ESA Document - Emits - ESA

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Figure 4-54: Solar irradiance on the Martian surface during one Martian year
Figure 4-55: Periods for which landing cannot be performed based on solar-cell design
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 307 of 422
For the designs without solar cells, this operations limitation simply disappears.
For example, the design based on primary fuel cells is not dependent the landing date nor the
latitude of the landing site.
4.3.5.5.2 Fuel storage for FC
Hydrogen and oxygen can be stored either in gaseous or in liquid form.
For the gaseous forms, high-pressure storage is necessary to limit the volume, especially for the
hydrogen that has a low density. Therefore, hydrogen is assumed to be stored at 700 bars.
The storage in a liquid state without losses due to boil-off can only be performed by cooling the
tanks to 20° K for H2 and 90° K for O2. Therefore, the corresponding power requested for this
thermal regulation has permanently to be supplied by the TV until the separation of the MEV.
On the Martian surface itself, with the tanks protected by the structure, the boil-off has been
estimated only around 1% per month. Consequently, the cooling of the tanks doesn’t need to be
continued during this phase.
4.3.5.5.3 PCDU
At this stage of definition, the power conditioning and distribution has not been analysed in
details. Indeed, this module is not as critical as the power generation and storage modules for all
aspects: mass, volume, technology, cost.