September 2013 - AMSAT-BB - mailman.amsat.org

Kick motors on Oscars: How does attitude control work?
by Burns Fisher 23 Sep '13

23 Sep '13

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

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Fw: Delfi C3 Close Approach Notification
by Peter Portanova 23 Sep '13

23 Sep '13

FYI 73's WB2OQQ Sir/Ma'am, The United States Joint Space Operations Center (JSpOC) has identified a predicted conjunction between Delfi C3 (SCC# 32789) and SCC# 38013. Primary Object: Delfi C3 (SCC# 32789) Secondary Object: SCC# 38013 Time of Closest Approach: 26 SEP 2013 02:05 UTC Overall miss distance: 796 meters Radial (dU) miss distance: -177 meters In-Track (dV) miss distance: 760 meters Cross-track (dW) miss distance: -158 meters Primary Radial Error (U): 24 meters Primary In-track Error (V): 1443 meters Primary Cross-track Error (W): 7 meters Secondary Radial Error (U): 11 meters Secondary In-track Error (V): 703 meters Secondary Cross-track Error (W): 5 meters Very Respectfully, JSpOC Orbital Protection Team Joint Space Operations Center NO WARRANTIES: The United States provides the enclosed Space Situational Awareness (SSA) services or information "as is" and makes no warranty, either express or implied, as to the condition or suitability of the information and services, nor its fitness for a particular purpose. IMMUNITY: The United States, any agencies and instrumentalities thereof, and any individuals, firms, corporations, and other persons acting for the United States, shall be immune from any suit in any court for any cause of action arising from the provision or receipt of SSA services or information, whether or not provided in accordance with 10 USC 2274, or any related action or omission.

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Another Delay For Cygnus
by B J 23 Sep '13

23 Sep '13

http://www.spaceflightnow.com/antares/cots1/130922delay/#.Uj8Tl9IwkQM http://www.parabolicarc.com/2013/09/23/cygnus-rendezvous-postponed-crew-arr… http://www.americaspace.com/?p=42942 73s Bernhard VA6BMJ @ DO33FL

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k8bl road trip
by k4feg 23 Sep '13

23 Sep '13

Here is the "Itinerary" for/*K*//**//*8BL's road trip starting today:*/ Be sure to listen for Bob on all satellites! Below is the email Bob sent me: /*Here is my plan for the week of 9/23-9/27.*/ /**/ /**//**/ /**/ /*I'll be driving around Lake Huron and activating as many of the Grids I pass through as possible. On Monday 9/23 I'll be headed north from Detroit and hit EN84, 85, 75, & 76, but I may make it to EN77/87 by late*/ /**/ /*afternoon depending on speed & traffic. On Tuesday 9/24 my plan is to quickly go through EN76 & 77 to hit rare EN87 and back down through EN77, 76 and into EN86. On Wednesday 9/25 I'll be in EN96 and go for rare EN97 and head down into EN95. Thursday 9/26 will take me through FN05, 04 and into EN94. On Friday 9/27 I expect to be in EN94, 93 & 92. All of this*/ /**/ /*is flexible based on road situations as they arise, but my goal is to activate*/ /**/ /*as many of these Grids as possible. By Saturday 9/28 my plan to to just dead-head back to my QTH in EN91. Hope to work a lot of the Grid Chasers on my journey!*/ /**/ /**//**/ /**/ /*Frank, please try to get this on Starcom & AMSAT tonight if possible so*/ /**/ /*folks will know I'll be available. Good Luck Everyone! */73 ALL FRM STARCOM DIV of the GGG K4FEG /The Commander GGHQ: EM55aj84ta "...no grid left behind..." /

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Re: Kick motors on Oscars: How does attitude control work?
by Daniel Schultz 22 Sep '13

22 Sep '13

>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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Re: Gygnus Delay
by Clint Bradford 22 Sep '13

22 Sep '13

Cady Coleman tweeted this morning - writing that Cygnus and the ISS each looked at their clocks, and they weren't in sync ... (grin) Clint

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Re: Phase 3
by Daniel Schultz 22 Sep '13

22 Sep '13

>>The apogee motors for OSCAR-10,and OSCAR-13 were solid propellant >>400 Newton trust motors donated to AMSAT-DL by the Messerschmitt Aerospace >>Company in Germany. Only Phase 3A had a solid fuel motor. AO-10 and AO-13 had liquid fuel bi-propellent motors the same as AO-40. No matter how well designed they are, they still have the potential to blow up the entire launch stack if something goes wrong. Since Dick Daniels is no longer with us, the knowledge has been lost and we will not be launching any more of these in the future. Dan Schultz N8FGV

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Re: Phase 3
by Daniel Schultz 22 Sep '13

22 Sep '13

Gordonjcp MM0YEQ wrote: >>You could conceivably rip the RF board out of a UHF and VHF one and couple it >>with your own CPU and audio board, and have a ~150 gramme mode V/U transponder >>on a standard 10x10 cubesat board. You could use a 10m SDR and a wee DSP board >>like the ones that TI does for a few beer tokens and build Bob Bruniga's >>crossband PSK transponder. You could do all this for the price of the buffet >>for four and a couple of pints at my local Indian restaurant, and you could do >>it in a weekend. >>You can cram a lot of radio into a tiny space these days, and with a cubesat >>you've got a bit of space about the size and weight of a bag of sugar. You >>could just about tape two big old Motorola GP340s together and fit them in a 2U >>launch. There's no excuse. I agree that you can pack a lot of electronics into small packages these days. I disagree that it is feasible to use commercial radios that were not engineered for space flight. Many student groups have in fact used HT guts for their LEO beepsats but if you want a mission that lasts ten years instead of six months, you need to do some serious engineering. The reason why Cubesats are too damn small is not about the electronics inside the cube, but the questions you need to ask are: Can the satellite deploy enough solar cells to generate sufficient electrical power? can the satellite deploy a large enough antenna to direct a usable signal to users on Earth? Can you keep that antenna pointed at the Earth, at the same time that you are keeping the solar array pointed at the sun? Is there sufficient external area on the satellite to radiate waste heat from the electronics? A Cubesat with a Chinese HT inside and 100 square centimeters of solar cells on all six surfaces can generate one or two watts into a whip antenna, but put one of those in high altitude orbit, 10,000 km from Earth, and only hams with EME class stations will be able to make use of it. This is the reason why LEO Cubesats are easy and HEO Cubesats are hard. I appreciate the motivational stories about deaf frogs who don't know what is impossible, but sometimes you do have to pay attention to the ugly laws of physics. That's why someone once defined an Engineer as a "Disciplined Dreamer". One of my favorite New Yorker cartoons was of a motivational speaker standing in front of a room full of people wearing Superman costumes, telling them "Now go out there and fly!". I guess that's the reason why Superman Halloween costumes come with a warning on the box that "wearing this cape will not allow you to fly"... Dan Schultz N8FGV

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Cygnus Docking Delayed 48 Hours
by Clint Bradford 22 Sep '13

22 Sep '13

Cygnus Rendezvous Delayed 48 Hours Sept 22, 2013 Orbital Sciences has confirmed Sunday morning, around 1:30 a.m. EDT, its Cygnus spacecraft established direct data contact with the International Space Station (ISS) and found that some of the data received had values that it did not expect, causing Cygnus to reject the data. This mandated an interruption of the approach sequence. Orbital has subsequently found the causes of this discrepancy and is developing a software fix. The minimum turnaround time to resume the approach to the ISS following an interruption such as this is approximately 48 hours due to orbital mechanics of the approach trajectory. -NASA.gov

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Cygnus Berthing To ISS Delayed
by B J 22 Sep '13

22 Sep '13

http://www.nasaspaceflight.com/2013/09/cygnus-cots-graduation-iss-berthing/ http://www.parabolicarc.com/2013/09/22/cygnus-rendezvous-delayed-48-hours/ 73s Bernhard VA6BMJ @ DO33FL

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