A satellite’s orbit determines what it can see and how often. Most Earth-observation satellites fly low, near-polar, sun-synchronous orbits that sweep the whole planet in consistent lighting; weather satellites hover in distant geostationary orbits watching one hemisphere continuously; and modern constellations multiply small satellites across orbital planes to compress revisit times to daily or better. Orbit mechanics quietly writes the rules of every monitoring programme.
Sun-synchronous: the mapper’s orbit
At roughly 500–800 km altitude, a sun-synchronous orbit precesses so the satellite crosses the equator at the same local solar time every pass — typically mid-morning. Consistent illumination makes images comparable across years, which is what long archives like Landsat’s depend on.
As the Earth rotates beneath the orbital plane, successive passes cover adjacent swaths, tiling the globe on a fixed repeat cycle — 16 days for Landsat, about 5 days for the paired Sentinel-2 satellites.
Geostationary: the unblinking eye
At 35,786 km over the equator, a geostationary satellite orbits exactly as fast as Earth turns, hanging motionless over one longitude. Weather satellites exploit this to image the same disc every few minutes — the source of every animated storm loop.
The price of that vantage is distance: pixels are hundreds of metres to kilometres across, so geostationary sensors monitor dynamics rather than map detail.
Constellations and tasking
Replacing one large satellite with dozens of small ones changes the arithmetic of revisit: PlanetScope images essentially all land daily at 3 m, and radar smallsat fleets now offer sub-daily tasking. Agile high-resolution satellites add pointing — slewing off-nadir to capture a target on request rather than waiting for the ground track.
For buyers, this turns imagery into a service question — archives versus fresh tasking, guaranteed windows, and constellation mixes — rather than a single-sensor decision.
Frequently asked questions
Why do imaging satellites pass at the same time each day?
They fly sun-synchronous orbits designed so lighting conditions are consistent for every acquisition, making mosaics seamless and change detection meaningful across dates and years.
Can a satellite hover over my project site?
Only geostationary satellites “hover”, and they are too distant for detailed mapping. High-resolution satellites instead point their sensors at your site as they pass, which is what commercial tasking orders buy.
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