[time-nuts] Pulsars make a GPS for the cosmos

mc235960 mc235960 at gmail.com
Sun Sep 29 06:42:46 EDT 2013


Le 28 sept. 2013 à 14:26, Magnus Danielson a écrit :

> On 09/28/2013 02:15 PM, Jim Lux wrote:
>> 
>>>> 
>>>> Don't forget the Doppler and relativistic effects of the earth moving
>>>> around the solar system barycenter.  But that's not much different
>>>> than you do for GPS (e.g. knowing satellite orbits, etc.)
>>> Naturally. You also needs to compensate for their decay-rate as you try
>>> to span longer periods.
>>> 
>>> You can use them for navigation and time, just like GPS. Even seen a
>>> presentation on that.
>>> 
>> 
>> The big hiccup is that you need a fairly good sized antenna to detect
>> the pulsars. They're "bright" in the sense of radio astronomy, but
>> remember that those folks think in terms of 1000 ft apertures at
>> Arecibo and huge arrays like the VLA or ATA.
>> 
>> http://www.radio-astronomy.org/pdf/pulsars.pdf
>> http://www.k5so.com/Radio_astronomy_pulsars.html - an 8.6 meter dish
>> with a UHF feed.   He's using a Rb, by the way
>> 
>> http://www.moetronix.com/pulsar/index.htm  They used a 26 meter
>> antenna.  Scrolling down, it looks like they're getting a whopping 0.5
>> dB SNR on the Crab Nebula pulsar.
>> 
>> 
>> So, pulsar nav seems a bit impractical for present day space vehicles.
>> NCC-1701 Enterprise might be big enough to carry a suitable phased array.

  I think the radio elescope(s) needed are much smaller. There are apparently 2 pulsar clocks installed here in europe, one in St Catherine's church Gdansk and the other in the European Parliament, Brussels. The Wiki article states "The pulsar clock consists of a radiotelescope with 16 antennas, which receive signals from six designated pulsars. Digital processing of the pulsar signals is done by an FPGA device" . I have tried to find more details without success, but the antennas must be reasonable sized to be installed in such places. I think the OP link indicates that X-ray wavelengths would be used which bring down the detector size. No use on earth though.

> On a space-craft it becomes easier to handle thermal noises thought.
> 
> Cheers,
> Magnus
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