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 http://128.54.16.15/amsat-new/satellites/satInfo.php?satID=11&retURL=/sa... http://128.54.16.15/amsat-new/satellites/satInfo.php?satID=11&retURL=/satellites/status.php and http://www.spacetoday.org/Satellites/Hamsats/Hamsats1990s/Hamsats90sMicrosat...) 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 interesting:
* 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 populated. * 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