[time-nuts] (no subject)

[Lux, Jim]

On 1/18/21 10:45 AM, Bob kb8tq wrote:
> 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

I'll bet they used those facilities because they were available, not 
because they needed that much aperture.

As an example, the TBIRD mission sent Gbps+ data rates from LEO to Earth 
with a few cm aperture on the spacecraft and <1 meter on Earth.

You can visually see a laser pointer on the Earth's surface from ISS 
with no additional optics (you can also see a 800+W metal halide 
spotlight) - there was an experiment where they did this from some 
fairly dark place in the Southwest desert.

The lack of easy multi-user access with two way systems is why GPS is a 
one way system.



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