Re: Kick motors on Oscars: How does attitude control work?
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
Which cubesat project ?
On Sun, Sep 22, 2013 at 5:49 PM, Daniel Schultz n8fgv@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
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Samudra Haque