Re: All Satellites (Alan P. Biddle)
On Sun, Sep 27, 2009 at 7:14 AM, Gordon JC Pearce gordonjcp@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
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
FDMDV uses a 1400 bps codec, occupies only 1100 Hz and operates with any SSB transceiver. Comunications doesn't have to be full duplex. At 12-16 kbps the satellite and ground stations could alternate with short bursts of voice or text. This wouldn't fit in a 2.4 kHz SSB bandwidth but would require a 16-20 kHz wide filter or use of a transverter and a simple SDR radio like the SoftRock.
73,
John KD6OZH
----- Original Message ----- From: "Gordon JC Pearce" gordonjcp@gjcp.net
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.
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.
The more I think about this digital cubesat constellation proposal, the more I see its merits.
I guess that would be if you had the slightest interest in digital satellite operation. Personally I have absolutely ZERO interest in digital satellite operation, only very little in the single channel FM birds, a lot more in linear LEO birds, and even more in linear HEO birds. For the most part, I don't care about DXing, but actually being able to talk to someone for more than a few minutes is rather nice. I will admit that I was happy to get Africa confirmed to complete my Satellite Worked All Continents a few years ago - only to have the ARRL lose the cards.
participants (4)
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Bruce Robertson -
Gordon JC Pearce -
Jim Walls -
John B. Stephensen