space Technology Mission Directorate.
"With ion propulsion systems you can go very far on very little," Sheehy said. "These are called continuous thrust systems. It could go on for years. Over a very long time, you wind up building up your velocity beyond what you could with a chemical system. It is the most efficient way to move mass with these big missions to anywhere."