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

Re: AO-16 reconfigured

Whoops -- In my first try, I accidentally hit the SEND key before I 
posted the message! Then, after composing this message, it got lost in 
the big stellar bit bucket & didn't get posted to AMSAT-BB. So I try a 
3rd time --

The news from Drew and the AO-16 command team came as a most pleasant 
surprise to me. As Drew, KO4MA said :
> After the conclusion that the spacecraft computer system was damaged and as 
> discussions about decommissioning were taking place, Jim recalled a series 
> of low level commands included in the spacecraft design by Tom Clark, K3IO 
> during construction. One of these commands allows an uplink receiver to be 
> directly tied to a downlink transmitter.
It is now Jan.22 and it is, to the day, the 18th anniversary of the 
Jan.22,1990 launch (for details, see 
when the Ariane-4 carried the first 4 Microsats (AO-16, DO-17, LO-18 and 
WO-19) and 2 UoSATs (UO-14 and UO-15)into orbit.

The success that Drew reported came about because of three engineering 
decisions we made 20 years ago while designing the Microsats (a 
fascinating narrative translated from Chinese can be found at 
http://tinyurl.com/2r82dv and also see KB5MU's report from the 1989 TAPR 
meeting at http://www.qrz.com/download/packet/tapr89.txt):

   1. Hugh Pett, VE3FLL designed the MBL bootloader as a finite state
      machine, independent of the computer. In addition to providing a
      way to reload the computer, the MBL has the ability to load
      commands into the AARTs in each module.
   2. I developed (with a LOT!! of help from Bob Stricklin, N5BRG) the
      new concept which I called the AART (Addressable Asynchronous
      Receiver/Transmitter) using the Motorola MC14469 chip. The AART
      board allowed two wire bus to send configuration commands to each
      module. . This was AMSAT's first spacecraft LAN (although it was
      only 6 inches long). Each AART board receives 2 byte packets (one
      for address, one for data) and returns a one byte response when it
      is addressed. The data byte is heavily multiplexed and sets up
      digital states and an analog telemetry multiplexer. The last time
      I heard, the AART on AO-16 had handled well over a billion
      packets. This is relevant because Hugh 's MBL allows a command
      station to send commands directly to each module even if the
      computer is brain dead.
   3. In designing the Microsat receiver (with much engineering help
      from Eric Gustavson, N7CL & Jim Vogeler, WA7CJO, and construction
      help from Dick Daniels, W4PUJ and component scrounging by Lyle
      Johnson, KK7P), I implemented a bypass mode that allowed the AART
      to pass raw "audio" output from each receiver directly into the
      PSK xmtr. This was done mainly to facilitate testing after the
      module stack was assembled.

I'll tell you that I am very proud that my boards are still working and 
the RX sensitivity is so good. Given 4 original Microsats with 5 
individual receivers (except Dove with only 2 RX channels) and 4 AART 
boards running for 18 years (plus IO-26, AO-27 & MO-31) with plastic ICs 
and a lot of consumer grade components, AMSAT's "design them well and 
use industrial grade parts" philosophy seems to vindicated with a total 
of hundreds of years of on-orbit experience.

Bob McGwier (N4HY) has collected a lot of Microsat photos on his website 
at http://n4hy.smugmug.com/AMSAT/245761. A few I spotted that might be 

    * http://n4hy.smugmug.com/gallery/2052687#105508793 -- This page
      shows several pix of my RX and AART boards . There are 5 RX
      channels, 4 for the users and one for command. The pictures of
      bare copper PCB were mechanical mockups for vibration testing. In
      each shield area, the long chip is the Motorola MC3362 single
      channel FM RX chip. The large silver can just to the left of the
      3362 (a dummy in mass model) in the middle of each RX channel is
      the 10.7 MHz 15 kHz wide xtal filter that Lyle Johnson found for
      us. The 2M front-end has a 3 section TOKO helical resonator
      following the MOSFET LNA.
    * At the bottom left of
      http://n4hy.smugmug.com/gallery/2052687#105508798 you see a
      resonant line that served as a 70 cm TX trap and part of the 2M
      input circuit.
    * http://n4hy.smugmug.com/gallery/2052709#105511134 -- shows eye
      patterns showing that the RX works @ 9600 Baud (i.e. 4800 Hz
      maximum audio frequency
    * http://n4hy.smugmug.com/gallery/2052709#105510099 -- the DOVE RX
      is on the left -- note that only 2 of 5 RX channels have been
    * http://n4hy.smugmug.com/gallery/2052709#105511041 -- Bob still has
      SOME hair.
    * http://n4hy.smugmug.com/gallery/2052709#105511088 &
      http://n4hy.smugmug.com/gallery/2052709#105511116 -- Bob still
      gives me a hard time about having a mustache!

Thanks to Drew, Gould, Doug, Jim, Mark & Bruce for this 18th Birthday 
present for AO-16.

73, Tom

Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb