ESA Document - Emits - ESA
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s 3.3.2.2 Assumptions and trade-offs HMM Assessment Study Report: CDF-20(A) February 2004 page 156 of 422 The data shown in this table refer to an open loop control. It suggests a mass of consumables of more than 47 tonnes. The life support system would have an approximate power requirement of 6.3kW and a volume of about 136m 3 . Taking into account that consumables need additional hardware for storage and use, as well as the need to treat and store the metabolic products, the use of an open loop system seems prohibitive. As a reference, the main parameters for an open loop life support system are shown in Table 3-13: CONSUMABLES TO BE LAUNCHED (kg) OXYGEN 4466.9 NITROGEN 91.0 POTABLE WATER 16457.9 HYGIENE WATER 23160.0 DRY FOOD 3899.4 PACKAGING 1392.3 INORGANIC MATERIAL EXCLUDING PACKAGING 3177.9 TOTAL 52645.4 WASTE PRODUCTION DURING MISSION (kg) WASTE GASES 6129.2 WASTE WATER 39535.8 SOLID ORGANIC WASTE 1006.2 SOLID INORGANIC WASTE EXCLUDING PACKAGING 3177.9 PACKAGING 1392.3 TOTAL 51241.4 ROUGH ESTIMATE ECLSS MASS (kg) TOTAL 31162.0 Table 3-13: Open Loop Life Support System Mass, Consumables and Waste production Generally, two classes of regenerative life support systems are considered: • Physico-chemical regeneration • Bio-regenerative systems These systems may be used to lower the cost for a human mission to Mars by reducing the mass of the consumables and perhaps life support system hardware. Some regenerative systems have been successfully flown on MIR and the International Space Station. The result of any trade-off would have to be measured on the criteria that have been selected. The criteria of equivalent system mass does not seem appropriate for such missions. The lack of incorporating the reliability of the system as well as the dynamic efficiency might deliver a less optimal system. In this study the sole criteria was to reduce system mass, and providing a sufficient level of redundancy. Less critical items were not increased in their fault tolerance whereas for critical systems, which would cause a catastrophic failure, a two-fault tolerant system was implemented in the model. Furthermore, this study projects about 20 years into the future. This causes a significant uncertainty in the performance and parameters of the subsystems. Therefore, if possible, the parameters have been selected using the best guess approach or data obtained on similar systems with lower readiness level. Some systems have not been optimised for spaceflight applications and some mass savings could be expected in the future. Each item

s HMM Assessment Study Report: CDF-20(A) February 2004 page 157 of 422 considered in this study has been selected from a database created on purpose. This database contains a large number of units relating to life support systems with its known parameters. However, some units have been added as ‘Generic’ or ‘ALS’, which indicates that these systems are generic good guesses or advanced life support items that have not been space-qualified yet. After arriving at the design of the life support system, the appropriate number of units has been selected and their duty cycle has been adjusted so that their performance matches the requirements on the life support system. 3.3.2.2.1 Hygiene water During the course of this study it has been shown that the hygiene water consumption has a significant impact on the overall system mass. The study suggests assuming a daily hygiene water provision of 4 l/crew/day. This would account for: • Flushing water (0.3 l/ day) • Dish washing (2.4 l/day), amounting to 12.0 l /day for such purpose • Personal hygiene water (1.6 l /day), The crew is assumed to take showers once a month, which makes the available water for this purpose around 30 litres and the daily allowance about 0.6 l/day • Losses (0.1 l/day) No water has been considered for washing cloths as this is assumed to be performed chemically without using water. 3.3.2.2.2 Drinking water The water release by the crew has been calculated using standard correlations based on the energy expenditure. A literature review revealed that the water intake by the crew is to some extent equal to the water release by the crew. Therefore, the amount of water intake has been calculated using the numbers for the sensible and insensible water quantities released by the crew. The advantage of this method is that the potable water estimate is based on the energy expenditure, similar to all other crew metabolic needs. 3.3.2.2.3 Cabin atmosphere The cabin atmosphere has been calculated as follows: Total Cabin Pressure: 101.3 kPa Partial Pressure Oxygen: 21.3 kPa Partial Pressure Nitrogen: 80.0 kPa Partial Pressure Carbon Dioxide:

s<br />

HMM<br />

Assessment Study<br />

Report: CDF-20(A)<br />

February 2004<br />

page 157 of 422<br />

considered in this study has been selected from a database created on purpose. This database<br />

contains a large number of units relating to life support systems with its known parameters.<br />

However, some units have been added as ‘Generic’ or ‘ALS’, which indicates that these systems<br />

are generic good guesses or advanced life support items that have not been space-qualified yet.<br />

After arriving at the design of the life support system, the appropriate number of units has been<br />

selected and their duty cycle has been adjusted so that their performance matches the<br />

requirements on the life support system.<br />

3.3.2.2.1 Hygiene water<br />

During the course of this study it has been shown that the hygiene water consumption has a<br />

significant impact on the overall system mass. The study suggests assuming a daily hygiene<br />

water provision of 4 l/crew/day. This would account for:<br />

• Flushing water (0.3 l/ day)<br />

• Dish washing (2.4 l/day), amounting to 12.0 l /day for such purpose<br />

• Personal hygiene water (1.6 l /day), The crew is assumed to take showers once a<br />

month, which makes the available water for this purpose around 30 litres and the<br />

daily allowance about 0.6 l/day<br />

• Losses (0.1 l/day)<br />

No water has been considered for washing cloths as this is assumed to be performed chemically<br />

without using water.<br />

3.3.2.2.2 Drinking water<br />

The water release by the crew has been calculated using standard correlations based on the<br />

energy expenditure. A literature review revealed that the water intake by the crew is to some<br />

extent equal to the water release by the crew. Therefore, the amount of water intake has been<br />

calculated using the numbers for the sensible and insensible water quantities released by the<br />

crew. The advantage of this method is that the potable water estimate is based on the energy<br />

expenditure, similar to all other crew metabolic needs.<br />

3.3.2.2.3 Cabin atmosphere<br />

The cabin atmosphere has been calculated as follows:<br />

Total Cabin Pressure: 101.3 kPa<br />

Partial Pressure Oxygen: 21.3 kPa<br />

Partial Pressure Nitrogen: 80.0 kPa<br />

Partial Pressure Carbon Dioxide:

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