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I am working on a orbit propagation project and need accurate position information of LEO satellites. I have until now used Sentinel 3A/3B (~800 km altitude), whose ECEF coordinates I can get with a 1 day delay from the browser.dataspace.copernicus.eu web-browser. But I am looking for additional satellites, preferably at altitudes below 800 km.

Does anyone know of other satellites whose "truth" position data (i.e., <1 m accurate) is publicly available within a few days? TLE's are way too inaccurate for my purposes.

Thanks in advance!

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    $\begingroup$ @PM2Ring Hubble is a great candidate! But for someone "working on a orbit propagation project" the ISS's giant, complicated shape that keeps changing (solar panels busy rotating), and particularly low altitude and irregular reboosts and jettisons, the ISS' variable drag might not provide a helpful dataset. How about something completely passive with laser retroreflectors, like LAGEOS? $\endgroup$
    – uhoh
    Commented May 17 at 13:07
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    $\begingroup$ @uhoh Horizons has both of the LAGEOS satellites, but they're at a much higher altitude than what the OP is interested in. The body data pages are very minimal. ssd.jpl.nasa.gov/api/… I agree they're great test bodies for orbit propagation software. $\endgroup$
    – PM 2Ring
    Commented May 17 at 13:26
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    $\begingroup$ Plenty of satellite operators provide "supplemental" info to Celestrak, often more accurate than the TLEs provided by the 18th. celestrak.org/NORAD/elements/supplemental $\endgroup$ Commented May 17 at 14:50
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    $\begingroup$ Thank you everyone for commenting! Very helpful! It doesn't seem like an easy task finding satellites at <600 km altitude with accurate data. The ISS is, as mentioned by unho, too complex at this stage. Some of the suggested sources has either too large encertainties (i.e. km scale) or unknown accuracy. Ryan C mentiones satellites using DORIS, which is indeed what I have used so far (Sentinel), so I guess my expectations have been somewhat warped by the sublime 2-3 cm accuracy. I will continue the search! $\endgroup$
    – Frederik
    Commented May 22 at 13:07
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    $\begingroup$ @uhoh generally speaking, it is impossible to measure accuracy as such. we estimate precision, and hope we're modeling it correctly. satellites are necessarily far away and moving fast, so nailing down "true" position is complicated. the orbits of DORIS-using satellites are estimated by a mathematical procedure that requires you to know the positions and velocities of each of the 60ish DORIS ground stations worldwide. The ground station motion is estimated to millimeters per year, by the same calculation run backward from the orbits. it's self-consistent, but truth remains unknowable. $\endgroup$
    – Ryan C
    Commented May 24 at 20:51

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