Reid Crowe wrote:
Drew, Do you think the bird will be able to support 2.4gig in the future? -Reid
I hope you don't mind if I copy this answer to the -bb as well. It's a good question. The batteries on AO-51 have lost significant capacity since launch six years ago, and in order to protect and lengthen their life as long as possible, we are limiting the load during eclipse by shutting off the UHF transmitter. We are also using the PL to only turn on the UHF transmitter when in use. Both of these actions are controlled by the flight software, specifically the PL and power management routines.
Since the S band transmitter on AO-51 is an added "experiment", the ways in which it reacts with the IHU and flight software are different than the UHF transmitters. The PL cannot be used to turn S on or off, only to gate the audio. The power management software is unable to control the state of the S band transmitter as well. The S transmitter is a fixed output, that draws about 730 mA. This is an equivalent load to running the 435.300 transmitter at over 1 watt. In other words, it is not an insignificant load.
Since the return of eclipses this summer, after a long period of total illumination, we have discovered that the S transmitter will pull the battery voltage too low during eclipses. This activates a software watchdog that shuts the S transmitter off until commanded back on from the ground. As a work around, we have been using the automatic mode scheduling software to re-enable the S transmitter a few minutes after exiting eclipse each orbit. This has worked very well. The downside is the scheduler only holds 18 events, as it was designed for the weekly mode changes. At 1440 minutes per day, and 100 minutes per orbit, you can see we need to upload a new schedule every day to keep S running every orbit. As long as the satellite is in the sun, there is no problem running the S downlink.
So, you can see why we have been frugal with S activity this summer, as it is a real load on the command stations to plan the daily schedule, encode it, and upload it to the satellite daily (at 5AM). The good news is we return to a no eclipse period at the end of August, and I plan to run S at a ~minimum~ of 1 week a month until eclipses return in 2011 for many years. This works out OK over the summer, as there are lots of folks on right now from their vacation spots, and out on the roads giving out rare grids.
I hope this long-winded, probably-too-detailed explanation answers your question.
73, Drew KO4MA
BTW, this AM Mark N8MH raised the 435.300 output to 1 watt.
On Behalf Of Andrew Glasbrenner
Sent: Wednesday, July 21, 2010 3:37 PM To: Reid Crowe; Amsat-BB Subject: [amsat-bb] Re: AO-51 S band Question
Andrew Glasbrenner wrote:
I hope this long-winded, probably-too-detailed explanation answers
73, Drew KO4MA
I appreciate your long-winded and detailed reply. Having purchased an S band antenna and down converter a few days before Field Day, and missing the single "good pass" on Sunday morning, I have been anxious to try S band operation. Looks like there will be plenty of opportunity this Fall. Thanks for the information, and great explanation.
Randy - KI4LMR