In praise of broken batteries. 13/1/2006

Oscar-7 has busted batteries.  First, about 24 years ago, they went short-circuit, effectively ending the mission.  Then in 2002, they decided to go open-circuit.  This brought the satellite back from the dead... the Lazarus sat if you will... and it's been working ever since when in sunlight.

The battery used in AO7.

 It works in sunlight because the batteries no longer drag the voltage down. On a good day it can support multiple QSO's provided users are sensible (a rare thing with those 'trained' on FM birds) and its in a VERY useful orbit that provides excellent coverage.  When the telemetry system works, it lets us know that apart from the batteries and some degradation of the solar generators power output caused by severe cosmic irradiation of the glass cover plates, its actually in reasonable shape. The power generation system is not quite so degraded as some at AMSAT would suggest.

IMHO There is a GREAT deal of sense in building simple comsats with no fragile CPU's as demonstrated bv 30 year old Oscar7.  It used simple cheap CMOS command and telemetry circuitry. On a good day, the telemetry system still functions.  With a useless battery and the unavoidable degradation caused by being in an extremely  harsh radiation environment, it's a surprise that it works at all.

The following telemetry frames were copied by John LA2QAA in December 2003 when we were actively monitoring the bird.  Frames that end in 649/650 or 651 are generally trustworthy.  The parameter is that of the voltage refeence for the A/D converter on board the craft.   649/650 or 651 shows that adequate bus voltage is available to operate the telemetry system.  The X's show unreadable data (QRM etc)

HI HI
100 145 176 156
297 245 200 254
370 34x 328 354
453 455 450 451
542 501 553 529
60x 601 601 651

HI HI
100 166 179 156
297 263 201 254
376 368 331 354
448 455 449 451
541 501 552 529
60x 601 001 651

HI HI
100 128 190 173
239 263 201 254
369 327 325 354
448 455 4x1 453
548 501 552 528
600 601 600 650

HI HI
100 103 197 182
213 266 201 2x6
330 383 3x3 361
449 455 451 453
547 502 526 500
603 665 601 658

HI HI
100 177 179 147
208 269 202 254
375 364 331 354
444 455 449 453
541 501 552 529
600 601 601 651

HI HI
10x 1x4 1x1 16x
240 210 266 203
302 302 322 353
403 437 493 462
567 507 560 561
636 676 618 662

HI HI
100 161 191 157
205 259 239 220
363 353 326 353
430 401 450 453
547 500 551 527
602 600 601 651

HI HI
100 128 190 173
239 263 201 254
369 327 325 354
448 455 451 453
547 501 552 528
600 601 600 650

HI HI
100 159 176 177
276 258 200 254
372 305 329 354
457 455 460 457
543 501 550 529
600 601 600 651

Were I involved in building satellites. the only other thing I'd want to see added  is a battery disconnect latching relay so that if the battery quit  'open' at least the bird could work in sunlight. This simple step might prolong the life of a spacecraft considerably.  Yes, batteries sometimes fail S/C..... but sometimes they fail O/C!  As an user on the ground, you have no influence over that except perhaps choosing your battery type carefully.
Relays are cheap, satellites are expensive!

Realistically, if the space were available, a dual battery system has some things to commend it ... rather than wasting space with unnecessary computer based modules.  Computers on a comsat... why bother. They are a liability.

And yes John, before you ask, I have been working on re-writing the telemetry decoding software.
Sad somehow that I have to get my kicks from a 30 year old bird with wrecked batteries.

Still, at least when its in sunlight it can do something genuinely useful.... provide communications for multiple users.

73 Al.