The motivating discussion here was that a commenter up a few levels was talking about how there just had to be some images of MH370 even if nobody tasked a satellite to track that specific plane. The suggestion was that we had constellations in operation that took images of everywhere on Earth every 20 minutes, so the plane had to show up somewhere, we just needed to sift through the images. But the commenter above me pointed out that was a silly assumption and I supported that comment.
It doesn't matter whether you have a few satellites with a wide field of view taking a few huge images, or a bunch of satellites taking a bunch of smaller images- the grand total is about 500 terapixels to image the Earth at a 1 meter resolution. That's a ton of data to downlink regardless of how you collect it. Assuming great compression, this hypothetical system would have to be downlinking 50 TB every 20 minutes- that's over 300 gigabit/s. That's more than the downlink of a $600 million satellite (https://en.wikipedia.org/wiki/ViaSat-2) just to get some crappy resolution images. No civilian company is collecting anywhere near the entire surface of the earth at resolutions good enough to spot a plane. You are not tracking down MH370 if your approach is to find it in old satellite imagery. No satellite is taking pictures of vast swaths of empty ocean because there was no profit in it.
It doesn't matter whether you have a few satellites with a wide field of view taking a few huge images, or a bunch of satellites taking a bunch of smaller images- the grand total is about 500 terapixels to image the Earth at a 1 meter resolution. That's a ton of data to downlink regardless of how you collect it. Assuming great compression, this hypothetical system would have to be downlinking 50 TB every 20 minutes- that's over 300 gigabit/s. That's more than the downlink of a $600 million satellite (https://en.wikipedia.org/wiki/ViaSat-2) just to get some crappy resolution images. No civilian company is collecting anywhere near the entire surface of the earth at resolutions good enough to spot a plane. You are not tracking down MH370 if your approach is to find it in old satellite imagery. No satellite is taking pictures of vast swaths of empty ocean because there was no profit in it.