[amsat-bb] US barriers to orbit (Re: Amateur communicationsatellites)
g.shirville at btinternet.com
Thu Jun 30 21:35:42 UTC 2016
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.
From: David G0MRF via AMSAT-BB
Sent: Thursday, June 30, 2016 11:07 AM
To: amsat-bb at amsat.org ; bruninga at usna.edu ; n8hm at arrl.net
Subject: Re: [amsat-bb] US barriers to orbit (Re: Amateur
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.
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.
On Wed, Jun 29, 2016 at 6:26 PM, Robert Bruninga <bruninga at usna.edu>
>> How big and or heavy will this 15/10 bird be?
> A small cubesat. To support a linear transponder takes a lot of power.
> might have to leave it off at night. Not sure until we do the analysis.
> -----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
>>> 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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