On Sun, Jun 1, 2008 at 8:38 AM, [email protected] wrote:
Hello Bruce,
Thanks for the positive response. Batting ideas around sometimes produces a concept that is a winner, so the more ideas voiced the better. Interleaving a response into your mail will be difficult so I'll do this list style.
- Cubesats and amateur radio.
Yes, Delfi C3 is the best but sadly one of the very few to carry a usable communications package. It's been a pleasure meeting the Delft students at the annual AMSAT-UK colloquium at Surrey University for the last few years. They started by asking us hundreds of questions, but by last summer it was the AMSAT members who were sitting back during the D -C3 presentation asking questions about their satellite and the innovative Op-amp (not MMIC) based transponder design. I'm certainly looking forward to hearing it in a couple of months time.
- Batteries or not? An interesting topic. Certainly DO-64 and AO-7 have
made the point that batteries are not essential and have in the past caused the demise of many AMSAT spacecraft. I have suggested placing the equivalent of a solid state relay in series with the battery a few times before. Basic idea is that when the battery fails, usually short circuit, it can be isolated allowing the spacecraft to be run in sunlight directly from the panels. Taking the topic forward a little.....How about Ultra capacitors as an alternative storage medium? I haven't checked the following, but if it's incorrect I know I can expect a reply from someone on the BB. Ultracapacitors are available at e.g. 470 Farads at 2.5V If we take 3 in series we have an energy store with useful voltage. But what can it power?
470F x 3 in series = 156F with a max voltage of 7.5V So total energy stored in Joules is
E = 0.5 x CV ^2 or E = 0.5 x 156x (7.5 ^2) or 4387 Joules
Now, and this where my memory gets a bit blurred.... Isn't the Joule a "Watt second" ? So, does this mean this small array of capacitors could supply 1 Watt to a load for about 1 Hour or 3600 seconds? - I included a bit of loss there for a buck-boost converter and not taking the voltage down to zero.
The downside could be what happens when a highly ionised particle impacts at high velocity with a charged Ultracapacitor. But that could be tested.
The latest (Jan Feb?) issue of the AMSAT journal had an article outlining an experiment using supercapacitors. The results were, if I remember correctly, not favourable compared to traditional storage cells. It would be a good place to start investigating this question.
- 29MHz antennas. Yes that would be a challenge. On receive it's not a
problem as the natural noise level is very high but path loss is very low indeed. A loaded whip or even a loop or ferrite antenna could work. On transmit the higher the efficiency the better, but again low pass loss works in our favour.
Perhaps we could encourage some future 1U cubesat developers to try a 29 MHz transmit system. I'm sure they've looked into it and rejected it for the reasons we've discussed. If there were some pre-built hardware available for them, they might think again, though, I suppose.
To complete the horse-before-the-cart approach, it would make sense to ask the cubesat people at CalPoly if they can foresee any launches to high LEO. Who knows, maybe there are opportunities along that line that we just don't know about. Or perhaps if we got together five projects built by amateurs, we could fund an entire cubesat component of a high LEO launch. This would be something like the multiple microsat launches in the past.
Finally, the kiwisat people have a good-looking bird that soon will reach the launch-funding phase. They are planning launch with Dnepr. If memory serves, this is the service that launched AO-51, whose 800 km orbit is more of a treat than the lower ones. Is there any practical way for greater donated funds to equal a higher orbit, or are we bound to the parameters of a given launch opportunity?
73, Bruce VE9QRP