Photo Credit: (NASA/Bill Ingalls)

With all the well-deserved attention that NASA astronaut Scott Kelly’s safe return to Earth is receiving this week, I can’t help but think about how fragile humans are.

Sure, he appears to have emerged from 340 days in zero gravity in good health. And he always seemed remarkably upbeat despite spending nearly a year enclosed within the same curving walls, far from his loved ones, breathing recycled air. At first glance, it’s hard to look at this unfailingly resilient man, probably one of the best members of our species, and feel anything but admiration and optimism for our future.

Then I remember that it may take humans two years – double the length of Kelly’s trip – to get to Mars and back. They’ll face double the isolation, double the physical challenges, spend twice as long eating vacuum-sealed food. They’ll also lose sight of Earth, its blue oceans and swirling clouds. Also, none of them will likely be Scott Kelly.

And yet we’ve already dropped two robots onto the Red Planet to take a look around and tidy up before we arrive. No sweat.

It’s not getting to Mars that’s hard, it’s getting humans to Mars that’s a pain.

Mary Roach probably said it best in Packing for Mars:

“To the rocket scientist, you are a problem. You are the most irritating piece of machinery he or she will ever have to deal with. You and your fluctuating metabolism, your puny memory, your frame that comes in a million different configurations. You are unpredictable. You’re inconstant. You take weeks to fix.”

As a science fan and science-fiction writer, it’s easy to get caught up in pondering all the technological advances that will be required for humans to push out into the stars. But even when we’ve got the propulsion, communications, and landing problems solved, we’re still going to be sending fallible, fragile humans on excruciatingly long journeys. Other than Scott Kelly, how many of us are equipped for that challenge?