[amsat-bb] Future radical satellite designs
N2OEQ at aceweb.com
Sat Jul 7 21:50:06 PDT 2007
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
>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.
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