Basically.... Money.

Dave wrote:

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

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: [email protected] [mailto:[email protected]]On Behalf Of James Duffey Sent: 06 May 2009 03:17 To: [email protected] 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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At 03:05 AM 5/7/2009, Gordon JC Pearce wrote:

On Tue, 2009-05-05 at 19:38 -0600, Dave wrote:

...

Seems our sats are so low powered they require extraordinary measures to receive.

What would you consider "extraordinary"? I'd consider shooting a signal across a couple of hundred miles line-of-sight with 5W on VHF and a 3-element yagi to be not *that* extraordinary.

Or working AO-51 with a pair of HTs and rubber ducks (yes, I have done this!). Hardly extraordinary. :)

73 de VK3JED / VK3IRL http://vkradio.com