Star Trek has taught us that in the future, when deadly radiation is about to infiltrate your space ship, all you have to do is yell "Shields up!", "Full deflectors!" or a similar utterance and a magical bubble of blue energy will spring from nowhere and keep you safe. In reality, such an order could instead see the crew desperately squeezing out number twos.
The image of Will Riker crouching in the middle of the Enterprise bridge, daks down with a creepy expression on his face, is a somewhat poor advertisement for the mystery of space travel. Yet, using human waste as radiation shielding is under serious consideration by those planning our first trip to Mars, as an article on New Scientist explains.
The idea stems from one already in NASA's sights, under its "Innovative Advanced Concepts" program, whereby bags of potable water would be pushed up against the ship's hull to absorb cosmic radiation. Astronauts could then drink this water and replace it with, well, their internal contributions, so the integrity of the shielding isn't compromised the longer the trip goes on.
You may have heard of one Dennis Tito, the US engineer and millionaire currently funding a manned mission to Mars. A fellow named Taber MacCallum, part of the team pulling Tito's plan together, had a go at selling the idea to New Scientist:
"It's a little queasy sounding, but there's no place for that material to go and it makes great radiation shielding ... Dehydrate them as much as possible, because we need to get the water back ... Those solid waste products get put into a bag, put right back against the wall."
I guess when you're out in space, without the benefits of 24th century technology -- replicators, transporters, holodecks and attractive Borg drones -- you have to make do with what you've got. Oh kids, if you only knew...