Space Microbes: Urine to 3D Printing Polymer?

Yes, urine can be used to help make a polymer for 3D printing in space, but not directly—it serves as a source of chemicals that, after processing, become the building blocks for plastic. This article explains the science behind the idea, how it works, the challenges, and what it means for future space missions.

Formula

The calculator estimates the amount of plastic (in kilograms) that could be produced from crew urine during a space mission. The formula is:

Plastic (kg) = (Time (days) × Crew size × Urine per person per day (L) × 0.001 (kg/L) × Conversion efficiency (%) / 100) × 0.8

Variables:

• Time – duration of the mission in days.
• Crew size – number of astronauts.
• Urine per person per day – average urine output in liters (typical 1.5 L).
• Conversion efficiency – percentage of urine mass that can be converted into useful chemical feedstock (assumed 50% for this estimate).
• 0.8 – factor accounting for losses in polymer synthesis (not all feedstock becomes plastic).

Worked Example

Using the default values (30 days, 4 crew, 1.5 L/day, 50% efficiency):

1. Total urine volume = 30 × 4 × 1.5 = 180 L
2. Mass of urine (assuming 1 kg/L) = 180 kg
3. Convertible mass = 180 × 50% = 90 kg
4. Plastic produced = 90 × 0.8 = 72 kg

So, with these assumptions, the crew could produce about 72 kg of plastic over 30 days. This is a rough estimate; real systems would have different efficiencies.

Why Urine? The Resource Problem in Space

Space missions face a critical constraint: every kilogram of payload costs thousands of dollars to launch. Carrying enough food, water, and materials for long missions is impractical. NASA and other agencies are developing closed-loop life support systems that recycle waste. Urine is 95% water, but it also contains urea, creatinine, and various salts. The water is already reclaimed for drinking, but the solids are usually discarded. Using those solids to make useful products—like plastic for 3D printing—would turn waste into a resource.

How Urine Becomes Polymer: The Chemistry

The key compound in urine is urea (CH₄N₂O). When heated, urea decomposes to form ammonia and carbon dioxide. Ammonia can be used to make a variety of polymers, but the most relevant is polyurethane—a versatile plastic used in foams, coatings, and adhesives. The process involves reacting a diisocyanate with a polyol. The polyol can be derived from glycerol, which can be produced from algae or other biological sources, but also from chemical synthesis using carbon dioxide and hydrogen. In space, carbon dioxide is abundant (from breathing), and hydrogen can be obtained from water electrolysis. So, the steps are:

• Extract urea from urine (after water removal).
• Heat urea to produce ammonia.
• Use ammonia to produce a diisocyanate (like methylene diphenyl diisocyanate, MDI).
• Combine with a polyol to form polyurethane.

Another route is to use urea to make urea-formaldehyde resin, but that is less desirable for 3D printing. The polyurethane route is more promising because it can be tailored for different mechanical properties.

3D Printing in Microgravity

3D printing in space is not new; the International Space Station has a printer that uses plastic filament. However, the filament is brought from Earth. The goal is to use recycled plastic or plastic made in situ. The challenge is that microgravity affects how materials melt and solidify. For example, molten plastic may not flow the same way without gravity. Researchers are testing different printing techniques, such as using a syringe-based extruder that pushes molten plastic out, rather than relying on gravity to feed a filament. The polymer made from urine would be processed into a filament or a paste that can be used in such a printer.

Common Problems and Misconceptions

Misconception: You can drink urine and then print plastic. No, the process is not direct. The urine is processed to extract urea, which is then chemically converted. It is not a simple filter.

Problem: Contaminants. Urine contains salts and organic compounds that can interfere with polymerization. Purification is essential.

Problem: Energy cost. Heating and chemical reactions require energy, which is limited on a spacecraft. The energy must come from solar panels or other sources.

Problem: Safety. Handling ammonia and diisocyanates requires careful containment. These chemicals are toxic, so the system must be sealed and automated.

Alternatives and Comparisons

Urine is not the only waste stream. Solid waste (feces) contains organic matter that can be broken down by bacteria to produce methane and other useful chemicals. Carbon dioxide from breathing can be combined with hydrogen (from water electrolysis) to make methanol, which can be a feedstock for plastics. Algae can be grown using urine as fertilizer, producing oils that can be converted to polymers. Each method has trade-offs in complexity, efficiency, and safety. Urine is attractive because it is relatively easy to collect and contains a high concentration of urea, but it also requires significant processing.

Costs and Practicality

The cost of developing such a system is high, but the potential savings in launch mass are enormous. For a Mars mission, carrying spare parts and materials could be prohibitive. If a crew can produce their own plastic, they can print tools, repair parts, and even medical devices. The initial investment in research and development is justified by the long-term benefit. However, the actual cost per kilogram of plastic produced in space is not publicly available, as the technology is still in early stages.

Safety Considerations

Any chemical processing system on a spacecraft must be fail-safe. The system must prevent leaks, handle toxic intermediates, and ensure that the final polymer is safe for use in the cabin. The polymer itself is inert, but the process chemicals are not. The system would likely be automated with multiple redundant safety systems. Also, the plastic produced must meet strict flammability and off-gassing standards for spacecraft use.

Frequently Asked Questions

Can urine be directly used as 3D printing material? No. Urine is mostly water and cannot be printed directly. It must be processed to extract urea, which is then converted into a polymer.

What kind of plastic can be made from urine? The most likely candidate is polyurethane, which is used for foams, coatings, and flexible parts. Other types, like polyamides (nylons), are also possible but require more complex chemistry.

Is this technology already in use on the ISS? Not yet. The ISS currently recycles water from urine, but the solids are not converted to plastic. Experiments are being conducted on the ground and in space to test the feasibility.

How much plastic can a crew of 4 produce in a year? Using the calculator with 365 days, 4 crew, 1.5 L/day, and 50% efficiency, the result is about 876 kg. That is enough to print many tools and spare parts.

What are the main challenges? Purification of urea, energy consumption, chemical safety, and adapting 3D printing to microgravity are the biggest hurdles.

Is this idea feasible for a Mars mission? Yes, it is being considered. For a mission lasting several years, the ability to produce materials on-site would reduce the need to carry everything from Earth.

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in t | Time in space | days | 30 | 0
in crew | Crew size | persons | 4 | 1
in u_rate | Urine per person per day | L | 1.5 | 0
in conv | Conversion efficiency | % | 50 | 0
out plastic | Plastic produced | kg | (t * crew * u_rate * 0.001 * conv/100) * 0.8 | 2