There’s nothing intrinsic in the physics of the GPS radio timing system and the corresponding receiver computations that would prevent good polar coverage.
But the whole system was designed to have no satellites passing up over the poles since there was no need for polar coverage for military purposes back when the system was being designed in back in the late 1960s. And launching polar satellites was pretty expensive back then. The satellites in use only get as far north or south as 55 degrees latitude, a bit less than 2/3rds of the way to the poles.
As a result, here in 2024 when viewed from the far polar regions we find all the satellites are down to the south near the horizon in one azimuth or another and the collective geometry between them increases the position uncertainty while the distance and amount of slant line of sight passing through the atmosphere and ionosphere weakens the signal strength and increases the propagation delay uncertainty. Which also synergistically increases position uncertainty.
If DOD wanted to launch another half-dozen satellites into a polar orbit plane they could as a matter of physics and engineering. How much the rest of their ground control infrastructure would need to be updated and how is a mystery to me. I’d expect that all the receivers everywhere, from phones to civil ships and planes to military devices on weapons and weapons systems would need to be updated / replaced to make use of the new signals. Given that huge transition inertia, for backwards compatibility they’d have to design the new satellites and signals so they would not fool old pre-polar receivers. Which isn’t impossible, but almost certainly raises the costs by yet another increment.
So it’s probably fiscally prohibitive absent some very compelling reason to do it. And in any case would be the work of a decade or two to plan, design, build, launch, and integrate. Which can’t start until at least the Phase 1 money is appropriated.
thx, good information - pretty much what i thought …
If you don’t mind - would you know if the russian and european systems (which names escape me now) suffer from the same degree of problems … or were they desinged for a more “generous” cover (being newer and electronics cost might have come down)
also, isn’t there something like “differential gps”, where (IIRC) you can create an anker point (gps-radio/emitter with known long/lat) that emulates a “satellite” (obv. covering a limited surface) - so would that be a workaround?
This is a pretty good primer on all the systems, collectively referred to as GNSS:
In a quick skim I did not see a listing of each constellation’s orbital inclination, but that’s (most of) what would determine their polar capabilities.
Now that you’re armed with the names of all the systems you can google up their inclinations.
As well, that article addresses differential GPS which is exactly the idea you described: put a transmitter at a surveyed spot on the ground and have receivers consider it as a weird form of slow-moving satellite.
The polar regions are not easy to install fixed stuff on, what with the challenges to supplying power and maintenance to remote sites. Plus the the lack of any actual, you know, land near the north pole.
If you want to read more about that, WAAS & LAAS are two good terms to begin your search. Or just start here:
Glonass and Galileo. Also the Chinese Beidou and Indian NavIC systems.
The US GPS constellation is being constantly renewed, and is up to the third major generation design. The oldest working GPS satellite was launched in 1997. So there isn’t a question of technology. One suspects that the launch costs are the dominant factor constraining launches.
The problem is that none of the systems place satellites in high inclination orbits. GPS puts its satellites in 55º inclination orbits, and Galileo uses 56º. The satellites are pretty high as orbits go, 20,000 km up, but altogether, this doesn’t get you much of the sky over the poles.
What is interesting is the Japanese Quasi-Zenith Satellite System which augments the GPS system with satellites that sit over Japan, one in geostationary orbit, the others in lower orbits set up to appear to run around a figure 8 in the sky over Japan and down as far as souther Australia. These satellites are always high in the sky over Japan, and so provide coverage into the depths of the city streets in the otherwise impenetrable jungle of skyscrapers. That they are compatible with GPS is the interesting thing. No doubt receivers need software that can use the different orbital parameters, but otherwise there little else to worry about. How easy it would be to augment GPS with a set of satellites in much higher inclinations is another matter. Launch costs would be evil, and the benefit perhaps marginal for the money.
The trick with differential GPS is in the name. A base station with a known location transmits the difference between its real location and the location it receives from the GPS satellites. This allows correction for local errors due to differences in propagation speeds through the ionosphere - which is the primary cause of error when you have reasonable coverage. It also corrects for any deliberate noise in the signal designed to degrade accuracy (Selective Availability. However SA was turned off 1996, and the claim is that newer satellites don’t even have the capability.) Differential GPS is unlikely to provide any useful improvements near the poles. And you would need a lot of them.
I wouldn’t be surprised if Russia’s system had satellites with higher inclinations. Russia, after all, is at a higher latitude than the US, and in particular, their usual launch site is also at higher latitude, so there’s less cost differential to them in launching into a polar orbit (i.e., it costs them as much to launch into a polar orbit as anyone else, but a lot of that extra cost is already built in to anything they launch, so it doesn’t make as much difference).
Also, I think that most receivers these days are designed to work with all of the satellite systems. Not only does this provide redundancy in case one country decides to limit their satellites somehow, but the more satellites you can connect to, the better your precision. The cost of the extra antennas, meanwhile, is negligible compared to the cost of other components of a phone (or whatever other device you’d put GPS in). Actually, for that matter, a major chunk of a phone’s location services don’t depend on any sort of satellite at all: From what I understand, the best data usually comes from which WiFi networks are in range and how strong they are.
FWIW, the pre-GPS Transit system exclusively used satellites in polar orbits. It was in use from the mid-60s to the mid-90s. You could get a fix off of a single satellite, but you might have to wait a few hours for a satellite to be in view, and you needed your own atomic clock.
It is perhaps not an coincidence that the USN-centric Transit system cared rather a lot about the north polar ocean, whereas the USAF- (plus a touch of US Army-) centric GPS system did not give a rat’s ass about the polar regions.
Within the DoD, never attribute to fine engineering nor carefully considered global geo-strategy that which can more easily be attributed to interservice spite and venal budget-poaching.
USAF is a global expeditionary force dedicated to the mission of spreading warm comfy beds, cold beer, good scotch, big BXs, and excellent golfing to every country on Earth.
Shortly after subduing the local government and citizenry whether they like that or not.
How so? The USAF operates a lot more in the arctic than the USN does. The direct air route from the US to Russia passes over or near the pole, while the only naval vessels that can reach the pole do so under the ice, where they wouldn’t be able to detect any satellites.
The LGM-30G ‘Minuteman’ ICBM (nor the forthcoming LGM-35 ‘Sentinel’) does not use GPS for navigation or any other satellite-based systems in flight, and even if the B-2 ‘Spirit’ planes flown by the 509 BW were to take a great circle route from it’s home at Whiteman AFB it would just fly over southern Greenland.
According to the wiki page on Transit, one of the requirements was that you could obtain a fix with less two minutes of reception–the subs would pop up just enough to expose the antenna for that long.
The page isn’t 100% clear but I suspect the computer had to churn on the data for more than two minutes. But that could be done fully submerged.
There’s some research today into low-power GPS trackers that just record the radio data without decoding it. Later, when there’s sufficient energy available, the recordings can be turned into positions. Useful for animal trackers, etc.
I’m sure Canada would be willing to rent space at Alert in Nunavut. As well, Canada and Denmark would likely do you a nice little fixer-upper on Hans Island, provided schnapps and rye are included in the lease payments.
The US Air Force has had a base in the Arctic for years. Thule Air Base in northern Greenland was constructed in the early 1950s, well before any satellites were launched. Apparently this base has now been renamed Pituffik Space Base.
While their are potential targets to the east of Moscow such as Murmansk (naval base) or Chelyabinsk (industrial center), they are going to be targeted by ICBM and SLBM attacks. The B-2 requires air tanker support to out of Mildenhall to reach targets in Eastern Europe. The B-2 is ostensibly intended as a second strike weapon, capable of precision followup to a missile exchange, although with fewer than 20 operational plans (and the questionable availability of refueling assets after a global thermonuclear exchange) its post-strike viability seems doubtful at best.
Quite right there are a couple of bits of land up there; some actually rather substantial. Thanks for the cites.
But as a general matter, the Arctic Ocean is not peppered with islands. A huge advantage to orbiting radio transmitters is the vast swath of surface below them which has direct line of sight back up to them. Which means one transmitter covers a lot of ground and water. Ground based transmitters have much shorter line-of-sight ranges just due to geometry on a sphere regardless of their power output.
And yes, there absolutely are non-line-of-sight radio systems, from ELF up through HF, where one transmitter can cover a lot of surface, however their limitations in other respects render them mostly useless for the precision required of GPS. LORAN was the limit case of a NLOS positioning system. It was damned good, but not like GPS & its peer systems.
