[RFC] Solar Positioning System (SPS)
09-27-2012, 09:13 AM
The Solar Positioning System (SPS) is a system which relies on being able to communicate with at least four SPS satellites of Sol with extremely well defined positions and which include on-board extremely accurate clocks. Given a very precise measurement of the speed of FTL communication (10k lights, or ten-thousand times the speed of light) this allows calculation of location relative to Sol with quite impressive accuracy. Sometimes referred to as FPS (Fenspace Positioning System). The system operates on similar principles to GPS (Global Positioning System), only using FTL instead of EM radio satellites.
http://en.wikipedia.org/w...lobal_Positioning_System
META: On what sort of time scale might such a service become available in Fenspace?
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No doubt this system is linked with http://www.fenspace.net/index.php5?titl ... Lagrange_2]Terra Beacon One.
META: That would be one of the first things that Artemis sets up, so somewhere between third-quarter 2014 and early-2015.
META-SILLY: I first read the names as "Sailor Positioning System"... There's a possible quirk somewhere in that misreading, ne?
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I am not sure it makes much sense to use Interwave for this... the precision of the GPS depends on the accuracy of the clocks of the satellites and not of the signal transmission speed. Higher transmission speed makes it even more difficult to get your position right.
So I would guess SPS sounds good, but with normal radio waves... or make it a PPS (Pulsar positioning system), which use some specialized waved antennas to listen to some known pulsars in our galaxy. 
HRogge Wrote:I am not sure it makes much sense to use Interwave for this... the precision of the GPS depends on the accuracy of the clocks of the satellites and not of the signal transmission speed. Higher transmission speed makes it even more difficult to get your position right.
So I would guess SPS sounds good, but with normal radio waves... or make it a PPS (Pulsar positioning system), which use some specialized waved antennas to listen to some known pulsars in our galaxy. The reason for using FTL comms for this is to ensure you can receive it anywhere in the Solar System, probably all the way out to the Oort Cloud. Yes, you get less accuracy than if you can be sure to pick-up EM signals (maybe you could do accurate local positioning using EM radiation?), but I was working on it being universal. It would require a really accurate measurement of the speed of FTL comms, and an assurance that it isn't going to drift.
The only problem I could see with using FTL comms might be causality issues if people tried to be too clever. Having an accurate clock anywhere in the Solar System would be nice, and likely useful for a number of scientific as well as commercial purposes.
Mind you, if you can 'see' the stars, which might not be possible everywhere, PPS sounds good.
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robkelk Wrote:No doubt this system is linked with Terra Beacon One.
META: That would be one of the first things that Artemis sets up, so somewhere between third-quarter 2014 and early-2015.
META-SILLY: I first read the names as "Sailor Positioning System"... There's a possible quirk somewhere in that misreading, ne? Sounds good...
META: You could have cheap/faulty early SPS receivers that only work if you are at least wearing a sailor's cap? They would always work for Senshi, of course. [grin]
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I don't know.
STL comms has the advantage that it's easy to compare timestamps on the signals and get an accurate position. When Earth is 2 light minutes behind you, Mars is 3 minutes behind, Atalante is 5 minutes behind and Jupiter's fifteen that's good enough to figure out where you are. You don't need to send much data, just enough to carry a timestamp. It should be possible to receive anywhere within the solar system.
That said, star-sighting was good enough for Apollo.
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Navigation via star-sighting, and by improvised STL SPS, are standard components of the General Spaceman curriculum (Navigation 102) at Greenwood U.
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ECSNorway Wrote:Navigation via star-sighting, and by improvised STL SPS, are standard components of the General Spaceman curriculum (Navigation 102) at Greenwood U. Navigation via Star-sihgting and other means are more precise, but not something that your random person in the street woudl be wiling to work on. The SPS may ony be precise withing a few kilometers,or even dozens/hundreds of kilometers far away from the inhabited zones, but it will be precise enough for normal use ("We want to go to Mars" "Turn twenty decrees left"). Before GPS, you needed to learn star navigation to cross the Atlantic ocean, but not to cross the English Channel or use a rowboat.
The General Spaceman curriculum would be for the profesionals pilots in cargo and passenger transports, military ships, astronomy/space hobbists and the like.
"All" you need for a stellar GPS is a group of satellites (maybe 6-12) flying on VERY EXACTLY KNOWN orbits around the sun (maybe at a radius of Saturn?) and very precise clocks on them. By comparing the incoming clock-timestamps of at least 4 satellites you can calculate your position (based on your knowledge of the orbits).
So if you want centimeter precision, thats how good you need to know the current position of the satellites
(FTL makes is more difficult because the time differences become smaller)
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Pulsars are clocks as good as atomic clocks... they just do not send binary encoded timestamps. *G*
Rakhasa Wrote:ECSNorway Wrote:Navigation via star-sighting, and by improvised STL SPS, are standard components of the General Spaceman curriculum (Navigation 102) at Greenwood U. Navigation via Star-sihgting and other means are more precise, but not something that your random person in the street woudl be wiling to work on. The SPS may ony be precise withing a few kilometers,or even dozens/hundreds of kilometers far away from the inhabited zones, but it will be precise enough for normal use ("We want to go to Mars" "Turn twenty decrees left"). Before GPS, you needed to learn star navigation to cross the Atlantic ocean, but not to cross the English Channel or use a rowboat.
The General Spaceman curriculum would be for the profesionals pilots in cargo and passenger transports, military ships, astronomy/space hobbists and the like. I'd expect any competent Spaceman to be able to navigate without SPS. After all, you might have poured coffee into it...
As to accuracy, I think that depends on how much you're willing to pay. Civilian GPS can be accurate to about metre level, and if you fiddle about enough, for surveying purposes you can get it down to sub centimeter level. If you say that FTL comms is 10k 'c', and proportionally affects accuracy (this assumes you can't wave-up better clocks) first generation SPS would be good for 10km accuracy, or 100m level for survey work.
Well away from civilized areas you would have difficulty getting better than the 10km accuracy. Technical improvements are likely to give 1km accuracy, but to get much better than that you'll need to do some serious work on the clocks.
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Ace, do you have any reason for using FTL tech? I see disadvantages but not a single advantage.
FTL works inside electro-magnetically shielded areas. Including Faraday Cages.
Ditto ignores EM interference, so should work anywhere in the Solar System. Like close to Jupiter.
It should be a lot easier to get an FTL signal that will cover the Solar System, and nearby, than to get a comparable EM signal, and you should be able to use much smaller receivers.
Having access to a real-time clock, accurate to nanoseconds, would be useful for all sorts of purposes. There might be enough spare bandwidth to fit-in solar weather warnings, which would get to you before light-speed radiation from the Sun would.
You could put in an argument for using PPS (Planetary Positioning System) based on EM, close to each planet, say when you might start to have to worry about moons, satellites, or other travel hazards.
Having a SPS might help interstellar craft (and invaders?) find Sol again.
I'd better leave anything else to those with something more than theoretical knowledge...
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HRogge Wrote:Ace, do you have any reason for using FTL tech? I see disadvantages but not a single advantage. I think we are forgetting the base material... handwavium. The "reason" may be someting as simple as the original designer believing that a FTL system would be better, and now the SPS is quirked that way...
Hmm... I wonder if Fenspace would get both systems with time... the FTL one needs more complex receivers (FTL tech is not small!) and has quirks, but is easier to receive in some regions. The sublight/hardtech one gets built later (it needs REALLY powerful transmitters!), but will be more exact because of all the quirky side-effects missing.
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As for the "interstellar" system looking at the stars (both by hand and by computer) might be much better than build huge, omni-directional FTL transmitters.
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