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Is Sky TV Borked

 
 
Craig Shore
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      04-02-2006
On Sun, 02 Apr 2006 18:41:49 +1200, http://www.velocityreviews.com/forums/(E-Mail Removed) (Don Hills)
wrote:

>In article <(E-Mail Removed)>,
>Dibley Fanshaw <(E-Mail Removed)> wrote:
>>
>>Mind you, either Stuff are mis-reporting him or Brian Carter has got his
>>facts crossed. A geosynchronous satellite would almost NEVER be shaded.

>
>Brian was correct. When in doubt, Google.
>
>http://celestrak.com/columns/v04n09/
>
>Geosynchronous satellites are shadowed by the earth during the equinox
>periods twice yearly. The time shadowed reaches a maximum of about 70
>minutes per orbit, so the batteries have to be sized appropriately. Battery
>and solar panel capacity decreases with age, and this is an old satellite,
>so I suspect it doesn't have a lot of reserve capacity left.
>
>Although a geosynchronous satellite's solar eclipse occurs during the
>"sunlit" side of the orbit, and usually lasts from 30 to 60 minutes, if the
>orbital geometry is just right it can last up to 2 hours from start to
>finish.
>
>There is also a "worst case" to consider, where the time of earth shadow and
>time of lunar shadow happen to occur consecutively, that is the satellite
>passes straight from one to the other without any illumination between.
>
>So, my theory is that they hadn't fully recharged the batteries from the
>last orbit's earth shadow period due to insufficient power from the solar
>panels (maybe exacerbated by less than optimal panel positioning). They were
>then hit by the moon's shadow, the batteries died, and they lost everything
>completely and had to wait until they got enough charge back for
>repositioning. If they'd shut off the transponders they'd have had enough
>charge to last the eclipse but given the SLA penalty cost of service
>interruptions, they may have gambled on the batteries holding out - and
>lost. I am assuming, of course, that they realised the eclipse was going to
>happen, because such eclipses are not an uncommon occurrence. But if they'd
>completely forgotten abcout it...


The Press article on Sat said "Optus is investigating the cause of the outage
and believes the most probable cause to be a fuel feed anomaly to one of the
thrusters on the satellite."

Someone else said that they probably had to use the battery power to recover the
Sat after the repositioning went wrong, and since it was in an eclipse they had
to wait until it got in the sun and recharged before they could finish
repositioning and get it going again.


 
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Don Hills
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      04-02-2006
In article <(E-Mail Removed)>,
Craig Shore <(E-Mail Removed)> wrote:
>
>The Press article on Sat said "Optus is investigating the cause of the outage
>and believes the most probable cause to be a fuel feed anomaly to one of the
>thrusters on the satellite."
>
>Someone else said that they probably had to use the battery power to recover the
>Sat after the repositioning went wrong, and since it was in an eclipse they had
>to wait until it got in the sun and recharged before they could finish
>repositioning and get it going again.


That would fit... Thruster failure causing a positioning error, with the
solar panels not aligned to the sun, then the eclipse not allowing the
batteries to recharge thus losing all power letting the bird tumble.
Recovering from this can take a while because you have to wait for the
batteries to gain enough charge to restart the command system which
presumably runs an attitude recovery routine. Once the bird is stable you
then have to wait for full charge before turning the transponders on again.

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
"New interface closely resembles Presentation Manager,
preparing you for the wonders of OS/2!"
-- Advertisement on the box for Microsoft Windows 2.11 for 286
 
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Craig Sutton
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      04-03-2006

"Craig Shore" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...

> The Press article on Sat said "Optus is investigating the cause of the

outage
> and believes the most probable cause to be a fuel feed anomaly to one of

the
> thrusters on the satellite."
>


That is correct, Early Thursday just after it happened my source said
"overburn" has put it off the arc.

> Someone else said that they probably had to use the battery power to

recover the
> Sat after the repositioning went wrong, and since it was in an eclipse

they had
> to wait until it got in the sun and recharged before they could finish
> repositioning and get it going again.
>

The power issues were really just a side effect of the mattter and were not
mentioned until 7 a.m on most radio reports.


 
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