[time-nuts] (no subject)

[Bob kb8tq]

Hi

That’s pretty neat !!!

At least as I read the posters ( and I could have easily missed something …):

Their pulse technique (using the giant telescopes) gives them an instant reading
on the distance / delay to the cubesat. Even if there are propagation issues, they are
measured (and eliminated) in that pulse process. With GPS, we don’t get that sort
of live data. 

In terms of setting up something to use it in my back yard ….yikes … that’s one
mighty big “antenna” on their ground station. Since you have to deliver enough power
to the sat *and* back via reflection to “trigger photo diodes” the “minimum” required
optics could be pretty big …. They don’t go into that so who knows ….

In the current implementation, this looks like a “one user at a time” sort of system. 
I suspect that’s fine if the minimum optics are anywhere near as big as what’s in that picture.
If this all *can* be done with a backyard sized telescope, scheduling could be interesting ….

Bob

> On Jan 18, 2021, at 10:53 AM, Skip Withrow <skip.withrow at gmail.com> wrote:
> 
> Hello time-nuts,
> 
> Came across this poster of the CHOMPTT cubesat mission.
> https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3494&context=smallsat
> 
> Obviously, they are doing measurements on a per orbit basis.  But if
> you had an optical ground station and the clock difference information
> (correction) you could calibrate your home clock.  Basically, this is
> what we already do with GPS with CORS correction information to get
> much better than 20ns accuracy.  One question that I have is the
> uncertainty with optical paths lower than for GPS (RF)?  I suspect
> maybe.
> 
> A system such as this might also provide an independent source of time
> to GPS.  But don't we already have that with GLONASS, Beidou, and
> Galileo?
> 
> Regards,
> Skip Withrow
> 
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