European Solar Polar Orbiter Mission

Power

The power sub-system analysis suggests no significant technology issues that we cannot reasonably except to be solved within other currently active studies.Error: Reference source not found^{, Error: Reference source not found} We note however that design techniques, such as advanced computer aided design allow the reduction of harness mass through better design methodologies, such mass savings are significant for enhancing solar sailing missions. The power system is supplemented by Lithium Ion batteries, which are designed to carry the power load during the launch phase and to absorb peak power loads during other mission phases, for example during the transfer trajectory when sail pitch may limit array performance. The nominal power loads for solar array and battery sizing are defined in Table 4, where we see that the power load is split into three main categories. The design power load is defined as the nominal power load (Table 4) plus a 20 % system level margin. Solar array design is based on Spectrolab 26.8 % Improved Triple Junction (ITJ) solar cells.¹⁰ In order to maintain the solar array within thermal bounds it is found that at end-of-life (EOL) the array must be pitched at over 63 deg from the Sun-line. However, the use of Carbon – Carbon substrates, as in BepiColombo, may also prove beneficial. The total array surface area is found to be 1.03 m², which is divided into two wings. The small surface area required allows for simple planar arrays to be envisaged, without the need for them to unfold following spacecraft launch. We note that despite the increased solar flux at 0.48 AU the solar array design point was found to be at EOL due to array degradation during the mission, the significant thermal losses encountered at 0.48 AU and that the power load is highest during this mission phase. The cell efficiency at EOL is 19 %.
Table 4 Power Budget

System	Launch Power, Design Point 1 AU		Transfer Power, Design Point 0.48 AU		Science Power, Design Point 0.48 AU
Science Instruments	0.0	W	0.0	W	24.7	W
AOCS	35.2	W	17.4	W	47.8	W
TT&C	0.0	W	73.9	W	73.9	W
OBDH	7.9	W	17.4	W	26.1	W
Thermal & Radiation	83.1	W	83.6	W	83.6	W
Power	35.4	W	27.0	W	27.3	W
Mechanisms & Structure	0.0	W	4.2	W	9.5	W
Solar Sail	0.0	W	10.9	W	0.0	W
Nominal Power Load	161.6	W	234.4	W	292.9	W