Warning: Spoilers ahead if you haven't seen "The Martian" movie or read the book.
Stranded alone on a freezing planet 140 million miles away from Earth is not a situation you'd want to find yourself in, especially with no way to phone home.
That is, of course, exactly what happens in the "The Martian" to fictional astronaut Mark Watney, who understands his survival depends on talking to people back on Earth.
Luckily, Watney knows his NASA history — so he locates and digs up Mars Pathfinder, a spacecraft NASA actually launched back in 1996. After a little tweaking, he uses the robot to communicate with engineers through a replica of Pathfinder at NASA's Jet Propulsion Laboratory.
It turns out this plan would probably work in real life because NASA really does have a working replica of Pathfinder. The spacecraft would need to be "turned on and dusted off," NASA's director of planetary science Jim Green told Tech Insider, but it does exist.
So NASA really could theoretically use it to communicate with a stranded Martian astronaut. He or she would, however, have to dig Pathfinder out of almost two decades' worth of grit blown around by wind and dust storms, then get it working again.
It's not a one-off occurrence: NASA builds a working replica of every spacecraft it launches. That way, in case something goes wrong afterward, engineers can troubleshoot the problem on Earth, come up with a fix, and send a patch to the identical robot in space.
The Pathfinder replica came in handy, for example, when NASA scientists discovered a bug in some of the computer code in the real thing, not long after it landed on Mars in 1997. They recreated the problem in the replica, and then worked out a way to debug it. The corrective instructions engineers sent to the Pathfinder on Mars fixed the bug.
It goes to show that, while NASA scientists and engineers are some of the best in the business, they can't anticipate everything that can go wrong in space. It pays to have a spare that's not 140 million miles away.
