Storage space is extremely limited on spacecraft. Furthermore, this space quickly fills with trash over time. In addition to taking up space, garbage creates biological and physical hazards, making waste management especially important during long-term missions.
The current practice on the International Space Station (ISS) is to compress garbage and store it on board. Astronauts then load the compressed trash onto expendable commercial supply vehicles that burn up when they enter the Earth's atmosphere. As a result, most of the down mass from the ISS has been scientific experiments.
This approach works fine when a spacecraft is orbiting Earth, but waste management becomes more complex when there aren't consistent resupply ships that can remove the trash or safe regions for jettisoning the waste. Options for resupply become more limited as it gets further from Earth. Spacecraft designs must therefore give greater consideration to recycling trash instead of merely disposing of it, since recycling allows vehicles to carry more equipment on long missions.
The use of heat and compression is one of the most promising approaches for turning trash into gas. One of the most important advantages of this approach is that it produces water in the form of steam. It also produces gases such as methane, which are highly useful onboard a spacecraft. NASA is calling on U.S. companies to create prototypes for trash compacting and processing systems that improve on current solutions. NASA is also looking for innovative designs that increase astronaut safety by removing hazardous materials from trash.
The limited storage space and opportunities for resupply mean that trash management systems must reuse existing materials. These systems must therefore remove recyclable materials before processing the remaining trash. The ultimate goal for waste disposal in deep space is to efficiently recycle as much as possible for reuse.
Proposed designs will likely draw inspiration from NASA’s existing technologies for processing carbon-based waste through thermal degradation processes such as combustion, pyrolysis and steam reforming. For example, NASA already operates a heat melt compactor, which uses evaporative heat transfer to recover water from items like juice boxes and wet wipes. This device then compacts the trash at a 10:1 ratio. In addition to the volume reduction that’s so important on spacecraft, the resulting disks may provide additional benefits, such as using them for shields that protect astronauts from ionizing radiation.
Designs based on trash to gas technologies use heat to convert trash into methane gas, which the right engines can use as fuel. For example, Orbital Syngas/Commodity Augmentation Reactor (OSCAR) is a test rig that NASA uses to explore the feasibility of converting trash to gas in microgravity. In addition, Pioneer Astronautics (PA) has developed a steam reformer that reacts oxygen and steam with carbon-based trash to produce methane, hydrogen and carbon dioxide. PA has also developed a device that performs wet air oxidation on polymers to produce hydrogen and carbon dioxide. The use of a chemical catalyst greatly reduces the heat needed to sustain this process.
A new reactor that converts solid waste into gases would support NASA's exploration efforts. This reactor must allow astronauts to recover several classes of products, including gas, solids and water. This system will also need to remove ash regularly and safely in microgravity, either directly from the reactor or immediately after it exits the reactor. The biggest challenge of treating waste with heat is that the system must be lightweight and consume little power. It must also minimize crew operation time, while still processing waste reliably and repeatably.
The next manned lunar landing could happen as early as 2025, paving the way for deeper exploration of the solar system. The missions will leverage open innovation to develop recycling technologies that maximize the use of limited resources and improve crew safety. NASA is currently sponsoring a crowdsourcing challenge to identify new ways of handling the challenges of recycling and disposing of waste. See the HeroX page for more information on The Trash-to-Gas Ash Management Challenge.