Revisit: the Constellation Arithmetic
How often can a constellation look at a given place, and how many satellites does a target revisit require?
Chapter summary
A satellite in low orbit moves over the ground at about 7 km per second, sweeping a strip about 605,000 km long each day.
Key takeaways
- 1
Multiplying that by the width of ground the satellite can point at (its field of regard) and dividing into the Earth's surface of about 510 million square kilometres gives the average time between opportunities to see a point.
- 2
Optical satellites only image on daylit passes, which halves their opportunities.
- 3
On Setcoin's approximation, one agile 30 cm optical satellite can look at a mid-latitude point about every three days; sixteen can look every four to five hours; a SAR fleet of 56 satellites, which works day and night, about every hour.
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Reading Fleet Claims: What "N Satellites" Really Means
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