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If I want to cover one single point on earth with 24 hour coverage using LEO satellites, how many are needed at minimum and what would be their orbit

jadine
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    See if this answer helps you: https://space.stackexchange.com/questions/60109/revisit-time-estimation-for-a-sar-constellation/60156#60156 – Ryan C Dec 24 '22 at 05:02
  • Unless that point is near the equator, it's not much different than covering all of the Earth. As any inclined orbit will see different parts of the Earth as it rotates. – Greg Miller Dec 24 '22 at 15:09

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To answer this question, more information about the satellite at hand is needed as well as the location of the point on Earth. In any case, I hope the below helps get an idea.

This is a plot of the ISS ground tracks for 1 full day. You can see on the left there is a repetition, but with a shift (Earth rotates).

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Depending on your fov (of a downward-looking antenna for example), your spatial coverage will be different. Here is an example of the spatial coverage from ISS with a fov of 40 deg.

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Another example with a fov of 100 deg. As you can see the main issue for this orbit is the equatorial regions. On the other hand, with this orbit, there is very good coverage at around +55 deg. latitude. So, if you want to look at a point in the equator, an orbit similar to that of ISS is probably not suitable.

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Now, to help you in getting closer to an answer, I don't have a plot of LEO orbits, but the principle should be the same. This is a frequency plot of GPS satellites at some point on Earth.

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As you can see, at all times, there are at least 6 GPS visible to that point. I repeated the simulation for other points around Earth and the coverage is similar. At all times, there are at least 4 GPS satellites visible from that point. The total number of GPS satellites is 31. You can perform these kinds of simulations and visualizations with TLEs found here: http://celestrak.org/NORAD/elements/

An important thing to consider when doing so is the reference frame. You must always know which reference frame the coordinates are given (depends on your source) and which coord system you want to work on. I compute the satellite positions and velocity in ECI, perform calculations and then convert to ECEF.

If any clarifications are needed please let me know, I'm not sure what your application is so, I'll try to fix/edit based on that.

Playstation_waifu
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