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If anyone's wondering about the orbit, it's a geosynchronous but not geostationary orbit. The geosynchronous part is so that they only need a few sats to cover

If anyone's wondering about the orbit, it's a geosynchronous but not geostationary orbit. The geosynchronous part is so that they only need a few sats to cover their region, unlike GPS which is global and requires some 32 sats. It's not an equatorial geostationary orbit so that receivers at higher latitudes (in Japan) will see a sat overhead instead of always over the equator. This is to deal with the "canyon" effect. Guaranteeing a bird overhead, rather than GPS's catch-as-catch-can, should definitely help signal reliability. These will be further away than GPS, which are medium Earth orbit. Some other info (including an animation) here: http://global.jaxa.jp/countdown/f18/overview/orbit_e.html http://global.jaxa.jp/countdown/f18/overview/orbit_e.html It should also be useful in Australia and parts between. They will also park spare sats in geostationary equatorial orbits. It's a bit inspired, I think, by the Molniya orbit, another technique to get long-duration high-latitude overflight: http://en.wikipedia.org/wiki/Molniya_orbit http://en.wikipedia.org/wiki/Molniya_orbit

dfc 13y ago
Another neat thing about the orbit, Pine Gap[^1] sits right in the middle of the bottom half of the figure eight. As far as "should be useful" goes do you know if Japan has ground stations in Australia? [^1]: https://en.wikipedia.org/wiki/Pine_Gap https://en.wikipedia.org/wiki/Pine_Gap
- jccooper 13y ago
  There's one in Canberra, as well as Guam, Hawaii, and Bangalore. I don't know if they're Japanese per se; "joint" is probably better. The US territory ones are NOAA or NASA in collaboration with JAXA. http://www.insidegnss.com/auto/popupimage/QZSS%20ground%20segment_lo.jpg http://www.insidegnss.com/auto/popupimage/QZSS%20ground%20se... Dunno if those will help with the "centimeter resolution" bit, but it'll certainly augment GPS. The dwell over Australia and other non-Japan areas for the non-stationary sats will be shorter, but still will be useful while they are visible. And outside of "canyon" areas that will be quite often. The geostationary sats will be useful over quite a lot of the west Pacific and east Indian oceans.
TorKlingberg 13y ago
I looks like the satellites will move much faster and lower over Australia, so they will only be overhead for shorter periods. I guess they could still be used for extra accuracy when one happens to pass by.
rdtsc 13y ago
> It's a bit inspired, I think, by the Molniya orbit, another technique to get long-duration high-latitude overflight: Isn't it closer to the Tundra (Тундра [in rus]) orbit? https://en.wikipedia.org/wiki/Tundra_orbit https://en.wikipedia.org/wiki/Tundra_orbit Found a video showing the difference in ground tracks between the two: https://www.youtube.com/watch?v=Yo9rFmfX42Q https://www.youtube.com/watch?v=Yo9rFmfX42Q
- jccooper 13y ago
  It is a Tundra orbit. Both are pretty clever, but the Molniya is more famous--being older and more used. Molniya is cheaper, certainly, and has the interesting property of dwelling over both the United States and Russia. Tundra orbit is aggressively regional, and thus has no plausible deniability about being for local use. If you're not a Cold Warrior, however, that doesn't matter much, so we'll probably see more Tundra type systems in the future. Europe would benefit from this exact system, as would the US. China perhaps, too.

dfc 13y ago

Another neat thing about the orbit, Pine Gap[^1] sits right in the middle of the bottom half of the figure eight. As far as "should be useful" goes do you know if Japan has ground stations in Australia? [^1]: https://en.wikipedia.org/wiki/Pine_Gap https://en.wikipedia.org/wiki/Pine_Gap

jccooper 13y ago
There's one in Canberra, as well as Guam, Hawaii, and Bangalore. I don't know if they're Japanese per se; "joint" is probably better. The US territory ones are NOAA or NASA in collaboration with JAXA. http://www.insidegnss.com/auto/popupimage/QZSS%20ground%20segment_lo.jpg http://www.insidegnss.com/auto/popupimage/QZSS%20ground%20se... Dunno if those will help with the "centimeter resolution" bit, but it'll certainly augment GPS. The dwell over Australia and other non-Japan areas for the non-stationary sats will be shorter, but still will be useful while they are visible. And outside of "canyon" areas that will be quite often. The geostationary sats will be useful over quite a lot of the west Pacific and east Indian oceans.

TorKlingberg 13y ago

I looks like the satellites will move much faster and lower over Australia, so they will only be overhead for shorter periods. I guess they could still be used for extra accuracy when one happens to pass by.

rdtsc 13y ago

> It's a bit inspired, I think, by the Molniya orbit, another technique to get long-duration high-latitude overflight: Isn't it closer to the Tundra (Тундра [in rus]) orbit? https://en.wikipedia.org/wiki/Tundra_orbit https://en.wikipedia.org/wiki/Tundra_orbit Found a video showing the difference in ground tracks between the two: https://www.youtube.com/watch?v=Yo9rFmfX42Q https://www.youtube.com/watch?v=Yo9rFmfX42Q

jccooper 13y ago
It is a Tundra orbit. Both are pretty clever, but the Molniya is more famous--being older and more used. Molniya is cheaper, certainly, and has the interesting property of dwelling over both the United States and Russia. Tundra orbit is aggressively regional, and thus has no plausible deniability about being for local use. If you're not a Cold Warrior, however, that doesn't matter much, so we'll probably see more Tundra type systems in the future. Europe would benefit from this exact system, as would the US. China perhaps, too.