[time-nuts] OT: Far-out space navigation from sideways satnav signals

Peter Monta pmonta at gmail.com
Thu Apr 18 15:15:04 EDT 2013


Hi Magnus,

> Would not an antenna with a deep zero focus on the earth center help to
reduce earth-noise (ground temperature noise as well as man-made noise)?

It might, although you'd need a large antenna to generate the angular
resolution needed to reject Earth noise while listening to a GPS bird near
the Earth's limb.  If you make the tradeoff of using GPS satellites further
from the limb (say at their max separation of ~5 degrees looking from lunar
distance), hoping for less Earth noise, then you're working with a fainter
sidelobe.  I'm sure the proper tradeoff is known.  The whole problem sounds
much easier if you're merely at GEO.

I wonder if there's any advantage in combining far-away GPS with X-ray
pulsar navigation (XNAV), which is said to be good to a few kilometers,
though long integration times are needed.  For example, the rough system
time from XNAV could enable very long (arbitrarily long?) coherent
integration for very faint GPS signals obtained with a gain antenna pointed
at the Earth.

Cheers,
Peter


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