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