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From the NASA TIROS page on TIROS-1:

The craft was spin-stabilized and space-oriented (not Earth-oriented). Therefore, the cameras were only operated while they were pointing at the Earth when that portion of the Earth was in sunlight.

What does it mean that the craft was space-oriented (not Earth-oriented)?

The US Navy describes Earth orientation, but this appears to describe an axis definition and the orientation of planet Earth, whereas the NASA TIROS page describes something related to the actual spacecraft orientation.

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What they mean in this context is that the orientation (attitude) of the satellite is fixed inertially (i.e. it points at a fixed point in space, such as a star, although it doesn't actually have to be pointed at any physical object). This is as opposed to an attitude that is Earth-referenced, i.e. maybe it points 15 degrees "off-nadir", where nadir essentially means "straight down".

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  • $\begingroup$ I see, so in reference to the Earth it effectively makes one rotation per orbit? $\endgroup$ – gerrit Aug 1 '13 at 14:48
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    $\begingroup$ Yes, effectively. I'm sure there are attitude profiles for which this is not quite true, though. $\endgroup$ – user29 Aug 1 '13 at 14:55

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