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Re: Ranging question (was PSK tone interesting on AO-40)



>From: "Greg D." <ko6th_greg@hotmail.com>
>Interesting!  Just what exactly is "Ranging", and what is going on
>with the waterfall?  I had assumed that Ranging was some sort of
>Radar thing, combined with observations of AOS, LOS, AZ, and EL,
>but I guess the satellite plays a more active role...
>
>Just curious,
>
>Greg  KO6TH
>
>>From: "Colin Hurst" <hurst_cj@msn.com.au>
>>To: "Greg D." <ko6th_greg@hotmail.com>, <amsat-bb@AMSAT.Org>
>>Subject: Re: [amsat-bb] PSK tone interesting on AO-40
>>Date: Wed, 4 Jul 2001 00:37:07 -0000
>>
>>Greg,
>>You probably heard the ranging that has been carried  out
>>by the command stations over the last few days.
>>Best regards,
>>Colin VK5HI

Greg,

In the past, ordinary radar plus correlating observations with predicts
provided ranging, but radar conducted at planetary distances requires very
high power due to the large space loss and target scattering loss.

With earth satellites [or planetary spacecraft] you have an on-board
transponder that can send back a much stronger signal.  So what they do [in
very layman terms] is send a special digital pulse train up to the
spacecraft which is looped back to earth.  By using precise frequency and
pulse timing, very accurate range information can be recovered.

To give an example, I operated ranging in 1974 on the Mariner-10 spacecraft
that I believe was first to use planetary gravity boost to a secondary
planet [Venus-to-Mercury].  The mu-II ranging system was accurate to 2
meters at 60 million km!  I suspect a similar digital ranging system is
being used on AO-40 {experts may step in now and bail me out}.

Ed

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