1. How would you the user react if say sometime in the next 2-3 years GPS got down to a stage where accuracy capability did not meet specifications (let alone accuracy expectations that some inspire GPS to be capable of) and at certain times could become unusable?
2. Do people rely on GPS that much that a lack of satellite coverage could change the way they go about their activities?
1. Is that like the old 'Transit'system, Sat Nav. Depends on the environment you're using it in. If I was deep sea I'd grab the sextant. Otherwise go back to using terrestrial marks and bearings.
2. In todays maritime world a lot would change their activities.
If the sats go we'll be back to DF, Decca, Omega or Loran, only guessing.
Aside from all that, what do you know about the GPS system used in Europe now? Not sure of the details as I haven't used it. A genuine request, not looking to yank any chains.
As far as accuracy goes, I've used differential satellites that have been extremely accurate, relatively speaking, well I didn't use them the surveyors did, I drove the boat. The surveys were for placement of oil drilling rigs.
Have I made a big mistake here?
Satnav,
I would be mighty pissed off more than anything.
All the marks I have sounded to wide to have land marked them would be lost. I could run by compas bearing to them but I recon I would miss them a lot more than hitting them
cheers
Garry
Garry
Retired Honda Master Tech
Like Spaniard King I wouldnt be the happiest person to be with but I use GPS as a guide only I do have a GPS marks bible of fishing spots but I tend to use my fish finder for whats its made for finding fish and I use marker bouys quite a bit aswell . Although when it come to bad weather I have to admit the GPS comes in very handy otherwise I only use it only as a guide .
1. I would doubt that GPS and all related uses would ever get to a stage that was comprising. However there are some indications there could be a period in which GPS will not be operating too (or possibly slightly less than) specifications. In other words it would still be operational but at more of a design capacity which is quite a few levels down from what users have come to "expect" now for quite a few years.
2. System like Omega don't exist anymore, Loran is only a US/European thing and limited at that.
3. Galileo, the European planned system does not exist, well apart from 1 test satellite with a life of 2 years and still a long way off with the proposed 30 satellite constellation, perhaps by 2012? Maybe?
4. Differential accuracy is still based on having a primary global satellite systems, Galileo doesn't exist, Glonass is in a poor shape and GPS "could" become marginal before it gets better ??
5. What has been suggested that might occur at this stage (loss of satellites for a period) is a possibility and the system will certainly never be let run down to an unusable stage but possibly an unknown period where the systems capacity will not meet users expectations and probably by quite a margin?
Satnav what you you say is the absolute minimum number of satellites that would be required to allow the system to keep running effectively ?
Satnav, I'm not doubting you, but do you have a source or some more info on this statement:
Link maybe ?What has been suggested that might occur at this stage (loss of satellites for a period) is a possibility
1. 24 Sats is minimum to still basically be effective as per spec BUT if the wrong combination of satellites have issues at the wrong time then there will be problems. Even now with 28-29 satellites if the wrong combination of satellites and especially in one particular plane have issues then there will be problems. At this point even with just 2 satellites from one particular plane drop out then there will be problems.
2. 22 satellites is the absolute minimum at which point accuracy will go out to 40 metres and more some of the time but then which 22 satellites are left makes the difference.
3. Link? Doubt you will find a link specifically for this at present. What many are looking at, at this point is the number of ageing satellites , oldest is nearly 16 years, the amount of redunancy left on the existing sats, the health of some/many of the existing sats, what satellites exist in storage for launch, launch issues and future launch dates to replenish the real unhealthy one/s first. The satellite with real problems at present will not have a replacement until September and even this totally depends on weather as it's in the middle of hurricane season.
All good info SatNav. Interesting how things have changed since I studied electronic navigation as a competency in 1997. Omega was gone, Decca was going, with only Loran C to stay in NE USA.
Concerning the NAVSTAR system, we were taught and examined on there being 27 sats up there at any time, working on minimum of 21 and 3 were spares. The life span was estimated at 7 years, as the fuel would be exhausted, the caesium isotopes would last longer but fuel for the rockets would run out.
Whether this was completely accurate, it was the literature at the time. Quite a few would have been replaced since then and more have gone on-line obviously, but how can they keep one for 16 years? don't they use as much fuel as calculated?
1. gelsec, Yes only when a satellite has no fuel left will they actually call it dead dead. SVN15 was launched Oct 1, 1990, became operational Oct 20, 1990 and is still going around today and is not the satellite right now with real problems anyway. There are a heap of 15's mates from the early 90's still going (some just going at that) and old age is really setting in up there.
2. GPS sats have exceeded all expectations as far as design life is concerned but this has been both a good thing and a bad thing
3. In any event this is getting a bit beyond the original query in what it might mean to users if the unexpected did occur based on what users have come to expect?
SatNav as usual blows us away with the info but I have an old crappy GPS on my boat that actually gives the official "health" of the satellites being interrogated and rarely if ever do I see one with a problem!
Anyway, responsible boaties only use it as a backup to their own knowledge and visual observations
G'day Satnav,
There isnt really much being said to directly answer your question.
If ever GPS became "useless" or unuseable, the outcry would be phenomenal.
It would be similar to having the mobile phone network disabled ....
There would be a lot more work for the CoastGuard ... people lost, run aground (more in moreton bay I am talking)
We would still fish for sure ... but just like the pre gps days, we would spend a lot more time looking for reefs etc by running on compass bearings, travel times, depth contours, land marks ... and again only find them when we were lucky.
In general (and I am not being nasty) I dont think there are too many people these days that have the knowledge to navigate via chart and compass
GPS has certainly tainted our navigation skills - there arent too many people that would pull out a sextant, slide rule etc, orient paper charts or do manual conversions from true to mag just for the sake of practicing their navigation skills.
If we were out fishing and the GPS failed ... I think the first comment would be "now where the F$%K are we????" then you would have to get busy trying to find out.
We all rely heavily on our GPS units, maybe a little too much at times. But in saying that, GPS is relatively cheap, accurate and by far the easiest way of navigating our waterways.
Cheers
Pete
1. The difference between "Healthy" and "Unhealthy" as sent in the nav message is purely for useability, black and white, on or off. If a satellite is on maintenance it will be set Unhealthy, if navigation capable then it will show as healthy.
2. What the healthy flag DOES NOT show in the nav message is the redunancies remining on the satellite and redunancies is where there could be a future concern. A satellite with all 3 or 4 clocks available, good power, good fuel is "healthy" as far as your GPS is concerned, so is a satellite with only 1 clock left, bugga all fuel and failing power.
3. The satellite "health" shown on many GPS receivers is better described as a "Use" flag.
4. There is generally a satellite on planned maintenance ("unhealthy") at most times apart from the odd one that looses the plot from time to time.
1. I don't think anybody is suggesting that GPS will become unueable as there are certainly contingencies in place if that was becoming evident and evidence is required quite sometime before the event as is does take some lead time to ready, launch and bring on line a satelite.
2. If GPS ever did get "unuseable" then the least of our worries would be mobile phones as they would not be working anyway along with the world's financial's and anything else requiring precise timing coordination. This timing scenario will not happen as timing doesn't require heaps of satellites in ideal geometry.
3. Compared to the past few years and even today where there are extra GPS satellites the more logical outcome if a few went down all at once, could be periods throughout the day where "reliable" navigation could be of concern?
Lucky I haven't thrown away my book of hand drawn line ups. Maybe I should add more to the book "just in case"
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