Houston, We Have a Diagnosis Problem: The Medical Limits of Deep Space

For the first time in the history of human spaceflight, an astronaut had to be brought home early for medical reasons. It happened in January, and most people didn't think much of it. But, they should.

NASA astronaut Mike Fincke, the commander of the International Space Station's Expedition 74, revealed this week that his medical condition cut the Crew-11 mission short by about a month. He and his three crewmates splashed down in the Pacific Ocean on January 15, weeks ahead of schedule.

NASA hasn't disclosed what was wrong. What they have said is that Fincke needed "advanced medical imaging not available on the space station." That one line tells you almost everything you need to know about where human spaceflight stands right now, and what's at stake as NASA prepares to send people back to the Moon.

How Far Is Too Far When Something Goes Wrong

The ISS is 250 miles up. The Moon is 239,000 miles away.