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CX2SA > SATDIG 20.07.14 14:02l 363 Lines 13583 Bytes #999 (0) @ WW
BID : AMSATBB9240
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Subj: AMSAT-BB-digest V9 240
Path: IW8PGT<IZ3LSV<IK2XDE<DB0RES<DB0ANF<CX2SA
Sent: 140720/1201Z @:CX2SA.SAL.URY.SA #:8077 [Salto] FBB7.00e $:AMSATBB9240
From: CX2SA@CX2SA.SAL.URY.SA
To : SATDIG@WW
Today's Topics:
1. Re: ANS-199 AMSAT News Service Special Bulletin - AMSAT
Fox-1C Launch Opportunity Announced (Robert Bruninga)
2. Re: ANS-199 AMSAT News Service Special Bulletin - AMSAT
Fox-1C Launch Opportunity Announced (Fabiano Moser)
3. Re: going digital (John / NS1Z)
4. Re: ANS-199 AMSAT News Service Special Bulletin - AMSAT
Fox-1C Launch Opportunity Announced (Phil Karn)
5. 2M1EUB/P NOW QRV IO78MC SCOTLAND (paul robinson)
6. Re: ANS-199 AMSAT News Service Special Bulletin - AMSAT
Fox-1C Launch Opportunity Announced (Wouter Weggelaar)
----------------------------------------------------------------------
Message: 1
Date: Sun, 20 Jul 2014 00:23:00 -0400
From: Robert Bruninga <bruninga@xxxx.xxx>
To: Phil Karn <karn@xxxx.xxx>
Cc: amsat bb <amsat-bb@xxxxx.xxx>, Paul Stoetzer <n8hm@xxxx.xxx>
Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin -
AMSAT Fox-1C Launch Opportunity Announced
Message-ID:
<CALdCfNKKLN6jU6E=LVsQPK579-CUYPWgObHMHHeY511LB7udWw@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset=UTF-8
> The lack of attitude control forces us to use simple omnidirectional
> antennas, which in turn keeps us on the crowded and narrow VHF/UHF
> bands. Worse, there's really no such thing as an "omnidirectional
> antenna" so our links are plagued by frequent deep fades of unlimited
> (or at least unknown) duration. Fading has driven every one of my
> modulation/coding designs for AMSAT telemetry links -- at the expense of
> making them much less power-efficient.
>
> And "power efficient" means smaller ground antennas, and that means a
> cheaper and more accessible ground station for the average ham. And THAT
> means a much larger potential AMSAT membership.
>
> With attitude control, our satellite could use directional antennas on
> the microwave bands. Directional antennas on higher frequencies mean
> much better link budgets.
Yes, but with who? 95% of everyone in view is more than 45 degrees OUT of
the main beam. Directional antennas have zero value on LEO birds that need
to serve everyone in view at the same time. And if you only serve those in
the main beam, then the duration is under 1 minute.
> A lack of attitude control also plagues thermal design....
> I think he found the equilibrium temperature of a 1U cubesat
> to be something like -30 or -40 C!
I cannot believe that. The equilibrium of a nominally black (solar panels
on all sides) spacecraft is something like about 0 to 30 C (32F to 90F) a
very benign operational range. The only time you DO have thermal issues is
when you DO have attitude control and have things that are not equally over
time seeing the sun and dark sky.
PCSAT is now 13 years in orbit and the above range is what it sees. And
that range is over a 2 month period. THe orbit-by-orbit temperature
changes are less than +/- 10 degrees C. The extremes are due to the
"seasons" of the orbit. When it is seeing eclipses it averages to about
10C and when it is in full sun for weeks at a time, it gets up to 30 C (90F)
I do agree that attitude control is nice to have, but my point is that it
only makes the thermal problem much worse and that "gain" is of no value
for a LEO where it must see everyone in a footprint at the same time.
(Remmebr you cannot have wide beamwidth and gain at the same time).
Gain for HEO's of course is another matter! (think AO-10, AO-13 and AO-40)
Bob, WB4APR
------------------------------
Message: 2
Date: Sun, 20 Jul 2014 10:52:34 +0100
From: Fabiano Moser <fabianomoser@xxxxx.xxx>
To: amsat-bb <AMSAT-BB@xxxxx.xxx>
Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin -
AMSAT Fox-1C Launch Opportunity Announced
Message-ID:
<CAM6o-mZ8smf9j-fCnr-M_A9y6y8w3TWCh__4yWZiR+OjF13n3Q@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset=UTF-8
Hi,
AMSAT can open a Project at KICKSTARTER in technology tag.
https://www.kickstarter.com/discover/categories/technology
I saw a lot of project getting 300, 400% more than originally goal. Some of
then looks like a stupid idea, but that?s no matter they get the found?s,
and what make no sense for me can be a good deal to others :)
Already donated via PAYPAL today, but in my opinion would be great if
AMSAT-NA use this way also to get founds for the project!
Please think about it, I believe that donations don?t need to come only
from amateur radio satellite operators, but also from everyone who likes
electronics, science and technology.
73
Fabiano Moser
CT7ABD
PY5RX
On Sat, Jul 19, 2014 at 10:50 PM, Phil Karn <karn@xxxx.xxx> wrote:
> On 07/19/2014 02:04 PM, Jerry Buxton wrote:
>
> > other three would be "ready to fly" if other opportunities came up. If
> > you're going to spend the time developing them, why not partner for free
> > launches (ELaNa) for more than one? The opportunities for an FM
> > transponder and educational outreach are good. I still have
> > universities looking to partner.
>
> Ah, because launches are scarce and expensive, and (re)developing even
> "the same old thing" consumes much of AMSAT's limited resources. And
> they're limited because we have yet to interest more than a tiny niche
> in what we're doing.
>
> It's great to have universities looking to partner, but what do they
> bring to the table, really? Are we sure they're not just looking for
> free spectrum?
>
> > one flying soon, so that we can learn how well they work and apply those
> > lessons to Fox-2 while we're working out the design.
>
> We already know how well they'll work because we've done the same thing
> many times before. I hate to say it, but this is no longer "rocket
> science". The physics is well understood, and those same physics tell us
> how we could accomplish so much more with our (currently) limited
> resources.
>
> --Phil
>
> _______________________________________________
> Sent via AMSAT-BB@xxxxx.xxx. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>
------------------------------
Message: 3
Date: Sun, 20 Jul 2014 06:45:41 -0400
From: "John / NS1Z" <ns1zjohn@xxxxx.xxx>
To: "Phil Karn" <karn@xxxx.xxx>, "Paul Stoetzer" <n8hm@xxxx.xxx>
Cc: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] going digital
Message-ID: <4E54A423C1EB4577B3D739822B172403@xxxxxx>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Is there some reason why a digital signal cannot be passed thru an
analog/linear transponder? What goes in is what comes out. It seems the lack
of transponder bandwidth limits the digital signal experimenter...
Maybe that is why commercial transponders on satellites are linear. They can
take any modulation and retransmit it : AM, FM, PM or CB
The biggest problem would be the taxi-cabs etc
-----Original Message-----
From: Phil Karn
Sent: Saturday, July 19, 2014 4:24 PM
To: Paul Stoetzer
Cc: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin - AMSAT
Fox-1C Launch Opportunity Announced
On 07/19/2014 12:28 PM, Paul Stoetzer wrote:
> Are FM repeater satellites what we all want in orbit? No. Personally,
> I'd like a Mode J linear transponder in a sun synchronous circular
> orbit of about 2,000km (if we can't get anything to HEO).
Getting a launch opportunity is difficult and expensive. Going digital
is not.
------------------------------
Message: 4
Date: Sun, 20 Jul 2014 03:59:29 -0700
From: Phil Karn <karn@xxxx.xxx>
To: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin -
AMSAT Fox-1C Launch Opportunity Announced
Message-ID: <53CBA111.7000304@xxxx.xxx>
Content-Type: text/plain; charset=windows-1252
On 07/19/2014 09:23 PM, Robert Bruninga wrote:
> I cannot believe that. The equilibrium of a nominally black (solar panels
> on all sides) spacecraft is something like about 0 to 30 C (32F to 90F) a
> very benign operational range. The only time you DO have thermal issues is
> when you DO have attitude control and have things that are not equally over
> time seeing the sun and dark sky.
See Dick's paper for the details; I'm just quoting his results. I know
the basic physics of heat transfer in space but I would never call
myself an expert. He is.
But I can do a back-of-the-envelope calculation that tells me he's right.
The solar cells they're using have an absorptivity and emissivity that
is both 0.98, as I recall, so a cubesat covered with them is essentially
a perfect blackbody.
A blackbody cube with one face normal to the sun at 1 AU will reach an
equilibrium temperature of -21.35 C. The problem is that the ratio of
radiating area to absorbing area for a cube is 6:1 (with the sun normal
to one surface). A sphere would be warmer because its ratio of radiating
to absorbing area is only 4:1. A thin flat plate normal to the sun (like
a solar wing) would be even warmer -- 2:1.
And that -21.35 C figure is for continuous sunlight. Throw in eclipses
and things get much worse. Yes, it would be a little better when the sun
shines on a corner rather than normal to a face, and Earth albedo and IR
radiation will warm things a little, but not enough to matter.
--Phil
PS: Temperature of 10 cm blackbody cube at 1 AU:
Area facing sun: .01 m^2
Solar constant: 1367.5 W/m^2
Absorbed power = 13.675 W
Total radiating area: .06 m^2
Emissivity = 1.0 (perfect blackbody)
Stefan-Boltzmann constant = 5.6703e-8 W/(m^2K^4)
T = (13.675 W / (5.6703e-8 * 1.0 * .06)) ** (1/4)
= 251.8K == -21.35 C
------------------------------
Message: 5
Date: Sun, 20 Jul 2014 12:33:39 +0100
From: paul robinson <pushbiker2004@xxxxx.xx.xx>
To: "amsat-bb@xxxxx.xxxx <amsat-bb@xxxxx.xxx>
Subject: [amsat-bb] 2M1EUB/P NOW QRV IO78MC SCOTLAND
Message-ID:
<1405856019.4620.YahooMailNeo@xxxxxxxxx.xxxx.xxx.xxxxx.xxx>
Content-Type: text/plain; charset=utf-8
Hi group im now qrv this week for 7 days from 20.july from io87mc de paul
2M1EUB/P ...2E1EUB
------------------------------
Message: 6
Date: Sun, 20 Jul 2014 13:45:28 +0200
From: Wouter Weggelaar <wouterweg@xxxxx.xxx>
To: Phil Karn <karn@xxxx.xxx>
Cc: AMSAT-BB <amsat-bb@xxxxx.xxx>
Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin -
AMSAT Fox-1C Launch Opportunity Announced
Message-ID:
<CAKXf1rF2dPAZ-on2qXjbTZpb2MLZE6pa+yJTutO1UoWO56AqRg@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset=UTF-8
Hi All,
I could start writing all kinds of angry E-mails, but I have always
resisted to reply on these kind of threads.
I'm glad the AMSAT-BB is not reflecting the great community that is amateur
radio and the many exciting things we are doing for our community to keep
communications alive.
I will go back to work on SDR transponders, D-ATV cubesats, CODEC2 speech
downlinks and FUNcube linear transponder improvements, but you guys are not
interested I hear, so I will shut up.
Wouter PA3WEG
On Sun, Jul 20, 2014 at 12:59 PM, Phil Karn <karn@xxxx.xxx> wrote:
> On 07/19/2014 09:23 PM, Robert Bruninga wrote:
>
> > I cannot believe that. The equilibrium of a nominally black (solar
> panels
> > on all sides) spacecraft is something like about 0 to 30 C (32F to 90F) a
> > very benign operational range. The only time you DO have thermal issues
> is
> > when you DO have attitude control and have things that are not equally
> over
> > time seeing the sun and dark sky.
>
> See Dick's paper for the details; I'm just quoting his results. I know
> the basic physics of heat transfer in space but I would never call
> myself an expert. He is.
>
> But I can do a back-of-the-envelope calculation that tells me he's right.
>
> The solar cells they're using have an absorptivity and emissivity that
> is both 0.98, as I recall, so a cubesat covered with them is essentially
> a perfect blackbody.
>
> A blackbody cube with one face normal to the sun at 1 AU will reach an
> equilibrium temperature of -21.35 C. The problem is that the ratio of
> radiating area to absorbing area for a cube is 6:1 (with the sun normal
> to one surface). A sphere would be warmer because its ratio of radiating
> to absorbing area is only 4:1. A thin flat plate normal to the sun (like
> a solar wing) would be even warmer -- 2:1.
>
> And that -21.35 C figure is for continuous sunlight. Throw in eclipses
> and things get much worse. Yes, it would be a little better when the sun
> shines on a corner rather than normal to a face, and Earth albedo and IR
> radiation will warm things a little, but not enough to matter.
>
> --Phil
>
> PS: Temperature of 10 cm blackbody cube at 1 AU:
>
> Area facing sun: .01 m^2
> Solar constant: 1367.5 W/m^2
> Absorbed power = 13.675 W
>
> Total radiating area: .06 m^2
> Emissivity = 1.0 (perfect blackbody)
> Stefan-Boltzmann constant = 5.6703e-8 W/(m^2K^4)
>
>
> T = (13.675 W / (5.6703e-8 * 1.0 * .06)) ** (1/4)
> = 251.8K == -21.35 C
> _______________________________________________
> Sent via AMSAT-BB@xxxxx.xxx. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>
------------------------------
_______________________________________________
Sent via amsat-bb@xxxxx.xxx. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
http://amsat.org/mailman/listinfo/amsat-bb
End of AMSAT-BB Digest, Vol 9, Issue 240
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