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Re. Keeping reliable UTC on board if all signals and all else  are lost. I do 
lunars for fun, not as a serious back up for a watch, but in my experience, 
reverse time sight from exactly known position will give you a more accurate 
independent time check. Then my 4 cheap quartz watches, protected as 
previously described, averaged, give me very accurate UTC or as I still feel 
GMT. Just need to correct every few weeks with reverse time sight from known 
position.
Francis

-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Antoine Couëtte
Sent: 02 October 2018 17:01
To: francis@pharmout.co.uk
Subject: [NavList] Re: Susceptibility of GPS to CME, Rationale for CN?


Dear Brad,
Thank you for your detailed reply referenced on top of the list.
John D. Howard and Robert VanderPol II have since expressed their personal 
views. I am totally endorsing them and they seem comprehensive by themselves.
Most importantly and to make CelNav-DR a fully independent and last resort 
back-up of the back-ups, it is quite important to find ways of keeping 
accurate Time on-board for extended periods of time and at reasonable cost 
and in a practical way.
Hence the current conversations between yourself Brad, Robert VanderPol II, 
Francis Upchurch and others are extremely interesting in this respect.
*May I suggest that the topic of "*Maintaining self contained UTC on board*" 
could be the title of a new series of dedicated posts devoted to accurately 
maintaining a sufficient Knowledge of UT1 onboard should UTC/UT1 broadcasting 
fail for some extended periods of time ?* If you can keep onboard an 
affordable device which does not drift by more than 0.1 s / month relatively 
to UTC, that would be a wonderful tool. In this case CelNav/DR would be an 
extraordinary un-defeatable back up [of the backups] worldwide Navigation 
system. Such very stable UTC clock should give more than adequate time to 
rejoin a known spot and update it through a Celnav Fix from a known 
position.* **Food for thought to many Members here ...*
Let us not forget either that Lunars can derive UT to +/- 30 seconds of time 
under normal conditions. This is far from being mirific but knowing one's 
Longitude to +/- 8' still makes landfall a reasonable exercise provided your 
exercise sufficient caution and judgement.
A last and non-essential point - far from being a rationale per se - is that 
[hand-held] electronic personal devices make CelNav much more "fun" than it 
used to be. This has also been pointed out by Hewitt Schlereth in 
"Susceptibility-GPS-CME-Rationale-for-CN-Schlereth-oct-2018-g42957", by 
Francis upchurch in 
"Susceptibility-GPS-CME-Rationale-for-CN-Upchurch-oct-2018-g42961" . 
Nonetheless should such electronic tools fail, it is a **must** to be able to 
tackle CelNav with tables, paper and pencil, and even starfinder. Many 
different "manual" methods are available as parts of "Emergency Celnav 
toolkits" earlier descriptions in NavList posts. Greg Rudzinski and others 
are extraordinary wizards in this area.
Dear Brad, I fully trust that my lateral thinking reply is not exactly up to 
your strong expectations. Unlike "planet phase correction" or others 
subjects, this current topic is not a scientific one.
It can and should accept multiple answers. Would you not agree now ?
Very Best Regards,
Antoine M. "Kermit" Couëtte

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