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Is there any history or merit to using a PIR (Pyroelectric ("Passive") InfraRed Sensor) as a sun sensor for determining the attitude or position of a Satellite?

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Is there any history or merit to using a PIR (Pyroelectric ("Passive") InfraRed Sensor) as a sun sensor for determining the attitude or position of a Satellite?

I can address the "merit" part to some extent. PIR detectors are more complicated than a simple photodiode for a couple of reasons. They usually are thermopiles and require a "hot" and "cold" side, and sometimes two of them are connected back-to-back to work in differential mode. Either way you need a sensitive amplifier to pick up the small voltage difference at very low current, and changes in the spacecraft's ambient temperature can cause drift problems.

For the Sun you would use a small, normal, simple photodiode because the Sun's output peaks in the visible part of the spectrum, not thermal IR, so you'll get a much stronger and drift-free signal. Because the output will be stable you may even be able to interpret the current as a measure of incident angle (cosine theta).

But for an Earth sensor a PIR *might be helpful. In visible light the Earth will have quite a variable fraction of sunlit to dark area, and you'd have to interpret the day and night geometry carefully. But using a solar-blind thermal IR sensor, you could have a more reliable detection of the limb of the Earth's atmosphere, day or night.

I don't know if thermal IR has in fact been used as an Earth limb sensor or not, but there's certainly more potential for that than for a Sun sensor where visible light is so much easier.

update: @Puffin points out that "it has - look up IRES "Infra-Red Earth Sensor". Several designs by different manufacturers" https://artes.esa.int/projects/coarse-infrared-earth-sensor-ires-c

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  • $\begingroup$ PIR sensors operated in differential mode need a moving IR source for detection of a movement. They should not react on a static non moving IR source. Not very useful for a sun sensor. $\endgroup$ – Uwe Jun 24 '19 at 15:19
  • $\begingroup$ @Uwe there are different varieties and designs of PIR sensors, the ones used in motion detectors are just one currently popular application. $\endgroup$ – uhoh Jun 24 '19 at 15:22
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    $\begingroup$ @uhoh "I don't know if thermal IR has in fact been used as an Earth limb sensor" - it has - look up IRES "Infra-Red Earth Sensor". Several designs by different manufacturers artes.esa.int/projects/coarse-infrared-earth-sensor-ires-c $\endgroup$ – Puffin Nov 21 '19 at 18:30
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    $\begingroup$ @Puffin thanks! duly noted and linked. $\endgroup$ – uhoh Nov 22 '19 at 0:22

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