Team:Calgary/Design

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Applied Design

Considering alternative applications of human feces on Mars

The current solid human waste management system on the international space station includes dehydration and storage. Meaning that the system attempts to recover all the moisture from feces and afterwards stores the remaining solid material in the vacuum bags which are in turn stored and shipped back to earth (where the solids are burned). It is essential to recover as much liquid from the feces as possible, as water is a precious resource in space and should ideally be fully recycled.

There are a couple of the application for the feces use on Mars, however no system for complete recycling of water and nutrients from the waste had been proposed yet. Pascal Lee and Robert Thrisk have both mentioned that one major proposed application for human feces on Mars is Ionic Radiation Shielding. Feces are suitable since they contain a lot of hydrogen atoms and hence create a neutron shield. Keeping these comments in mind we have proposed to use torrefaction (mild pyrolysis) as a way to process the solid remains from the solid-liquid separation step. The advantages of employing torrefaction as the by-product treatment process is the production of chemically stable char, which does not support biological activity and can be used in radiation shielding, as a building material, as a substrate for food production and and as a carbon,hydrogen,oxygen storage. Additionally torrefaction allows the production of pyrolytic water meaning greater water recovery, which is essential to close the water system loop.

This means that our system can exist without compromising the existing feces applications.

Developing the process for space travel

Shooting for the development of a process applicable to space travel we decided to contact professionals in the industry to get their advice and guidance. Chris Hadfield (Canadian Astronaut) and Mattew Bamsey (runner up to become a Canadian astronaut and an engineer by profession) have both highlighted the importance of stating our assumptions regarding the environment, capacity, human waste generation rates, mission duration and power availability.

In order to gain a better understanding of space travel, mission parameters and the human body functioning the engineers on the team examined the Life Support Systems Baseline Values and Assumptions Document (BVAD) which was recommended to us by Mattew Bamsey. The document was developed by the National Aeronautics and Space Administration (NASA) in order to provide a set of guidelines to be used by researchers across the USA and thus allowing the proposed systems to be easily comparable and ensure that they are capable of withstanding the same duration, loads and conditions.

In order to develop a solution for Martian colonies application it was crucial to take into account the comments from the professionals.

• Analysis of the existing waste management processes is important to prove that the proposed system doesn’t compensate a better solution
• Considering the volumetric, power and weight footprint
• Creating an easily accessible and maintainable system
• Automatization

Assumptions developed by the engineering team:

Crew-size: The maximum (6 people) crew size from the BVAD is used for the calculations.

Duration: Our system is developed for the Nominal Surface habitat duration from the BVAD: 600 days

Table1: Martian missions duration. Retrieved from BVAD, 2015. Feces production: The maximum value for the feces mass (150g/CM-d) and volume (150ml/CM-d) is used to design system parameters and load capacity, while the nominal value (123g/CM-d and 123ml/CM-d) is used to make predictions for water recovery, VFA production and PHB production. Energy Availability: Based on BVAD the current solar technologies can provide between 28 and 100kW electric. The nuclear solutions have the power output ranging from 16 to 550kW electric. Pascal Lee argued that it would not be long, before NASA would choose to switch to the nuclear power source on Mars (considering that it would be placed away from the habitat unit), meaning that more electrical power would be available with the same. To play it safe we can assume 100kW electric being available from one solar panel. Table 2: Average feces production per Crewmember per day. Retrieved from BVAD.

Process Components Selection Criteria

The proposed PHB production system can not be imagined as a single component system and hence it was important to create a way of comparing different proposed process and evaluate the feasibility of implementing them in space and on Mars. To do so the team employed the Equivalent System Mass (ESM) Guidelines (Ames Research Center, 2003).

ESM is the tool often used by the NASA agency to evaluate different advanced life support systems, or its individual components. It allows to convert parameters like power, cooling requirements, volume and crew-time commitment to a single unit of mass (kg). This is achieved by multiplying each requirement/parameter by the equivalency factor. The aim of the analysis is to provide each system in consideration with an ESM number (kg) and then choose the system with a lower value, since it would mean more economical and feasible solution. ESM formula used by our team is a simplification of an original formula found in the ESM Guidelines document published by NASA:

It was chosen to remove the crew-time parameter from the equation due to the difficulty in estimation and lack of data, however to account for the missing component of the equation the maintenance requirements for all systems were examined outside of the equation.

The equivalency factors were recovered from the Life Support Baseline Values and Assumptions document (M. Anderson, M. Ewert, J. Keener, S. Wagner, 2015) table 3.4: Mars Mission Infrastructure “Costs” assuming Surface time parameters:

According to the Baseline Values and Assumptions for Advanced life support systems document the nominal long-term duration of Martian missions is 600 days, and therefore the ESM calculations would be performed with this duration in mind.

The other parameters which were considered when choosing a system component were ease of maintenance, spares and consumables requirements, the by-product stability and usability. As such the process was more favorable if it could be fully automated and if it would produce stable by-products which could be used on Mars.

Feasibility of system implementation in space

Power

Another important assumption/consideration suggested by both: Pascal Lee and Matthew Bamsey was the power availability of Mars. It was noted that the power requirement of our system should be attainable using the current power production technology developed for Mars, as well it should be no larger than the power requirements of other systems currently used on the ISS and/or suggested for the Martian application.

Based on BVAD [1] current solar technologies can provide 28 to 100kW electric. The nuclear solutions have the power output ranging from 16 to 550kW electric. To play it safe we can assume 100kW electric being available from one solar panel. However, Pascal Lee had assured the team that assuming the availability of nuclear power generator on Mars is totally valid, since their high energy production would eventually be employed on Mars.

The following table allows easy comparison of the power requirement of the system to the currently employed processes on Mars. It can be noted for example that the total power Environmental Control and Life Support System (ECLSS) is 5.31kW assuming constant operation, while our “safe” estimation for the system power requirements is around 2.8kW with only 0.566kW of power being used continuously.

Total system ESM Estimations

(1) Calculation of mass based on the ____ wall thickness, 10L volume of liquid and stainless steel material (?). The mass also includes a 20kg pump. (2) The system is assumed to be shielded (placed inside the habitat) thus removing the need for the bioreactor heating to the 22 degrees Celsius. The power of pump retrieved from ____ (3) (6) Volume of the tank estimated based on the maximum feces production per crew member per day plus a safety parameter of ____ (4) Calculation of mass based on the ____ wall thickness, 10L volume of liquid and stainless-steel material (?). (5) (6) (7) Mass = mass of table top centrifuge (5kg) + mass of the pump (30kg) (8) Russel Finex brochure on the centrifugal separators (9) Russel Finex centrifugal separator brochure (10) Soulre Xcellerex bioreactor brochure. The total mass of the whole system is 100kg (including hardware, scales, cabels ad vessel) yet the instruction say that vessel can be lifted by hands, while the laptop needs to be mechanically placed (much heavier) --> the mass of the vessel is assumed to be 15 kg. (11) 100V * 3.8A = 0.38kW. Soulre Xcellerex stirred tank bioreactor brochure. The power includes the analytical equipment power. https://www.gelifesciences.com/gehcls_images/GELS/Related%20Content/Files/1440509368472/litdoc29117039_20161016015647.pdf (12)Xcellerex bioreactor brochure https://www.gelifesciences.com/gehcls_images/GELS/Related%20Content/Files/1392320581787/litdoc29092927_20161015134411.pdf (13) (14), (15) Eaton Self-cleaning filter brochure:

The following table summarizes different ISS support systems and their ESM parameters and values. It can be noted that the estimated system ESM compares well to the other available systems on the ISS. For example the total ESM of the water Processor (WP) is 5,324kg. The feces collection and treatment would be a sub-system of the process thus meaning that it would only take a small fraction of the ESM value. Hence the estimated value of 425kg seems realistic and feasible for the space application.