[amsat-bb] Re: ideas

[Bruce Robertson]

Quoting Nick Pugh <quadpugh at bellsouth.net>:

> Hi Amsaters
> 
> The cubesat team at the University of Louisiana is in the process of
> defining its second mission for its cubsat project. The team has decided
> to fly a cubesat that has a educational component. We are asking for
> ideas that would excite K through 12 students that can be flown on a
> cube sat  i.e. 1 watt of dc power in a 4 inch cube. In addition to the
> education component the team is thinking of flying a high efficient
> radio per haps bpsk with a forward error corrected  code with Eb/No of <
> 3 db. Again here we are asking for input in the mission definition and
> help in the implementation including pier review.
> 
> 
> Please put your vision in gear and help us.
> thanks
> nick K5qxj

Nick:

This is not a proper mission, per se, but for some time I have had in mind
something that I think would be of great help to the amateur community, and
also would make the basis for some interesting experimentation by students.
It also would cost very, very little of your power budget. This is a QRPp
CW beacon on S-band. A very low-power beacon which could be identified off
the air with basic equipment (unlike a 9600 baud signal) would go a very
long way toward helping amateurs mount equipment for HEO s-band work. As
recent debate showed, there are some good open questions about this band:
how noise-polluted is it in my area, for instance. 

Some math:

Say P3E has a 5w beacon with a 2dB gain antenna out 35000km that's roughly
37dBm + 2dB - 190 dB in path loss = - 151 dBm to the antenna.  With a LEO
bird out a maximum 3000km, the path loss lowers to 170 dB. A 70 mW (18.5
dBm) signal to a 2 dB antenna - 170 dB will be roughly the same kettle of fish.

For builders, the s-band offers many interesting opportunities for small
gain antennas. For students, S-band is interesting to observe due to its
dramatic doppler shift: in the high school classroom, for instance, it
would make an interesting complement to observing a 70cm signal near the
same time. It also opens opportunities of building interesting gain antennas.

Even nuttier idea:
Furthermore, it might be possible to provide a fully-functioning
communication satellite if the output could be goosed up to .25w into a 8
dBi patch antenna (the bird would have to point well, I suppose). That
would provide, what -158 to about -128 dBm to the ground-station. 

Most nutty idea:
You could try to build a one-channel CW transponder in software: if the S/N
is over a threshold on input, the (s-band) output is keyed in real time,
avoiding the need for a linear transponder and allowing for some software
safeguards to avoid jamming signals, etc.

On the whole, if I were a dispassionate assessor, I'd prefer Bob's idea,
but I thought I'd mention some of the crazy ideas that have been rattling
around in my head. In any case, I *do* think we should continue to
encourage cubesats to undertake the additional effort to help us colonize
s-band, as some will be doing in the future months. I also think that if
we're interested in affordable LEO analogue communications birds, we need
to think about how we can fit our needs into a cubesat (or 2x or 3x
cubesat). If we cracked that nut (and it will probably entail shifting some
of the complexity onto more advanced ground stations), we might find a very
rosy future for LEO communications.

73, Bruce VE9QRP