Hello Ted / Mark.
Ted wrote:Typical whole orbit data for the panel and chassis temperatures are as follows:
Black panel Max 25 Min -15
Silver panel Max 29 Min -12
Black chassis Max 25 Min -12
Silver chassis Max 25 Min -12
The black panel should absorb and radiate heat faster than the silver panel, if these changes are only due to radiation. The temperature of the black panel should then rise and fall more quickly than that of the silver panel.
Similarly, the silver panel should reflect heat more effectively than the black panel. Therefore the temperature of the silver panel should rise and fall more slowly than that of the black panel, assuming temperature changes are only due to radiation
Looking at your examples above, hopefully the black and silver chassis sensors are essentially the same temperature because the chassis sections are physically connected. This demonstrates that conduction is the dominant form of energy transfer. i.e. the difference between the sections ability to absorb and emit heat energy by radiation is not seen in the data because the temperatures are equalised by conduction.
Re the black and Chrome plated samples. I would be interested in your views on this. My personal view is:
1) The black panel reaches a lower temperature in eclipse because it radiates energy at a higher rate than the 'silver' panel.
2) The silver panel reaches a higher temperature in sunlight because it does not radiate energy as efficiently as the black panel.
Okay, No 2 disagrees with Teds comments but it's worth a discussion. My reason for saying this is that while the black sample absorbs a lot of Infra red in sunlight, it also emits it very well (see answer 1). The final temperature will depend on the balance between absorption and emission. Black does both very well and so in sunlight will not be subject to temperature extremes.
The silver panel does not absorb as much energy as the black sample, but it is an extremely poor emitter. On balance more energy is retained in sunlight and so its temperature exceeds the temp of the black sample.
Ground based tests can show this. Take identical Aluminium sheets. Spay one matt black and polish the other. If you place them on an insulated surface facing the sun, (preferably on a calm hot cloud free day) after 20 minutes you will find the black sheet is hot, but the silver sheet is even hotter...as it does not radiate much of the energy it has absorbed. - It needs to be a calm day as airflow across the surfaces ruin the results.
Thanks for your interest.
Incidentally, have you noticed how the solar panel that supports the MSE samples drops to a lower temperature in eclipse than the black MSE sample. - I've puzzled over this one. The only theory I have is that the solar panel is fabricated from a metal substrate and not the usual FR4 PCB material. (To protect the solar cells and add some radiation protection to FUNcube's electronics) The solar panels have a black finish. My contention is that the panel drops to a lower temp in eclipse because it has a greater surface area to mass ratio than the Black MSE sample. - Reasonable??