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Re: Troubleshooting the bird



The statements about the "command asssist" mode make it quite clear that this
cycles through various combinations of antennas, transmitters and receivers.
That's why the command team tried sending "blind" commands.  Since they don't know
if the spacecraft heard one without responding it's necessary to wait another ten
orbit period to see if the software reset will work and then see if a blind
command will be recognized.

"Edward R. Cole" wrote:

> 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.
>
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