[time-nuts] Pulsars make a GPS for the cosmos
Jim Lux
jimlux at earthlink.net
Sat Sep 28 12:15:59 UTC 2013
>>
>> 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.
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