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Future radical satellite designs




Greetings from Patrick N2OEQ

Let me preface my comments by stating the following;

The solar energy in space, outside the atmosphere, is approximately 1400 watts per square meter.
This equates to about 130 watts per square foot. AO-51 ( amsat Echo ) is roughly a one foot cube 
covered with 27 percent efficient GaAs solar cells which cost approximately 20,000 dollars. With 
that efficiency and almost complete side coverage with solar cells, I would guess the satellite 
solar cell power conversion is about 25 to 30 watts for half the orbit time. Conservatively, that 
is about 300 watthours or more per day. Now, the transmitter might use 2 watts of energy to provide 
the 500 milliwatt downlink RF power and the satellite control electronics uses about 1 watt of 
energy. The Digital transmitter might use another couple of watts. For argument sake, I'll say the 
satellite uses 5 watts continuously for 24 hours per day or about 125 watthours per day. For some 
reason, it seems the full potential of the solar cells is lost or underutilized.
The transmitters power is kept low to reduce the batteries depth of discharge to a minimum to 
extend the battery life.

The point I am trying to make is that if amsat is going to pioneer new technologies in satellite 
design, they should keep their eye on the big picture or the basics of operation. I'm aware that 
people are trying to find a replacement for batteries but I would go further in saying that perhaps 
for future designs that amsat resort to solar dependant power output or specifically, full 
transmitter power directly powered by the solar cells and a sleep mode while the satellite is in 
darkness.

>From what I have learned about satellites, batteries are the weakest link often spelling disaster 
and limited satellite lifetimes. I would rather enjoy a high power intermittent solar satellite for 
many years more than the average lifespan of one dependant on battery life and cycling.

Some will argue that they want continuous duty whenever the satellite is in range, day or night.
I would like to see a longer lived satellite capable of full power half the time that could 
potentially last several decades in orbit.

Another point to ponder is the idea of asking to have auxilliary or piggyback payloads on larger 
commercial satellites. This was done with the russian RS satellites and more recently with India's 
Hamsat. The larger commercial satellites would probably have much larger and more efficient power 
budgets. I just read on the space.com website ( linked from amsat ) that the new Directv satellite 
is about 6 or 7 thousand pounds and probably utilizes the most advanced and reliable technology 
available. Wouldnt it be cheaper and easier to build an auxilliary payload versus an autonomous 
satellite? This question has probably been answered many times but I'll bring it up again.
If it is a costly idea, is the additional cost justified by better, more reliable operation?

Thanks for allowing this forum and thanks for all replies.

73, patrick


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