[eagle] A new opportunity (Phase 4 lite?)
rwmcgwier at gmail.com
Tue Jul 17 14:52:25 PDT 2007
In the last few weeks we have been presented with a new opportunity to
launch RF platforms into space. This note will necessarily be cautious
because we do not wish to do or say anything that will throw a monkey
wrench into the works. More specific details than are given here will
come from one voice, and that is from Rick.
This is a major development. One which will refocus some of the energy
of the organization should it come to pass. That said, no one in
management has proposed we stop Eagle and Jim Sanford will remain its
project manager irrespective of what goes forward on the new project
because we are still looking for rides for it.
The following is adapted from Rick's note to the board of directors,
with comments from me (and edits). We are being asked to propose that
we ride on someone else's satellite with our RF gear and antennas. The
primary is not a small satellite. It will go to geosynchronous orbit.
There are MULTIPLE rides being discussed but we have to get our act
together for round one. The planned lifetime of the large satellite is
over a decade and they have a track record of exceeding it. At the
beginning of life it produces 1 kw of excess power and we are trying to
ask for at least 1/3 of that because at the end of life, after years of
solar degradation, that is what the primary expects it to produce as
excess power. They do station keeping to maintain their subsatellite point.
They provide the ride. Thus, we do not need a motor, fuel tanks,
hydrogen bottles, propellant flow assemblies, or liquid ignition units.
They provide the electricity, thus we do not need solar cells or a battery.
We will not need an attitude control system at all or even attitude
sensors except for "gee whiz" like cameras or experiments.
They could easily provide us about as much space and mass as the Eagle
would have consumed, BUT WE DO NOT NEED IT. Rick suggested to them that
we would probably need as much antenna space as we have proposed for
Eagle, and they did not blink. Mechanical constraints (moment of
inertia ratios) allowing for a motor are completely out of the picture.
We will be rigidly mounted to their frame and they do the work.
They will be asked to provide some thermal control for our RF modules,
which will sit on the Nadir pointing side of their spacecraft, which is
3 axis stabilized, and will of course be subjected to hours in the sun
and hours in the dark. A careful thermal design is required.
We will never need to point another antenna on the ground after the very
first time should their payload behave. We will not need to despin a
phased array at 3 rpm. WE WILL need a phased array but it will be
adjusted in tiny increments on a daily basis at most. No more spin
modulation unless there is some failure on their bird.
We need our very high efficiency power amplifiers, both the proposed
linear and hard limiting design to be, as much as possible, producers of
RF and not heat. They are offering this opportunity because they have
discovered that if a goodly portion of the heat that is dumped from
their solar arrays at the beginning of life is consumed in RF, light,
etc., it saves them a considerable number of resources. This was one
clever study by an in house engineer.
They have been given some basic technical information on our proposed
payload. We, AMSAT, must get together now and provided them with real
answers on our proposed payload in a formal written proposal, but they
were given these rough estimates. We need to provide the follwing which
includes but is not limited to:
1) Size & Mass [less than 50kg, probably closer to 20kg, no batteries, ]
Antenna Configuration (space required) [they were told the same as
Eagle, a 60cm per side hexagon or some equivalent] Frankly, it needs no
symmetry at all. It can be completely determined by the needs of the
antennas and the envelope restricting us.
2) Given that, there is no need for a very thick spacecraft since it has
NOTHING in it but RF modules and computer(s).
3) Power requirements [they were told about 300 Watts]
4) Efficiency (how much power becomes heat) [we agreed to choose 0% to
start thermal design] (sic, from Rick. I don't understand what needs
to be calculated if we agree that we produce 300w of heat, then our body
will quickly rise to a very high temperature and melt. I think they
want to upper bound the thermal control needed for us. ;-) . )
5) Need for some of their on board resources to be specified and more
details follow after our study.
6) They must be told a REALISTIC schedule that we can meet. That will
determine what launches will be available to us and where the multiple
payloads will be placed.
We do know their power bus is many times our planned voltage, and we
need to decide if we or they build the power converter. This is pretty
obvious because they don't want to power TWT's, etc. from 5 or 14V!!!
If we do multiple payloads with them, as is currently proposed, they
would consider providing a "LAN" for us to communicate between
satellites to our payloads (think direct, bird to bird interlinking).
If the design study says we will not impact them greatly, they can
provide us this link.
For Eagle, we have planned to use 3400-3410 MHz for Earth->Space and
5830-5850 MHz for Space->Earth. It may be necessary to switch these to
be compatible with their transponders which are on nearly identical
frequencies BUT IN THE OPPOSITE DIRECTION. We don't want to transmit
near their receive frequencies. This raises a serious problem as Region
1 does not permit us to radiate signals from the satellite in the
3400-3410 MHz band if they can see it.
So it is clear, I will need to call engineering meetings, and more than
one, in the next couple of months. We are prepared to spend the money
on these meetings and bet this will be pulled off. If it looks like we
really will close this deal (as in signing an MOU) then we will
definitely bet the farm on it.
Right now, we probably should think we are basing the payloads
initially on what has been thought of for Eagle and we need to rethink
this because one thing should be crystal clear. THESE ARE NOT ADEQUATE.
Think about what it will mean to have a very loud transmitter, either
analog or digital, available 7/24/365.25 at the same spot in the sky.
We do not have sufficient capacity in our current design, period. We
would not want to do the SMS text messaging in the linear transponder,
but would likely move it back to Microwave for example. This relieves
the phase noise demands on the system for SMS (maybe not other
considerations TBD). Also, the user antennas on the ground are fixed.
We need some redesign starting from our basic payloads and then building
them out to meet what capacity we think we can support but this will be
the first time we have ever spent all of our power on the RF and very
little on anything else!
I hope you can see that we must be both bold and professional with a
dash of caution. A dash only because the probable time schedule will not
allow us to pontificate for half a decade. If we pull this off, there
is very little doubt in my mind that this will change not only AMSAT,
but amateur radio in general, and if we do our job well, in a big way.
We must thank Lee McLamb profusely for finding out this opportunity was
becoming available. Special circumstances allowed us, following his
notice to us, to move VERY quickly to "go in at the top of the
organization". That was done (MAN do I love low friends in high places
and in this case, at the very top).
More details will follow as the okay comes from Rick. Please refrain
from speculation or much gossip. I know I would be heart broken if the
wrong leak or wrong public statement caused us to lose this major
opportunity. I will not be entertaining a thousand questions but I do
want everyone to think about the redesign of the payloads carefully to
support a geosynchronous bird.
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
"If you're going to be crazy, you have to get paid for it or
else you're going to be locked up." Hunter S. Thompson
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