Required hygiene water mass
7 Trade Study
7.3 Application and Results
7.3.1 ESM-Results
The approach described in 7.1 is applied to the different functions of the subsystems.
Below are the results of this analysis.
7.3.1.1 ESM Atmosphere Control and Supply
Hydrogen peroxide is selected out due the reasons mentioned in 6.1.4. The remaining 3 technologies for oxygen storage are stated in Table 7-3. As can be seen, the cryogenic storage is superior for short durations, while the high-pressure system is better for longer mission times. This is because the tank mass of the cryogenic system increases more than the high-pressure tank and the additional mass for leakage is just over the break-even point. The ESM values in Table 7-3 are for the Evolved-SpaceHab design, while the used design has no influence on the ranking. The oxygen candles are by far the worst system and should not be used. The break-even point between the cryogenic and the high-pressure system are outlined in 8.1.
Table 7-3: ESM ranking of oxygen storages for repressurisation and leakage
Case1 Case4
Technology ESM [kg] Rank ESM [kg] Rank
Cryogenic 808 1 843 2
High-pressure 814 2 822 1
LiClO4 1,615 3 1,615 3
For the storage system, Table 7-4 shows, that cryogenic and high-pressure systems have comparable ESM values. While the values for mass, volume, power, and cooling stay the same, the ESM volume factor changes. This results in a ranking change between the cryogenic and the high-pressure system, since the cryogenic one needs far less volume, the stricter ESM volume factor for the SpaceHab prefers the cryogenic system. The oxygen candle system is not considered for a storage system.
Table 7-4: ESM ranking for oxygen storage system
Case1 Case4
Technology ESM [kg] Rank ESM [kg] Rank
Cryogenic 1,696 1 31,561 2
High-pressure 1,711 2 31,116 1
For nitrogen repressurization and leakage, a different behavior can be seen in Table 7-5 where cryogenic storage is always superior. Much bigger tanks are needed for N2
repressurisation, because 76 % in the air are N2 and the fact that N2 has a lower density at high-pressure cryogenic temperatures than O2. Therefore, the difference for leakage is lower than for oxygen repressurization and no ranking switch occurs. Hydrazine is selected out due to safety concerns.
Table 7-5: ESM ranking of nitrogen storages for repressurisation and leakage
Case1 Case4
Technology ESM [kg] Rank ESM [kg] Rank
Cryogenic 1,841 1 2,806 1
High-pressure 2,078 2 3,011 2 7.3.1.2 ESM Temperature and Humidity Control
Only the CAMRAS and CCAA are considered for humidity removal of a storage system, since the other technologies have a too low TRL. This step is used in advance of the ESM analysis, as explained in 7.1. For a recycling system, only the CCAA is feasible as explained in 6.2.1. As can be seen in Table 7-6, the CAMRAS is superior in all cases (only Case4 is shown for clarity).
Table 7-6: ESM ranking of humidity removal assemblies for storage system
Technology ESM [kg] Rank
CAMRAS 650 1
CCAA 951 2
7.3.1.3 ESM Atmosphere Revitalization
The atmosphere revitalization (AR) analysis is separated into CO2 removal, CO2
reduction, and finally O2 generation.
Several technologies were selected out due their low TRL of under 5. These are 2BMS, SAWD, and APC. This step is used in advance of the ESM analysis, as explained in chapter 7.1. Additional, LiOH, METOX, sodasorb, as well superoxide is not considered since they all have an inferior performance. The CAMRAS system is only considered for a storage system, since it vents high amounts of water vapor. As can be seen in Table 7-7, the SAWD process has the lowest ESM, closed followed by the EDC.
Table 7-7: ESM ranking of CO2 removal technologies for recycling system
Technology ESM [kg]
Rank
EDC 2,122 2
4BMS 3,403 3
SAWD 1,989 1
The ranking for a storage system is different. The CAMRAS system is superior, since it has a low power consumption and by far the lowest mass. Following are the SAWD, which uses the same process as CAMRAS. The EDC has a considerable higher ESM as in the recycling system analysis, since no production of oxygen or hydrogen are considered for a storage system and therefore tanks must be used for this technology.
Table 7-8: ESM ranking of CO2 removal technologies for storage system
Technology ESM [kg]
Rank
CAMRAS 657 1
EDC 28,038 4
4BMS 3,403 3
SAWD 1,989 2
For the carbon dioxide reduction analysis, only the Sabatier and the Bosch process are further considered, since the ACRS has to too low TRL. As can be seen in Table 7-9, the Sabatier requires over 4 times less resources as the Bosch.
Table 7-9: ESM ranking of CO2 reduction technologies
Technology ESM [kg]
Rank
Bosch 3,770 2
Sabatier 894 1
Only electrolysis processes are considered for oxygen generation. CO2 electrolysis, WVE, SEOS, and HPE are selected out, since they have a TRL of lower than 5. The remaining two technologies can be seen in Table 7-10, where SFWE is best ranked.
Table 7-10: ESM ranking of oxygen generation technologies
Technology ESM [kg]
Rank
SPWE 1,858 2
SFWE 1,546 1
7.3.1.4 ESM Water Recovery and Management
Electrodialysis is selected out due to a TRL of 4. This step is used in advance of the ESM analysis, as explained in 7.1. As can be seen in Table 7-11, RO and VCD are ranked first and second respectively. The analysis of the different trade cases and water recycling architectures have shown, that there is no difference in the ranking of the considered alternatives with variation in duration and crew size and not even with the processed amount of waste water. Therefore, RO should be used for humidity condensate and hygiene waste water recycling.
Table 7-11: ESM ranking of humidity condensate recycling processes
Process ESM [kg]
Rank
AES 785 4
MF 843 5
RO 279 1
TIMES 549 3
VCD 443 2
For the combination of all waste waters, EDI and VAPCAR processes are selected out due their low TRL. MF and RO are no longer included because they are only considered for relatively clean waste water, as explained in chapters 6.4.2 and 6.4.3 respectively. The remaining ones are ranked in Table 7-12. VCD is best for all considered trade cases and should therefore be used for waste water recycling.
Table 7-12: ESM ranking of waste water recycling processes
Process ESM [kg]
Rank
AES 1,821 3
TIMES 1,332 2
VCD 1,086 1