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.
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
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
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
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
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
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
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
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
