[AR] Re: Future Exploration Policy (was Re: Re: Congrats SpaceX
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Thu, 8 Feb 2018 17:53:18 -0500 (EST)
On Thu, 8 Feb 2018, Uwe Klein wrote:
...imagining comsat builders salivating over how many transponders...
you can do endless numbers of downbeams.
But you can not easily do more than the available bandwidth slots as uplink.
How narrow can you do the receiving uplink antenna beam for good geograhical
separation?
Depends entirely on how big your ground station's transmitting antenna is,
and what uplink frequency you are using (doesn't *have* to have any
particular relation to the downlink frequency). To pick semi-random
numbers, an 8GHz X-band beam from a 10m dish is about 0.2deg wide.
In practice, the large existing population of ground receiving dishes for
a given broadcast downlink band limits satellite spacing more -- it's much
harder to get all those users to upgrade to bigger dishes than it is to
upgrade a handful of uplink stations, especially since the receiving
dishes often are fitted into restricted spaces or otherwise constrained.
Hence Bill's 1.5deg number. (I didn't think it was quite that small but
it's not something I keep up with.)
Henry
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