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 codecs.
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...
Gordon MM0YEQ