The Trash-to-Gas Ash Management Challenge

One of the challenges of long duration space exploration is waste management.   As waste streams are generated, unwanted trash items begin to accumulate in the cabin. During long duration missions, this aggregates into several tons of trash being stored inside the habitat, which makes orbital maneuvers more expensive and reduces the amount of habitable volume for the crew.  NASA is taking a multi-pronged approach to waste management on long-duration spacecraft (see Waste to Base Materials Challenge: Sustainable Reprocessing Space and NASA Waste Jettison Mechanism Challenge). Three primary approaches are currently being investigated to help solve the problem with space trash: 

1. Thermally degrade the waste via a process called Trash-to-Gas. This approach gasifies the waste items, producing water and syngas which can be reutilized onboard or vented overboard for mass and volume reduction.
2. Dry, stabilize, and compact the trash items. This approach removes the water from the trash, reduces trash volume, and produces trash tiles that may be effective for radiation protection. However, another method of removing the trash mass from the spacecraft is still required in conjunction with this approach.
3. Jettison the trash via an airlock. This approach removes all of the trash mass and volume from the habitat but may not recover any of the resources within the discarded trash items.

This challenge will help support the development of the first approach, Trash-to-Gas. Trash-to-gas reactors are considered a sustainable approach to both near- and long-term waste management during long-duration space missions.  The primary goal of this challenge is to create actionable design concepts for ash removal from a trash-to-gas reactor in microgravity.

A trash-to-gas reactor uses thermal degradation processes to gasify waste into a product that can be vented or repurposed as raw material for other spacecraft processes. Figure 1 depicts a high-level Trash-to-Gas process that will be utilized on future long-duration missions.  Several products can be recovered from the trash reactor, including gas, water and solids. One of the solid by-products will be ash. This ash must be removed regularly, just like ash needs to be removed from a fireplace or grill. The ash removal step has not yet been designed for a space trash reactor.  In Figure 1, the two dotted lines express the potential to either remove the ash by-products directly from the reactor or immediately after the reactor but before the ‘Post-Processing & Recovery” stage. Modifications to the existing reactor design are sought that will allow ash to be regularly and safely removed in microgravity conditions.

This challenge has a total prize purse of $30,000 and will recognize the top three design concepts with first, second, and third prizes of $15,000, $10,000, and $5000 respectively.  

Background

Trash-to-Gas is the process of thermally degrading astronaut trash items into gaseous products to be reused as functional commodities or vented overboard for mass and volume reduction benefits. Combustion, using oxygen and heat to convert trash into mainly carbon dioxide and water, has been demonstrated in microgravity at a sub-scale level. At a full-scale level, such a system will be capable of reducing the mass and volume of trash onboard long-duration space habitats while producing usable commodities such as water, oxygen, carbon dioxide, methane, and hydrogen. The Trash-to-Gas process is a sustainable trash management solution currently being developed by NASA, recovering resources from various trash items that include metabolic, biological, inorganic, and logistical solids (plastics, clothing, foam packaging, etc.). The Trash-to-Gas process also minimizes the concerns with trash disposal in orbit and on planetary surfaces; gas venting does not produce orbital debris and decreases planetary protection risks on the surface (microbial growth on disposed trash items). Several Trash-to-Gas publications are referenced in the Resources tab for more detail.

The state of the art Trash-to-Gas system is the Orbital Syngas/Commodity Augmentation Reactor (OSCAR). OSCAR has flown on two suborbital flights via Blue Origin’s New Shepard launch vehicle, demonstrating key functionality in microgravity at the sub-scale level.  Now that trash combustion in microgravity has been successfully demonstrated, NASA aims at developing a full-scale system for use on future long-duration crewed missions. The removal of ash from a reactor is imperative to this next phase of development. As waste items will be continuously processed through the reactor on a daily basis, residual ash by-products will begin to accumulate in the reactor, leading to reactor fouling and eventual inoperability of the system. Thus, the goal of this challenge is to design an effective method of removing ash from a full-scale trash-to-gas reactor in microgravity and to safely store it for later use or disposal. The residual ash can be potentially repurposed into other useful mission needs or vented overboard to reduce mass for fuel cost savings. A basic CAD model of the current trash-to-gas reactor is shown in Figure 2.

If you’ve ever had to remove ash from a fireplace or a grill, you know that this can be a messy process.  Ash is not a very homogeneous material, and sudden movements can cause the finer particulates to linger in the air.  Now imagine you are doing this in a spacecraft in microgravity, where ash will not settle to the ground.  Not only is this messy and inconvenient, it is also potentially hazardous to both the crew and equipment.  Ideally, the ash removal system would be integrated seamlessly into the trash reactor or trash processing system, and would be automated - or require minimal human operation.

In the current concept of operations, the reactor will run in a batch-mode, with an average daily ash production of about 540gm. This residual solid, or ash, will also include inorganic compounds or metals (such as aluminum from the food packaging).   The ash will be fully contained within the reactor after each batch run.  You may assume the reactor will be intermittently 'baked out', or brought to temperatures >500°C, between ash removal steps to further clean the system.

For this effort, please assume while the majority of the ash is loosely packed, some may also be stuck to the reactor walls. If you have ideas for how to process ash to further reduce its volume, we are very interested in learning more about them.  More information about ash composition and consistency can be seen below. Ash composition will vary greatly due to the wide variety of input trash materials. The ash removal solution should be capable of removing ash with varying particle sizes, densities, and compositions. 

Table 1: Trash-to-Gas Ash Specifications

When the reactor is in operation, oxygen is injected during the combustion process to convert trash into gas as effectively as possible. The gas composition primarily includes oxygen, carbon dioxide, water vapor, and carbon monoxide. These gaseous products will vary in concentration due to changes in input trash composition and completeness of combustion. Trace amounts of larger hydrocarbons and other volatile organic compounds (VOCs) will also be produced. VOCs that are likely to be present within the product gas stream include acrolein, acetaldehyde, benzene, toluene, furan, and acetone, produced at ppm concentrations within the reactor volume.

Use the basic reactor model in Figure 2 as a starting point for your design.  Modifications to the reactor are encouraged to meet the needs of your ash removal solution but should not inhibit combustion operations.   Your design concept for ash removal may be integrated into the reactor itself or occur just prior to the post-processing and recovery steps (see Figure 1).  Your ash removal strategy must incorporate storage of removed ash for up to one day.  The stored ash will then be moved on a daily basis to a longer term storage area.  Disposal of stored ash is not part of this challenge.

The design concept must:

• Accommodate the critical interfaces to the combustion chamber, such as trash inlet, oxygen inlets, and gas outlet.
• Allow ash to be removed and stored on a daily basis, at minimum (assume an ash production of 540 gm/day and a density of 300-500 kg/m³).
• Prevent gaseous combustion products from entering the cabin air
• Allow for periodic opening of the combustion chamber for manual cleaning purposes of the interior surfaces.
• Be ready for operational deployment within 0-3 years
• Provide durable and safe ash storage, while adding minimal mass and volume to the ash itself.
• Remove no less than 90% of the ash by-products from the system each day of operation
• Be operable within the microgravity environment

Performance specifications of any proposed ash removal and collection system:

• Occupies a volume no larger than 700 in³, or roughly 12 L (which is about the size of an average shoe box).  Note that the volume can be occupied in any form factor.
• Adds no more than 10 kg to the trash-to-gas system.
• Consumes no more than 500W at peak power.
• Able to tolerate temperatures up to 1000°C for parts interfacing directly with the reactor.
• Accommodates up to 30 PSIG during reactor operation and cannot cause higher pressures within the reactor.
• Compatible with a 100% O₂ environment (at the listed pressures and temperatures)
• Generates noise levels below 50 decibels.  Brief or intermittent noise in the range of 50-80 decibels is acceptable.
• Minimizes the amount of ash that may get introduced into the cabin (ideally none). If ash particles are introduced into the cabin, particles can be no larger than 250 µm.

NASA is interested in effective solutions that are simple and effective at removing these ash constituents from the reactor on a regular, or at least daily basis. The microgravity environment poses several challenges to seemingly trivial processes on Earth.  Simple, elegant approaches that are automated and can be demonstrated in the near-term are preferred.  Also, minimization of crew time for reactor maintenance is crucial. Thus, solutions that both clean interior walls of the reactor while removing the loose ash from within would be most favorably reviewed. 

Possible approaches include technologies adapted for operation in a microgravity environment, such as:

• Cyclone filters
• Technologies that use a pressure differential to move ash
• Technologies that use forced gas to move ash
• Plasma processing

APPROACHES NOT OF INTEREST

• Any system dependent on gravity for transferring/handling ash
• Any system which cannot meet the energy consumption target
• Any system which depends on a large number of consumables (i.e. frequent filter exchange)

Prize

NASA will award the three most compelling design submissions first, second, and third prizes of $15,000, $10,000, and $5000.

In addition to the cash awards, winners will have an opportunity to present their design concepts to a panel of NASA scientists, engineers, and/or project managers.

It is NASA’s intent to prototype winning technologies and assess their relative merits within the next 1-3 years.

Timeline

Open to submissions March 3, 2022

Submission deadline May 12, 2022 @ 5pm ET

Judging May 12 - June 16, 2022

Winners Announced June 23, 2022

How do I win?

To advance through pre-screening and be eligible for an award, your proposal must, at minimum:

• Meaningfully complete all fields of the submission form.
• Thoughtfully address the submission form prompts.

Responsive solutions will:

• Clearly and concisely describe the design and its operation
• Provide a strong design rationale
• Include a high level design drawing

Competitive solutions will additionally:

• Include a detailed design file or CAD file
• Provide a bill of materials (BOM) for design implementation
• Provide high-level mass, power, and volume estimations for the ash removal and storage solution
• Use as many commercial-off-the-shelf (COTS) parts as possible and provide respective part numbers (ie McMaster-Carr part numbers)
• Address how the base reactor design will need to be modified to accommodate the ash removal capability
• Address ease of routine maintenance

Judging Criteria

Rules

Participation Eligibility:

The Prize is open to anyone age 18 or older participating as an individual or as a team. Individual competitors and teams may originate from any country, as long as United States federal sanctions do not prohibit participation (see: https://www.treasury.gov/resource-center/sanctions/Programs/Pages/Programs.aspx). If you are a NASA employee, a Government contractor, or employed by a Government Contractor, your participation in this challenge may be restricted.

Submissions must originate from either the U.S. or a designated country (see definition of designated country at https://www.acquisition.gov/far/part-25#FAR_25_003), OR have been substantially transformed in the US or designated country prior to prototype delivery pursuant to FAR 25.403(c). 

Submissions must be made in English. All challenge-related communication will be in English.

You are required to ensure that all releases or transfers of technical data to non-US persons comply with International Traffic in Arms Regulation (ITAR), 22 C.F.R. §§ 120.1 to 130.17.

No specific qualifications or expertise in the field of mechanical sensors is required. NASA encourages outside individuals and non-expert teams to compete and propose new solutions.

To be eligible to compete, you must comply with all the terms of the challenge as defined in the Challenge-Specific Agreement.

Intellectual Property

Innovators who are awarded a prize for their submission must agree to grant NASA a royalty-free, non-exclusive, irrevocable, worldwide license in all Intellectual Property demonstrated by the winning/awarded submissions. See the Challenge-Specific Agreement for complete details.

You may be required to complete an additional form to document this license if you are selected as a winner.

Registration and Submissions:

Submissions must be made online (only), via upload to the HeroX.com website, on or before May 12, 2022 at 5pm ET. No late submissions will be accepted.

Selection of Winners:

Based on the winning criteria, prizes will be awarded per the weighted Judging Criteria section above.

Judging Panel:

The determination of the winners will be made by HeroX based on evaluation by relevant NASA specialists.

Additional Information

• By participating in the challenge, each competitor agrees to submit only their original idea. Any indication of "copying" amongst competitors is grounds for disqualification.
• All applications will go through a process of due diligence; any application found to be misrepresentative, plagiarized, or sharing an idea that is not their own will be automatically disqualified.
• All ineligible applicants will be automatically removed from the competition with no recourse or reimbursement.
• No purchase or payment of any kind is necessary to enter or win the competition.
• Void wherever restricted or prohibited by law.