February 2007 - AMSAT-BB - mailman.amsat.org

Celestrak Keps
by kromestars＠frontiernet.net 22 Feb '07

22 Feb '07

Hi All: What does the brackets [-] [+] [P] mean beside each amsat on Celestrak's website. My sat database has AO51 listed twice as a [-] and [+]. The epoch time for each AO51 I have listed is not the same. Which bracket sign should I use. Thanks, Ron

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Re: Could we raise orbit thru magnetorque?
by Marc Vermeersch 22 Feb '07

22 Feb '07

Hi Jim, Is this the same principle? I believe this has to do with the gravitational field not the magnetic field. -----Original Message----- From: amsat-bb-bounces(a)amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of James C. Mankin Sent: Wednesday, February 21, 2007 7:16 PM To: Bruce Bostwick Cc: amsat-bb(a)amsat.org Subject: [amsat-bb] Re: Could we raise orbit thru magnetorque? I seem to remember back when they were testing tethered satellites from the Shuttle that one of the possible applications being discussed was that if you could deploy enough wire and put the right current through it that it was possible to change orbits. I dont see why it wouldnt work if a large loop of wire could be created say between three satellites in a triangle. Jim Mankin n5x(a)psu.edu Bruce Bostwick wrote: > That's been my understanding as well. Magnetorquing by itself can > drive rotation but not translation. Its main benefit is that it > saves propellant, weight, and complexity, as well as moving parts and > the risk of a hypergolic plumbing assembly exploding and taking out > half the spacecraft's systems, by allowing the spacecraft to handle > rotation with more reliable torquing coils and get its energy for > that from the PV panels. Changing orbits still requires firing a > reaction thruster of some sort. > > On Feb 20, 2007, at 9:47 AM, John Mock KD6PAG wrote: > > >>> Argument is: if when satellite is in the north, a north magnetic >>> field is >>> applied on z plane, will satellite raise orbit ? Same but opposite >>> on south. >>> Considering limited energy available could this raise be >>> significant if >>> applied on all orbits ?. >>> >> I believe magnetorquing can only change the orientation of a >> satellite and >> not its orbit. It is certainly used in the process of changing an >> orbit, >> in order to get a thrusting device pointing in a direction where it >> will >> do something useful. But by itself, it can't change an orbit. It >> can help >> point antennas in the proper direction, etc. >> >> -- KD6PAG (Networking Old-Timer, Satellite QRPer) >> > > "People don't like to be meddled with. We tell them what to do, what > to think, don't run, don't walk. We're in their homes and in their > heads and we haven't the right. We're meddlesome." -- River Tam, > "Serenity" > > > > _______________________________________________ > Sent via AMSAT-BB(a)amsat.org. 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(a)amsat.org. 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

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Advice on antennas for working the LEO's
by John Kopala 21 Feb '07

21 Feb '07

Hi Gary, I just thought I'd throw in my 2 cents. I don't have a great deal of experience with satellites, but I will offer a few comments based upon my limited experience. The antenna by Tonna with 13 DBi on 2 and 16 DBi on 70 is going to have a fairly narrow beamwidth and is obviously a fairly long antenna. It will need to be pointed with reasonable accuracy. If you are 30 degrees off you might as well be pointed the other way. With that much gain, you should be able to work most satellites without the preamps. The problem is aiming the antennas. I recommend using azimuth and elevation rotors. Azimuth alone won't do it with narrow beamwidth antennas if the satellite pass reaches a significant elevation. The software programs will tell you where to aim the antenna and you can easily do that with the rotor control boxes while working stations on the radio. The adjustments are easy and don't take that much time away from operating. I tried an experiment with a tripod and a set of KLM antennas mounted on a cross boom. Aiming a large set of antennas manually can quickly turn into a full time job. I was testing this to see if it was practical to take to scout outings. After trying the tripod setup, I modified the setup and put in my rotors. Using the rotor controllers, made this very workable. I'll send you a picture separately of the setup. Basically, I had a stake in the ground, a 5 ft mast slipped over the stake with a rotor at the top end. The rotor is guyed with 3 additional stakes. Above the rotor is another 5 ft mast section, elevation rotor, crossboom, and VHF and UHF satellite antennas. Obviously, if you are using a single dual band antenna, the whole setup is somewhat simpler. What you see in the picture is destined for my roof plus additional antennas. If you use an antenna that is small enough to hold and point by hand, you will lose a lot of gain vs the big antenna, but it will be a lot easier to point. You still need real time data for the azimuth and elevation and some sort of azimuth and elevation aids would help. Some people enjoy working satellites with the Arrow antenna. Personally, I have not have a lot of luck with reading azimuth and elevation, manually aiming, talking on the radio all at the same time. John Kopala N7JK Date: Wed, 21 Feb 2007 09:44:00 +0000 From: Gary McKelvie <garym(a)garym.org.uk> Subject: [amsat-bb] Advice on antennas for working the LEO's To: amsat-bb(a)amsat.org Message-ID: <6.2.3.4.2.20070221092821.023911f8(a)mail.btinternet.com> Content-Type: text/plain; charset="us-ascii"; format=flowed Hi to the List, My names Gary, I'm just getting started in the sats, initially looking to work the LEO's with FO 29 in particular. The station is going to consist of a Yaesu FT 847 cat controlled by Ham Radio Delux to control the radio for Doppler. It's suitable antennas that I have a problem with from web pages etc a lot of people seem to use the arrow antenna, which unfortunately as far as I can see is not available here in the UK. There is an antenna by Tonna which is a 9 element on 2 and 19 element on 70 claimed gain is 13 dBi on 2 16 dBi on 70. The feed line I will be using to get to the antenna will be a short run of West Flex 103 (which is half the loss of RG 213) I'm hoping to avoid the use of pre amps if possible as getting power to them is a problem. This antenna set up will be temporary in nature, with it being set up each time it is in use. I will be able to rotate the antenna in azimuth by hand or using a azimuth rotator. So would this setup work? So really all I'm not sure is how effective this setup will be and am looking for ideas and suggestions. Regards Gary G7USC Gary McKelvie G7USC Web : www.garym.org.uk

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Re: Could we raise orbit thru magnetorque?
by lu7abf 21 Feb '07

21 Feb '07

I got positively excited reading the amount of wise and elaborate comments on BB regarding raising a bird's orbit thru magnetic fields. It is showing expertise and individuals capable and knowledgeable aimed to the future. Just to add some thoughts will like to comment experience on recent satellites. It is amazing what recent CO Japanese Cubesats are doing with magnetorquers. They can keep a 1 degree Z plane accuracy pointing to earth !! . It is also amazing I can copy 80mw CW from these birds quite strong and readable, due their antennas are pointing right to earth. These sats have magnetometers able to resolve a small fraction of a Gauss in three planes, so they know where they are, and which direction is pointing the earth magnetic field. So at the right point at the right satellite position these birds could send controlled pulses to one or more magnetorque coils with objective of producing a repelling force against earth magnetic field. Being satellite in stable and known attitude, then a small force can do things and perhaps raise her orbit. Their small keps decay rate possibly could be overcomed thus keeping a healthy and longer life for the bird. This could be useful for valuable satellites endangered by low orbit as those launched from the ISS. Just dreaming on possibilities. Thanks much for time and comments ! > > All, > > So why is the maglev principle (magnetic levitation) > http://www.google.be/search?hl=nl&q=maglev&meta= > not applicable in space? > > Magnetic levitation applied to trains generates an upward force equal and > opposite to the earth's gravitation. > > BR, > -- There are no steel rails up in the sky... ;-) -jari oh3uw

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Re: Earths Magnetic Field strength
by lu7abf 21 Feb '07

21 Feb '07

Tks Tony for comment, What I was trying to explain is that magnetic field is a dipole, with each pole pointing away of the magnet. Rotation in the compass needle is caused by rejection of alike poles and attraction of different poles, and as such is producing a force. So the needle moves and in fact does receive energy otherwise it will not be moving. I was not speaking on using an speaker magnet, we have a free magnet that is mother earth. This marvelous magnet is causing auroras as one demonstration of its energy. Why not use this magnet by opposing a magnet created at the satellite at the right earth spot where magnetic lines are pointing straight away from earth?. It is amazing what recent CO Japanese Cubesats are doing with magnetorquers. They can keep a 1 degree Z plane accuracy pointing to earth !! . It is also amazing I can copy 80mw CW from these birds quite strong and readable, due their antennas are pointing right to earth. These sats have magnetometers able to resolve a small fraction of a Gauss in three planes, so they know where they are, and which direction is pointing the earth magnetic field. So at the right point at the right satellite position these birds can send a controlled PWM pulse to one or more magnetorque coils with objective of producing a repelling force against earth magnetic field. As satellite is at a stable height situation, then a small force can do things and perhaps raise her orbit. Their small keps decay possibly could be overcame thus keeping a healthy and longer life for the bird. This could be useful for satellites in orbit endangered by low orbit as those launched from the ISS. Just dreaming on possibilities. Thanks much for time and comments ! Best 73, Pedro Converso lu7abf(a)amsat.org.ar www.amsat.org.ar ============================ Tony Langdon wrote: Subject: [amsat-bb] Re: Earths Magnetic Field strength From: Tony Langdon <vk3jed@xxxxxxxxx> Date: Thu, 22 Feb 2007 07:12:15 +1100 At 03:00 AM 2/22/2007, lu7abf wrote: >If the separation between poles of a small magnet defines strength >of force, then a small separation as in a magnetic compass needle >only 1 inch long placed at equator, over 6000 miles from poles will >not move. Instead it does. But that is rotation, which is equivalent to magnetotorquing, and we all agree this works well. However, your compass for a rare earth speaker magnet doesn't actually move across the table top in Earth's magnetic field, does it? THAT would be equivalent to trying to move the satellite into a new orbit. 73 de VK3JED http://vkradio.comIf the separation between poles of a small magnet defines strength of force, then a small separation as in a magnetic compass needle only 1 inch long placed at equator, over 6000 miles from poles will not move. Instead it does. Also much smaller magnetic dipoles even molecular inside a melted ferrous material does orient and keep their mood if material crystallize. I think it is a matter of poles orientation i.e. on small needle, north pole is opposite to south, so it does not exert force in the same direction of the south pole, but opposite. (It's difficult to explain without using a sketch, and in a not my mother language, excuse me) Regards to everybody and thanks for lending some brain cells to the idea of trying control bird's height. 73, Pedro Converso lu7abf(a)amsat.org.ar www.amsat.org.ar Robert Bruninga wrote: >> I moved a handheld compass towards a heavy... speaker magnet. >> When the compass was a few inches away from the magnet, >> it changed direction from North to the direction of the magnet. > >As someone else pointed out earlier, that is because of the >gradient or difference in "force" on one end versus the other. >One end of the compass was an inch or so closer to one pole of >the magnet than the other end. > >But in space, the pole of your spacecraft magnet that you are >trying to repel, is only one foot closer to the Earths pole, >than the other pole which is attracted. So the difference in >distance of the force that is pulling to the one that is pushing >is only 1 foot out of say 21,120,000 feet to the Earth's pole. >Hence the net force difference is a 21 millionth SQUARED or >.00000000000004 of the force that you observed on the compass. > >Or something like that. >Bob

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Re: Could we raise orbit thru magnetorque?
by George Henry 21 Feb '07

21 Feb '07

In your example of the train, the force that overcomes gravity to levitate the train is not generated by magnetic repulsion of the train against the earth, but rather against the rail above which the train rides, which contains strong sequenced electromagnets to generate both the lifting force and the propelling force. In space, there's no nearby "rail" to push against. George, KA3HSW -----Original Message----- >From: Marc Vermeersch <amvm(a)skynet.be> >Sent: Feb 21, 2007 12:55 PM >To: amsat-bb(a)amsat.org >Subject: [amsat-bb] Re: Could we raise orbit thru magnetorque? > >All, > >So why is the maglev principle (magnetic levitation) >http://www.google.be/search?hl=nl&q=maglev&meta= >not applicable in space? > >Magnetic levitation applied to trains generates an upward force equal and >opposite to the earth's gravitation. > >BR, >-- >/\/\arc > >

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Re: Could we raise orbit thru magnetorque?
by Andrew O. Ojwang 21 Feb '07

21 Feb '07

The craft could push-off the magnetic field of the planet, using it as a rail. Andrew. KI4LTH/5Z4FT.

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Re: Earths Magnetic Field strength
by lu7abf 21 Feb '07

21 Feb '07

If the separation between poles of a small magnet defines strength of force, then a small separation as in a magnetic compass needle only 1 inch long placed at equator, over 6000 miles from poles will not move. Instead it does. Also much smaller magnetic dipoles even molecular inside a melted ferrous material does orient and keep their mood if material crystallize. I think it is a matter of poles orientation i.e. on small needle, north pole is opposite to south, so it does not exert force in the same direction of the south pole, but opposite. (It's difficult to explain without using a sketch, and in a not my mother language, excuse me) Regards to everybody and thanks for lending some brain cells to the idea of trying control bird's height. 73, Pedro Converso lu7abf(a)amsat.org.ar www.amsat.org.ar Robert Bruninga wrote: >> I moved a handheld compass towards a heavy... speaker magnet. >> When the compass was a few inches away from the magnet, >> it changed direction from North to the direction of the magnet. > >As someone else pointed out earlier, that is because of the >gradient or difference in "force" on one end versus the other. >One end of the compass was an inch or so closer to one pole of >the magnet than the other end. > >But in space, the pole of your spacecraft magnet that you are >trying to repel, is only one foot closer to the Earths pole, >than the other pole which is attracted. So the difference in >distance of the force that is pulling to the one that is pushing >is only 1 foot out of say 21,120,000 feet to the Earth's pole. >Hence the net force difference is a 21 millionth SQUARED or >.00000000000004 of the force that you observed on the compass. > >Or something like that. >Bob

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Re: Could we raise orbit thru magnetorque?
by John Mock KD6PAG 21 Feb '07

21 Feb '07

> Argument is: if when satellite is in the north, a north magnetic field is > applied on z plane, will satellite raise orbit ? Same but opposite on south. > Considering limited energy available could this raise be significant if > applied on all orbits ?. I believe magnetorquing can only change the orientation of a satellite and not its orbit. It is certainly used in the process of changing an orbit, in order to get a thrusting device pointing in a direction where it will do something useful. But by itself, it can't change an orbit. It can help point antennas in the proper direction, etc. -- KD6PAG (Networking Old-Timer, Satellite QRPer)

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recent thread
by Al Zoller 21 Feb '07

21 Feb '07

I know the recent thread has dwindled but I just received a news letter with these two quotes that are very germane: “In stirring up tumult and strife, the worst men can do the most, but peace and quiet cannot be established without virtue.” —Cornelius Tacitus “Speak when you are angry, and you will make the best speech you will ever regret.” —Ambrose Bierce If you'd like the source, email off list. 73 de N7UB, Al LM1505

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