[amsat-bb] Re: New satellies / Shuttle question
G0MRF at aol.com
Sun Jun 1 04:38:30 PDT 2008
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
1) 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
2) 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.
3) 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
In a message dated 01/06/2008 02:04:27 GMT Standard Time, ve9qrp at gmail.com
On Sat, May 31, 2008 at 5:40 AM, <G0MRF at aol.com> wrote:
> Hi Edward / group.
> Most current construction or feasility study is centered on P3E / Eagle /
> Intelsat /HEO where launch opportunities are rare and costs are high.
> Perhaps we should look at this problem from another viewpoint. Start with
> what launch opportunities AMSAT can afford and then retake the technology
> initative and investigate what minaturised payloads can we launch for
> For example. Imagine a 2 or 3U cubesat type structure, or even one half
> size of AO-51 on last weeks Russian launch to 1500km. With payloads
> to transponders and a basic onboard computer and an Electrical Power
> it would be feasable to put RF comms equipment into a decent orbit on
> 145MHz 435MHz with an RX on 1269.
> For bands higher than 13cm doppler is a problem and path loss is quite
> It may not be possible to provide the necessary DC power for transmitters
> in a small structure.
I asked the same question at the end of a thread decrying the lack of
HEO satellites, hoping to start a conversation on the topic. Let's
have one here. The best of this group is when we bat around ideas such
First, very soon we will have a great basis for future discussion in
Delfi C3. Already, though, it shows that a 3x cube can hold
transponder and deploy enough solar for a good transponder U/V
(judging by its fantastic downlink now). Could we replace the science
on board D C3 with a battery of chargeable cells and still stay within
the cubesat weight requirements? Or, even more radically, can we do
without batteries, given how we can live with AO-7 and D C3?
My guess is that deploying a 29MHz antenna could be hard with that
limited space. But it would represent a fascinating challenge.
Perhaps the hardest part would be finding a ride to high LEO without
propulsion. My sense is that Cubesats work economically because there
are lots of them. Won't university groups interested in remote sensing
see this as something worse than what they have with low LEO, for a
greater cost? Maybe we could get a bunch of projects interested in
high LEO together for one launch. Or, perhaps we could help one of the
national groups that still have access to their countries' launch
facilities, such as Japan or India or China. These might include a
p-pod or two in a high LEO launch as a charitable act: much cheaper
than a micro-sat.
> Talking of DC power, the number of cubesats that fail due to power problems
> is huge. The answer is to get inventive with deployable solar arrays. With
> the engineering excellence AMSAT possesses it should not be impossible to
> arrange a structure where the entire outer layer contains extra solar
> are deployed after seperation from the launcher. Imagine a 3U cube which
> orbit becomes a 3U box of electronics covered in cells, with an extended
> 3U shell that deploys forming a 6U structure producing nearly double the
> power. The 6U structure also makes antenna design easier
A neat idea. What about film solar panels that would be unfurled once
in orbit? I think these probably have such a lower efficiency that
they wouldn't be worth the extra area they might cover. In any case,
Delfi C3 gives a pretty great worst-case scenario.
> For a slightly more risky idea.....small satellite propulsion. Again,
> perhaps 3U cube, with the last section comprising a small motor. A single
> unit could provide a really nice elliptical LEO orbit, perhaps 680km to
> Wouldn't that be interesting. I notice that there is an Austrian
> team who have developed a cubesat sized ion propulsion system asking if
> anyone would like to try it. So, while this may initially seem a 'wild
> is based on technology that is very nearly a reality.
Regarding the ion propulsion, what if we were willing to wait a year
or two before use, so that all solar energy went into boosting the
orbit for that time?
And then there's the transponder. How efficient could a SDX be?
William, PE1RAH, is working on cubesat format UV transponders, I
> Worth investigating?
I really think we should look into S-band downlink, too. The stats on
s-band in HEO might be scary, but I think in LEO it would still be
high enough signal to be great fun. And we'd be colonizing an
> David G0MRF
More information about the AMSAT-BB