[amsat-bb] Re: Kick motors on Oscars: How does attitude control work?

Bryce Salmi bstguitarist at gmail.com
Mon Sep 23 17:13:13 PDT 2013

```Found this intersting web page:

http://www.isispace.nl/cms/index.php/projects/nks

Bryce
KBL1QC

On Mon, Sep 23, 2013 at 12:46 PM, Burns Fisher <burns at fisher.cc> wrote:

> Very interesting stuff.  Thanks to everyone who responded.  Using a model
> rocket engine has occurred to me :-)  I noticed that the smaller ones (A,B)
> tend to peak at 10s of Newtons (presumably to get the model rocket going
> fast enough to be stable after it leaves the launch rod) and then settles
> down to sub-10 Newtons for the rest of the burn (a second or two).  So it
> is quite a whack over a short period for a small bird.  I did not look up
> the higher power size.  It would be interesting and not too difficult to do
> the math to see what kind of a perigee raise would happen if someone fired
> one of these on a 3U cubesat of modest mass in GTO while it was at apogee.
>
> Don, there is enough interesting stuff to keep me watching the list.  There
> is also a lot of complaining.  We'd love to have you rejoin AMSAT.  Fox-1,
> the upcoming launch, IS an FM bird, but I hope you noticed that the last
> AMSAT bird, ARRISat-1 was indeed a linear.  We need to continue to learn
> and experiment.
>
> Burns, W2BFJ
>
> On Sun, Sep 22, 2013 at 5:49 PM, Daniel Schultz <n8fgv at usa.net> wrote:
> >
> > > >I just want to ask a question:  If you have a motor of a few hundred
> > > >Newtons, how to you keep the attitude stable during the burn?  For
> that
> > > >matter, how do you get the attitude correct for the start of the burn?
> > >
> > > Simple question, simple answer: You use the magnetotorquers to point
> the
> > > spin
> > > axis in the right direction, check and check again to make sure you got
> > > that
> > > right, then use the magnetotorquers again to spin up the satellite at a
> > > high
> > > angular rate (maybe 20 RPM). The angular momentum of the spinning
> > satellite
> > > keeps it stable while the motor is firing. The motor thrust must of
> > course
> > > be
> > > well aligned with the spin axis, but if the thrust vector is not
> perfect,
> > > the
> > > spinning satellite tends to even out the small deviation.
> > >
> > > One of the recent Cubesats carried high power model rocket engines to
> try
> > > an
> > > experimental orbit adjustment. They forgot to spin the satellite and
> the
> > > Cubesat tumbled wildly as a result of the motor burn. Some of these
> > groups
> > > are
> > > really lacking in basic physics knowledge (and we are not talking about
> > wet
> > > behind the ears students in that case.)
> > >
> > > Dan Schultz N8FGV
> > >
> > >
> > > _______________________________________________
> > > Sent via AMSAT-BB at 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
> > >
> >
> >
> > ------------------------------
> >
> > Message: 7
> > Date: Sun, 22 Sep 2013 22:22:11 -0400
> > From: Joe Fitzgerald <jfitzgerald at alum.wpi.edu>
> > To: AMSAT BB <amsat-bb at amsat.org>
> > Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude
> >         control work?
> > Message-ID: <523FA5D3.3020001 at alum.wpi.edu>
> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> > On 9/22/2013 4:19 PM, Burns Fisher wrote:
> > >   I would not think that electromagnets
> > > operating against the earth's magnetic field would have enough power
> with
> > > such a large motor.
> >
> > The electromagnets had some "oomph"  I seem to remember the engineering
> > beacon moving in frequency slightly when they switched on ... I don't
> > remember if it was because of a sag on the DC bus, or the magnetic field
> > affecting the tuned circuits of the transmitter.
> >
> > But you bring up important points,  if we are to do orbit adjustments,
> > we need to do attitude determination and control in addition to getting
> > a motor aboard.  No easy feat in a 3U cubesat!
> >
> > -Joe KM1P
> >
> >
> > ------------------------------
> >
> > Message: 8
> > Date: Mon, 23 Sep 2013 08:14:44 +0200
> > From: "i8cvs" <domenico.i8cvs at tin.it>
> > To: "Peter Guelzow" <peter.guelzow at kourou.de>,  "Amsat - BBs"
> >         <amsat-bb at amsat.org>, "Daniel Schultz" <n8fgv at usa.net>
> > Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude
> >         controlwork?
> > Message-ID: <000901ceb824\$34922710\$0301a8c0 at i8cvs>
> > Content-Type: text/plain;       charset="iso-8859-1"
> >
> > Hi Peter,DB2OS
> >
> > If I well remember in addition with the Magnetorquing ,AO40
> > was equipped with a 3 axis X-Y-Z stabilization wheel/EPU
> > acting as gyroscopes that never where used except one time
> > I remember to have seen on the P3T TLM the wheels were
> > tested rotating for a short time at a very low numbar of turns
> > ....... or I am wrong ?
> >
> > Why the 3 axis stabilization wheel/EPU whre never used on
> > AO40 ?
> >
> >
> > 73" de
> >
> > i8CVS Domenico
> >
> > ----- Original Message -----
> > From: "Peter Guelzow" <peter.guelzow at kourou.de>
> > To: <amsat-bb at amsat.org>
> > Sent: Sunday, September 22, 2013 11:21 PM
> > Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude
> > controlwork?
> >
> >
> > > Hi Burns,
> > >
> > > yes - all Phase 3 satellites use Magnetorquers to control attitude
> > > during perigee. They were pulsed by the IHU on-board computer which was
> > > running a model of the physics and orbital dynamics to trigger the
> > > correct coils at the right moment.   This Timing was synchronized with
> > > the Sun sensor...   indeed P3 spacecrafts are Spin stabilized...
> > > There was no feedback. Command stations did some calculations based on
> > > Earth and Sun sensor data, but once calibrated the system worked quite
> > > smoothly and predictable...
> > > For the motor burns, the attitude was indeed determined by the Sun and
> > > Earth sensors and several times corrected until the perfect attitude
> was
> > > achieved.. this took a few days.
> > > Basically a very simple system was simple physics involved...
> > >
> > > 73s Peter
> > >
> > >
> > > On 22.09.2013 22:19, Burns Fisher wrote:
> > > > There has been a lot of discussion about AO-10, 13, and 40 (and maybe
> > > > others) with various kinds of apogee kick motors (and inclination
> > > > changers etc).  Rather than fanning any flames, I just want to ask a
> > > > question: If you have a motor of a few hundred Newtons, how to
> > > > you keep the attitude stable during the burn?
> > > > For that matter, how do you get the attitude correct for the start
> > > > of the burn?  I would not think that electromagnets operating against
> > > > the earth's magnetic field would have enough power with
> > > > such a large motor.
> > > > Obviously it depends on the balance of the satellite relative to the
> > > > position of the kick motor, but still...was the balance really good
> > > > enough to allow magnetic attitude control?
> > > > Was it active (i.e. with feedback)?  Does that imply a rate gyro?
> > > > (No MEMS then, I suppose).
> > > >
> > > > Thanks in advance for the technical history lesson...
> > > >
> > > > 73,
> > > >
> > > > Burns W2BFJ
> >
> >
> >
> >
> > ------------------------------
> >
> > Message: 9
> > Date: Mon, 23 Sep 2013 20:51:19 +1200
> > From: don <donmc at xtra.co.nz>
> > To: amsat-bb at amsat.org
> > Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude
> >         controlwork?
> > Message-ID: <52400107.9060000 at xtra.co.nz>
> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> > Hi,
> >
> > After a long absence I decided to check out the AMSAT mailing list again.
> >
> > It's been on my spam list for some time now, (mainly because of the
> > insane FM square collecting posts)but I thought it time to check again.
> > Amazingly I now find real technical discussions being carried on, is
> > this now normal? could some one reply to the affirmative.... I may even
> > find some funds to rejoin amsat if the board now reflects the
> > experimental and technical pursuits of real satellite enthusiasts.
> > Please no more FM sats. I like "beep sats" and enjoy getting data from
> > them.....
> > Don.
> >
> >
> >
> _______________________________________________
> Sent via AMSAT-BB at 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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