From: dumoulin@titan.ksc.nasa.gov (Jim Dumoulin)
Newsgroups: sci.space.shuttle
Subject: Re: Space Shuttle Frequencies Scannable?y
Date: 11 Nov 92 21:32:10 EST
Distribution: usa
Organization: NASA, Kennedy Space Center

In article <1992Nov9.083041.22946@dartvax.dartmouth.edu>, flowerpt@coos.dartmouth.edu (Bill McGonigle) writes:
> I can't find a FAQL, so lets hope this isn't a FAQ... 
> 
> I was looking at scanners, and I was wondering if its possible to pick
> up space shuttle frequencies on any scanners.  
> 
> Is that information publically available?  
> Are the transmissions scrambled?
> Can someone post the frequencies?
> Any info would be appreciated. Thanks. 
> -Bill

  Using a scanner to pickup actually communications between the shuttle
 and the ground won't be of much use to you unless you live very close
 to Kennedy Space Center, one of the Shuttle Landing strips or one of
 the few remaining S-band tracking stations.  Your best bet are the
 number of Ham radio 2-meter repeater stations that have land lines to 
 NASA centers.  They rebroadcast the Public Affairs link.  At KSC, the 
 active 2-meter repeater is at 146.940 Mhz.  You may also have luck
 if the crew is running the SAREX experiment.

 The Flight shuttle frequencies in use at KSC are:
 
         Air-Ground Control    VHF 126.300 Mhz
         Orbiter Air-Ground 1  UHF 259.700 Mhz
         Orbiter Air-Ground 2  UHF 296.800 Mhz
         Air-Ground Control    UHF 284.000 Mhz
         Emergency Commercial  VHF 121.500 Mhz
         Emergency Military    UHF 243.000 Mhz
 
 We also use a number of Ground Frequencies.  In my Icom IC-R1
 Scanner, I've got the following programmed:

   KSC RF Net 101 - Utilities      171.000  Mhz
   KSC RF Net 102 - Meas/Safety    165.1875 Mhz
   KSC RF Net 103 - Security       173.6875 Mhz
   KSC RF Net 104 - Launch Support 162.6125 Mhz
   KSC RF Net 105 - Safety         173.6825 Mhz
   KSC RF Net 106 - Supply         170.4000 Mhz
   KSC RF Net 107 - Base Comm      170.1500 Mhz
   KSC RF Net 108 - PAO/Hurricane  163.5375 Mhz
   KSC RF Net 110 - Orbiter Ops    165.4125 Mhz
   KSC RF Net 111 - Loan Pool      153.5375 Mhz
   KSC RF Net 116 - Fire/Rescue    173.5625 Mhz
   KSC RF Net 117 - Medical        173.4375 Mhz
   KSC RF Net 408 - PAO-TV Coord   171.2625 Mhz

 The reason your scanner won't do you much good during normal mission
 operations is that most of the time the uplink and downlink audio is
 multiplexed into the data stream.  Since I'm a payload person, I'll
 use a payload command uplink to explain how the POCC or CAPCOM's voice
 is multiplexed.

   1.  A Payload command word can vary from 3 to 31 16 bit words and they
       are sent from the Payload Operations Control Center (POCC) computers
       to the Mission Control Center (MCC) computers.

   2.  The MCC appends an additional 16 bit destination word that is used
       by the orbiter data processing system (DPS) for routing the data
       to the correct payload.  Next, a command overhead word is then
       appended to each pair of 16bit payload words.  This word specifies
       to which orbiter (the encoding system is capable of supporting 
       multiple orbiters in space) and to which GPC on that orbiter the 
       words are to be delivered.  By now the original 496 bits 
       (31 x 16bit words) have turned into 768 bits and have been broken
       up into 48 bit chunks (32 data bits and 16 overhead bits)

   3.  The MCC, in order to provide a way of detecting uplink errors, 
       then generates a 77 bit Bose-Chandhuri-Hocquenghem (BCH) code
       for each 48 bit data segment. In order for the encoding scheme
       to work properly, 50 bits are required to be input into the 
       coding process to produce the 77 bit BCH code.  Thus, 2 dummy
       bits are then added at the front end of each 48 bit data word
       and this produces an 128 bit word for each pair of original
       command words.  Our original 496 bits have turned into 2048.

   4.  In order to provide a means of authenticating a command to 
       protect against unauthorized recording and then re-uplinking
       the command at a later time (ala Captain Midnight), a 128 bit
       permuted GMT word is generated for each of the 16 128 bit words
       we currently have.  This 128 bit word is added bit-by-bit using
       modulo-2 addition to produce the 128 bit word that is sent to
       the Network Output Multiplexer (NOM) at the MCC.

   5.  The NOM then interleaves the command data with voice data.  
       Depending on the data rate, either one or two voice channels
       (640 bits/channel) are interleaved with each 128 bit command
       data word to form an uplink frame that is then sent at 50
       frames/sec.  This 72 Kb/s (2 voice) or 32 Kb/s (1 voice) 
       uplink (no CD quality sound here) is then sent to a convolutional encoder that generates
       3 bits for every bit of data.  This the actual data rate that
       the orbiter sees is 216 Kb/s (2 voice) or 96 Kb/s (1 voice)
       but only 1.6 Kb/s (less than 1 percent) of this is our actual
       command.

   6.  The onboard systems inside the shuttle (the Network Signal
       Processor) then reverses all this process to send the voice
       and commands to the proper locations.

  To sum it all up, you probably don't have a SB's CIH of decoding
  any of this with a scanner.  Sorry.


--------------------------------------------------------------------------
   Jim Dumoulin                      INTERNET: DUMOULIN@TITAN.KSC.NASA.GOV
   NASA / Payload Operations      SPAN/HEPnet: KSCP00::DUMOULIN
   Kennedy Space Center
   Florida, USA  32899
  
 
Newsgroups: sci.space.shuttle