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Re: Communication thru P5-A



http://www.amsat-dl.org/p5a/p5a-weaksignal.pdf

<<

Hello Ed.  Here is what needs to be the starting point for any discussion.

I read this sometime back in the Mag but it highlights what some of the 
discussions/tradeoffs that there are.

I will have to reread it again but on my reread tonight a few things stand 
out.

What they are looking at is 100 watts at 10ghz into a 2 meter antenna.  
Thats ok because at EArth orbit the power supply (solar arrays) gives about 
500 watts.  At Mars that drops to around 250 which the article states is 
just enough to run a 50 watt transmitter.

But if you want to recieve things on little dishes (read 2 meter ones here 
on earth) they are going to need all 100 watts and data rates of around 500 
bit/s.  I would be curious how long in a solar orbit they can run 50 
watts...with the solar offpointing angles required for fixed arrays.

There are two points here.

1.  They arent going to be able to run 100 watts at Mars...and 2.. 500bit/s 
isnt really going to be enough to support any serious "relay" stuff on Mars.

Thats why the "main" antenna is going to be a 20 meter one.  I have no doubt 
that it might be detectable.  I wouldnt count on the "average" ham doing a 
lot of data collecting.

Of course there are other "nice" things to like three axis stabilization, a 
finer touch on propulsion then AO-40 demonstrated etc.

Robert WB5MZO

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