As nomadic tribes knew, horses are the perfect closed-loop transportation system. Their fuel is grass, and their waste product is fertilizer. Given an appropriate climate and a route that includes sources of water, you can travel indefinitely. The rider only needs to carry fuel for themself, and when the rider needs to eliminate, they can hop off of the horse and answer nature's call.

"The sign said 93, but this tastes like 87 to me." (Image credit: eberhard ?? grossgasteiger on Unsplash)

Spacecraft are just about the opposite. Every bit of fuel you'll need must be carried onboard, and all waste generated along the way also stays onboard; astronauts cannot temporarily disembark to pee on a cactus. With these constraints, we've only managed to make it as far as the moon. Those astronauts wore diapers for the 6-day round trip (and yes, they dumped the dirty diapers from the outbound leg of the journey on the surface of the moon).

"Well, too bad. I TOLD you to go to the bathroom before we left."

Astronauts could've traveled to the moon and back without missing any episodes of their favorite weekly TV show. Astronauts traveling to Mars might return to a new President. This brings a lot of challenges, which has led NASA to launch the "Waste to Base Materials Challenge: Sustainable Reprocessing in Space," a competition for ideas of how to manage refuse in space over a long period of time.

A sight for sore eyes (and a full bladder.) (Image credit: Planet Volumes on Unsplash)

"The journey to Mars and back is going to take two to three years, and there may not be any supply ships. To be as efficient and self-sufficient as possible, you will need to be able to recycle, repurpose, or reprocess things and make what you need from base materials. A completely efficient cycle is almost impossible, and some waste will have to be jettisoned to reduce mass and free up space inside the spacecraft. But ideally, you will have little to almost no waste since everything gets broken down and remade into new things. There are a lot of different kinds of waste on a spacecraft. What are the different ways that those useless waste streams can be repurposed?"

"This challenge is all about finding ways to convert waste into base materials and other useful things, like propellant or feedstock for 3D printing. We are looking for your ideas for how to convert different waste streams into useful materials that can then be made into needed things and cycled through multiple times - and we are looking for ideas to convert waste into propellant. Eventually, we would like to integrate all the different processes into a robust ecosystem that allows a spacecraft to launch from Earth with the lowest possible mass. For now, we are asking you to share your ideas for waste management/conversion in several specific categories:"

1. Trash

2. Fecal waste

3. Foam packaging material

4. Carbon dioxide (CO2) processing

Winners of each category will receive $1,000, with those deemed to be "best in class" winning an additional $1,000. You can enter as many categories and ideas for each as you like.

Learn more here.