Global Positioning System in Twilight 2000

[Claidheamh]

Would the GPS network still work by the year 2000?

Of course EMP would play havoc with many GPS receivers, which would kill a lot of its value, but my limited understanding of EMP is that it doesn't propagate well in vacuum, so the satellites would still work. Anti-Satellite weapons will definitely have been used throughout 1997, but I believe that the GPS satellites are in geosynchronous orbit, well above the orbit of most LEO craft that would have been attacked by ASAT weapons.

An acquaintance told me about timing issues between satellites that requires a ground broadcast station to give offset details for receivers, but I assume that if that's offline, the accuracy of the GPS system gets worse, but it wouldn't disable the system.

I don't have an actual plan for using GPS in an upcoming campaign, but I have been noodling around with this question.

[kcdusk]

I've decided in my game, that satellites and GPS is still working. BUT.

If players are in a foreign country (ie USA players in Europe) then they know nothing about the wider map. While they can determine north, south, west due to the sun for instance, they are unlikely to know what towns/villages/enemy/friendlies are in which direction.

I also try to rely on paper maps more. So in contrast to the above, PCs have a map so they know where towns are and have some idea where enemy v friendly forces are likely to be. This increases the reliance on navigation rolls, which suits my game because it becomes an important skill and tension point that isn't combat related. Also, my players tend to travel off road, insuring more navigation rolls and modifiers than most others i think.

I can see some cases where GPS might be used. I'd explain the patchy way i might use it as the amount of satellites and support network is no longer 100% maintained. So sometimes you get no signal, sometimes you get a strong or weak signal. And the randomness becomes part of the game tension and story arc.

So in summary i say yes GPS would work, some of the time. And how you apply that to your game is up to you.

[micromachine]

Should all the GPS uplink stations be down, the system will degrade rather quickly to the point of uselessness. Some talking heads say that positional accuracy will reduce to half a kilometer within two weeks and by ten kilometers after six months.
There are only four ground uplink stations that can make the adjustments, and they are at Cape Canaveral, Ascension Island, Diego Garcia and Kwajalein Atoll. The master control station is Schriever AFB outside of Colorado Springs.
In my humble opinion, I would guess that GPS is a thing of the past in any version of the T2K universe. OPFOR would have them very high on the strike package list in almost any conceivable war scenario.

[Claidheamh]

Thanks, Micro -

I didn't realize that the positioning Uplink stations were so critical to the accuracy, I was guessing a much slower reduction in accuracy, but that's based purely on limited knowledge.

[Vespers War]

GPS satellites are in a Medium Earth Orbit, lower than geosynchronous. Each satellite orbits Earth twice per day. They're still really high up, at around 12,500 miles, whereas the highest ASAT test that I'm aware of was China's 2007 strike on Fengyun-1C, at just 537 miles of altitude.

The Starfish Prime nuclear test damaged quite a few satellites, but most of them were also much lower than GPS satellites - TRAAC at 590 miles, Transit 4B at 690 miles, and Ariel 1 at 247 to 747 miles in an elliptical orbit.

I think it's certainly plausible the satellites are still in orbit and transmitting, but they would lose accuracy over time. The atomic clocks aboard the GPS satellites drift by about 10 nanoseconds per day, which is equivalent to about 3 meters of distance on the ground. There's some randomness in that, so it won't be a steady loss of 3m/day of accuracy, but it would degrade over time. Galileo is roughly the same; GLONASS is an order of magnitude worse.

[castlebravo92]

Would the GPS network still work by the year 2000?

Of course EMP would play havoc with many GPS receivers, which would kill a lot of its value, but my limited understanding of EMP is that it doesn't propagate well in vacuum, so the satellites would still work. Anti-Satellite weapons will definitely have been used throughout 1997, but I believe that the GPS satellites are in geosynchronous orbit, well above the orbit of most LEO craft that would have been attacked by ASAT weapons.

An acquaintance told me about timing issues between satellites that requires a ground broadcast station to give offset details for receivers, but I assume that if that's offline, the accuracy of the GPS system gets worse, but it wouldn't disable the system.

I don't have an actual plan for using GPS in an upcoming campaign, but I have been noodling around with this question.

GPS satellites would be completely unaffected by EMP. One, EMP is an atmospheric phenomenon caused by high energy photons (ie, gamma rays) hitting the atmosphere. No atmosphere = no EMP. GPS satellites are 20,000 km away.

[kcdusk]

There are only four ground uplink stations that can make the adjustments, and they are at Cape Canaveral, Ascension Island, Diego Garcia and Kwajalein Atoll. The master control station is Schriever AFB outside of Colorado Springs.

You've just listed 5 sites that could suddenly be very important in any new T2K modules/private games looking for a location or reason for a mission!

[kato13]

Some prior discussion which connects with this.

https://forum.juhlin.com/showthread.php?t=5068

[Ursus Maior]

Should all the GPS uplink stations be down, the system will degrade rather quickly to the point of uselessness. Some talking heads say that positional accuracy will reduce to half a kilometer within two weeks and by ten kilometers after six months.
There are only four ground uplink stations that can make the adjustments, and they are at Cape Canaveral, Ascension Island, Diego Garcia and Kwajalein Atoll. The master control station is Schriever AFB outside of Colorado Springs.
In my humble opinion, I would guess that GPS is a thing of the past in any version of the T2K universe. OPFOR would have them very high on the strike package list in almost any conceivable war scenario.

I'm not sure this is how it worked in 1997. By then all Block II and Block IIA as well as at least one Block IIR satellites were in orbit and functioning. Block II satellites worked for 14 days withouth contact from the control segment, while IIA could go on for 180 days. However, up until 2007 the modern operation control segment (OCS), providing maintenance and keeping GPS operational and performing within specification, was not implemented. Up until then, it is my understanding, only the legacy 1970s-era mainframe computer at Schriever Air Force Base was able to calculate data needed to do maintenance and keeping everything up to specifications.

It is my understanding, that once Schriever AFB is gone, pre-2007 Navstar GPS would degrade irrecoverably, until the capabilities of the mainframe at Schriever AFB could be replaced elsewhere.

The bright silver line is: I cannot find Schriever AFB in the official target list from Challenger magazine.

[Tegyrius]

The bright silver line is: I cannot find Schriever AFB in the official target list from Challenger magazine.

Using Nukemap (https://nuclearsecrecy.com/nukemap/) to put a 3MT ground burst on top of Stargate Command, it looks like Schriever was outside the light blast damage and third-degree burn radii. However, any winds out of the west would have put it under significant fallout. Fort Carson and a good chunk of Colorado Springs would've been flat or on fire, and anything still standing would've been subject to the same fallout considerations, so there goes any of your trained workforce who weren't on base at the time of the attack (or who abandoned their posts to find their families). There's also the possibility of EMP zorching any non-hardened equipment, including the ground station antennas. So, yeah, by 2000, there may be a fenceline and some buildings still there, but I'd have a hard time saying Schriever AFB retained any operational status once Cheyenne Mountain was subjected to nonconsensual landscaping.

(This leaves aside the broader issue of Colorado Springs being sufficiently salvageable to serve as the Joint Chiefs' capital even once the radiation decays enough for safe long-term habitation.)

- C.

[castlebravo92]

Using Nukemap (https://nuclearsecrecy.com/nukemap/) to put a 3MT ground burst on top of Stargate Command, it looks like Schriever was outside the light blast damage and third-degree burn radii. However, any winds out of the west would have put it under significant fallout. Fort Carson and a good chunk of Colorado Springs would've been flat or on fire, and anything still standing would've been subject to the same fallout considerations, so there goes any of your trained workforce who weren't on base at the time of the attack (or who abandoned their posts to find their families). There's also the possibility of EMP zorching any non-hardened equipment, including the ground station antennas. So, yeah, by 2000, there may be a fenceline and some buildings still there, but I'd have a hard time saying Schriever AFB retained any operational status once Cheyenne Mountain was subjected to nonconsensual landscaping.

(This leaves aside the broader issue of Colorado Springs being sufficiently salvageable to serve as the Joint Chiefs' capital even once the radiation decays enough for safe long-term habitation.)

- C.

Given that T2K puts Colorado Springs as the capitol of MilGov, has Cheyenne Mountain / NORAD still largely intact, and Fort Carson operational, I would uh, recommend moving ground zero for the 3 MT blast several (~10) km to the west / southwest. Otherwise most of the Fort Carson base infrastructure and a fair amount of Colorado Springs itself gets flattened. Also, a 3 MT warhead will excavate a ~980 meter radius crater. It's unlikely that Cheyenne Mountain - or least it's occupants - would survive a direct hit (ground shock, if nothing else, would kill them).

[Vespers War]

GPS satellites would be completely unaffected by EMP. One, EMP is an atmospheric phenomenon caused by high energy photons (ie, gamma rays) hitting the atmosphere. No atmosphere = no EMP. GPS satellites are 20,000 km away.

That's type one EMP. Type two is a gamma ray pulse that doesn't rely on atmospheric effects (but tends to be very weak), and type three is caused by magnetic field distortions from the nuclear blast. Earth's magnetic field extends to 65,000 kilometers on the day side and 6,300,000 kilometers on the night side, so good luck being outside of that.

While there probably won't be EMP effects at GPS satellite altitude from a nuclear bomb, satellites in LEO are definitely vulnerable, and even modern satellites are still vulnerable to type three EMP - a natural geomagnetic storm wiped out a few dozen Starlink satellites last year from the same sort of magnetic field distortions that a nuclear blast would cause.

[SpaceGlowie]

You've just listed 5 sites that could suddenly be very important in any new T2K modules/private games looking for a location or reason for a mission!
They would be useless.
In case of a situation with threat to a site, all non-essential personal will be released and sent to take their families to safety. All non-essential systems will be shut down at the site. Essential personnel may remain on-site depending on what core systems must remain online. If the world situation continues to worsen, then the site administrator will make the decision to shut everything down depending on how long the site could stay powered. For example, if local power grid is going to be offline for quite possibly months and the site only has 15 days worth of power, then everything will be powered off and any remaining essential personnel will then be released and sent to take their families to safety.
So, even if the site was intact and not subject to a nuclear surface or air strike or damaged by an EMP burst, you will need those essential personnel to start powering on all of those systems and not screw things up. And those personnel will have likely run for the hills and will unfortunately most likely be dead.