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I was doing some MATLAB simulations on LEO satellites using TLEs obtained from n2yo websites and I observed that n2yo was displaying a different TLE for the same satellite after a few days. I don't exactly remember but I had to change the TLEs in my simulation maybe once a week.

I know why the TLEs change because the actual track of satellite changes due to actual forces acting on the satellite.

So, is there any historic data that tells me how frequent the TLEs are changes for LEO satellites. If the changes are grouped depending on the altitude, that kind of data is fine too

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I don't mean to nitpick, TLE's don't change. They are issued with a specific epoch (or time stamp) (line #1, columns 19-32 and exist forever.

Instead of changing TLEs, NEW TLEs are issued.

For special and important spacecraft where you really need to know fairly accurate information, TLEs can be updated several times a day. See for example Why did the frequency of TLEs for the Hubble Space Telescope drop by a factor of 3 in 2009? where the time between one TLE and the next changed from 0.7 days to 2 days.

When orbits are changing quickly or there are other issues, like right after a group of satellites are deployed and they are starting to move away from each other, it's not uncommon to have two or three updates per day. Other times you might see one update every few days or a week. For some satellites that are far away from Earth, they might be even less frequently.

Something I have been meaning to ask about is the occasional double TLE, two of them existing at either the same epoch, or separated only by microseconds or milliseconds, or sometimes seconds. I think that the reason will probably turn out to be both a) secret and b) not very interesting.

So I think the best thing to do is to figure out which spacecraft you'd like to follow and just check a few times a day for a week to see how often your spacecraft are receiving new TLEs.

You can also consider joining Space-Track.org where you can download historical data and see for yourself. See this answer for more information on joining.

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