[amsat-bb] Re: All Satellites

Bruce Robertson ve9qrp at gmail.com
Fri Sep 25 21:26:36 PDT 2009

I will attempt a reply to both of these responses.

On Fri, Sep 25, 2009 at 9:27 PM, Tony Langdon <vk3jed at gmail.com> wrote:
> At 09:34 AM 9/26/2009, James Craig wrote:
>>Good point. Not everybody is interested in monitoring the one way
>>downlinks on the majority of these more recent birds. Why is it that
>>there is no problem getting large numbers of these types of satellites
>>into orbit, yet good old fashioned two way linear and FM transponder
>>birds are relatively far and few between?

The reason cubesats are being built is because they are seen as an
excellent platform for educating space science students at the
undergraduate level. The amount of money being spent per launch is
pretty doable for many institutions or local granting agencies. These
agencies and universities are likely simply not interested in
providing you or me with a platform for two-way terrestrial
communication if it is going to slow down their project or lower its
probability of success.

The cubesat design is quite constrained moreover, typically 10cm^3 and
under one kg, even the milk-carton sized 3U format is pretty small for
the power needs of a linear or FM transponder of the sort we are
typically using. We owe a debt of gratitude to Delfi, which showed
that a linear can be put up as a secondary mission, and to William for
his 10cm^2 transponder implementation.

Those are very recent developments, and I'd agree that we should jump
on them as golden opportunities, noting however, that the result will
still be very low altitude orbits and therefore small footprints.
Similarly, SDX technology might be able to miniaturize the transponder
further and reduce its power needs (while making one circuit a
do-everything transponder!), so we're lucky that we're testing that
technology in the near future.

Please note that there is no contention for resources here: the
opportunities the universities made use of are not available to us. If
we want this phenomenon to work to the advantage of those of us who
enjoy two-way voice communications, we need to either launch a cubesat
ourselves or offer the university projects a reason that adding this
capability will *improve* the time-to-launch or probability of
success. This might be in the form of a free, tested, reliable
communications board that happens to have two-way voice capability
integrated into it. It also could be in the form of increased amateur
enthusiasm for the transponder-bearing cubesat and the resulting
increase in telemetry collection, a bargain which we proved to be good
for in Delfi C3.

> I for one was never a SWL, so I tend not to follow the one way
> satellites, unless there's a compelling reason (e.g. for test
> signals, or telemetry decoding - had fun decoding telemetry on AO-40
> when it was first launched).

Nor was I, yet I very much enjoy listening to telemetry from cubesats,
along with other activities in this corner of the hobby. I can offer
you this reason: when I listen to telemetry, I'm listening to
something which is in space and in orbit around the earth, one of the
most exotic locales from which you could receive a message. If I talk
to you on AO-51, I'm talking to you on earth by means of a space-borne
vehicle. It turns out that what's fun about that for me is not
necessarily your voice, but the vehicle. Telemetry tells me about
those vehicles: how fast they are moving, how they are tumbling and
the contents of the telemetry stream: how much power they're
collecting and using. Moreover, with some of the cubesats, the
decoding of this is very easy if one knows CW.

Two more points in my brief  "apologia pro cubesatibus"

1. So-called 'telemetry only' birds are not necessarily that. We had
the opportunity to control COMPASS during its crisis last year. The
low cost of the mission meant that any one of us was solicited to
enter the appropriate codes. I'll never be a control station for a
major bird, but I thrilled to do this for COMPASS.

2. Given that you admit above that telemetry collection is necessary
for the maintenance of communication satellites, shouldn't you be glad
that this steady stream of cubesats has allowed some enthusiasts to
continue to hone their skills in this field?

Finally, a truism that probably bears repeating, though not addressing
the two comments quoted above: if we call cubesats 'not amateur
radio', then we should tar OSCAR 1 with that same brush.

73, Bruce

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