[amsat-bb] AMSAT HEO design evolution (longish)

[G0MRF@aol.com]

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 
launch.
 
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 
spacecraft.
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.
 
Conclusion: 
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!  
 
David
 
Could we do HEO within a 50kg budget?  = 1.5million Euros spread over  a 10 
year lifespan?