Managing the battery discharge by adjusting current draws - by
turning things on/off or changing the power level of the
transmitter, has been done since the 1990 AMSAT Microsats (or the
SSTL birds before them). At least we did that in one the ones I
worked on. I think it's still true that the most common cause of
satellite failure is batteries doing bad, and the one's I'm
familiar with were because the batteries got pulled down to the
resting voltage (about 1V/cell for NiCads). They will reverse
polarity or short when you mistreat them. With chemistries like
LiPoly, if you mistreat them they just die, or explode.
You prevent that by making sure you never pull the voltage too
low, and by not overcharging them. Another feature in the
Microsats was to reduce battery charging when they got near "full"
by moving the solar panel off the optimum point in the I/V curve.
I have seen many examples of missions that sat on the shelf for
months with the battery (whatever chemistry) discharging. Then at
separation they turn on a bunch of stuff and, drew the batteries
into the ditch, reset, and maybe came back on. And a few that did
that over and over until operators managed to stop it by command.
Or they died.
In the Microsats, and others I worked on, we took a very conservative approach. At sep, turn on only what is absolutely needed, beacon at a slow rate and lower power, let the batteries charge up and let the operators decide when to turn on the ACS or other stuff - after being sure there was enough power available.
So to the extent batteries are managed properly as in Falconsat 3 and SO50, yes, that definitely extends the life.
Having said that if you design goal is a year of operation at higher TX power with a full ACS running, or gathering a lot of science data, you accept the satellite life will be shorter.
It's all a trade-off. Actually, many trade-offs all tangled up with each other.
Jim
Jim
On Mon, Jul 22, 2024 at 1:17 PM Jim White via AMSAT-BB <amsat-bb@amsat.org> wrote:
I'll provide a bit of input here since I worked on SO50. Here are some considerations.
- The hardware was mostly built by SpaceQuest and used proven designs that had been flown several times
- The design goal was long life. The orbits would provide that, unlike some current launches were the orbit will last a shorter time. The idea was to provide a long life resource for all to use.
- The software followed proven designs dating back to the 1990 Microsats. All software except the boot loader (in rad protected RAM) was uploadeable. The SCOS real-time operating system allowed individual tasks to be killed and uploaded without disturbing other tasks or the OS. SCOS was quite robust.
- There were no I2C busses to latch up, and no flash cards (both of which cause problems in current designs)
- The program memory was rad hard, the OS 'washed' that memory every 10 minutes to eliminate bit flips from passing through the SAA. The data memory used Huffman software rad recovery.
- Antennas we not deploy-able and were made of piano wire so were quite robust.
- The batteries were NiCAD so were robust and hard to hurt. They work fine over a wide temperature range and don't need heaters. Don't need to manage charging as carefully and don't need to be concerned about not charging if outside a temp range.
- The software automatically adjusted TX power output to prevent pulling the battery V too low and causing a reset. There were three steps of battery management, each turning off more stuff to reduce load and attempt to prevent full discharge.
- Batteries were very carefully matched using the process first developed for the Microsats.
- The power system included adjusting the solar panel input impedance to constantly maximize power from the panels. And another algorithm prevented overcharging. A manual process is used to adjust those algorithms as the battery capacity drops with time and the panels loose efficiency.
- The software kept the dept of discharge of the batteries to no more than about 20%, resulting in much longer battery life.
Jim, WD0E
On 7/22/2024 10:46 AM, JOHN GEIGER via AMSAT-BB wrote:
Unfortunately I don't know much about IO-117 so that is a question I can't answer.
73 John AF5CC
Sent using Zoho Mail
---- On Mon, 22 Jul 2024 11:31:20 -0500 <crohtun@aim.com> wrote ---
And what have we learned from IO-117 about radiation resistance, etc?
Ray Crafton KN2K
On Monday, July 22, 2024, 12:02 PM, JOHN GEIGER via AMSAT-BB <amsat-bb@amsat.org> wrote:
SO-50 will be 22 years old in December and seems to be still be going strong, in sunlight and in eclipse. No other satellite launched since then has lived near that long. So what is SO-50s key to long life? Is it how the satellite was built? Something in its operation, like lower power on transmit? Its orbital setup?
Any ideas why it has lived so much longer than the recent crop of AMSATS?
73 John AF5CC
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