[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Troubleshooting the bird



To properly anlayze the probelms on AO-40 we must:
1.  Have full access to the facts
2.  Have the blueprints of the bird plus a full understanding of how it works

I would say we have neither, only the general bulletins for the general
public which is made simple for those not well grounded in technology or
those who just want the basics.   All I have is the block diagram in "P3D
to P3G" which shows the IF matrix as a single box.  It also leaves out the
L-band receivers {;-) ...oops!  Ever try to repair a radio with only a
block diagram?

Saying that, I agree it is not "crib death" since all these systems were
well burned-in on ground.  So that leaves environmental or random failure!
Or a command glitch: "computer please compute pi to 1,000,000 decimal
places...we're in no hurry"!  Hopefully the shut-down command wasn't given!

I'm guessing {like the rest of you}:  The few facts we have point to a cpu
fault, hopefully a program hickup that can be solved by the built-in
recovery routines or a reset.  If IHU-1 is "toast", then hopefully IHU-2
can be used as backup!  I assume {and this is the crux of why we are not
likely to solve this here on the list...poor assumptions} that the IF
matrix, antenna relays, Tx activation are all controlled by the IHU's.  BTW
in my 30+ years as an engineering analyst and "real world" technician, by
far most of my troubleshooting difficulties came from starting with bad
assumptions.

BTW there are 9 receivers on-board.  Which one is currently switched-on?
You need to know that before any successful command transmissions are made.
 But we will not know unless the bird can auto-recover the beacon.  We know
the beacon initially was programmed for 70 cm.  So even if it resets to
default programming, we will not hear it.  I suspect the cmd stations have
already looked at this since the interuption of the beacon.  How did they
hear it right after launch??  What steps were taken then to get things
working?

How do we know the IF matrix isn't malfunctioning?  Or maybe LEILA went
"mad" and notched all the beacons ;-)  {just joking}

Regarding the 400N engine problems, the arc-jet thrusters are a possible
back-up.  Can they get us to our orbit?  I don't know enough to say.  That
is for Ken and the orbit specialists to determine.

So you see, we are the monday morning {oops Tuesday} quarterbacks in this
game.  The discussion fills the time, but are we really close to
understanding?

Ed


Previously written as "Open letter...":
>> For this to work (and I am speculating here although
>> it could be cleared up pretty quick) this would require as a minimal thing
>> that at least one command reciever be working and two the "master reset"
>> circuitry be intact and three that their be something functional to reset.
>
>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.
>
>There is always a possibility that the RF circuitry failed, but having been
>an RF designer, I know a little about that.  Most of the time you have
>either an "infant mortality" or failure after a long, long period of time.
>Very rarely does something work for a couple of weeks and then stop.  It is
>not impossible, but IMHO, unlikely.
>
>> 
>> So to summarize based just on what the folks have let us know it strikes me
>> that 1) there is a window that closes at whatever time plus interval that
>> the on board reset will fire then 2) there is a last ditch chance to send
>> this master reset.  I would wonder what has to be working on the satellite
>> for that to work...?
>
>There is no window that closes as you speak of.  The COMMAND-ASSIST mode
>goes into affect after a certain amount of time of no commands being
>received.  From what I have read, we have never reached the point of the
>COMMAND-ASSIST routine activating.  When it happens, the bird will try to
>transmit telemetry or a carrier or whatever on various combinations of bands
>and antennas.  If this functionality works, we will all know it.  Again,
>this bird is loud.  If it begins transmitting, we won't need EME arrays to
>hear it.

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home