[time-nuts] Fundamental limits on performance
bruce.griffiths at xtra.co.nz
Sun Sep 13 12:30:16 UTC 2009
Magnus Danielson wrote:
> Mike S wrote:
>> At 01:49 AM 9/13/2009, Hal Murray wrote...
>> Time synchronization between spacecraft might take advantage of
>> pulsars, reducing the bandwidth used on inter-craft comm links. As
>> frequency sources, they are as good as Rb short term, and as good as
>> Cs long term. It should also be possible to use pulsars in a GPS-like
>> way, for position and speed.
> I doubt it. Looks like another antenna and set of receiver
> electronics. Unless someone does something smart, it looks like it can
> be ruled out from power and weigth constraints. Pulsars are there
> thought and if several can be observed their beat frequency would be
> fairly low such that phase-relationships can act like a positioning in
> space and time. It may be good to have redundancy such that
> gravitational potential can be resolved separately.
> Space-ship to space-ship or earth station needs to rely on the link
> between them. Synchronous carrier helps alot and stable clocks in each
> end require less dynamics for steering.
Pulsar signals are weak and its difficult to detect more than a few with
a small antenna even with DSP techniques.
Adding a 210ft diameter antenna to the spacecraft just to detect a
sufficient number of pulsars is probably not an option.
Unless a multibeam phased array is used simultaneous observation of
several pulsars isnt possible.
Kolmolgorov turbulence in the interstellar medium can cause all but the
singals from the most distant pulsars to fade randomly.
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