sun-synchronous satellite (let's consider
Sentinel-1) go over the same place, one time in an
ascending pass and the next time (or few times after) in a
Sentinel-1 definitely takes images of the same point on Earth in both ascending and descending passes. Just search for all images intersecting a point (or tiny area) on any service that provides Sentinel-1 image access (SciHub, Google Earth Engine, AWS, etc.) and you'll see that images from both descending and ascending passes are returned.
Descending and ascending images will differ quite a bit though. In the case of SAR imagers such as Sentinel-1 that is because the radar waves come from a different direction and hence radar shadows, foreshortening, etc. will look differently. For optical imagers, there will be huge differences too because either of ascending and descending passes will be at night and the other one at day, as explained in nicksan's comment.
It seems to me that many
satellites are programmed to go over a certain
area at the same
time and in the same
This increase coherence between each
pass's images, which facilitate operations such as
change detection on the
image series generated from the set of images collected from the different passes.
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For a sun-synchronous system with two opposite passes it seems that you need more than one satellite. For the consideration of Sentinel-1 it actually consists of two satellites, Sentinel-1A and Sentinel-1B, which share the same orbital plane with a phase difference of 180°. Some services package the constellation into a single data source. When both are considered, than one will pass a particular location every 12 days in ascending orbit, while the other satellite will pass that same location every 12 days in descending orbit. Because of the phase difference of 180° and the sun-synchronicity, the time interval to revisit that same location in both passes is maximum 6 days.
This image from ESA Sentinel website visualises the orbits of the Sentinel-1 constellation with sunlight locked on the left side:
Image source and additional info: https://sentinel.esa.int/web/sentinel/missions/sentinel-1/satellite-description/orbit