[AR] comsats and bandwidth (was Re: Re: Future Exploration Policy...)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 10 Feb 2018 19:33:09 -0500 (EST)
On Fri, 9 Feb 2018, Uwe Klein wrote:
"ground antenna dish. beamwidth"
Wrong viewpoint. ( that works on GEO slots.)
Works on any sort of uplink, actually; it's just simpler in GSO.
you don't have endless bandwidth available.
if you have covered that set of coverage
you can only expand by using uplink ranges twice.
This would require sat side receiving antennas
that can geographically resolve distinct groundstations.
Or ground stations that can aim their beam so there is only one satellite
in it. Which is what's often done right now, and not just for GSO.
Of course, for non-GSO satellites that don't stay in fixed formation with
respect to each other, the aiming problem is dynamic, and if two
satellites briefly are physically close together, it may be briefly
impossible to beam to only one of them. These things are nuisances but
can be dealt with.
It would certainly help to put directional receiving antennas on the
satellites too, but antenna area and antenna pointing are expensive on
satellites, and at higher altitudes your receive "beam" has to be quite
narrow to be useful (e.g., at GSO, the whole Earth is only about 17deg
wide).
The long-term answer is optical uplinks, although it will be necessary to
have multiple ground stations available to work around bad weather closing
one or two of them.
(Realistically, in the long term, optical is the answer to almost any
communications problem where it's not precluded by weather or other
constraints. The RF spectrum will need to be reserved for things that
*can't* reasonably be done optically, e.g. mobile terminals outside urban
areas. Even your cellphone and your laptop will look around for optical
relay stations before resorting to radio; people are already exploring
that idea.)
Henry
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- » [AR] comsats and bandwidth (was Re: Re: Future Exploration Policy...) - Henry Spencer