ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 382 of 422
Since, the top ring is protected during the surface operations until the launch phase by a fairing,
no power loss is expected from the dust deposit.
Moreover, for geometry rationales, the shape allocated for the solar cells will be difficult to
optimise. Therefore, a filling factor of 80% is a low but reasonable value.
An efficiency of 32% AM0(28°C) is assumed for 2015. As a comparison, 25% efficiency cells
will be body-mounted on Proba-2.
To cover the failure of a string on the solar panel, the solar panel is oversized by 5%.
4.5.4.1.4 Power conditioning and distribution
For the power conditioning, a regulated bus topology is assumed with a conservative efficiency
value of 90% for the BCR (Battery Charge Regulator) and for the BDR (Battery Discharge
Regulator).
This type of architecture fits the requirement of this mission. Others architectures (MPPT, S4R
regulated…) may have similar or better performances. Such a trade-off is too early to be studied:
The possible benefits of another architectures are relatively low in term of masses and volumes
of the power modules compared to the level of detail reached on that phase of the study.
4.5.4.2 Budgets
The sizing case for the power storage and power generation system is during the parking orbit
when:
• the solar flux is minimal
• the eclipse duration is maximal
• the equipments is operational during the eclipse
Solar Panels AsGa Improved
Size (m 2 ) 14.52
Mass (kg) 43.77
PCU
Mass (kg) 14.13
PDU
Mass (kg) 9.00
Battery Li-ion Improved 150 Wh
Capacity (Wh) 2239
Mass (kg) 16.17
Figure 4-116: MAV budget
82% of the area allocated for the solar cells is used.
During the rendezvous, the depth of discharge of the battery is estimated to 20.8%.
The total mass of the power subsystem (excluding the harness) is:
• 83.1 kg without margin on equipment level
• 91.4 kg with margin on equipment level