On 4/18/13 11:02 AM, Magnus Danielson wrote:
On 04/18/2013 04:01 PM, Jim Lux wrote:
On 4/18/13 4:01 AM, David J Taylor wrote:
An interesting novel use of GPS "stray" signals....
"ESA’s retired GIOVE-A navigation mission has become the first civilian
satellite to perform GPS position fixes from high orbit. Its results
demonstrate that current satnav signals could guide missions much
further away in space, up to geostationary orbit or even as far as the
Moon. " See:
http://www.esa.int/Our_Activities/Space_Engineering/Far-out_space_navigation_from_sideways_satnav_signals
Interesting..
I know there's a bunch of analysis about how to use GPS at the moon. you
need to look at the GPS satellites on the far side of the earth, grazing
the limb.
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)?
But then you'd need to point it. A bigger issue might be the sun.
Either way, the question is whether it makes much difference. The
typical GPS receiver has a hemisphere field of view (granted, mostly at
3K) and the satellite is at 20-40,000 km.
At the moon, your antenna would have a 4-5 degree field of view (if
pointed at the earth), so 30dB more gain, but looking at a 300K load, as
well.
At 300,000 km, that's about 10 times the distance, or 40 dB less signal..
So a net of -10dB..
Typical GPS receiver Tsys is 100K or something (in space).
So, 3 times the noise.
Maybe you need more gain (earth is 2 degrees wide viewed from the sun,
so you could go to a 3 degree beamwidth.. that's like 36 dB gain
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