ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 61 of 422
All up Split case 1 Split case 2
Crew of 3 Crew of 3 + MEV Crew MEV cargo
Mass to LEO (tonne) 1336 837 984 1189 236
Total (tonne) 1336 1821 1425
Table 2-18: Masses for all-up and split scenarios
Split scenario 1:
The overall mass is larger than in the all-up case, and both composites will have to be assembled
in orbit at the same time, introducing more complexity in operations.
Split scenario 2:
The mass of the THM composite would be lower than in the split case but the overall mass in
LEO is higher (more launches). The only advantage would be the reduction in assembly time of
the THM composite which will reduce boil-off losses, but the overall assembly time will be
increased.
For the mission case the all-up scenario has been selected, as it looks the most simple and
effective.
2.7.6.9 Artificial gravity / centrifuge
The overall mission duration is around 1000 days, therefore some means will have to be
provided to reduce the effects of such a long exposure to microgravity.
To provide these countermeasures, artificial gravity can be generated by two methods: either
spinning the whole spacecraft or providing it with a centrifuge for crew exercise.
The spinning spacecraft option was found to lead to a very complex configuration with limited
benefits and was therefore discarded for the mission case.
2.7.6.10 Crew number
The number of crew is one of the mission drivers, but it has not been traded off during the
present study. A crew of six people has been adopted since the beginning of the mission
following recommendations from the customer and due to similarities with other, comparable
studies.
2.7.6.11 Summary
Table 3-20 lists the concluded trade-offs and options: