Second Design Cycle

This chapter is dedicated to a further investigation of the subsystems. In chapter 7.3, the optimal technologies and processes are assessed. Now, the optimal architecture of the subsystem has to be found, based on the result of the first design cycle. For this, either the top-ranked technology or several ones are used for a specific function. All functions and their assigned assemblies build the subsystem. The different possible options are compared by using the ESM with and without crew time. The results of this design step are the foundation for the detailed Final design in chapter 10.

8.1 Second Design Cycle for Atmosphere Control System

Several considerations outlined below lead to the conclusion, that a high-pressure storage system for repressuriation and leakage should be used instead of a cryogenic storage system.

No different technologies for comparable functions should be used to have more commonality and synergetic effects. For N2 repressurisation and leakage as well as for an O2 storage system, high-pressure is the superior technology.

The multi-criteria-method like all sensitivity analysis prefers a high-pressure system.

The mass of a cryogenic system is much higher and the volume savings could not be taken into account, since the tanks are outside the pressurized compartment.

The break-even point for ESM on the O2 repressurisation and leakage system is after 114 days as can be seen in Figure 8-1. This is shorter than the mean mission time of 132 days.

Figure 8-1: ESM break-even point between cryogenic and high-pressure system for repressurisation and leakage

790 800 810 820 830 840 850

88 113 137 162 186 211

[kg]

[days]

Cryogenic High-pressure

8.2 Second Design Cycle for Thermal and Humidity Control

The purpose of this design cycle is to measure, if the CAMRAS is worthwhile to include, since the CCAA is already needed to remove heat, but the WS could be removed. This unit has a mass of 11.93 kg [63, p. 160], which is around 12.41 % of the mass of the CCAA, while the volume is around 1.46 % of the whole assembly. The average power of the WS is 44 W [38, p. 73]. A breakdown of the different considered assemblies for the function with the measured ESM for Case4 is listed in TAB. As can be seen, CAMRAS has a bigger impact on the ESM as the removal of WS from the CCAA. The ranking did not change for the other cases. Hence, only the CCAA and IMV will be used in the final system (see 10.2).

Table 8-1: ESM analysis of the thermal and humidity control subsystem in the second design cycle

8.3 Second Design Cycle for Atmosphere Revitalization

Before a final conclusion about the optimum AR architecture can be made, several architectures must be compared. The trade study in chapter 7 selected the best alternatives for every function. Overall, 14 different options are compared based on ESM as can be seen in Table 8-2. There are no differences on the ranking between the shown ESM and a non-crew time ESM. Not shown in the table above are function for which the same technology is used for every option. These are Multi Bed Trace Contaminant Control (TCCS) for requirement 4.2.3.b, BFE for the requirements Control Airborne Particulates (4.2.3.d) and Control Microbes (4.2.3.f), and major constituent analyzer (MCA) for requirement Detect Hazardous Atmosphere (4.3.2.a). The calculations in Table 8-2below includes considerations like an oxygen and hydrogen storage for option 2. As can be seen, the combination of SAWD, SFWE, and Sabatier has the least equivalent weight, followed by the similar configuration with EDC instead of SAWD. The ISS system (option 7) is only ranked fifth, while the best storage system (option 1) uses the CAMRAS and has an over 5 times higher ESM. For the final design, the best ranked option (14) is used.

Table 8-2: ESM analysis of the atmosphere revitalization subsystem in the second design cycle

Option Remove Gaseous Atmospheric Contaminants (4.2.3.b)

(Re)generate Oxygen (4.4.3.a)

Process Gaseous Wastes (4.4.3.b)

ESM Rank

1 CAMRAS none none 33,521 11

2 EDC none none 54,667 14

3 EDC SFWE none 30,298 7

4 EDC SFWE Sabatier 6,311 2

5 4BMS none none 36,267 13

6 4BMS SPWE none 32,021 10

7 4BMS SPWE Sabatier 8,064 5

8 4BMS SFWE none 31,579 9

9 4BMS SFWE Sabatier 7,622 4

10 SAWD none none 34,853 12

11 SAWD SPWE none 30,607 8

12 SAWD SPWE Sabatier 6,620 3

13 SAWD SFWE none 30,164 6

14 SAWD SFWE Sabatier 6,177 1

After the selection of the final system, additional trade-offs where made to make a decent decision on the final system architecture.

8.3.1 System Trade

To minimize the necessary power for the AR system, several options between the SFWE and the Sabatier are analyzed. Overall 11 different operational options, given in Table 8-3, are considered.

Table 8-3: Considered operational options for oxygen generation and CO2

reduction

Option SAWD Sabatier

1 metabolic demand H2 demand 2 metabolic demand constant 3 metabolic power safe H2 demand 4 metabolic power safe constant 5 reduction demand CO2 demand 6 reduction demand (constant) Constant 7 reduction power safe CO2 demand 8 reduction power safe Constant

9 fuel cell H2 demand

10 fuel cell Constant

11 metabolic constant Constant

Besides this operational consideration, 4 different system architectures where considered:

1) One central TCCS and CO2 removal assembly on Deck 4 and oxygen generation for the minimum metabolic need with altered working time (Option 3).

2) CBA´s in each level and one big COA & SBA and the CO2 removal assembly on deck 4, while the SFWE is oversized to produce enough H2 for full CO2 reduction through the Sabatier maximum (Option 6). SAWD and Sabatier are also on deck 4.

3) TCCS´s in each Level before CCAA and SAWD on deck 4, while the SFWE produces minimum required O2 for metabolic needs which means the Sabatier is also sized to a minimum. Both have altered working times (Option3) on deck 4.

4) All AR equipment is decentralized and housed in every deck.

The final system with the best compromise between mass, volume, and power requirements are system architecture 1 with a total ESM of 24,188 kg. For comparison, the worst-case system (4) has a ESM of 34,986 kg. The result of the ESM analyses is shown in Figure 8-2. The power demand of the chosen operational option 3 is given in Figure 8-3.

Figure 8-2: Final system architecture trade

Figure 8-3: Total power demand of AR subsystem with operational option 3

8.4 Second Design Cycle for Water Reclamation Management

The considered water recycling architectures (WRA) in Table 6-36 are evaluated in this section. First, the needed water and the corresponding tanks are assessed and then an ESM analysis is performed based on selected technologies for the functions of the WRM subsystem.

8.4.1 Water Tank Assessment

The required water tanks for the different water reclamation architectures (see Table 6-36) are depicted in the following sections.

8.476,36 8.600,87 8.803,54 8.907,87 15.711,60

26.385,23

16.195,20 18.024,20

0 5.000 10.000 15.000 20.000 25.000 30.000 35.000 40.000

system1 system2 system3 system4

ESM [kg]