[time-nuts] eLORAN will be on the air GRI 99600

[jimlux]

On 8/6/20 4:28 PM, Forrest Christian (List Account) wrote:
> If you look at generally-available GNSS PNT solutions, you'll find a few
> failure modes:
> 
> 1) Loss of a satellite (or two).   This is why the constellations have more
> satellites than is strictly necessary, so not a big deal.
> 
> 2) Loss of control/failure in the control system/constellation wide
> software failure, aka the recent Galileo failure.   This is why you have
> multiple GNSS constellations.
> 
> 3) Ground based interference (jamming, spoofing), etc.    This is why you
> need a terrestrial backup, which doesn't really exist.
> 
> For timing, I wouldn't be opposed to someone flying (or adding a payload
> to) a couple of geostationary satellites which live in a separate band from
> GNSS.  It would be interesting to be able to put up a small satellite dish
> and get a highly reliable and hard to interfere with timing alternative to
> GNSS.    I know there are two way time transfer options out there, I'm more
> thinking basically a fixed-location cesium clock in the sky.
> 

Well, the GPS folks found that a Rb works better than a Cs, and both 
need ground monitoring and updating.

One could rent a Single Channel Per Carrier transponder slot on a GEO 
satellite, feed a carrier derived from your ensemble of clocks to the 
uplink, and there you go.

My google-fu is failing and I can't find even a rough cost for such a 
service.  Maybe something like $50k/month? $600k/year.

That 600k would probably buy you *one* space qualified Rb oscillator of 
"good enough" performance, maybe.   USOs like used on GRAIL were 
$1M/each sort of items in qty 4. And then you need some TWTAs to amplify 
the signals for transmission - those are also pretty pricey.

And then the launch cost.. I happen to know (because I just bought it at 
work) that you can push about 100-120kg to a GEO+1000km orbit for right 
around $10M.  Rocketlabs might do 20-30kg to a similar orbit for half that.


All in all, I suspect that there are better uses of the $50M it would 
cost - You could buy a LOT of Cesium clocks for terrestrial use.

If you're willing to do CSAC level performance, and you're willing to 
have it be in LEO, so you see it a couple times a day for 20 minutes, 
and you're willing to do some design and fab in your garage - under $5M.

Look up CHOMPTT  - CSAC and optical links.

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4407&context=smallsat