[amsat-bb] Re: Question

[Jim Heck]

And dont forget the antennas on the sattelite. They cant necessarily be optimal. A
directional antenna needs a platform, the orientation of which is known and
controlled. To do this is space is not trivial; vbarious mechanism exist, gravity
gradient boom, megnetostorquing, spinning wheels. Its also expensive and adds
complication to the satellitte.

Some amateur sats have been stablised, and have used directional antennas
successfully, eg AO-40, AO-13, but not only were these costly to build and launch,
they also required considerable ground control efforet (globally) to ensure their
solar cells we never parrallel to the suns rays. (If that happens, no power=death of
the sat).

73 Jim G3WGM

> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org]On
> Behalf Of James Duffey
> Sent: 06 May 2009 03:17
> To: dave at mynatt.biz
> Cc: Amsat BB
> Subject: [amsat-bb] Re: Question
>
>
> Well more power means more solar cells and bigger batteries.
>
> The number of solar cells that one can fit on the outside of a
> satellite depends on the size of the satellite. More solar cells means
> a bigger spacecraft or deployable cells. There is a limit to the size
> of deployable panels and added complexity risks the mission if they
> should fail. Bigger spacecraft cost more to build and launch.
>
> The size of the solar panels determines the battery size. Ideally you
> want a battery that can be fully charged by the solar cells while in
> sunlight and maintain its charge to a useful level in eclipse. Bigger
> batteries weigh more and weight pretty much determines how much a
> satellite costs, particularly the launch costs.
>
> So it pretty much boils down to optimizing the solar panel/battery
> combination with the size of the spacecraft and the mass lift
> capability available to us on a launcher.
>
> I am not sure what you mean by extraordinary measures to receive, or
> what satellite you are trying to receive, but the requirements to
> receive many satellites is modest. Low loss feedline, helps, as do
> directional antennas and preamps, but these are all available with
> modest effort, either through building them yourself or purchasing
> them. - Duffey
>
> >
> >   Okay, time for my stupid question of the week.
> >
> >
> > Why are our sats so low powered? Why don't we have better batteries,
> > solar
> > power systems, or generators?
> >
> > Seems our sats are so low powered they require extraordinary
> > measures to
> > receive.
> >
> > Is this an accurate perception?
> >
> > Dave
> >
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> --
> KK6MC
> James Duffey
> Cedar Crest NM
>
>
>
>
>
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