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Re: An Open Letter To AMSAT



>The master reset circuitry is able to be activated independent of the IHU.
>Additionally, the L band RX is on ALL the time.  And either the 2m or 70cm
>RX is on.  So there is always at least 2 receivers functional at all times.

I don't know about receivers on 2m or 70cm, but I suspect you're right
that the 23cm receiver is always active.

Which is why I must confess to being rather puzzled by the announced
strategy of waiting for a "command assist" timer to expire. Here's
why:

1. This timer is implemented in IHU software. This relies on a
properly functioning IHU.

2. If the IHU is functioning properly, it should already have
responded to ground commands. It has not.

3. If the IHU is *not* functioning, e.g., due to a software crash,
then there is no reason to wait to send the reset sequence. Indeed,
there might be good reason to send it ASAP, to reduce the chances of
the spacecraft condition degrading further while out of control.

The only scenario that calls for waiting for a command assist timeout
involves the failure of a primary command receiver and the automatic
activation of a backup that isn't already running. Yet I find it
difficult to conceive of a credible failure scenario that would
simultaneously stop telemetry transmissions *and* deactivate the main
command receiver while the IHU and the rest of the spacecraft
continued to operate normally.

Phil
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