NASA's Universal Waste Management System during preflight testing, 2019. Image: NASA
An overlooked system
Between commercial stations, lunar programs and private missions, the number of people living off Earth at any moment is on track to pass a hundred within about twenty years. Each of them will depend on a waste management system that is used several times a day, works without gravity and sits directly upstream of the water supply.
“Everyone wants to design the cupola. Nobody wants to own the toilet. But the toilet is the thing that decides whether a hundred people can actually live up there.”Anthony Sims, former Principal of Industrial Design, SpaceX1
Programs rarely treat waste management as a development priority. It is procured as a subsystem, judged mainly on mass and volume, and replaced with a refined version of the previous design. This report sets out what the system has to do, how the current generation performs, and the changes to procurement and certification that would let new designs compete for flight.
What a space toilet has to do
A terrestrial toilet relies on gravity and a water supply. In orbit there is neither. A space toilet performs five coupled functions in a few cubic feet, for crew members of different body types, and has to keep performing them for years with in-flight maintenance only.
- 01Separate and capture. Directed airflow from a fan-driven separator replaces gravity. Urine and feces are routed into separate streams, and the unit has to seal against cabin air between uses.
- 02Recover water. On the ISS, urine is chemically pretreated and then distilled in the Urine Processor Assembly. The station's life support system now recovers about 98 percent of the water brought aboard.2
- 03Control air. Odor, microbial load and moisture are filtered before air returns to a sealed cabin that cannot be ventilated.
- 04Meet acoustic and privacy limits. The unit sits inside the shared habitable volume. NASA's human systems standard sets limits on noise, and noise and lack of privacy affect sleep and crew cohesion.3
- 05Fail safely. Crews repair the unit themselves with limited spares. Mean time between failures and crew maintenance hours matter as much as mass.
How the design has evolved
NASA contracted Collins Aerospace to develop the Universal Waste Management System (UWMS) for exploration missions. The goals were to reduce mass and volume, to share one core design across vehicles, and to improve usability for female crew members.4
The ISS unit of the Universal Waste Management System during electromagnetic testing before launch, December 2019. Image: NASA
The Orion unit was delivered in December 2019 and installed in the Artemis II vehicle in March 2021. The ISS unit launched in October 2020. By most measures it is the most capable toilet NASA has flown.
It still rests on the same principle as its predecessors. Airflow moves waste away from the body, and the fans, separators and seals that produce that airflow remain the most common points of failure. Each generation has been smaller, lighter and easier to use, and none has been a different architecture.
A fault on Artemis II
Artemis II was the first mission to take the UWMS beyond low Earth orbit. Shortly after launch on April 1, 2026, the crew reported a blinking fault light, and NASA said the toilet fan had jammed. Working with mission control, the crew restored the unit to normal operation on the first day of the mission. The crew also wore ear protection while using it.5
The fault was resolved quickly, and the response worked as designed. It also shows the operating constraint for exploration missions. Beyond low Earth orbit there is no resupply and no return within hours, so a fault that is an inconvenience on the station carries more weight on a lunar transit or a surface stay.
Earth from Orion's window after the Artemis II translunar injection burn, April 2026. Image: NASA / Reid Wiseman
Why problems persist
The engineers who built the UWMS solved hard problems, and the unit is a real improvement. The failures return for a structural reason: the way programs select, certify and fund flight hardware makes it very hard for a new waste architecture to reach orbit.
Certification cost favors flight heritage
Program managers are judged on whether a mission flies safely and on schedule. Hardware that has flown carries test data, a certification record and a supply chain. A new design has to buy all three, starting from a low technology readiness level. Each vehicle therefore inherits a refined version of the last system and its failure modes. We call this the heritage trap. Waste systems and carbon dioxide removal are the two clearest examples.
The system is coupled to life support
The toilet is the front end of water recovery, part of air revitalization and a noise source in a small cabin. A redesign changes interfaces with all three, which turns a toilet project into an environmental control and life support (ECLSS) project, the slowest and most expensive kind to certify.
No organization owns the problem
Waste management sits between life support engineering, human factors and crew health. Each group touches it and none is funded to rethink it. Without a dedicated budget line there is money for sustaining engineering and anomaly response, and little for a clean-sheet design.
Failures are survivable, so they are tolerated
On a short mission the crew has backups, mission control has procedures and everyone gets home. That resilience is good engineering. It also means the cost of an unreliable unit is paid in crew time and discomfort rather than mission loss, and costs of that kind are easy to accept one mission at a time.
A co-founder of Paragon Space Development Corporation has spent a career in environmental control and life support, the field where waste and water systems live. Anthony Sims, former Principal of Industrial Design at SpaceX, shaped a crew vehicle around the people inside it. Their combined view covers both halves of the problem: the systems that keep a crew alive, and the design that makes those systems livable.
Requirements for long stays
On a station where people live for months, or a lunar base where the next resupply is weeks away, waste system reliability becomes a question of hygiene, water balance and whether the mission can continue as planned.
Commercial stations add a further requirement. NASA's Commercial LEO Destinations program will certify private stations to host NASA astronauts, and their crews will also include private astronauts and researchers with less training than career astronauts. A unit that only an expert can recover from a fault does not meet the needs of a commercial operator competing on livability.6
What would improve it
Changing the pattern does not require new physics. It requires treating waste management as a design priority and giving new architectures a credible path to flight. We recommend four measures.
The toilet is where the gap between what spacecraft can do and what people need is easiest to see. Closing it is part of making space a place people can live, not only visit.
Sources
- NASA Exploration Toilet Hardware Status and Crew Feedback, ICES-2024-071
- NASA UWMS and Toilet Integration Hardware Operations on ISS, ICES-2022
- UWMS paper, ICES 2025
- NASA-STD-3001, NASA Space Flight Human-System Standard, Volume 2
- Artemis II crew troubleshoot Orion toilet, BBC Sky at Night
- What Is Going On With the Artemis 2 Toilet?, Gizmodo