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
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