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

i8cvs domenico.i8cvs at tin.it
Sun Sep 22 23:14:44 PDT 2013

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 ?   

Thanks for your answere.

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

> 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

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