On Sun, Mar 02, 2003 at 11:32:36AM -0800, [EMAIL PROTECTED] wrote:
> Interestingly enough, the public references long ago published the
> shuttle comm frequencies. Summarizing from:
>
The frequencies have never been secret, but in recent years some
or perhaps even almost all of the Ku band TDRSS relayed telemetry and TV
and a good bit of the S band relayed traffic has been encrypted. This
was, I have been given to understand, part of the upgrades to the comms
and TV systems on the shuttle completed in the last few years which
converted analog TV transmission to digital TV.
This encryption was originally publicly justified in part on the
grounds that medical information was passed between crew and physicians
on the ground and that federal privacy laws required protection of this
information.
And as far as I know, NASA while publishing link frequencies
(which I have no particular reason to believe are wrong), has never
released full details of modulation, multiplexing, error correction
coding, randomization, interleaving, frame sync formats, channel
assignments and scale factors for the data even for those links and
modes that aren't encrypted. And actual link frequencies are but a
small part of the data base of information one would need to
successfully intercept useful information from the shuttle links - even
1980s to early-90s era digital telemetry signals are pretty complex and
non trivial to deal with even if you know the frequency.
Finally, the TDRSS spacecraft are also used for relaying
information from NRO spacecraft and other classified military missions,
and there is a significant chance that at least some of the details of
the access protocols and signal formats used with these spacecraft are
classified in order to protect sensitive military links.
--
Dave Emery N1PRE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass.
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2 5D 27 BD B0 24 88 C3 18
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