Last night at the pacsat developers meeting, we had a good conversation
about what we were aiming for. This started out with the question "what is
our power budget", and the answer seems to be pretty tightly bound to the
satellite that is hosting us, and what else that satellite is carrying.
It seems to me that thinking about it this way gives us a round and round
series of thoughts: What is our power budget?->What satellite will we fly
on->Unknown but we can guess how much power is available on a 3U or a
1U->But that depends on what else is in the satellite, is it only us?->What
is our power budget :-)
My (current) thought is that pacsat is in the ASCENT program, which is
specifically designed for "trying things out" without necessarily having a
flight in mind for them. So I would suggest that our first job is to just
get SOMETHING that works with a TMS570 and 4 AX5043s. Then we will have a
very good idea how much power we use under different circumstances (fewer
TMS570s, slower processor, etc) and for that matter whether we would be
better off with an STM32L lower power processor.
In all cases, we should design for flexibility. As an example, don't do
anything that absolutely REQUIRES 4 AX5043 chips and don't do anything that
REQUIRES unique capabilities in a TMS570.
Then we should of course be prepared to make the required modifications for
a specific flight. (Example: We are Jonathan's 5043 Pi boards; the RT-IHU
is the specific implementation of those and the TMS570 for Golf.)
This is quite different from a typical approach where initially software is
given many requirements and a date, and then (usually) the requirements
turn out to be unachievable within the given time and cutbacks have to be
hacked out. But I think it is appropriate for the organization and the
program we are in.
Burns Fisher, WB1FJ
*AMSAT(R) Engineering -- Flight Software*