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

[Peter Guelzow]

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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