6 ms·

Given the orbit used: * https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System * https://en.w

Given the orbit used: * https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System * https://en.wikipedia.org/wiki/Tundra_orbit https://en.wikipedia.org/wiki/Tundra_orbit Australia, Indonesia, and Papa New Guinea will also benefit.

photonbeam 3y ago
Looking at the picture of the orbit, its a lot wider around Australia, is that a benefit given the shape of the country or happenstance
- bewaretheirs 3y ago
  It's a consequence of the orbit's eccentricity - the perigee (low point) in the orbit is to the south. The satellite is moving faster around the perigee, and slower near the apogee (high point) over Japan. More info here: https://gssc.esa.int/navipedia/index.php/QZSS https://gssc.esa.int/navipedia/index.php/QZSS
  - throw0101b 3y ago
    Per that Navipedia article, the Centimeter Level Augmentation Service (CLAS) of QZSS also allows for ionospheric correction data for the Indian and Pacific Oceans, which could be helpful for other GNSS systems: * https://gssc.esa.int/navipedia/index.php/QZSS#Centimeter_Level_Augmentation_Service_.28CLAS.29 https://gssc.esa.int/navipedia/index.php/QZSS#Centimeter_Lev...
- shagie 3y ago
  It's a version of the tundra orbit ( https://en.wikipedia.org/wiki/Tundra_orbit https://en.wikipedia.org/wiki/Tundra_orbit ) In https://en.wikipedia.org/wiki/Tundra_orbit#/media/File:Animation_of_Tundra_and_QZSS_orbit_-_ECEF_-_front_view.gif https://en.wikipedia.org/wiki/Tundra_orbit#/media/File:Anima... its the green orbit. The figure 8 shape can be seen in https://commons.wikimedia.org/wiki/File:Qzss-01-120s2.gif https://commons.wikimedia.org/wiki/File:Qzss-01-120s2.gif though it isn't quite as extreme in its eccentricity as orbits that are trying to service further north. The shape is based on what is known as "apogee dwell" - that from the ground perspective a satellite at apogee (the furthest distance from earth) will be moving the slowest compared to the ground view. When the satellite is closer to Earth that same velocity will be covering more ground distance (there will also be some actual change in velocity based on how far down Earth's gravity well it goes in and out of, though I haven't done enough orbital mechanics to say with certainty). Judging by https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System it changes by about 10% as it gets closer to earth. The main issue (and you'll see this if you use GPS in a city) is that GPS can have difficulty in canyons - either urban or natural. https://www.traffictechnologytoday.com/news/connected-vehicles-infrastructure/gps-vs-urban-canyons-new-breakthrough-in-nyc-connected-vehicle-pilot.html https://www.traffictechnologytoday.com/news/connected-vehicl... You need line of site to GPS in order to get an accurate fix. If there's mountain or building in the way, it can have difficulty. Japan's cities are susceptible to this. The QZSS system is designed to have a satellite directly overhead of Japan so that when you are in a city there is a satellite visible. > The primary purpose of QZSS is to increase the availability of GPS in Japan's numerous urban canyons, where only satellites at very high elevation can be seen. A secondary function is performance enhancement, increasing the accuracy and reliability of GPS derived navigation solutions. The Quasi-Zenith Satellites transmit signals compatible with the GPS L1C/A signal, as well as the modernized GPS L1C, L2C signal and L5 signals.
  - deleted 3y ago
    [deleted]
- dkjaudyeqooe 3y ago
  It's the narrow bit over Japan that is intended, but as it happens the orbit tracks closest to the most populated parts of Australia, on the coast. The central parts (tan on the map) are more or less unpopulated.
placesalt 3y ago
comment retracted
- icegreentea2 3y ago
  Dunno who down-voted you - but what environment are you operating in? One of the claims for the Japanese system (you can see it in its orbital design) is that it specifically provides more opportunities for overhead signal coverage, increasing reliability/accuracy in mountainous and heavily urbanized (ie, skyscraper canyons) terrain. That all being said, I'm also of the opinion that this is more of a defense play. QZSS has the nice property have using geosync/geostationary orbits - I'd imagine that makes ASAT work a bit harder.
  - deleted 3y ago
    [deleted]
- throw0101b 3y ago
  > In peacetime, at least That's a huge proviso given recent geo-politics (and the possible change of that premise may be why Japan is hedging). * https://news.antiwar.com/2023/04/16/defense-official-confirms-leak-american-smart-bombs-are-failing-in-ukraine/ https://news.antiwar.com/2023/04/16/defense-official-confirm... * https://gpsjam.org https://gpsjam.org See also: * https://www.zdnet.com/article/criminals-are-using-gps-jammers-to-hijack-trucks-and-down-drones/ https://www.zdnet.com/article/criminals-are-using-gps-jammer...
- kortilla 3y ago
  GPS is shit in Japanese cities because of the angle. Read the article on QZSS.
  - johnwalkr 3y ago
    In a place like Ginza or Shinjuku it can be really frustrating to navigate using GPS when you exit a station and your location is off by 20m and your compass is also wrong by 90 degrees (I guess because of all the steel buildings). I haven't read up on it in a while but I think local augmentation for GPS, including indoors in malls, etc will eventually arrive once we figure out how to provide it as a public service instead of a bunch of companies competing to make a proprietary services that serve location-based ads.
bragr 3y ago
My phone regularly picks up QZSS here in southern California for what it's worth. At least at certain times of the day with a good western view of the sky.
- trillic 3y ago
  How do you know this??? Is there an app for displaying the exact signals your phone's GNSS receiver is getting? I've played with cgps and am familiar with it on the desktop side but never on mobile.
  - Rebelgecko 3y ago
    On Android you can read the raw NMEA sentences. Or just use an app that parses it out and tells you which constellations/augmentation sources are being used
  - skzv 3y ago
    Here's an Android app from Google called GnssLogger [0] [0] https://play.google.com/store/apps/details?id=com.google.android.apps.location.gps.gnsslogger&hl=en_US&gl=US https://play.google.com/store/apps/details?id=com.google.and...
  - bragr 3y ago
    I've used this app [1] for years. It has some paid features you probably don't need or want, but the free version will show you all kinds of constellation info. [1] https://play.google.com/store/apps/details?id=com.chartcross.gpstest https://play.google.com/store/apps/details?id=com.chartcross...
  - ChuffedToBits 3y ago
    There's SatStat[1] and GPSTest[2] on F-Droid. Simple little apps that show information about the satellites your phone is currently receiving signals from. [1]https://f-droid.org/packages/com.vonglasow.michael.satstat/ https://f-droid.org/packages/com.vonglasow.michael.satstat/ [2]https://f-droid.org/en/packages/com.android.gpstest.osmdroid/ https://f-droid.org/en/packages/com.android.gpstest.osmdroid...

photonbeam 3y ago

Looking at the picture of the orbit, its a lot wider around Australia, is that a benefit given the shape of the country or happenstance

bewaretheirs 3y ago
It's a consequence of the orbit's eccentricity - the perigee (low point) in the orbit is to the south. The satellite is moving faster around the perigee, and slower near the apogee (high point) over Japan. More info here: https://gssc.esa.int/navipedia/index.php/QZSS https://gssc.esa.int/navipedia/index.php/QZSS
- throw0101b 3y ago
  Per that Navipedia article, the Centimeter Level Augmentation Service (CLAS) of QZSS also allows for ionospheric correction data for the Indian and Pacific Oceans, which could be helpful for other GNSS systems: * https://gssc.esa.int/navipedia/index.php/QZSS#Centimeter_Level_Augmentation_Service_.28CLAS.29 https://gssc.esa.int/navipedia/index.php/QZSS#Centimeter_Lev...
shagie 3y ago
It's a version of the tundra orbit ( https://en.wikipedia.org/wiki/Tundra_orbit https://en.wikipedia.org/wiki/Tundra_orbit ) In https://en.wikipedia.org/wiki/Tundra_orbit#/media/File:Animation_of_Tundra_and_QZSS_orbit_-_ECEF_-_front_view.gif https://en.wikipedia.org/wiki/Tundra_orbit#/media/File:Anima... its the green orbit. The figure 8 shape can be seen in https://commons.wikimedia.org/wiki/File:Qzss-01-120s2.gif https://commons.wikimedia.org/wiki/File:Qzss-01-120s2.gif though it isn't quite as extreme in its eccentricity as orbits that are trying to service further north. The shape is based on what is known as "apogee dwell" - that from the ground perspective a satellite at apogee (the furthest distance from earth) will be moving the slowest compared to the ground view. When the satellite is closer to Earth that same velocity will be covering more ground distance (there will also be some actual change in velocity based on how far down Earth's gravity well it goes in and out of, though I haven't done enough orbital mechanics to say with certainty). Judging by https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System it changes by about 10% as it gets closer to earth. The main issue (and you'll see this if you use GPS in a city) is that GPS can have difficulty in canyons - either urban or natural. https://www.traffictechnologytoday.com/news/connected-vehicles-infrastructure/gps-vs-urban-canyons-new-breakthrough-in-nyc-connected-vehicle-pilot.html https://www.traffictechnologytoday.com/news/connected-vehicl... You need line of site to GPS in order to get an accurate fix. If there's mountain or building in the way, it can have difficulty. Japan's cities are susceptible to this. The QZSS system is designed to have a satellite directly overhead of Japan so that when you are in a city there is a satellite visible. > The primary purpose of QZSS is to increase the availability of GPS in Japan's numerous urban canyons, where only satellites at very high elevation can be seen. A secondary function is performance enhancement, increasing the accuracy and reliability of GPS derived navigation solutions. The Quasi-Zenith Satellites transmit signals compatible with the GPS L1C/A signal, as well as the modernized GPS L1C, L2C signal and L5 signals.
- deleted 3y ago
  [deleted]
dkjaudyeqooe 3y ago
It's the narrow bit over Japan that is intended, but as it happens the orbit tracks closest to the most populated parts of Australia, on the coast. The central parts (tan on the map) are more or less unpopulated.

placesalt 3y ago

comment retracted

icegreentea2 3y ago
Dunno who down-voted you - but what environment are you operating in? One of the claims for the Japanese system (you can see it in its orbital design) is that it specifically provides more opportunities for overhead signal coverage, increasing reliability/accuracy in mountainous and heavily urbanized (ie, skyscraper canyons) terrain. That all being said, I'm also of the opinion that this is more of a defense play. QZSS has the nice property have using geosync/geostationary orbits - I'd imagine that makes ASAT work a bit harder.
- deleted 3y ago
  [deleted]
throw0101b 3y ago
> In peacetime, at least That's a huge proviso given recent geo-politics (and the possible change of that premise may be why Japan is hedging). * https://news.antiwar.com/2023/04/16/defense-official-confirms-leak-american-smart-bombs-are-failing-in-ukraine/ https://news.antiwar.com/2023/04/16/defense-official-confirm... * https://gpsjam.org https://gpsjam.org See also: * https://www.zdnet.com/article/criminals-are-using-gps-jammers-to-hijack-trucks-and-down-drones/ https://www.zdnet.com/article/criminals-are-using-gps-jammer...
kortilla 3y ago
GPS is shit in Japanese cities because of the angle. Read the article on QZSS.
- johnwalkr 3y ago
  In a place like Ginza or Shinjuku it can be really frustrating to navigate using GPS when you exit a station and your location is off by 20m and your compass is also wrong by 90 degrees (I guess because of all the steel buildings). I haven't read up on it in a while but I think local augmentation for GPS, including indoors in malls, etc will eventually arrive once we figure out how to provide it as a public service instead of a bunch of companies competing to make a proprietary services that serve location-based ads.

bragr 3y ago

My phone regularly picks up QZSS here in southern California for what it's worth. At least at certain times of the day with a good western view of the sky.

trillic 3y ago
How do you know this??? Is there an app for displaying the exact signals your phone's GNSS receiver is getting? I've played with cgps and am familiar with it on the desktop side but never on mobile.
- Rebelgecko 3y ago
  On Android you can read the raw NMEA sentences. Or just use an app that parses it out and tells you which constellations/augmentation sources are being used
- skzv 3y ago
  Here's an Android app from Google called GnssLogger [0] [0] https://play.google.com/store/apps/details?id=com.google.android.apps.location.gps.gnsslogger&hl=en_US&gl=US https://play.google.com/store/apps/details?id=com.google.and...
- bragr 3y ago
  I've used this app [1] for years. It has some paid features you probably don't need or want, but the free version will show you all kinds of constellation info. [1] https://play.google.com/store/apps/details?id=com.chartcross.gpstest https://play.google.com/store/apps/details?id=com.chartcross...
- ChuffedToBits 3y ago
  There's SatStat[1] and GPSTest[2] on F-Droid. Simple little apps that show information about the satellites your phone is currently receiving signals from. [1]https://f-droid.org/packages/com.vonglasow.michael.satstat/ https://f-droid.org/packages/com.vonglasow.michael.satstat/ [2]https://f-droid.org/en/packages/com.android.gpstest.osmdroid/ https://f-droid.org/en/packages/com.android.gpstest.osmdroid...