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Re: AMSAT HEO design evolution (longish)



At 03:00 AM 8/12/2008, G0MRF@aol.com wrote:

>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.

Well, you're not going to get too many arguments from those of us 
south of the equator. :-)  Inclination change is the most expensive 
manouvre, in terms of fuel consumption, so minimising this will 
dramatically reduce fuel consumption.  Raising perigee, OTOH, is much 
less of a drain on fuel reserves.

>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.

There might be a fly in the ointment here.  Many US hams are unable 
to erect any outside antennas.  Down here, we're a bit more 
fortunate.  It is true that dishes are cheaper than launches, but one 
has to find the "sweet spot".  And maybe some of the money saved can 
go towards making it easier for newcomers to setup a suitable ground station.

>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

Good idea.  And that's where raising the satellite's perigee can have 
a big advantage.  A higher perigee means fewer eclipses, which 
translates to less discharge cycles on the batteries, and longer 
periods of solar only operation possible.

If you look carefully, you'll see a series of compromises between 
cost, groundstation cost (has to be multiplied by the number of 
potential users) and groundstation practicality, coverage and the 
ability to run on solar power alone.  Where is the sweet spot?

73 de VK3JED
http://vkradio.com

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