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

Daniel Schultz n8fgv at usa.net
Sun Sep 22 14:49:07 PDT 2013

>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 

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