Persistent observation, a persistent problem
For all the improvements in spatial and spectral resolution, agility and accuracy, satellites suffer from one serious drawback: they have to follow the laws of orbital mechanics and keep moving around the Earth. This means they cannot hang around an interesting location, to keep a persistent watch on it, except if they are in geostationary orbit.
However, geostationary orbit is so far from the Earth that to get any kind of reasonable resolution (say 1m), huge mirrors are required (20m for a 1m resolution), making this an unworkable proposition in the near term for optical surveillance.
Alternatives exist, in the form of large constellations that always have at least one satellite over the area of interest. This requires on the order of a hundred of satellites: for instance, the Oneweb communication constellation will use around 600 satellites to provide continuous connectivity. So it’s a significant…
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