October 2006 - Eagle (INACTIVE)

Module Thermal Dissipation
by Dick Jansson-rr 10 Oct '06

10 Oct '06

Eagle module power dissipations as noted in my paper recently published for the AMSAT Space Symposium, are shown below.. The allowable dissipations presume a module temperature of 20°C in a 0°C spacecraft. Table 1 Mean Emittance, v Allowable Power Dissipation, Q 0.045 0.4 W 0.15 1.3 W 0.45 3.9 W 0.91 7.9 W It would be exceptionally presumptuous on my part to assume that all modules will be of 7.9W dissipation as the spacecraft will not have that level of power generation (12 "low power" modules at 7.9W = 94.8W, plus 4 "high power" modules at 50W = 200W, totaling 295W). To achieve that level (7.9W) of power will require the use of internal heat sinking. On the PCB dissipation, if we are to limit the temperature rise, in a 20°C module, to 40°C or a PCB of 60°C total, then the PCB dissipation would be 5.35W, somewhat less than the 7.9W allowed in a 20°C module. Thus to achieve the 7.9W other heat sinking methods would need to be used. I fully realize that modern-day electronics are quite compact and have significant power densities, but I personally shudder at some of these above noted power densities in a vacuum environment. This is the basis of my previously noted conservatism in PCB power densities. There are some particularly critical modules that MUST be low power. These are those involved in the commanding of the spacecraft, the command receiver and the IHU. The noted reason for this mandate is that of the cooling effects of the spaceframe during eclipse and the need to maintain the command-loop equipment in suitable operating condition regardless of the radical eclipse cooling of the spaceframe. During a 2-3hour eclipse, the spaceframe can cool to as low as -80°C or below. These conditions have been observed in prior P3 spacecrafts. This whole ongoing discussion merely further reinforces my concept that close work between the electronic designers and the thermal designer for Eagle is sorely needed. In this environment I feel that the days of wily-nily electronic design, damn the thermal torpedoes, are gone. Module design must be done as a cooperative, multi-technology effort. This is why I again emphasize that all designers should read my recently presented paper. Dick Jansson --------------------------- <mailto:rjansson@cfl.rr.com> rjansson(a)cfl.rr.com ---------------------------

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comments on Li-ion batteries
by Phil Karn 10 Oct '06

10 Oct '06

I read through some of the comments on this list about lithium-ion batteries and have a few things to add. Lithium-ion batteries require *very* tight control of the charging voltage. If you let it go too high, metallic lithium can be produced inside the cell with disastrous results. The expected lifetime of a li-ion battery depends on more than the number of cycles and the depth of discharge. Unlike Ni- or Pb-based batteries, li-ion batteries degrade significantly even when unused. The rate depends on state of charge and temperature, with high states of charge and high temperatures being the worst. You may have noticed that while NiCd and NiMH batteries arrive from the factory fully discharged, li-ion batteries usually arrive at 40-50%. This is the level at which degradation is the slowest. This means we should probably design our li-ion battery management algorithms to keep them half full rather than completely full. We can still use the extra capacity to get through an eclipse season, but when the extra capacity is not needed the batteries should not be kept at 100%. Like all batteries, li-ion batteries are better cold than hot. Since they perform fairly well when cold, some thought should be given to a spacecraft thermal design to keep them cold. --Phil

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Service class names
by Jim Sanford 10 Oct '06

10 Oct '06

Team: I learned at Symposium that some don't like some of the class names we've been using to discuss various services. I reaffirmed at Symposium that we need consistent names for the services we'll provide, just like we've settled on band names. To give us the precise nomenclature I think we need for effective communication, I propose: Class A for what we used to call Class 0 (A from the old "Analog", which we need to stamp out.) Class S for what we used to call Class 1 (S from SMS) Class V for what we used to call Class 2 (small station digital Voice) Class H for what we used to call Class 3 (High rate) I started with A, B, . . . and decided to propose more intuitive names. Unless one of you strongly objects in the next few hours, I'll have the ANS announcement and AMSAT web page updated. It was great to see many of you this weekend. Thanks & 73, Jim wb4gcs(a)amsat.org

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TeamSpeak conference for Tuesday 10 Oct
by Jim Sanford 09 Oct '06

09 Oct '06

Team: Since many of you will be still at SFO or travelling back, I don't think there's a point in having a conference. HOWEVER, tomorrow represents a GREAT opportunity to brief those who weren't there on Symposium. SO, I will be there. I ask all of you who were at Symposium to attend. There will only be one agenda item -- to brief those who weren't there on Symposium. And the discussions can range from there . . . . NEW SUBJECT: I've read the feedback on my "classes of service" note. Several people told me to just do it, I'm glad I didn't. Here's where I am. 1. I feel VERY strongly that we need a concise class of service designation. I don't much care what the designations are. 2. It was very clear to me, particularly in watching Matt's presentation at Symposium, the value of having such designations. Things like "mode U/V" have precise meanings to our designers, members, and users. We need similar precision in defining our classes of service. "Analog" is very confusing when we're talking about an SSB transponder that is more digital than analog. 3. Some are offended by calling the traditional or old analog transponders "class 0". I think that's crap, but remember that perceptions are reality. 4. I'm going to make and publish a decision in the next few days. I'm going to tell the members and readers of the web site and -bb what those are, so we can all speak from a common understanding of terminology. 5. The proposal I sent was the best I could come up with to get the discussion started. 6. I've seen some good suggestions. I'll digest the suggestions tomorrow night, send a proposal before the teamspeak conference, and we can go from there. Thanks & 73, Jim wb4gcs(a)amsat.org

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2nd Tuesday
by John B. Stephensen 09 Oct '06

09 Oct '06

Is there a teleconference scheduled for tomorrow (10/10)? 73, John KD6OZH

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The thorny issue of SDX/Analog linear transpnder
by Howard Long 04 Oct '06

04 Oct '06

Folks I know that the current documented thinking is to have two SDX's and no analog transponder, however we did say we'd bring up for discussion at a telecon prior to the Symposium. I know that this was brought up in July 2005 where it was clear that the answer to the members was yes, we'd have a backup _analog_ linear transponder. As we won't now have an opportunity to discuss this in a telecon, can we have a clear line on this? I can just see that someone's gonna ask me this question at my presentation. 73, Howard G6LVB

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S2
by Grant Hodgson 02 Oct '06

02 Oct '06

Hello Thanks for being invited to join the group. For clarification, am I correct in reading that the plan is to formally propose S2 (3.4GHz) as the uplink for the ACP? Regards Grant Hodgson G8UBN

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Proposed Eagle Antenna Arrays
by Louis McFadin 01 Oct '06

01 Oct '06

Here is a proposal for arranging the Eagle antennas that Stan Wood and I worked out today. By moving the 2M dipoles to the corners we have sufficient room for full sized elements over the ground plane. The 2M antennas should get about 8dB. Three L band patches in cavities should give us greater than 12 dB gain. By putting the S1,S2 and C band patches in hex shaped cups we maximize the available space. The cup arrays can be NC machined out of a solid blank and therefore attain precise control of the spacing. It may also serve as heat a radiating device. Each patch will be circular polarized and fed with a single feed from it's matching amplifier. The 70 CM Circular polarized patch should have around 6 dB gain. We will look at getting more gain on 70 cm. Seven S1 patches will be mounted on top the 70CM patch. They should get about 15dB gain. Tom's S2 interferometric patches are included. Omni antennas similar to that used on P3D will be required on the opposite side of the spacecraft. There should also be room for the Sun Sensors on both sides of the spacecraft. Lou McFadin W5DID w5did(a)mac.com

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