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Why is this the case? Is triangulating your position from LEO harder somehow? Or is it something like that satellites don't have accurate enough clocks? Or some
by gpm 6y ago
Why is this the case? Is triangulating your position from LEO harder somehow? Or is it something like that satellites don't have accurate enough clocks? Or something else?
- Joeri 6y agoNavigation satellites carry atomic clocks, oneweb satellites do not.
- ivalm 6y agoGeostationary satellites have very well known position and use atomic clocks to ensure they are synchronized. So when you get a signal for 3 geostationary sats you can have both extreme precision in their position and in time delay between your and sat locations. For LEO sats the sat position is more complicated and they don’t have atomic clocks to synchronize. Now, their position IS somewhat known and they do have clocks so they can work somewhat, just not as well (alternatively since there will be a ton of Leo sats maybe you can do statistical analysis to improve?)
- Denvercoder9 6y agoGNSS constellations do not use geostationary satellites.
- jhayward 6y ago> GNSS constellations do not use geostationary satellites. This is not quite accurate. The main body of GNSS constellations are usually MEO cut in to several orbital planes, but GPS and Beidou, (Global systems) as well as QZSS and IRNSS (regional systems) all have GEO satellites broadcasting a NAV signal payload.
- manquer 6y agoGNSS systems typically use MEO ~20,000 KM.
- Rebelgecko 6y agoYou can't really use geostationary satellites for finding your position (problem akin to gimbal lock, you lose an entire degree of freedom so you don't know if you're north or south)
- d_silin 6y agoYes, on-board clock accuracy is the limiting factor here.
- manquer 6y agoPerhaps something like NTP could be used to keep the clock accurately in sync to the precision required? I mean do you need the atomic clock to be onboard ? could there not some error correction with multiple satellites to handle skew problems ?
- gpm 6y agoA light nanosecond is 0.3m (1ft), I know no more than you do about the tech, but it seems plausible that NTP isn't accurate enough.
- manquer 6y agowell i didn't mean literally NTP itself, but a similar sync protocol and error correction, it may not be the best approach obviously or give best precision..just that it could made to work ?
- tartoran 6y agoIf you don’t care about error rates and want an approximate location it could be done. If one finds satisfying a device which would tell you that you’re in such and such neighborhood but not give you the exact location sure.. We’re in 2020, that would be like travelling back in time
- jhayward 6y agoThese satellites don't have the on-board clock capability to do very high precision, high stability timing which is one foundational bedrock positional accuracy is based on. Just as important though is that they don't have the world-wide network of ground tracking stations monitoring their orbit. The orbital positions and velocity need to be known to within a meter or so, and not only are these not being tracked at that level, which is a very expensive undertaking, but they are also in LEO which means their orbits are much more affected by atmosphere and are less stable.