October 2006 - Eagle (INACTIVE)

Re: [Bod] FCC Omnibus R&O
by Dr. H. Paul Shuch 01 Nov '06

01 Nov '06

Hi, Tom, I too am still in CA (funny, I didn't see you on the street last night!) With restricted access. Unfortunately, your 301 kByte PDF confounded Mr. Blackberry. It got stuck in his windpipe and blocked 68 othetr messages (not to worry, they were all spam). My point is, we should be careful with large email attachments. Rather than posting them to multiple lists, anything other than brief ASCII text should probably be posted to a website somewhere, and only the URL forwarded around. That way, we can download the files at will, when back home connected to the Real World. Mr. Blackberry thanks you for your consideration. 73, Paul -- H. Paul Shuch, Ph.D., Chief Engineer Microcomm Consulting +1 (570) 494-2299 121 Florence Drive, Cogan Station PA 17728 paul(a)microcomm.net http://microcomm.net ---------- This document may contain proprietary information, intellectual property, trade names, and logos which may be confidential to Microcomm Consulting. Dissemination for any purpose of any part of the data contained herein without specific prior written authorization from Microcomm Consulting is hereby prohibited.

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Power system thoughts and comments
by Phil Karn 01 Nov '06

01 Nov '06

I was fascinated by Lou's talk at the Symposium. His idea of a "parallel" power system is an excellent one if a few potential problems can be addressed. The first and most obvious one is efficiency. Switching converters tend to be much less efficient at low voltages and high currents, though power MOSFETs have gotten very good of late. Every Pentium 4 motherboard has had a DC-DC converter that takes 12V and produces ~1V at up to 100A to power the CPU. The fact that there isn't a massive heat sink and fan for the supply as well as the CPU says that these converters can't be too terribly inefficient. I'll be interested in some actual figures for the "virtual battery" converters. The second issue is robustness. Just as serial architectures are vulnerable to single-point open faults, parallel architectures are potentially vulnerable to single-point shorting faults, e.g., of the power transistors and diodes in the converter. I'm hoping a judicious application of fuses can take care of this. Super caps look very promising thanks to their claimed long cycle lives, but I wonder about their radiation robustness. Imagine what a highly energetic, totally ionized particle might do as it rips through the Aerogel holding large numbers of electrons a few microns apart from large numbers of holes. Have any radiation tests been performed on these things? Also, I would not take their cycle life claims as gospel without some tests to back them up. Electrolytic caps have become some of the most unreliable components in electronics today. They fail on a regular basis in computer power supplies and motherboards, often spectacularly. While super caps aren't built quite the same way, both kinds of caps achieve their high capacities with lots of extremely thin dielectric material. Cycling the cap must place some pretty serious electrostatic compression stresses across this material. What happens, e.g., after many cycles at very low temperatures? At a system level, I see a potential "gotcha" with multiple paralleled virtual battery units. You can never get multiple voltage references to exactly agree, so if the control loop gains are too high, then one virtual battery might think the bus voltage is a little too low when another might think it's too high. Then you'll have large amounts of current flowing from one virtual battery into another, obviously an undesirable situation. The simplest fix I can think of is to program the control logic in each virtual battery to follow a specified current vs voltage characteristic. The slope of this curve must be gentle enough so that small differences in reference voltages across the units will not produce significantly different I/V curves. Bus regulation won't be quite as tight, but hopefully the loads won't mind. Overall I think Lou's proposed architecture is an excellent idea, and with attention to a few details it should be a lot more reliable than the conventional power systems we've had in the past. --Phil

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Eaglepedia articles
by Alan Bloom 29 Oct '06

29 Oct '06

I have set up a new category on Eaglepedia called "Hardware Design Guidelines". http://www.amsat.org/amsat-new/eagle/EaglePedia/index.php/Category:Hardware… I seeded the new category with two new articles, "SMT Thermal Design" and "HEO Radiation Environment". I also added several old Eaglepedia articles that should be useful to hardware designers. I'm new to posting Wikepedia-type articles so I'm not sure I got the category thing right. Also I'm not an expert on thermal design or the space radiation environment, so I hope other members of the Eagle team will do the Wikipedia thing and add to, modify, correct what I've done. Al N1AL

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AMSAT award
by Robert McGwier 28 Oct '06

28 Oct '06

It pleases me greatly to announce that Eric Ellison has been presented with an award from AMSAT. It is sometimes easy to take for granted what seems to many to be a small thing. In the case of AMSAT, Eric's work made virtual meetings not only possible but easy. AMSAT has literally run its Eagle project using VOIP facilities which Eric set up on behalf of the technical groups active today in amateur radio in satellites, technology, and in particular software defined radio. AMSAT and TAPR both recognize Eric's work, AMSAT with the award and TAPR membership with Eric's election to its board of directors. Someday Eric's TEAMSPEAK server will be universally recognized for the spectacular impact it has had and will continue to have. Eric, the award is in the mail from the AMSAT office along with a gift membership in AMSAT for a year. Jim Sanford, Eagle project manager, and I and the entire organization give you our thanks for your generosity and help. 73's Bob McGwier N4HY -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat." - Einstein

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CONGRATULATIONS TO N2UO
by Robert McGwier 24 Oct '06

24 Oct '06

I know all of the Eagle designers will join me in congratulating Marc Franco, N2UO on his being granted permanent residency here in the U.S. His skills represent a major asset to Eagle, Lintech, and the U.S. [in that order ;-)] and it is good when the immigration office does something sensible for a change. CONGRATULATIONS Marc! Bob N4HY -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat." - Einstein

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Eagle Team Leadership change announcement
by Jim Sanford 22 Oct '06

22 Oct '06

Team: I wish to announce that Bob Davis, KF4KSS, has assumed the role of Structure and Mechanical Team Leader. Bob has experience in finishing and integrating AO-40, and is employed in the aerospace industry, where he has acquired significant experience since the AO-40 campaign. Dick Jansson, WD4FAB, has led this team for several years and is not going away. Dick will support Bob as a team member, focussing on structural team coordination and thermal design and analysis. Dick told me this afternoon, "I'm really excited to see the new blood coming in and assuming leadership roles. I look forward to supporting Bob and being on his team." I thank Dick for all that he has done for AMSAT and WILL do for Eagle and AMSAT. Thanks for all you've taught us. Bob, thanks for stepping up to the plate. I look forward to working with you, and I look forward to learning from you. Thanks and very 73 to all, Jim wb4gcs(a)amsat.org Eagle Project Manager

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AVP -Engineering team
by Robert McGwier 21 Oct '06

21 Oct '06

I have asked the following folks to be AVP for Engineering. Jim Sanford as Eagle project manager Lou McFadin as Manned Space chief engineer Bob Davis as lab director and spacecraft integration leader Please add them to the officers mailing list if they are not already on it please. Welcome and thank all of them for their continued great service to AMSAT. Bob N4HY -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat." - Einstein

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S1 downlink coordination and interference mitigation
by Howard Long 18 Oct '06

18 Oct '06

Folks, Coincidentally at the Symposium, Graham Shirville spent some time coordinating proposed frequencies to some satellites, including Eagle, and after a suggestion I had from from Drew KO4MA, I reiterated to Graham that it may be advantageous to propose S1 frequencies right down at the bottom 1MHz of the 2.4GHz satellite allocation. 802.11 specifies a 1MHz guard band at 2400 to 2401MHz for regulatory OOB emission reasons. Signals +/-11MHz from the centre must be at least 30dB down from the carrier. Channel 1 is at 2412MHz. Taking into account Doppler, the recommended S1 coordinated frequencies will be at the bootom end of 2400MHz without the possibility of OOB emissions on Earth due to Doppler. 73, Howard G6LVB

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Service class names
by Jim Sanford 17 Oct '06

17 Oct '06

Team: A few days ago, I made a proposal for naming Eagle's communications services and solicited comments. I received many good comments. I really think it important that we have unambiguous service class names. Based on all the comments, I propose: U/V "linear" L/S "linear" Text messaging Low Rate ACP High Rate ACP While I'd prever something less ambiguous than "linear", our customers seem to understand that "linear" means SSB/CW/PSK31/SSTv . . . . etx. Any strong objections to this? If not, I'll get the announcement on AMSAT.org changed. It's time to get precise. Thanks & 73, Jim wb4gcs(a)amsat.org

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Module Paper
by Dick Jansson-rr 15 Oct '06

15 Oct '06

I have been asked if I can provide a copy of the module paper of mine that was so skillfully presented by Bob Davis at the recent AMSAT Space Symposium. This is for those of you who were not able to be at the symposium and receive the Proceedings. This paper is now available on Eaglepedia at: <http://www.amsat.org/amsat-new/eagle/EaglePedia/index.php/Module_Design> http://www.amsat.org/amsat-new/eagle/EaglePedia/index.php/Module_Design Dick Jansson --------------------------- <mailto:rjansson@cfl.rr.com> rjansson(a)cfl.rr.com ---------------------------

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Module Temperatures
by Dick Jansson-rr 14 Oct '06

14 Oct '06

Last evening I tried to convey the concept that the critical-command modules needed to be of low-power design to insure their operability during the occasional rather lengthy eclipse cooling of the spacecraft. My message apparently did not sink in. John reports that his design of such a U band receiver would be dissipating some 3.5W due to its bullet-proof nature against 3rd-order IM products needed for protection on the U band. If we go forward with such a module of that nature, it will need to have thermal control tapes on it to provide a mean emittance of about e=0.45. In a 3 hour eclipse we can expect to see spaceframe temperatures down to -100°C (173K) or lower. With such an environment John's module would be expected to see temperatures down to at least -44°C, which is a bit frosty for electronics that are expected to provide the critical services of commanding the spacecraft. Such operating temperatures are not felt to be advisable for that service. If John's module were of the 1W category, temperatures of the receiver could be expected to be in the range of -15°C to -20°C which would be more operable for the service. The above numbers are, of course, based on estimates which will be confirmed after we have the new spaceframe fully designed and analyzed. The "warmer" temperatures of the lower power modules are those that have been experienced and measured by telemetry from AO-10 and AO-13. These projections are thus based on 25 years of experience in these design concepts. Dick Jansson --------------------------- <mailto:rjansson@cfl.rr.com> rjansson(a)cfl.rr.com ---------------------------

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ARRL Letter Mentions Eagle
by JoAnne Maenpaa 13 Oct '06

13 Oct '06

The ARRL Letter, Vol. 25, No. 41 released on October 13, 2006 mentions Eagle. Here is a copy of the Eagle item for those who don't get this via ARRL channels ... -- 73 de JoAnne K9JKM k9jkm(a)amsat.org ==>AMSAT'S PROJECT EAGLE SATELLITE SHIFTS DIRECTION AMSAT-NA has announced it's revamping the design of its high-Earth orbit (HEO) Project Eagle satellite, currently in the development stages <http://www.amsat.org/amsat-new/eagle/>. The next generation satellite will take maximum advantage of software-defined transponder (SDX) technology to offer a broader range of easily accessible Amateur Radio payloads. The AMSAT Board of Directors okayed the Eagle upgrade plans during the 2006 AMSAT-NA Space Symposium and Annual Meeting held October 6-8 in San Francisco. Eagle Project Manager Jim Sanford, WB4GCS, outlined the changes at his Space Symposium forum October 7. "The structure which we have been presenting for several years is not going to meet our mission needs," Sanford explained. "We have moved on to a later structure." Under the new plan, Sanford says, Eagle's communications payloads will include a mode U/V linear transponder for SSB, CW and other modes. A second SSB/CW transponder will uplink on L band (1.2 GHz) and downlink on S1 band (2.4 GHz). Both would be usable over 75 percent of the satellite's orbit by an AO-13 or AO-40-capable ground station, AMSAT says. Something new to Amateur Radio satellites is a planned low-rate text messaging system similar to cellular telephone SMS. Sanford said the text-messaging capability may prove valuable for providing emergency and disaster communication. It will operate in mode U/V and also will be available to modest ground stations over 75 percent of Eagle's orbit. Eagle will also carry an advanced communications payload (ACP). The ACP will accommodate voice communication using an S2 band (3.4 GHz) uplink and a C band (5.8 GHz) downlink via a single 60 cm dish on the ground. As an alternative -- for stations in those parts of the world where 3.4 GHz is unavailable -- Eagle will provide an additional L band uplink. The ACP also will offer high data rate communication including the possibility of full-motion compressed video in S2/C mode. The same mode also could support an Internet link. Ground-station antennas for Eagle may even pass muster in neighborhoods governed by private deed covenants, conditions and restrictions (CC&Rs), Sanford suggested. During a presentation on the ACP, Matt Ettus, N2MJI, said one of the goals of the package is to open up the satellite to a new base of users, not just restrict it to elite satellite operators and sophisticated ground stations. Embracing SDR technology simplifies signal handling, he explained, because going digital is just a matter of transmitting bits up and down. "The satellite doesn't really care what the bits mean," he said. The satellite "just reflects bits," and most policy-type issues will be handled by ground stations. The satellite's signal will present one wideband downlink containing multiplexed data. "There will be room for many, many carriers in the passband," Ettus predicted. The mix of users would be apportioned among both low and high-rate modes, depending on overall traffic. Plans call for electronically steering the satellite's antennas to mitigate the effects of the spacecraft's spin and maximize the spacecraft's accessibility. In a subsequent forum, AMSAT board member and well-known satellite expert Tom Clark, K3IO (ex-W3IWI) discussed some of the mathematics and physics that would permit steering a 37-element S band antenna array on Eagle. "We would intentionally steer that pattern, so the array is always pointing toward Earth," Clark said, regardless of spin factor. He described a system of interferometers to do the pointing on the basis of "master beacon signals" uplinked from different points on Earth's surface. "It [Eagle] will measure where they are and know where to point the beam," he explained. In a presentation on applying SDR techniques to satellite transponders, Howard Long, G6LVB, described and demonstrated a prototype SDX board. "This is the holy grail of what we've been trying to do," he told his audience. Long showed how his hand-soldered SDX could be configured to accommodate various signal strengths and types within the same passband and even to easily notch interfering signals quickly and flawlessly. Sanford concluded his presentation by saying it's time to take the AMSAT board's concrete decisions and plan, schedule and build Eagle. "We're about to start spending some serous money," he said. During a later question-and-answer session, Sanford stressed that reliability of the ultimate Eagle satellite is a key goal. "I want no single-failure mission kills on this satellite," he said. Project Eagle still needs to raise $33,500 by December. Eagle could launch by 2010. The whole project will cost some $600,000. During the AMSAT-NA annual meeting October 8, President Rick Hambly, W2GPS, expressed his enthusiasm for Project Eagle. "I think it will be the greatest thing we've ever done!" he said. The 2007 AMSAT Symposium and Annual Meeting will take place in Pittsburgh.

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Amateur Radio Newsline Mentions Eagle
by JoAnne Maenpaa 13 Oct '06

13 Oct '06

Bill Pasternak, WA6ITF sends out a pre-release copy of the Amateur Radio Newsline broadcast script to the ANS editors. This week's Newsline will include news about Eagle. Here's a copy for anyone interested ... -- 73 de JoAnne K9JKM k9jkm(a)amsat.org HAM RADIO IN SPACE: THE EAGLE WILL FLY AMSAT's Board of Directors has approved the payloads for the upcoming Eagle ham radio satellite. Bill Pasternak, WA6ITF reports: -- Of primary concern to most radio amateurs world-wide was the decision to include an SSB and C-W transponder transponder with uplink on 70 centimeters and a downlink on 2 meters. What AMSAT calls U-Band and V-Band. This means that Eagle will be usable over 75% of an orbital pass by any AO-13 or AO-40 capable ground station. In other words, Eagle will be backward compatible with most previous ham radio satellites. Other transponders include SSB and C-W with an uplink on L-band and a downlink the 2.4 GHz S1-band and a low rate text message system operating on the UHF and VHF bands. These transponders will be implemented using Software Defined Radio technology. But thats not all.. AMSAT says that Eagle will also carry an advanced communications payload or A-C-P. The A-C-P will allow voice communications uplinking on the S2-band at 3.4 Ghz and downlinking on C-band at 5.8 Ghz. It will do all of this using a single 60cm dish. The satellite antennas will be electrically steered to reduce spin modulation and allow use over 75% of any given orbit. An additional, fix-pointed, uplink will be available at L-band. This L-band uplink will require a separate antenna at the ground station. Also on-board will be C-band equipment for high rate data communications such as streaming video. For the Amateur Radio Newsline, Bill Pasternak, WA6ITF, in Los Angeles. -- The AMSAT board announced its selection following a meeting on October 5th in Sam Francisco. It also said that AMSAT will develop and make available an affordable ground segment for the ACP system. Additional information will be posted at www.amsat.org in the near future. (AMSAT)

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3.4 GHz
by RaySoifer＠cs.com 13 Oct '06

13 Oct '06

Hi all, Further to my earlier e-mail about the Omnibus R&O, my recommendation for now is that AMSAT proceed with the IARU coordination process for the proposed Eagle frequency plan, but that any out-of-the-ordinary action with FCC is unwarranted. The proposed orbital debris language is not now in effect, for the reasons discussed in my earlier e-mail. It is AMSAT's position, as stated in our recon petition, that FCC does not have the authority to adopt or enforce it. The ITU notification process provided for in the R&O is just that, notification, and is not in any sense a scheme for licensing space stations in advance. FCC's position on that is very clear, and stated in Sec. 97.207: any amateur station may be a space station. Full stop. We may not like that for whatever reason, but as the shady mutual-fund operator Bernie Cornfeld once said about the SEC, "they may be schmucks but they're the government." The way things will work in practice is that when we file our notification with FCC, they will in due course inform the ITU Radiocommunication Bureau. The Bureau will, in turn, inform member states, any of which may object. If they do, it is up to them and FCC to work it out. In such a case, our response would be very simple: "Our uplink causes no interference, harmful or otherwise. If you don't like it, just tell your country's amateur licensees not to use it." In the meantime, the fewer waves made, the better. My 3 cents worth (before tax, that is). 73, Ray

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Re: [Advisors] Re: Re: FCC Omnibus R&O
by RaySoifer＠cs.com 13 Oct '06

13 Oct '06

Rick, Bob, Art et al, I finally got around to reading the Report and Order, and agree that FCC is out to lunch. In footnote 169, they say that orbital debris matters have already been addressed in Docket 02-54, and are therefore moot. The footnote also goes on to state that a recon petition (ours) is pending in 02-54. However, the revised regulation language includes all of the orbital debris garbage (pun intended) they adopted in 02-54, which would thus become effective 30 days after publication in the Federal Register unless FCC takes the same "escape hatch" that they did in 02-54, where the actual Fed Reg notice excludes Sec. 97.207. My suggestion, then, is that someone (Perry, Art, Paul Rinaldo??) call FCC and ask them if, in view of the recon pending in 02-54, they plan a similar exclusion in the Fed Reg notice of this Report & Order. If so, then we need not do anything until action is taken on our recon petition, whenever that is. If not, then we should file a recon petition in 04-140 that mentions the footnote, and incorporates by reference our earlier recon petition and the associated Reply to Oppositions. Such a new petition could also include new material as suggested by Art. When thinking about this, please bear in mind that the purpose of a recon petition is not to persuade FCC to change its mind. That won't happen: their mind is already made up and don't try to confuse them with the facts. Rather, its purpose is to lay the groundwork for a possible future challenge in court (as ARRL is now doing in the BPL matter), since you cannot raise in court any issue that was not before FCC when it made the decision you are challenging. Hope this helps. 73, Ray

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Matt Ettus, IEEE Spectrum
by Robert McGwier 13 Oct '06

13 Oct '06

In the October issue of the IEEE Spectrum is a review of GnuRadio and the USRP and in the contents is a picture of Matt with his USRP and some attachments. The article by Stephen Cass is in the "Tools and Toys" section. It is quite favorable and points out what we all know. The software needs to be easier to install and maintain and as always, there needs to be better documentation. The one software module they mention as working is the FM Stereo demodulator I wrote so I am awfully glad we did it. He mentions that he got the TV demodulator going but that its rasterization was as yet, incomplete. We in the process of getting the digital subcarrier demodulated and decoded (RDS) at this moment. This is being done by someone else. This was a thoroughly written, and very positive review for Matt and GnuRadio, both important contributors to Eagle. Congratulations to Matt of USRP and Eric Blossom of GnuRadio, both Eagle team members. Bob N4HY -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat." - Einstein

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FCC Omnibus R&O
by Tom Clark, K3IO 13 Oct '06

13 Oct '06

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Re: [Advisors] Re: Re: FCC Omnibus R&O
by RaySoifer＠cs.com 12 Oct '06

12 Oct '06

Rick, Bob et al, I have not read this document yet as I have been occupied with other matters. I'll get to it in the next couple of days and make whatever recommendations then seem appropriate. 73, Ray

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SMT heat dissipation in the space environment
by Alan Bloom 11 Oct '06

11 Oct '06

This is a note I wrote some years ago during the AO-40 project. If people think it's useful, perhaps I could post it to Wikipedia. Alan N1AL ------------------------------------------------------------------- Our local PC board technical expert here at HP has done an extensive study on power dissipation of surface-mount parts. While his report is based on non-space applications, there are a number of conclusions that are very interesting. I won't include the entire report, partly because it is much too long, and partly because it is HP proprietary. But here are a few highlights. He found surprisingly little discussion of these issues in the literature. So he performed a series of experiments using an Inframetrics 760 infared camera system to measure component temperatures. All measurements were taken on similar-sized PC boards mounted horizontally with no significant airflow. One main conclusion: "Part ratings by the vendors have little meaning by themselves since trace width and part density have a huge impact on heat dissipation." For example, what is the allowable power dissipation of an 0603 resistor? The answer is somewhere between 12 mw and 526 mw, depending on layout! This is based on a 60 degC temperature rise. (Most resistors have a 125 degC max case temperature spec.) Temperature rise is directly proportional to power dissipation. The 12 mw number was measured on 112 parts packed into a 0.75 square inch area and all dissipating the same power. The 526 mw measurement was on a single part soldered between two half-board-sized ground planes and tied through many vias to another ground plane on the back side of the board. Manufacturers rate 1206-case resistors at 125 mw, versus 62.5 mw for 0603-case resistors, a 2:1 ratio. Actually, for most reasonable trace widths, an isolated 0603 resistor can dissipate roughly 80% as much as a 1206. When parts are packed densely together, power dissipation is limited by the maximum watts per square inch. Note that I used a 30 degC temperature rise for the following table: 0603 1206 Isolated Resistor: Large ground plane: 263 mw 403 mw 0.060 inch traces: 170 mw 199 mw 0.040 inch traces: 148 mw 177 mw 0.012 inch traces: 106 mw 128 mw 0.005 inch traces: 77 mw 100 mw 0.0025 bond wires: 55 mw 79 mw High-density part layout, 0.75 square inch (4.84 cm^2) area: Number of parts 112 32 Power per part 6 mw 20 mw Total power 672 mw 640 mw Number of parts 56 16 Power per part 11.5 mw 43 mw Total power 644 mw 688 mw Number of parts 20 8 Power per part 31 mw 80 mw Total power 620 mw 640 mw Since the power dissipation depends so strongly on trace width, then clearly most of the heat must be conducted, not radiated, on SMT resistors (and other parts). Even in the thin-trace case, much of the heat is conducted to, and radiated from, the PC board. You can see that on the infared photos: the PC board surrounding the part is quite hot. Thermal resistance of isolated SOT-23 transistors was very similar to 0603 resistors up to 0.040" line widths. SOIC-8 voltage regulators had about 1/2 the thermal resistance of SOT-23. The above numbers are probably conservative, since they are based on still air, even though most earth-based applications have forced-air cooling or at least natural convection (vertical PC board). The rule of thumb I generally use is 1 watt per square inch (155 mw/cm^2), which gives an average temperature rise of around 35 degC in still air. I have been told that for space applications, 15 mw/cm^2 is a more appropriate limit. Assuming radiation cooling is only 1/10 as efficient as convection cooling, then that seems a reasonable spec. Conclusion: I have heard several rules of thumb on what percentage you should derate component power specifications for space applications. For through-hole devices, such a rule of thumb probably makes sense. THD devices dissipate most of their heat from the component body, and relatively little heat is conducted out the leads. On earth, most of that heat is conducted to the air; only a little is radiated. In space, radiation is the only heat-dissipating mechanism, so the power must be derated by a large factor. But SMT devices are cooled mainly by conduction out the leads to the copper traces on the PC board, so they are not directly affected by the lack of air. It seems to me that as long as I keep within the 15 mw/cm^2 limit on the PC board, that allowable power dissipation of individual components should be governed by trace width, per the above table. If I have a hot component, I'll connect it to lots of copper and make sure no other hot components are nearby. <END>

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programmable I/V curves for power devices
by Phil Karn 10 Oct '06

10 Oct '06

After thinking about it some more, I recommend that each device on the power bus have a programmable I/V characteristic. This is especially important to avoid wasteful "sloshing" of large currents between energy storage devices. Ideally, the storage devices would have a dead band in their I/V curves around a nominal operating point. They'd begin discharging only when the voltage falls below the lower edge of the dead band, and they'd begin charging at voltages above the dead band. Also, the I/V slopes outside of the dead band (i.e., their effective resistances) would be set to balance charging and discharging currents. The controllers would act like ballasting resistors, only they'd do it more efficiently. You can do some useful things by reprogramming these I/V curves. For example, if you have both supercaps and conventional batteries, you might want to discharge the supercaps in an eclipse before the conventional batteries. You'd do this by setting a higher discharge kick-in voltage for the supercap modules than for the chemical batteries. The IHU could also reprogram the I/V curves to run periodic tests on the individual storage modules. While normally you'd want to keep the batteries at equal charge states, you might want to intentionally charge and deplete one battery to measure its capacity while keeping the others full. Some care will have to go into this to ensure that the module controllers always come up from a power failure with reasonable default I/V curves, but I think this is doable. Phil

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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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