ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 381 of 422
As regards the parking orbit, the attitude of the satellite is not constrained at all (use of a patch
antenna, no payload pointing requirement…). Consequently, solar panels can be body-mounted
and always assumed sun-pointed during this phase. This solution is selected because it offers:
• the lightest system
• the most reliable system (no deployment or SADM mechanisms)
On top of the spacecraft, a flat area of 17.5 m² is available and will be used for mounting the
cells (Figure 4-115).
Solar Cells
Location
4.5.4.1.2 Power storage
Figure 4-115: MAV solar cells location
The use of a secondary battery is the best-qualified and efficient way of storing the required
energy. Currently, Li-Ion cells offer the best performances (around 94% of energy round
efficiency, a specific energy of 100Wh/kg). As for the Habitation Module, a specific energy of
150Wh/kg is expected to be reached in 2015 and will be considered in this study.
When these batteries will be in use (from the launch from the Martian surface until the
rendezvous with the TV), the batteries will not have an important cycling effect degradation but
are already between 2 to 5 years old (depending on the LEO assembly time). Hence, a maximum
depth of discharge of 60% that should cover also the failure cases is selected.
4.5.4.1.3 Power generation
In this architecture, AsGa MJ cells are body-mounted on the top ring of the MEV because they
offer the best conversion efficiency.