[amsat-bb] US barriers to orbit (Re: Amateur communicationsatellites)

[Graham Shirville]

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: amsat-bb at amsat.org ; bruninga at usna.edu ; n8hm at arrl.net
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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