The Carrington Event of 1859 was the largest solar event in the last 500 years, according to one of the articles. The next largest event was less than 1/2 the magnitude. Several other recent events were mentioned. One of those recent events produced an outage in GNSS lasting 10 minutes.
Your point regarding cloud cover does play very strongly into this discussion. Relying upon CN as a backup is only useful when it can provide a fix. I would further suggest the duration of the outage also may preclude the use of CN as a backup. If the event duration is less than the time during which we can get an AM or PM fix, then CN didn't serve as a backup. Having an occluded sky permits the GNSS outage to last longer before CN can be a backup.
While it would be fantastic to have an independent backup, nothing but CN provides 100% world coverage. eLoran isn't going to provide anywhere near that level of global coverage. To your point, CN provides sporadic data, orders of magnitude less frequent than GNSS. Cloud cover impacts the frequency.
My objective these past few weeks has been to find a rationale for CN. I have been poking at every possible cause I can think of to provide a case for CN, looking for failure modes in the GNSS system. This latest line of questions with Dr. Langley has shown, to my opinion anyway, that we cannot hang that rationale on a solar event. Suggesting that a mariner prepare and practice CN for a 'once in 500 year' event is a bridge too far. The more recent events provided in the recommended articles suggest that CN will not be the backup, again, in my opinion. Outages lasting 10 minutes or providing small fix errors due to propagation delays will never provide a reasonable rationale for CN. In my view, solar events are a dead end. I was hoping Dr. Langley, with his far better understanding of the GNSS system, would concur on those points.
I absolutely understand that rendering an opinion that CN is not a backup for GNSS is heresy. We are a CN group. The statement is contrary to our purpose. If we wish to really preserve CN, then we need to come up with a rationale that CN is a backup because ...[ please fill in this blank ].
As our group euphemistically 'ages out of the system', the count of practitioners of CN will approach 0. Of course, the mandated licensing requirements will keep CN alive on life support, but these aren't practitioners. The bulk of them study to pass the exam, then put the book away.
Brad you wrote: "Given your (meaning Dr. Langley's) knowledge of the GNSS system and its susceptibility to solar events, is celestial navigation a prudent backup to GPS navigation if a solar event occurs?"
I don’t think you can suggest alternates to cover the extremely remote possibility of World wide temporary failure of all GNSS systems without first looking at the reliability of the suggested alternative itself. In the case of CN, before even looking at accuracy, we need to look at availability. For most people operating at the Earth’s surface, the probability of the sky being obscured by cloud (as it is for me right now) must be many orders greater than the possibility of GNSS being unavailable. Don’t we read in the maritime classics of vessels standing into danger because of the Sun being obscured for days at a time? The situation was different for aircraft flying above the troposphere where CN was available most of the time and in mid-ocean was of comparative accuracy with existing systems well into the 1980s. Have an alternative to GNSS by all means, but choose one which will be viable to most users most of the time, not just in choice locations like the Arizona Desert or with star trackers which can work though cloud. A good question to ask in this particular situation is how might e-Loran be affected by intense solar events? DaveP
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