Issue #4(26) 2020 Astronautics

Taking out the trash in space

Annie Meier Kennedy Space Center, Florida, USA

We all know that dealing with waste, rubbish and litter is a huge environmental concern on Earth but transfer the problem to the restricted confines of a long term space mission and it becomes an even bigger issue. Rigorous housekeeping to ensure crews remain safe and healthy on future deep space missions will be of paramount importance and one of the less glamorous challenges not often talked about is how to handle the large amounts of rubbish and waste that will be produced. NASA’s Orbital Syngas/Commodity Augmentation Reactor (OSCAR) is one project offering a way to design new and innovative technology for dealing with garbage in space.

When planet Earth sends humans into space, they are guaranteed to create waste. In fact, it is estimated that a crew of four on a one-year mission would generate around 2500 kg of rubbish, garbage, trash or waste, whatever term you prefer. The waste is either from natural, biological processes or from items on a spacecraft that are deemed no longer useful. Here on Earth, the recognised solution often involves recycling in one form or another, but how can this philosophy be extended to space?

For NASA, the answer lies in its Logistics Reduction Program (LRP), which seeks to use all items sent into space in as many reusable scenarios as possible. Currently, waste generated during a mission such as on the International Space Station (ISS) is either carried on board the spacecraft during the mission or stored inside a logistics module, such as a Cygnus or Progress transport capsule, which are de-orbited into Earth’s atmosphere for destruction.

The idea is to develop space technologies to convert trash and other waste materials into high-value products

The LRP, by contrast, is in line with the vision of NASA’s In-Situ Resource Utilisation (ISRU) campaign, which follows the philosophy of using as much of the surrounding resources as possible to generate useful commodities for a space mission and minimise mass that has to be launched from the gravitational well of Earth.

Trash to Gas

The face of astronaut Don Pettit peers out from rubbish stowage bags in the Harmony node of the ISSThe face of astronaut Don Pettit peers out from rubbish stowage bags in the Harmony node of the International Space Station. The bags, containing rubbish and no longer needed equipment, are routinely transferred to a docked Progress spacecraft for subsequent disposal.

A key part of the overall LRP is the Trash to Supply Gas (TtSG) project – colloquially known as ‘Trash to Gas’. The idea is to develop space technologies to convert trash and other waste materials from human spaceflight into high-value products, which might include propellants or power system fuels in addition to life support oxygen and water.

The Trash to Gas team at NASA’s Kennedy Space Center is looking for ways to convert no longer needed mission waste such as food packaging, clothing and hygiene items into inert gases and recoverable water. The inert gases can then be used for venting off a spacecraft to reduce mission mass prior to an entry decent and landing manoeuvre or to reduce volume so that the crew does not have to be surrounded by their trash on a long duration mission. The project also seeks to recover water and convert it to a useful commodity, namely methane (CH4) gas, that can be stored and later converted into a fuel.

It is estimated that a crew of four on a one-year mission would generate around 2500 kg of rubbish

The team has investigated many varying technologies for solid-to-gas conversion for space applications, including pyrolysis, incineration, gasification and steam reforming (see panel on page 40).

OSCAR suborbital payload.OSCAR suborbital payload.

When technology is being developed for space exploration, time is usually spent testing on the ground before any type of microgravity demonstration is attempted; so, over the past several years, the Trash to Gas team has conducted tests in Earth’s ‘1g’ gravity. NASA uses a scale to measure technologies called Technology Readiness Level (TRL). It has nine levels, which extends from TRL 1, showing scientific research is just beginning on a technology to TRL 9 or ‘flight proven’ technology used during a successful mission. Operating in a microgravity environment has many challenges not found on Earth, and performing tests to validate a technology in microgravity often sends scientists and engineers back to the drawing board. The ultimate goal is to figure out what is needed to make the components or technology fully successful at the highest TRL level. In the case of Trash to Gas, a payload was created under the project called Orbital Syngas/Commodity Augmentation Reactor (OSCAR).

The OSCAR payload.The OSCAR payload.

OSCAR

NASA’s OSCAR project was designed to investigate waste conversion operations for trash-to-gas development specifically on deep space and long duration missions beyond low Earth orbit. The systems analysis for a Trash-to-Supply-Gas system was developed from prior ground testing results and experimental metrics that suggested that, for a crew of four on a one-year mission, a TtSG system could reduce waste volume by 19 cubic metres per year and produce between 800 and 1500 kg of methane (CH4) per year.

According to the mission architecture under which this assumption was made, a TtSG system could enable potential future missions by providing yearly station keeping at an Earth-Moon Lagrange point, providing enough CH4 to send one 200 kg payload from a Lagrange point to the lunar surface each year, or potentially providing course corrections (depending on spacecraft size) for a Mars mission.

Conversion technologies

The team has investigated many varying technologies for solid-togas conversion for space applications, including pyrolysis, steam reforming, incineration and gasification

Simulated microgravity tests were performed on Earth with OSCAR, including testing at the NASA Glenn Research Center microgravity drop tower and zero gravity facilities. These tests were used as preliminary microgravity demonstrations to learn about the microgravity process and make changes before moving forward with a longer duration microgravity experiment.

During OSCAR tests, operation of the system included trash injection into a hot reactor where it was ignited and converted from solid to gas. The gas was sent through a condenser to cool it down and remove the water, and the cooled gas was then collected and analysed for composition.

A trash simulant, a mix of different types of material cut into tiny pieces, is weighed on a scale for use in OSCAR.A trash simulant, a mix of different types of material cut into tiny pieces, is weighed on a scale for use in OSCAR.

Launch demo

On 11 December 2019, the OSCAR payload was successfully flown and operated on Flight NS-12 of Blue Origin’s New Shepard vehicle. It is understood to be the largest payload (in volume and mass terms) flown to date on the New Shepard vehicle.

The OSCAR payload, which occupied six traditional single stack New Shepard payload boxes, recreated a gravity-driven, solid-to-gas conversion process in microgravity that mimicked a downdraft gasification reactor. The reactor was designed to accept simulated logistical waste (with a composition similar to that on a crewed spaceflight mission) and convert it from solid to gas.

The payload successfully demonstrated feeding trash into the reactor, ignition of solid and liquid feedstock, combustion during microgravity and subsequent gas collection processes in a flight automated sequence. The waste materials selected for the suborbital flight included items such as food packaging, food simulant, faecal simulant, hygiene wipes, cotton washcloths, toilet paper, toothpaste, shampoo and nitrile gloves.

Annie Meierand Jamie Toro assemble the flight hardware for the OSCARAnnie Meierand Jamie Toro assemble the flight hardware for the Orbital Syngas/Commodity Augmentation Reactor (OSCAR) in the Space Station Processing Facility at KSC.

An oxygen and steam-rich environment was created within the reactor for ignition conditions, and the gases produced were quantified to verify the composition of the reaction product. Remaining trash and char in the reactor were also collected for post launch analysis to compare with the gravity-driven operation and reaction. The gas produced from the flight experiment was largely consistent with lab testing, the primary products being carbon dioxide and carbon monoxide. Trace compounds that were also produced are being researched and fully understood for future reduction or elimination with an eye to safety assessments for a human mission.

OSCAR was successfully flown and operated on Flight NS-12 of Blue Origin’s New Shepard vehicle

This test marked the longest flight Trash to Gas has achieved in microgravity thus far and full qualitative and quantitative results are being reported in technical detail in public, peer-reviewed scientific papers.

It is important to note that the gas heating system, power supply and trash feed system were customised and designed only for operation on a short suborbital flight, so some systems are currently at a low TRL and need to be redesigned for any long duration flight unit. NASA is advancing technological capabilities, like OSCAR, that transforms the world around us, and expands human presence in space. The OSCAR team is making improvements to the hardware and a second payload is slated for a suborbital New Shepard flight in 2021.

The OSCAR payload was flown to the edge of space in December 2019The OSCAR payload was flown to the edge of space in December 2019 aboard Blue Origin’s New Shepard suborbital rocket. OSCAR attained around three minutes of microgravity to demonstrate its features.

About the author

Annie Meier is chief of the Exploration Systems & Development Office which includes a multi-discipline team of engineers and scientists focusing on various In-situ resource utilisation technology developments for NASA at Kennedy Space Center. She has a PhD in chemical engineering from the University of South Florida and has spent much of her time at NASA as a principal investigator researching logistical waste management and conversion technology, as well as ISRU, specifically reactor and catalysis processes. She has supported microgravity demonstrations on platforms such as NASA’s Drop Tower and commercial suborbital rocket test campaigns. Dr Meier has also served as an analogue astronaut in 2014 during a NASA psychological study at HI-SEAS, a simulated Mars habitat.

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