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Re: Has AO-40 telemetry stopped?



>From: Achim Vollhardt <avollhar@physik.unizh.ch>
>Hi all,
>concerning ranging, as I remeber it is done with the help of a
>transponder. Therefore, a command station sends a pseudo random
>bitstream which is sent back by the satellite.. the ground station then
>shifts the tx and the rx stream as long as they are no in phase, if they
>are, the delta-t is measured and converted in to range.. (taken out of
>memory from an article of AMSAT-DL journal.. i don't know if published
>online..)..
>
>73s Achim, DH2VA
>
>MCGWIER ROBERT wrote:
>> 
>> It is probably ranging.

Didn't realise that there was ranging on AO-40?  I can confirm what Achim
says:  NASA had ranging experiments on several spacecraft.  On the
Mariner-10 s/c that was first to close encounter Venus and then Mercury in
1974, there was a ranging system that sent a specially coded data stream
that permitted determining the location of the s/c within 2 meters accuracy
at >100 million km!  But this took about 30 minutes of continuous data to
make a calculation, not a brief "chirp".  The signal had to maintain phase
lock for the entire period else the system was unable to determine a number
[timing was ref to a hydrogen maser time std to do this}.  

Ed 

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