[amsat-bb] Re: S band downlink on P3E
rwmcgwier at comcast.net
Fri Sep 8 03:19:07 PDT 2006
Dave Guimont wrote:
> 73, Dave wb6llo at amsat.org
> Disagree: I learn....
> Pulling for P3E...
As are many of us. That said, The S transmitter is not the primary
mode of P3E. The S band transmitter on P3E will be hooked to a dish.
This dish will have a half power beam width which will limit the
usefulness of the S band transmitter to those times of nadir pointing.
The revelation of the results of our meeting, weeks before we could be
ready to explain carefully that we are taking a system approach to the
design of Eagle, is unfortunate. Not because the conclusions are made
public but because there is no context for the decision making process.
We cannot build an AO-40 class spacecraft. We do not have the
personnel, the facilities, and we likely do not have sufficient talent
that we can devote to such an enterprise. We have talent in this
organization and around the world. But all of that talent leads a life
outside of AMSAT. As an engineering manager for AMSAT it is my
responsibility to make cold hard decisions based on personnel,
calculation, advice, studies, equipment availability, the
availability of launches that we can use and on and on.
The organization overreacted to AO-40. It downsized Eagle
considerably. It set a goal of no motor. It said "let's do digital"
and "give them a whip antenna on two meters". It did not say this in a
crass manner but those were absolutely the conclusions of the
organization policies when captured into engineering possibilities.
It has literally taken me 11 months to ALMOST right the ship. If the
other people in the room will admit to it, I single handedly saved the
linear transponders in our current designs by
a) picking the receiver designer
b) picking the transmitter designer
c) choosing SDX as the overall concept for the linear transponder
EVERYONE is on board. But do you think such things are done overnight?
NO. They are done with leadership and not by whining. These decisions
and their outcome led to a MUCH improved antenna system, power
amplifier, and absolutely cutting edge efficiencies achievable for this
transponder in our current plans. It went from 25 kHz fed to a quarter
wave monopole on the back side of the spacecraft to serious antenna
absolute eating valuable territory on the business side of the
spacecraft and with bandwidth UP TO (but not necessarily) 100 kHz wide.
The bandwidth will be determined by the TYPE of customers we wish to
serve. We do not want to serve only those who can transmit 10 kW
EIRP. We do want to support 1 KW EIRP SSB contacts. We also want to
support a text messaging service that will require a shortened dipole on
70cm and 2m which will not be limited to APRS users.
The goals stated by the AMSAT board of directors for its next HEO
spacecraft design as a follow on to P3E (besides supporting P3E in the
interim) included aiding those people who live in CC&R (covenant
restricted) communities. It included aiding the first responders by
giving them the ability to take a back pack full of equipment, set it
up, and operate quickly. It stated that it wanted to produce a system
of such satellites over a decade to be available 7/24.
We have a concept, not a design, for a spacecraft. This concept is an
"upsizing" of the near cubical Eagle. We are filling in the blanks on
the concept in an attempt to present a design.
The concepts we are building to include the ability to use the
transponders on this spacecraft 365 days a year, in EVERY year the
spacecraft is functional and to try and build a spacecraft that will be
there and still usable when the third in the constellation is launched.
Do you think this is easy? Of course not. It is easy to pitch mud when
you are not responsible for an outcome.
We are attempting to have NO bad seasons. We are attempting to have NO
funny orbital problems. We are attempting to have the gain antennas
solidly usable over 70% of the entire orbit. For these reasons and
because of the desire to serve the CC&R customers, this meant we had to
use microwaves to get sufficient gain on the antennas on the spacecraft
and the ground. We fully understand that Dick Jansson, Drew, Dave,
Tony, and others can give us anecdotes of how they can throw enough gain
on their antenna system and make S band work for them. I believe they
will not be happy with a 60 cm dish but will require a much larger dish
to be happy and I am certain they would do it. I do not care. They are
not who I am computing for. These are not the customers I am trying to
serve. The customers I want to serve for the future of AMSAT cannot be
served by a scratchy SSB signal and a (now) 4 foot dish. I have a
mission directive from the board of directors you elected and voted for
to serve these NEW customers. Those who will be here when the third
satellite is launched. They will not be where Dave will be by then. I
apologize for the crassness of this remark, but I am trying to make a
point. I know Dave and have for nearly 30 years.. We are building for
a guessed audience, with a guessed legal and RF environment, with a
guessed ability to deliver 3 such payloads over the next 13 years.
COLD HARD CALCULATION went into this analysis based on our best guesses
and analyses. Given what we believe the environment will be We can
only do this on microwaves and we can only do it digitally. PERIOD.
End of story. God (as demonstrated through the mathematics of Claude
Shannon) has dictated this outcome. We did not sit in a back room and
decide what new toys we would throw your way to delight ourselves and to
screw you (no more smoke and no more drink in there, we have grown old
and boring) . To do it, I have to build a very complex antenna system
that will take up most of the available area on the spacecraft for
antennas. I cannot build a three axis stabilized spacecraft (I do not
have the team or the money to do it), so I must do it with phased
arrays. Matt Ettus has given us a great head start on this design and
Tom Clark and John Stephensen have done great work on the antennas so
far. We will test these antenna designs in the next twelve months
thanks to a very generous antenna test range offer and design help by
one of our members.
The direction Jim and I gave our engineering team was that we cannot
rely on this to work perfectly and meet every operational goal
perfectly. STUFF HAPPENS. We are attempting to be ambitious but we
absolutely must have a credible back up in case this system does not
meet our expectations. We now have the upgraded Mode B transponder
design which I believe will be the sweetest one flown since Oscar 7's
Mode B. Fully equipped with the channelized AGC (Leila or Stella),
generating HELAPS with modern technology and new fantastic amplifier
I gave the argument to our engineering team that I have witnessed one
experimental, new widget after another get built, flown, and then have
its designers disheartened and dejected because it got "RUDAK'ed". It
never really gets used or fully developed. It drifts into an inert lump
that people mumble about when they are asked of their involvement. I
insisted on enough spacecraft power generation to run BOTH the linear
transponder and the digital transponder simultaneously and 365 days a
year, EVERY year. This is the single most expensive decision we have
made. We might spend 1/2 to 3/4 MILLION dollars on solar panels to
accomplish this. I have insisted we have enough antenna space to make
all of the antennas credible and based on calculation of the required
antenna gains to close the links. Again, Claude Shannon has
interpreted the natural laws and dictated the outcome. Cold hard
calculation has gone into the needed solar generators, and the size of
spacecraft required to support this.
It will be about 4 feet across and look initially like a scaled DOWN
AO-40 at launch if the concept becomes our design.
We cannot deliver the quality of services we are demanding of ourselves
if we fly all of the bands to be flown on P3E. We do not have the power
or the antenna territory to meet our goals for these services.
I have taken my direction from the board of directors of this
organization. They made the vision statement. They can change it. You
Several things will happen in October. We will install four
directors. I may, or may not, be one of them. The board will vote
whether or not to retain me as the VP Engineering. I have made almost
NO ONE happy by slowing down those who drive me crazy with wanting to
rush head long in a ready fire aim approach by demanding that we
calculate our way to the vision statement to show the directors the
consequences of the decision making processes. I have to tell you, I
am damn proud of how much has been done in eleven months. Stuff got
put on hold that aggravated many. We all make decisions about the way
things have to go but I have done my best to aim us in a technically
feasible direction. I do not have time to do all the everyone wants me
to do. I will continue to do my best if I stay in the job.
I offer the following. If the board votes to change their vision
statement and not to build the spacecraft we are proposing, I will
tender my resignation as VP Engineering since I will have failed to do
the job they elected me to do which was to produce a usable concept to
meet their vision. I am not interested in flying a carbon copy of P3E
when I know it makes no sense whatsoever. I am 52 years old and one of
the most active technical contributors in all of amateur radio. I will
not waste my time doing what I know in my heart and my head is not in
the best interests of amateur radio even if it is currently perceived to
be for the good of the shrinking aging membership of AMSAT. It would
be irresponsible of me not to attempt to aid the organization in
addressing a new group of members while attempting to thread the needle
of serving our current members. If elected to the board, and it changes
direction, I will offer my seat to the first alternate. Vote for
someone else if you do not want P3E built and you do not want the AMSAT
vision statement attempted if you have not cast your vote.
The story you have just been told should not have come out in this
form. It was NEVER meant to be displayed in this form. The
calculations were made at the first of July. They have undergone
several iterations and were not really put in there latest form until
August. In an attempt to get further interest from the microwave
community, we made a decision to give a sneak peek to get some technical
aid from RF specialists. This has backfired badly because we, the
volunteers who have sacrificed countless hours on your behalf, have not
had the time to put together a hundred pages of supporting documentation
to tell the story in a coherent fashion so not only do we look like
idiots, we have had to do things like waste 3.5 hours writing this
silly note when I should have been asleep.
Lastly. I have been accused here of being a con artist. I resent
it. I don't need to con anyone. Frankly, I don't have to be here at
all. I choose to be.
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
"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
More information about the AMSAT-BB