[amsat-bb] Re: All Satellites (Alan P. Biddle)
Gordon JC Pearce
gordonjcp at gjcp.net
Sun Sep 27 13:32:12 PDT 2009
On Sun, 2009-09-27 at 16:02 -0300, Bruce Robertson wrote:
> In a recent conversation on this list, I did the math and
> conservatively estimated that 125 1U cubesats could be launched for
> the current quoted price of a HEO launch alone.
I think Bob Bruniga mentioned something like $400 to build a packet
satellite. If that's correct - $400 per unit - then I will split in
$100 to get the first one started (and more, if the exchange rate swings
in my favour again).
> The problem, as I think Bob has noted before, is momentum: a
> constellation of these is very useful; one of them is much less so.
> The group that puts up the first of them, then, is not doing much of
> interest and hopes that others will follow to increase the 'network
> effect'. For this reason, we cannot expect (most) university cubesat
> missions to look merely like this, unless their institution has a
> special interest in emergency communications, as Bob's uniquely is.
I personally have no interest in emergency comms, but I would like to
see useful packet satellites. If they're that cheap to build, then we
should have a big stack of them ready to fly.
> KD6OZH's mentioning of a 1200 bps voice codec is very interesting,
> too. I see that DSTAR's AMBE is down to 2000 with error correction,
> and Speex operates down to 2000, too, though I think without error
> correction. (I find the latter much more engaging as a ham, since it
> is open source.) It would be a hoot to do a voice conference over the
> Internet using a sample of low bitrate codecs and just get a sense of
> what might be possible. One downside of voice is that it would occupy
> the transponder far more than messaging, and Bob's favorable power
> calculations would need to be estimated downwards.
Would the packet satellite be capable of bent-pipe operation though?
You'd need to transmit and receive simultaneously to get that working.
I'd far prefer to use Speex rather than the locked-down proprietary AMBE
> I guess another aspect of the cubesat approach is that the cost of
> failure is much lower. If a low bitrate audio codec doesn't really
> work well, it would be a less expensive enterprise and easier to chalk
> up to experience.
You could also just blow new firmware on it remotely. If it bricked,
that's a shame but at least you tried...
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