Hi All,
Just to expand on David's comments.
The AO73 "Loopback" Mode is an AO16 type FM in and DSB out mode. It is intended only to be used in event that our on-board microprocessor dies! We have never done it but i guess that if were to run the high power telemetry continuously then this would be also power negative over an orbit.
The first thing that I always check on the Data Warehouse is that (in the sun) the "total photo current number" is higher than the "total system current" number. This positive situation has been achieved in part by running the on-board oscillators at very low currents. This has resulted in some unwanted temperature dependency of their performance. However the internal temperatures on this 1U spacecraft vary by some 25C each orbit so it is perhaps to be expected.
You will note that UKube-1 which has a similar FUNcube sub-system is more stable as the internal temperatures, it being a 3U spacecraft, only vary by approx 6C each orbit.. Please be aware that Nayif-1, expected to be launched late this year uses much more stable oscillator chains but that this has only been achieved at the cost of them being more power hungry. We will have to wait and see how the power budget actually works out in orbit.
We do have a capability to set both FUNcube-1 and Nayif-1 spacecraft to only switch autonomously to operate in transponder mode every "x" orbits/eclipses with an adjustable ratio of "receive only" eclipse periods. On FUNcube-1 we have never had to implement this (outside the test lab). If we do get to middle age with lower battery capacity and lower solar panel efficiency then we have this as an available option or "workaround".
We are quite proud of the number of different use cases that we thought up and satisfied during the early design phase. We considered all manner of different possible power and temperature scenarios. Hopefully most will never be needed.
73
Graham G3VZV
-----Original Message----- From: David G0MRF via AMSAT-BB Sent: Thursday, June 30, 2016 11:07 AM To: [email protected] ; [email protected] ; [email protected] Subject: Re: [amsat-bb] US barriers to orbit (Re: Amateur communicationsatellites)
Hi Paul / Bob
We are fortunate with AO-73, If I recall correctly, it is power positive in all modes except "Loopback" where it does drain the battery if left on 24/7
Elipse detection was our key to success. However, we have come to realise that an adjustable timer that allows a satellite to charge for X minutes after entering sunlight provides much more control over long term management of the power budget and battery life. - Another lesson learned.
Thanks
David G0MRF
AO-73 is a 1U cubesat and power positive with a 20 kHz wide linear transponder at about 300 mW PEP. With a 10m downlink, you have less path loss to contend with than on 2m (but more loss through the ionosphere), but I'd think it would be doable if the passband is kept relatively narrow and the power output low.
73,
Paul, N8HM
On Wed, Jun 29, 2016 at 6:26 PM, Robert Bruninga <bruninga at usna.edu> wrote:
How big and or heavy will this 15/10 bird be?
A small cubesat. To support a linear transponder takes a lot of power. We might have to leave it off at night. Not sure until we do the analysis. Bob
-----Original Message----- From: Robert Bruninga [mailto:bruninga at usna.edu] Sent: Wednesday, June 29, 2016 3:28 PM To: AMSAT-BB Cc: bruninga at usna.edu Subject: RE: [amsat-bb] US barriers to orbit (Re: Amateur communication satellites)
Within the US, when someone like Bob, WB4APR, tries to build amateur communication sats, he runs into needless obstacles from FCC and NTIA.
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