3 ms·

Interestingly despite becoming "fully operational" in 1995, GPS was in use in the 1980s and played a huge part in the Gulf War in 1990/1991. "Fully operational"

Interestingly despite becoming "fully operational" in 1995, GPS was in use in the 1980s and played a huge part in the Gulf War in 1990/1991. "Fully operational" probably means 12 satellites in view at all times for any point on the earth between 55°N/55°S, but it's still very useful even at lower levels of service. It's pretty amazing that a system like that could be envisioned in the 1970s and be fundamentally life-changing by the 1990s. Truly a modern marvel of engineering that we rely upon for precise timing, power grid synchronization, navigation, and a lot more.

dweekly 4y ago
Fully operational in 93, but IMO the real slam dunk was disabling of Selective Availability in 2000, which made GPS significantly more useful. WAAS has been amazing for aviation, allowing for RNAV instrument precision approaches to airports with no RF equipment installation required onsite. And there are still innovations getting rolled out, including L2C, L5 and more! https://www.gps.gov/systems/gps/modernization/civilsignals/ https://www.gps.gov/systems/gps/modernization/civilsignals/
- 13of40 4y ago
  IMO the secret sauce wasn't necessarily the precision but the ability, granted by technology outside the GPS system, to put a dot on a digital map versus your PLGR giving you a pair of coordinates that you had to look up on a paper map.
tzs 4y ago
> "Fully operational" probably means 12 satellites in view at all times for any point on the earth between 55°N/55°S Whenever I've checked how many are visible here (around 48°N) I most commonly see 8 or 9, with 7 or 10 next most common.
- jhugo 4y ago
  the 12 number probably assumes the middle of a flat plain with no tall structures nearby. buildings, hills etc will reduce the number.
  - tzs 4y ago
    I just checked it for some place in the middle of South Dakota that is a flat plane with no tall structures (or any structures...) nearby [1]. It looks like right for today it is 12 or more about 40% of the time [2]. That includes satellites very close to the horizon which most devices won't use. Limiting it to satellites that are at least 10 degrees above the horizon, the max visible at once today there is 11, with 9 being the number visible that vast majority of the time. Looking at other days it looks like the pattern of number visible at various times throughout the day repeats, but with a period that is slightly off from 24 hours, so the percent of time that a given number of satellites is visible is about the same every day, the the specific times that number is achieved slowly changes day to day. [1] https://www.google.com/maps/@44.5831536,-99.4535123,3a,75y,175.04h,91.36t/data=!3m7!1e1!3m5!1stxumfNa9QQ2jxdNf3neXFA!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3DtxumfNa9QQ2jxdNf3neXFA%26cb_client%3Dmaps_sv.tactile.gps%26w%3D203%26h%3D100%26yaw%3D79.22481%26pitch%3D0%26thumbfov%3D100!7i3328!8i1664 https://www.google.com/maps/@44.5831536,-99.4535123,3a,75y,1... [2] https://satpredictor2.deere.com/chartvisibility?addr=&lat=44.5831536&lon=-99.4535123&timeZ=17&evMask=0&gps=YES&glonass=NO https://satpredictor2.deere.com/chartvisibility?addr=&lat=44... [3] https://satpredictor2.deere.com/chartvisibility?addr=&lat=44.5831536&lon=-99.4535123&timeZ=17&evMask=10&gps=YES&glonass=NO https://satpredictor2.deere.com/chartvisibility?addr=&lat=44...

dweekly 4y ago

Fully operational in 93, but IMO the real slam dunk was disabling of Selective Availability in 2000, which made GPS significantly more useful. WAAS has been amazing for aviation, allowing for RNAV instrument precision approaches to airports with no RF equipment installation required onsite. And there are still innovations getting rolled out, including L2C, L5 and more! https://www.gps.gov/systems/gps/modernization/civilsignals/ https://www.gps.gov/systems/gps/modernization/civilsignals/

13of40 4y ago
IMO the secret sauce wasn't necessarily the precision but the ability, granted by technology outside the GPS system, to put a dot on a digital map versus your PLGR giving you a pair of coordinates that you had to look up on a paper map.

tzs 4y ago

> "Fully operational" probably means 12 satellites in view at all times for any point on the earth between 55°N/55°S Whenever I've checked how many are visible here (around 48°N) I most commonly see 8 or 9, with 7 or 10 next most common.

jhugo 4y ago
the 12 number probably assumes the middle of a flat plain with no tall structures nearby. buildings, hills etc will reduce the number.
- tzs 4y ago
  I just checked it for some place in the middle of South Dakota that is a flat plane with no tall structures (or any structures...) nearby [1]. It looks like right for today it is 12 or more about 40% of the time [2]. That includes satellites very close to the horizon which most devices won't use. Limiting it to satellites that are at least 10 degrees above the horizon, the max visible at once today there is 11, with 9 being the number visible that vast majority of the time. Looking at other days it looks like the pattern of number visible at various times throughout the day repeats, but with a period that is slightly off from 24 hours, so the percent of time that a given number of satellites is visible is about the same every day, the the specific times that number is achieved slowly changes day to day. [1] https://www.google.com/maps/@44.5831536,-99.4535123,3a,75y,175.04h,91.36t/data=!3m7!1e1!3m5!1stxumfNa9QQ2jxdNf3neXFA!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3DtxumfNa9QQ2jxdNf3neXFA%26cb_client%3Dmaps_sv.tactile.gps%26w%3D203%26h%3D100%26yaw%3D79.22481%26pitch%3D0%26thumbfov%3D100!7i3328!8i1664 https://www.google.com/maps/@44.5831536,-99.4535123,3a,75y,1... [2] https://satpredictor2.deere.com/chartvisibility?addr=&lat=44.5831536&lon=-99.4535123&timeZ=17&evMask=0&gps=YES&glonass=NO https://satpredictor2.deere.com/chartvisibility?addr=&lat=44... [3] https://satpredictor2.deere.com/chartvisibility?addr=&lat=44.5831536&lon=-99.4535123&timeZ=17&evMask=10&gps=YES&glonass=NO https://satpredictor2.deere.com/chartvisibility?addr=&lat=44...