[amsat-bb] Re: New satellies / Shuttle question

G0MRF@aol.com G0MRF at aol.com
Sun Jun 1 04:38:30 PDT 2008

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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.

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.

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
favour.

Regards

David

In a message dated 01/06/2008 02:04:27 GMT Standard Time, ve9qrp at gmail.com
writes:

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
that  price?
>
> For example.  Imagine a 2 or 3U cubesat  type structure, or  even one half
the
> size of AO-51 on last weeks  Russian launch to  1500km.  With payloads
reduced
> to  transponders and a basic onboard computer  and an Electrical Power
System,
> it would be feasable to put RF comms equipment  into a  decent orbit on
29MHz
> 145MHz 435MHz with an RX on 1269.
> For  bands higher than 13cm doppler is a problem and path loss is  quite
high.
>  It may not be possible to provide the necessary DC  power  for transmitters
> in a small  structure.

David:

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
as this.

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
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
cells   that
> are deployed after seperation from the launcher.  Imagine  a  3U cube which
in
> orbit becomes a 3U box of electronics covered  in cells, with an  extended
outer
> 3U shell that deploys forming a  6U structure producing  nearly double the
DC
> 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
burn
> unit could provide a  really nice elliptical LEO orbit, perhaps 680km to
2000km.
>  Wouldn't that be interesting.  I notice that there is an  Austrian
university
> 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
idea'  it
> 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
think.

> 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
important band.

> David   G0MRF

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