ESA Document - Emits - ESA

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Figure 4-26: Total pressure vs. Oxygen in atmosphere
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 275 of 422
4.3.3.8.1 Impact of the selected atmosphere composition on safety considerations
To further investigate the favoured atmosphere composition, the impact on the material selection
was investigated. The following equation was used to determine if the material selection would
be influenced by the atmosphere composition:
23.
45 23.
45
% = = =
p(
atm)
0.
5
33.
16%
Due to the fact that the atmosphere contains 50% oxygen and the fire-safe limit is calculated as
33%, the material selection will be affected by the atmosphere composition. However,
comparing with the Apollo missions, the material selection will be less restricted and a suitable
solution could be possible without severely compromising the safety of the crew and equipment.
4.3.3.8.2 Impact on testing
The selected atmosphere would have a significant impact on the testing of the equipment. Tests
on the capsule as well as the systems inside it must be done at the considered atmosphere.
However, the vehicle is exposed to space vacuum and therefore needs thermal testing in a
suitable facility independent of the choice of internal pressure. Furthermore, an extrapolation of
the experiences gained with ISS and the shuttle could help to reduce the cost of testing. In both
vehicles the cabin pressure is lowered to 70 kPa prior to scheduled EVAs.
4.3.3.8.3 Impact on Martian surface habitat design
As stated earlier, no prebreathing time is necessary and the crew could enter the suits directly
from the habitat. However, due to the remoteness a DCS treatment chamber is necessary. The
design of a DCS treatment chamber is similar to the design of an airlock and the study suggests
that the DCS treatment chamber could serve as airlock as well fulfilling several functions: