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CX2SA > SATDIG 30.10.14 14:04l 262 Lines 8285 Bytes #999 (0) @ WW
BID : AMSATBB9369
Read: GUEST
Subj: AMSAT-BB-digest V9 369
Path: IW8PGT<IZ3LSV<IW0QNL<JH4XSY<JE7YGF<7M3TJZ<CX2SA
Sent: 141030/1201Z @:CX2SA.SAL.URY.SOAM #:11863 [Salto] FBB7.00e $:AMSATBB9369
From: CX2SA@CX2SA.SAL.URY.SOAM
To : SATDIG@WW
Today's Topics:
1. Re: Torque Coil turns vanish? (Robert Bruninga)
2. K1N Navassa (Andrew Glasbrenner)
3. Re: whoops ! (Alan)
4. WTB IC 910 (Jim White)
5. Re: Torque Coil turns vanish? (Greg Dolkas)
6. Re: Torque Coil turns vanish? (Luke Stras)
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Message: 1
Date: Wed, 29 Oct 2014 10:18:33 -0400
From: Robert Bruninga <bruninga@xxxx.xxx>
To: Joe Leikhim <rhyolite@xxxxxxx.xxx>, amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] Torque Coil turns vanish?
Message-ID: <7a3c9b3b5c8848cd4cdf85a7e8803da1@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset=UTF-8
> I am no rocket scientist, but wouldn't the earths magnetic fields tend
to bias those diodes on as the satellite cuts through them, creating
subtle drag?
Yes and no. In theory some, but in practice, no. It takes a coil that is
thousands of meters in length (usually called a "tether") to generate any
appreciable torque. And since torque goes as the area, then our coil
which is 10,000 times smaller would be 0.000000001 as effective or
something like that. Maybe
Bob
------------------------------
Message: 2
Date: Wed, 29 Oct 2014 10:24:15 -0400
From: "Andrew Glasbrenner" <glasbrenner@xxxxxxxxxx.xxx>
To: "'AMSAT BB'" <amsat-bb@xxxxx.xxx>
Subject: [amsat-bb] K1N Navassa
Message-ID: <05ad01cff384$04fd5e60$0ef81b20$@xxx>
Content-Type: text/plain; charset="us-ascii"
If you follow DX news at all, you've probably heard that the same group that
put K5D on the air from Desecheo has been granted approval for Navassa.
AMSAT provided a radio and antenna for the K5D operation and many ops got a
brand new one on satellite. I've offered to the group to again provide gear
and training for satellite operations, including linear transponders this
time. I received an immediate response indicating they would inquire with
the team for any interested ops.
I've gotten several inquiries about this, and just wanted to share that we
did indeed reach out to them with an offer of gear and assistance.
73, Drew KO4MA
AMSAT VP Operations
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Message: 3
Date: Wed, 29 Oct 2014 12:53:21 -0500
From: Alan <wa4sca@xxxxx.xxx>
To: <amsat-bb@xxxxx.xxx>
Subject: Re: [amsat-bb] whoops !
Message-ID: <000001cff3a1$3b3ef660$b1bce320$@xxxxx.xxx>
Content-Type: text/plain; charset="us-ascii"
Another view from the air:
https://www.youtube.com/watch?feature=player_embedded&v=zarWT7H9t54
73s,
Alan
WA4SCA
------------------------------
Message: 4
Date: Wed, 29 Oct 2014 19:23:49 -0600
From: Jim White <jim@xxxxxxxxxxxxxxxxx.xxx>
To: AMSAT-BB <amsat-bb@xxxxx.xxx>
Subject: [amsat-bb] WTB IC 910
Message-ID: <54519325.4000107@xxxxxxxxxxxxxxxxx.xxx>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Looking for an ICOM 910 to buy. H or not. Please reply direct.
Jim
jim@xxxxxxxxxxxxxxxxx.xxx
------------------------------
Message: 5
Date: Wed, 29 Oct 2014 19:07:25 -0700
From: Greg Dolkas <ko6th.greg@xxxxx.xxx>
To: Robert Bruninga <bruninga@xxxx.xxx>, Joe Leikhim
<rhyolite@xxxxxxx.xxx>, amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] Torque Coil turns vanish?
Message-ID: <ece5527e-097f-4380-9fa3-efdb9ce20988@xxxxx.xxxxxxx.xxx>
Content-Type: text/plain; charset=UTF-8
I think that, should you get enough induced voltage in the coil to forward
bias a diode, all it would do is to slow the satellite's rotation around
that axis, not drag against the satellite's orbit. Think about it in
reverse - if it could change the orbital velocity, then we'd all be running
current into coils to push satellites into higher orbits. And we're not.
So it can't.
Something like that...
Greg KO6TH
On October 29, 2014 7:18:33 AM PDT, Robert Bruninga <bruninga@xxxx.xxx> wrote:
>> I am no rocket scientist, but wouldn't the earths magnetic fields
>tend
>to bias those diodes on as the satellite cuts through them, creating
>subtle drag?
>
>Yes and no. In theory some, but in practice, no. It takes a coil that
>is
>thousands of meters in length (usually called a "tether") to generate
>any
>appreciable torque. And since torque goes as the area, then our coil
>which is 10,000 times smaller would be 0.000000001 as effective or
>something like that. Maybe
>Bob
>_______________________________________________
>Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
>to all interested persons worldwide without requiring membership.
>Opinions expressed
>are solely those of the author, and do not reflect the official views
>of AMSAT-NA.
>Not an AMSAT-NA member? Join now to support the amateur satellite
>program!
>Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
------------------------------
Message: 6
Date: Wed, 29 Oct 2014 23:31:49 -0400
From: Luke Stras <luke@xxxxxxxxxxx.xxx>
Cc: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] Torque Coil turns vanish?
Message-ID:
<CAEO5a2bYZ46W7RfovdVGwpyWSieL6UQ0oiwTv8y+v1Z9LeA7OA@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset=UTF-8
Yes, that's right -- it turns out that, given a target dipole (or
torque), and volume, you can adjust the coil resistance by selecting
the right wire gauge. If you run twice as many turns, you get twice
the resistance, and so (for a fixed voltage) half the current. That
gives you the same dipole, regardless. Fundamentally, the dipole is
proportional to the mass of copper that's in the coil.
It also turns out that the power required to generate a given dipole
varies as the square of the dipole, given constant geometry. Let that
guide your ADCS sizing!
-- Luke Stras (VA3LNS)
On Mon, Oct 27, 2014 at 4:35 PM, Robert Bruninga <bruninga@xxxx.xxx> wrote:
> I keep coming up with the number of turns of a torque coil vanishing with
> respect to torque (for a given wire size).
>
>
>
> Given that Torque = A x B x I x n where A is area, B is field, I is current
> and n is number of turns.
>
> But I is inversely proportional to the length of wire (resistance). I = V/R
> but R is proportional to n.
>
> Hence the number of turns. So I is proportional to V/n.
>
>
>
> But V is fixed in the cubesat, (5v) area is fixed (where we can put the
> coil) and so plugging in,
>
> T = A x B x V/n x n and the n?s cancel.
>
>
>
> So I can get the same torque with ?any- number of turns for a given size
> wire.
>
>
>
> What changes with turns, of course, is the current. So to save spacecraft
> power, the more turns, the less current, and thus, the least power for the
> same torque.
>
> Interesting result.
>
>
>
> We ended up with 600 turns of #34 wire to keep the current at 25 mA so we
> can drive it directly from a CPU pin.
>
>
>
> I wonder where?s the limit? Infinitie number of turns? Zero current? I
> guess you run out of space.
>
>
>
> AH HA! Yes, that was it. We started with #30 wire but it took so many
> turns to get to below the 25 mA, that there wasn?t room for the coil. So
> we went to smaller wire and ended up with the #34 to give us a ?? thick
> coil with 600 turns to give 25 mA.
>
>
>
> But I just always found it interesting that once you have chosen the wire
> size, the number of turns is only determined by the current you want. The
> Torque is constant.
>
>
>
> Bob, WB4APR
> _______________________________________________
> Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. Opinions
expressed
> are solely those of the author, and do not reflect the official views of
AMSAT-NA.
> 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.
AMSAT-NA makes this open forum available to all interested persons worldwide
without requiring membership. Opinions expressed
are solely those of the author, and do not reflect the official views of
AMSAT-NA.
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 369
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