[time-nuts] Timing Distribution in Mountainous Terrain
lists at rtty.us
Fri Sep 10 17:26:12 UTC 2010
An event that totally takes out every single GPS sat probably takes out everything else in orbit. A single GPS sat, no longer under ground control would be fine for timing a system like this. You don't need a full constellation or ground segment steering.
About the only non-end of the world 6 day no GPS situation would be a jammer. Directional antennas could take care of terrestrial sources. You might need a steered dish, but those are available items (you can all look at the same sat at the same time). That get you to fleets of orbital jammers sync'd to the GPS birds. Pretty far out....
On Sep 10, 2010, at 10:02 AM, jimlux <jimlux at earthlink.net> wrote:
> Peter Monta wrote:
>>> Aren't pulsars a reliable accurate time source or do they not provide the 30nS over ten days accuracy?
>> By using them in common view, though, any absolute error would drop
>> out. I'm not sure pulsar pulses are fast enough to do discrimination
>> at 30 ns time scales, though. VLBI with broadband sources (quasars)
>> would be fine here, but large amounts of data would need to be
>> exchanged, and the sources are weak, requiring large antennas.
>> Satellite laser ranging using LAGEOS and friends? But the original
>> poster said no satellites (not even passive rocks in MEO?), and
>> weather is a problem.
> Hmm.. here's an idea
> look for the 217 MHz signals reflected from LEO satellites and NAVSPASUR.. big illuminating fence, fairly easily detectable signals, LEO satellite so ionosphere isn't a big deal. You get many satellites per hour crossing the fence.
> Actually, if any satellites are available, how about using TV signals from GEO relays? (or is the presumption that everything above 50,000 ft MSL has been wiped out?) Some folks at JPL have used such signals to do microwave holography on big antennas (big signal, essentially plane wavefront, etc.)
> For that matter, LEO satellites aren't that far away, and your Lband interrogator for the transponder could probably light them up and reflect some power back. You'd have to run the radar equation and see how much power you get back... I have no idea about the RCS of a LEO satellite, but I'll bet its "many" square meters (if you count ISS as a candidate.. thousands of square meters RCS) ISS passes over several times a day, and while its orbit isn't particularly well known or controlled (at least not to a scale of meters), it might be good enough for you.
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