Re: Magnetic field's effect on dish position

André Coutanche wrote:
> DAB sounds worse than FM wrote:
>
>> If the solar panels do rotate then it is necessary to stop the
>> satellite spinning after they've been rotated. The only way I can
>> think of to stabilise the satellite would be to put the thrusters
>> on.
>
> Sure. I don't know that they do, and I can think of some good reasons
> why they wouldn't - more moving parts to go wrong; need for finite
> fuel reserves to be used correcting for the motion etc.


True, but see below.


> Either someone
> here, or the excellent Mr Google, could tell us whether the energy
> required (presumably for the transponders, which aren't high power) is
> such that every last drop of solar input is critical. I'm inclined to
> doubt it, but - like you - I don't know.


It says here that "The satellite keeps the solar panels pointed toward
the Sun."

http://encarta.msn.com/encyclopedia_761551926_3/Artificial_Satellite.html

Part of the time the satellite will be blocked from the sun behind the
earth, and the rest of the time the 'projection area' of the solar
panels would be multiplied by sin(theta).

Ultimately, it's a trade-off of solar power input versus power required
to turn the solar panels, and we're talking about kW levels of
transmitter powers, so I don't think it would take a great deal of power
to move the panels. Also, the higher the solar power input the higher
the satellite data capacity can be, so there's a good financial argument
for maximising the solar power.


>> That's fair enough. I'm sceptical that relativistic effects are
>> significant though.
>
> I didn't mean relativistic effects. As Kristoff has said, there are
> plenty of old-fashioned Newtonian gravitational variations - moon,
> sun, even large lumps of the earth (mountains).


Right.


>> But isn't the solar wind just a stream of charged particles?
>
> Yes it is. And the particles have mass. And what happens to a body
> when it's hit by something with mass?


It says on here:

http://science.nasa.gov/newhome/headlines/ast01jun99%5F1.htm

"His criterion for gusts is a sharp increase in pressure, ranging from 1
to 15 nanoPascals. That's 1 to 15 billionths of a Pascal - softer than a
baby's breath."

I think we can neglect the solar wind. ;-)


>> Yeah, if the thrusters weren't there it would either drift out into
>> space or crash down to earth.
>
> Exactly so - but for many and various reasons.


Sure.


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

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