Kick motors on Oscars: How does attitude control work?
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
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 _______________________________________________ Sent via [email protected]. 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
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" [email protected] To: [email protected] 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
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.
Hi Domenico,
Yes, AO-40 is equipped with magnetically suspended reaction wheels for 3-Axis stabilization. They were turned on, spun up and functioned very well, even at higher speed... The 3-Axis stabilization was needed to generate enough electrical power to "hot" operate the ArcJet/EPU with fully deployed solar panels... After the Motor incident we ended up in a nicely high apogee, but the perigee was too low and withing a very short time AO-40 would have burned up in the atmosphere. For that reason it was decided not to take any further risks and run the ArcJet "cold" to quickly raise the perigee.. this goal was successful achieved and AO-40 was finally in a safe orbit... but this life saving maneuver consumed all the Ammonia, if I remember correctly.. There was no immediate need to go into 3-Axis mode and to deploy the solar cells. I think there was more concern about what else might have got damaged and thus I think it was decided to be more on the safe side and stay in Spin mode.. At least we got 4 more years to operate S-Band....
73s Peter DB2OS
On 23.09.2013 08:14, i8cvs wrote:
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" [email protected] To: [email protected] 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
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
participants (5)
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Burns Fisher -
don -
i8cvs -
Joe Fitzgerald -
Peter Guelzow