Re: AO-73 Question (mode efficiency?)
The satellite is only in transponder mode when it is in eclipse.. In full sunlight it is in beacon mode only.
Just curious about the overall design goals of this operating mode? Putting solar energy into and then taking it out of batteries suffers about a 30% loss in efficiency. All else being equal it is usually better to use solar power directly if possible.
Maybe the value of this mode is for hams to use the satellite in the evenings during play time instead of during the day when schools and students could benefit.
Just curious. Thanks
Bob, WB4aPR
Hi Bob,
Yes the mission requirements are exactly as your last paragraph. We have a dual mission and needed a simple, autonomous, on board system to make the change between the two modes. The sunlight/eclipse transition is fairly easy to detect and forms a valid decision criteria.
The system current in daylight is around 220mA and when in eclipse it is "only" 140mA. If the transponder is in use then this can rise momentarily up to 250mA but the average eclipse consumption is probably only around 160mA as many of the eclipse periods are over the sea or unpopulated land areas.
Presently the power budget seems pretty good and we are hopeful that the solar cells and battery will maintain their present performance for some time to come. The bus voltage is usually around 8.3V at the end of the sunlight period and drops only to around 8.1V at the end of eclipse. Apparently this equates to less than 5% discharge.
cheers
Graham G3VZV
-----Original Message----- From: Robert Bruninga Sent: Friday, December 27, 2013 6:01 PM To: David Johnson ; Peter Budnik Cc: AMSAT-BB@amsat.org Subject: [amsat-bb] Re: AO-73 Question (mode efficiency?)
The satellite is only in transponder mode when it is in eclipse.. In full sunlight it is in beacon mode only.
Just curious about the overall design goals of this operating mode? Putting solar energy into and then taking it out of batteries suffers about a 30% loss in efficiency. All else being equal it is usually better to use solar power directly if possible.
Maybe the value of this mode is for hams to use the satellite in the evenings during play time instead of during the day when schools and students could benefit.
Just curious. Thanks
Bob, WB4aPR _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
From Graham earlier in November on the BB:
............................
Hi All,
Yes in telemetry (also known as educational) mode we have around 300mW and this is a much higher average RF output than when in amateur (also known as transponder) mode.
Total current drain is therefore greater when in educational mode. This is convenient because we had planned that educational mode would be more useful when the spacecraft is in local daylight - ie schools would be more likely to be open. This is the primary mission of course. Also amateurs often have to work during the day so would appreciate the availability of the transponder during the local evening passes.
We were not, before launch, 100% certain that we would have a good enough power budget to run the transponder during every eclipse period but, at the moment, this seems to be ok - we still have quite a positive power budget.
Its a bit late here and we are quite tired after three very hectic days but I hope the above explanation makes some sort of sense:)
best 73
Graham G3VZV
On Fri, Dec 27, 2013 at 12:01 PM, Robert Bruninga bruninga@usna.edu wrote:
The satellite is only in transponder mode when it is in eclipse.. In full sunlight it is in beacon mode only.
Just curious about the overall design goals of this operating mode? Putting solar energy into and then taking it out of batteries suffers about a 30% loss in efficiency. All else being equal it is usually better to use solar power directly if possible.
Maybe the value of this mode is for hams to use the satellite in the evenings during play time instead of during the day when schools and students could benefit.
Just curious. Thanks
Bob, WB4aPR _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
participants (3)
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Graham Shirville -
Robert Bruninga -
Stefan Wagener