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 > _______________________________________________ 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
