Albedo – what is that?

Agnes is working hard to complete her analysis of available solar panel power. In doing so she is taking the”albedo effect” into account. This refers to sunlight shining on the satellite that is not direct but scattered from the Earth’s atmosphere and especially clouds. The “reflectivity” of Earth in visible light – the “albedo” is about 25-30% depending on location and season. In our analysis we assume a uniform albedo of 30%. At every position of the satellite the light reflected from the whole illuminated part of Earth visible from the satellite has to be computed. Lots of number-crunching! But how much does it contribute to the available power on the satellite?

In the graph below you can see the orbit-average electrical power available to a hypothetical 3U Cubesat all covered in solar cells. The orbit is sun-synchronous at 640 km altitude with the local time of the descending node at 1030. The longitudinal axis of the satellite points along the orbit tangent (the attitude we call “Arrow”). The top curve is with all sunlight accounted for and the lower is for direct sunlight only. So albedo contributes some! (The value for each month is computed for the 21 st day of the month – to coincide with equinoxes and solstices).

End of tutorial!