Re: Kick motors on Oscars: How does attitude control work?
Very interesting stuff. Thanks to everyone who responded. Using a model rocket engine has occurred to me :-) I noticed that the smaller ones (A,B) tend to peak at 10s of Newtons (presumably to get the model rocket going fast enough to be stable after it leaves the launch rod) and then settles down to sub-10 Newtons for the rest of the burn (a second or two). So it is quite a whack over a short period for a small bird. I did not look up the higher power size. It would be interesting and not too difficult to do the math to see what kind of a perigee raise would happen if someone fired one of these on a 3U cubesat of modest mass in GTO while it was at apogee.
Don, there is enough interesting stuff to keep me watching the list. There is also a lot of complaining. We'd love to have you rejoin AMSAT. Fox-1, the upcoming launch, IS an FM bird, but I hope you noticed that the last AMSAT bird, ARRISat-1 was indeed a linear. We need to continue to learn and experiment.
Burns, W2BFJ
On Sun, Sep 22, 2013 at 5:49 PM, Daniel Schultz [email protected] 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
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
Message: 7 Date: Sun, 22 Sep 2013 22:22:11 -0400 From: Joe Fitzgerald [email protected] To: AMSAT BB [email protected] Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude control work? Message-ID: [email protected] Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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
Message: 8 Date: Mon, 23 Sep 2013 08:14:44 +0200 From: "i8cvs" [email protected] To: "Peter Guelzow" [email protected], "Amsat - BBs" [email protected], "Daniel Schultz" [email protected] Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude controlwork? Message-ID: 000901ceb824$34922710$0301a8c0@i8cvs Content-Type: text/plain; charset="iso-8859-1"
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
Message: 9 Date: Mon, 23 Sep 2013 20:51:19 +1200 From: don [email protected] To: [email protected] Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude controlwork? Message-ID: [email protected] Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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.
Found this intersting web page:
http://www.isispace.nl/cms/index.php/projects/nks
Bryce KBL1QC
On Mon, Sep 23, 2013 at 12:46 PM, Burns Fisher [email protected] wrote:
Very interesting stuff. Thanks to everyone who responded. Using a model rocket engine has occurred to me :-) I noticed that the smaller ones (A,B) tend to peak at 10s of Newtons (presumably to get the model rocket going fast enough to be stable after it leaves the launch rod) and then settles down to sub-10 Newtons for the rest of the burn (a second or two). So it is quite a whack over a short period for a small bird. I did not look up the higher power size. It would be interesting and not too difficult to do the math to see what kind of a perigee raise would happen if someone fired one of these on a 3U cubesat of modest mass in GTO while it was at apogee.
Don, there is enough interesting stuff to keep me watching the list. There is also a lot of complaining. We'd love to have you rejoin AMSAT. Fox-1, the upcoming launch, IS an FM bird, but I hope you noticed that the last AMSAT bird, ARRISat-1 was indeed a linear. We need to continue to learn and experiment.
Burns, W2BFJ
On Sun, Sep 22, 2013 at 5:49 PM, Daniel Schultz [email protected] 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
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
Message: 7 Date: Sun, 22 Sep 2013 22:22:11 -0400 From: Joe Fitzgerald [email protected] To: AMSAT BB [email protected] Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude control work? Message-ID: [email protected] Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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
Message: 8 Date: Mon, 23 Sep 2013 08:14:44 +0200 From: "i8cvs" [email protected] To: "Peter Guelzow" [email protected], "Amsat - BBs" [email protected], "Daniel Schultz" [email protected] Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude controlwork? Message-ID: 000901ceb824$34922710$0301a8c0@i8cvs Content-Type: text/plain; charset="iso-8859-1"
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
Message: 9 Date: Mon, 23 Sep 2013 20:51:19 +1200 From: don [email protected] To: [email protected] Subject: [amsat-bb] Re: Kick motors on Oscars: How does attitude controlwork? Message-ID: [email protected] Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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.
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
participants (2)
-
Bryce Salmi -
Burns Fisher