[amsat-bb] AMSAT HEO design evolution (longish)
G0MRF at aol.com
Mon Aug 11 10:00:55 PDT 2008
Given the understandable negative content of the posts recently regarding
the AMSAT HEO satellite debate, perhaps it's time to return to basics and ask
some fundamental questions about the way we design satellites and fund their
The problem: AMSAT High Earth Orbiting satellites have historically had a
mass between 150kg for P3 and 650kg+ for AO-40 and at 30,000 Euros per kg, we
do not have the resources to self finance the launch costs of 4.5 million
(30k x 150) to 15 million Euros to launch.
However, AO-40 was probably a 1-off and will never be repeated. So let's say
4 - 5 million.
The way forward?
1) Raising the funds for the standard launch cost of the typical AMSAT HEO
is beyond us. So other external funding solutions are needed either by
providing a service which is paid for. - An example of exploring this route is the
AMSAT NA proposed Advanced Communications Project via Intelsat.
A second approach, is to include commercial payloads within the AMSAT
spacecraft, or perhaps including AMSAT 'functionality' within other commercially or
educationally funded spacecraft. Again, there are examples of this approach
for LEOs. Delfi C3 is one success story. Also, and had it worked for more
than a few orbits the ESA Education department / SSETI Express XO-53 was
another. But at HEO the opportunites are very rare indeed, the only project
currently being persued is the ESA ESEO educational mission with AMSAT UK providing
a U/S transponder as part of a redundant communications system for the
As we have been reminded in the past few days, self funding never worked
before and it wont work in the future. I feel some sympathy for the AMSAT NA
board who have an apparently impossible task to fulfil, but their enthusiasm to
elicit support has let expectations exceed funding ability. - The response ha
s been vocal. But at least they are trying.
Finally on the funding issue, what have we done in the last 8 years? We've
had the Eagle fund. We've had the successful AO-51 fund raising campaign, but
really, since the launch of AO-40 in November 2000 we haven't saved for this
'HEO' eventuality. If we are ever going to replace spacecraft in the future,
fund raising needs to be more sustained and less impulse led. We have little
to show for the last 8 years.
2) There is however another option which may be self financing. A
fundamental spacecraft redesign to reduce the mass to a figure we can afford to launch.
Over the last 25 years, the mass of a P3 spacecraft has remained fairly
constant. About 90kg of structure and payload with an additional 60kg of
bi-propellent fuel. There are probably ways of trimming this back substantially.
In LEO sat design we have seen a reduction in size from 400kg to the SSTL
microsat of about 120kg in the 1980's. These days the SSTL 'microsat' has
evolved down to 3 - 5kg. with projects like the NASA Nanosail design. But no such
revolution has taken place in HEO satellites
So, a few possibilities. You can probably think of more......
a) The 60kg of fuel has been needed to raise perigee and increase
inclination from a typical geostationary transfer orbit. But there have been orbital
change manoeuvres that have not gone to plan e.g. AO-10 and AO-40, but those
satellites have still given us usable communications. Do we need all 60kg?
How about raising the perigee to give a long life and a slight increase in
inclination to get us out of the GTO belt around from around 7 degrees to 15
degrees? I wonder what the saving is there, 400 Newton motor down to 50 Newton
motor. Fuel from 60kg down to 15kg? Saving = 45 + 5kg = 1.5 million Euros?
OK the figures are guesswork, but there must be savings.
b) Spacecraft design. During our time with P3 spacecraft, we have seen
transponder power change dramatically. I recall the first few days of AO-40 when I
heard the 2m beacon stronger than many local FM stations. But then it used a
300 Watt BLF278 type device and was designed to give a huge signal. Equally,
I also recall receiving a worked all continents satellite award for QSOs I
made on the experimental AO-13 mode S transponder. That was 1 Watt (max) into a
5 turn helix on 2400. So, in the future, do we need 45 or 50 Watts of power
in a 100kHz wide transponder? After all, if there are fewer amateurs, we can
use less bandwidth saving power and mass in the process. 8 Watts and
50kHz? A consequence of such a design change would require a groundstation with
more than a patch antenna to pick up the signal. But is that unreasonable,
dishes are cheaper than launches.
c) Two final thoughts. Firstly, isn't the world moving away from metal
structures to carbon and ceramic composites. Mass saving perhaps. Secondly, I
don't think AMSAT with it's limited resources can afford to put spacecraft into
orbit that will fail the moment the batteries die. Let's not dwell on the
excellent Delfi example, but instead look at the Intelsat spacecraft. Is it not
the case that they have a 10 year lifespan which is limited by stationkeeping
fuel? While they operate 24/7 the power comes from the solar cells. The
batteries are used only in eclipse. With our P3 designs, as I understand them,
the spacecraft can not function on solar cells alone. Unfortunately, the
advantage of our chosen HEO orbits also mean that the batteries on a P3 satellite
go through a couple of eclipses a day. As battery life is proportional (or
worse) to depth of discharge of the batteries, it's not surprising that most
AMSAT spacecraft suffer battery failure. But with limited funds we really need
to design in a mode so that 5 years on, the batteries can be switched out of
circuit and a sensible geometry of solar panels can continue to provide some
daylight only functionality.
Funding campaigns need to run over several years within a rolling plan to
supply launch funding.
Designs need to evolve to include new technologies. Mass reduction = lower
launch cost should be near the top of the list.
With fewer amateurs, and modern digital modes we need less bandwidth.
It is not unreasonable for an AMSAT member to need a moderate size of
antenna to work an HEO. So, lower power in space.
Lifespan needs to be increased and with HEO that means battery failure
should be anticipated and mitigated in the design. A daylight operating spacecraft
is better than no spacecraft at all.
Thanks..........a quiet day here!
Could we do HEO within a 50kg budget? = 1.5million Euros spread over a 10
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