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RE: AO-07 PARADOX?



Thank's for the info's Tom here is some comments.

On 24 Jun 2002, at 0:15, Tom Clark (W3IWI) wrote:

> 
> A standard mode for a NiCd battery to fail is for a cell to become short
> circuited. When AO-7 died years ago, the telemetry showed that several cells
> became shorted, and then the satellite went silent. At the time the
> spacecraft was running hot (about 40 C) and we felt that the cells failed in
> the "cooked" mode.

Just retreive this note from my batteries file folder

Old Nicads batterys usually end up with several cells being short circuit, as
they suffer from crystal growth in the electrilite. To reclaim the cell before
charging, (as charging will not remove the short) a very high current pulse
must be used.

With a sealed battery pack this can blow any internal safety fuse! So it is
best done when U have opened the pack. The good cells will withstand the high
current OK, but having them in series can reduce the current depending on how
you are applying it, if you have a really bad cell.

Current up to 10xC (eg 5A on a 500mAH AA cell, 40A on a 4AH D cell) can be
safely applied until the pack warms, (how fast chargers detect 70% charge &
drop back to trickle).

For more difficult cells, current over 10xC may be required, this can distroy
the internal cell wires, but you have nothing to loose! Charge up a 10,000uF
to 40V & connect to cell (computer must not be nearby!) with thick wires, the
100A pulse usually clears the short after a few pulses.

Once all the cells are over 1V, then trickle charge (Cx0.1) until warm or 14
hours. A few cycles of discharge & charge will bring back old cells to 100%.

If the capacity is less than 100% after a few cycles or there is excessive volt
age (>2V) across a cell when charging, it is O/C or dry & will need to be
replaced.


 
> Now we speculate that (at least) one of the shorted cells has acted like a
> fuse, becoming an open circuit. If this is the case, then the satellite is
> running only on solar power, and then only in sunlight.

Are you speaking about an internal safety fuse as above 
or as martin says: 
          Speculation that long term chemical changes in one
	    or more battery cells have led to increased cell
	    resistance enabling the spacecraft to operate while
	    in sunlight are correct...

There is no Zapping power available at the satellite and did you know any documented ni-cad batteries 
resurection here on earth after a so long period? I know AO-10 is also now solar powered but he never 
pass throught a 28 year sleep period.
 
> 
> If this is true, then the satellite turns itself on/off each orbit as it
> enters sunlight. The mode it chooses to select is probably random.
> 
> It would be interesting if the folks on AMSAT-BB would confirm that the
> satellite only operates in sunlight. Here is a simple way to know if the
> satellite is in sunlight: Look at a graphical view of the visibility circle
> on a map that also includes the sunrise/sunset line. If any part of the
> coverage circle lies inside the daylight area, then the satellite sees the
> sun.

As the orbit is sun-synchronous will this be ever possible to verify


    Planned Orbit:

        Similar to that of OSCAR 6; 1460 km altitude circular orbit, 102
        degree inclination (retrograde, sun-synchronous orbit), period or
        115 minutes, about 1/2 orbit (1 hour) out of phase with the OSCAR 6


Here is some questions Tom that i'm asking to myself as stated in the satellite parameters:

 The two repeaters are operated alternately by means of a timer arrangement,
    but repeater selection and output power control can also be accomplished by
    ground command.

 Is it possible that something else could have trigger AO-07 on? accidently or on purpose?

Due to the nature of the frequencies in use aboard as you stated Tom:

If the Mode-B transponder is in fact ON as indicated by the telemetry that
Pat Gowen sent, and if the uplink rcvr has survived 28 yrs later, then the
uplink is on ~432.15 MHz. Of course, the use of this frequency predates the
WARC '79 allocation of 435-438 MHz by the ITU for the Amateur Satellite
Service (hereinafter denoted "ASS") and puts the uplink in 70cm Weak Signal
"turf" outside the allocated spectrum.

Potential users may not realize that when they are uplinking to a satellite,
they are no longer operating in the Amateur Service but have a different
status operating in the ASS are subject to ASS rules. Therefore uplinking to
AO-7 is possibly illegal since the ASS is not permitted at 432.1 MHz!

Also, since the IARU bandplan has the 432.1 MHz range earmarked as "weak
signal" in all three Regions, then it would appear that users trying to
access the uplink are also immoral!

The fact that the satellite coming out was on field day week end time slot and as stated by Peter Guelzow 
DB2OS

The return of AMSAT OSCAR-7 is indeed a pretty amazing story.

The Mode-B transponder was designed and build by Karl Meinzer DJ4ZC and
Werner Haas DJ5KQ, who unfortunately left us in 2000 (he had his birthday
today)

Today was june 23...

With the Arabsat saga will AO-07 be better dead than alive? and there is a bunch of  "coincidences"
who let me speculate a lot up here!  But ill bet you that i will try it you never know the way it goes 
FREQUENCY the film could be not a fiction...HI 







Luc Leblanc VE2DWE (AMSAT 33583)
Coordonnateur AMSAT pour le Québec
Quebec AMSAT coordinator
SITES WEB:http://www.sorel-tracy.qc.ca/~luclebla/
          http://www.qsl.net/ve2dwe/
C.P.341
Sorel-Tracy QC.
Canada
J3P 5N6


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