JM_Runs said:
Your ability to build each hyperboloid depends on your ability to hear
both birds at once. If both birds had a hole in the transition, a
short missing bit, it would create a dark spot. Just the locations
where the two missing signals overlapped would be a problem.
I'm not sure what you mean by this.
The satellites transmit precise time of day and ephemeris information
saying exactly where they are at specific times. Receivers note the
positions of the satellites at the specific times when they broadcast a
message, then observe the delay in receiving the message and use this to
calculate the receiver's distance from each satellite. With a few
satellites, it's straightforward to locate the receiver in
three-dimensional space.
So how would you change these transmissions to leave certain specific
solutions "dark" in practice?
You could turn off the transmissions completely, or transmit false data.
So far, so good. The problem is that, at any given point on the Earth's
surface, there are typically half a dozen satellites visible, and often
a dozen. Each satellite has a footprint that nearly covers a
hemisphere. It would be very difficult to change transmissions in a
pattern that would make all satellites visible to a certain region look
different from the way they look to the rest of the world. And it would
incidentally be almost impossible to keep secret as well.
Now, if you had special transmitters on the satellites that could cover
specific areas on the planet, the situation would change. But I don't
know if that's the case now. I don't see how it could be done with
single transmitters for the entire footprints of the satellites.
It's a bit more complicated than that. You need multiple dark bands
caused by missing bits from all the birds in the sky. And they all
need to be synced to blackout the target.
I'm not clear on how the transmissions would be changed to produce dark
bands only in certain locations. Remember, nearly half the
constellation is visible from many points on the planet at any given
time.
Because the satellite keeps moving the math for the blackout
hyperboloids would have to be done in real time. Based on second hand
reports from the field I suspect the function has been operational for
at least ten years. Therefor I suspect the function is built in to
the satellites OS.
A sophisticated denial system could be built into the satellites. But
without highly directional transmitting antennas, I'm not sure I see how
it could be done. Of course, nothing prevents the installation of
exactly these types of antennas on the satellites to facilitate the
task.
Of course, Galileo would incorporate exactly the same thing. But it's
hard to say who would be controlling the off switch in the European
system.