[amsat-bb] Re: All Satellites (Alan P. Biddle)

[Bruce Robertson]

On Sun, Sep 27, 2009 at 7:14 AM, Gordon JC Pearce <gordonjcp at gjcp.net> wrote:
> On Fri, 2009-09-25 at 22:19 -0400, Robert Bruninga wrote:
>> >> At a SmallSat conference... this summer,
>> >> I was amused at the casual assumption by
>> >> a researcher that 50, cubesats could be
>> >> launched as part of an upper atmosphere
>> >> project using ham frequencies for the
>> >> downlinks.
>>
>> And wouldn’t it be a hoot if everyone of them could put their
>> RX/TX into a bent-pipe packet mode, and then we would have
>> amateur radio global hand-held text messaging satellite
>> system...
>>
>> >>  (They would have a lifetime of only 3-4 months.)
>>
>> But it would be FUN for a while!
>>
>> Using some of the 2-way very small micro APRS packet systems, a
>> 2 to 5 Watt transponder will easily fit on a singl circuit card
>> in a small cubesat.  See  www.aprs.org/cubesat-comms.html
>>
>> Bob, WB4APR
>
> If you could have maybe five or six cubesats with an FM transponder
> orbiting in such a way that there was a good 15-minute pass every hour,
> then I suspect that would work wonders for getting people interested in
> satellites again.  The technical requirements for getting into them
> would be low enough for "entry-level" amateurs all over the world to
> have a crack at them - dual-band HT and a homebrew Arrow clone, and
> you're good to go.  Cheap, simple satellites, and cheap, simple ground
> stations.  How many could you fly for the cost of one HEO sat and
> launch?
>
> Gordon MM0YEQ
>

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.

The more I think about this digital cubesat constellation proposal,
the more I see its merits. Beyond the plain fact that it is
financially doable, as an emergency services platform it would be
genuinely useful, since even a low LEO will provide communication
outside the disaster zone in most cases, and compared to a HEO setup,
it would have the advantage of being usable for nearly every ham
anywhere.

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.

Perhaps we could turn the tables and offer university groups a small
amount of space  in the cube for an experiment in exchange for
defraying the launch cost. Those universities that are especially
interested in the natural science side might jump at this, and doubly
so if they knew that they'd have an international APRS network
collecting their data. We could play the role of IntelSat for a change
:-)

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.

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.

73, Bruce
VE9QRP