1. Command Type/Format. All satellite commands transmitted by an RTS will be digital NRZ. Command formats will be as follows:

    (a) Digital command messages of any word length and data format within the 1.75 to 1.85 GHz frequency band will consist of 1, 0, and S (space) data bits). The latter shall indicate the beginning and end of each data word, or periods of "no data" transmission.

    (b) Command formats within the 370 to 470 MHz frequency band may be either of two modes. In mode A, command messages of any word length and data format will consist of 1, 0, S, and R (repeat) data bits. The S-bit shall indicate the beginning or end of each data word or periods of "no data" transmission. The R-bit shall be transmitted in lieu of a consecutuve 1, 0, S bit. Command messages in mode B will consist of 0 or 1 data bits only in any word or data format. Command transmission shall be inhibited to indicate the beginning or end of each data word, or during "no data" periods.

  2. Rates. The capability shall exist for transmission of digital commands within the 1.75 to 1.85 GHz frequency band at selectable rates up to 2 kb/s. Transmission of commands within the 370 to 470 MHz frequency band shall be possible at rates up to 1 kb/s (or otherwise limited by the frequency of the audio command tones.)

  3. Modulation. Both commands shall be transmitted as phase modulation of the command carrier by audio frequency tones which represent the 1, 0, S, and R data bits (FSK-PM). Audio tone frequencies shall be as shown in table 1.

  4. Synchronization. A command clock (equal to the bit rate) shall be transmitted as amplitude modulation of the 1, 0, S command tones in the 1.75 to 1.85 GHz frequency band. A command clock shall not be transmitted with commands in the 370 to 470 MHz frequency band.

TABLE 2-1
AUDIO TONE FREQUENCIES
(Commands)

            Data         Frequency
Mode        (bit)          (kHz)
  SGLS        1            95.0
              0            76.0
              S            65.0

Non-SGLS,     1            11.0
 Mode A       0            13.5
              S             6.0
              R             8.5

Non-SGLS,     1             2.0
 Mode B       0
2.9

    1. Secure Mode. Commands may be transmitted in either the secure or nonsecure mode.

  1. Command Echo Check. A command "echo check" will be performed to demonstrate correlation of the transmitted command with the ordered command. Digital command echo check data will be recorded and time correlated.

  2. Command Verification and Authentication. The capability shall exist for validating command communication by evaluating telemetered vehicle information.

2.2.4    Telemetry

Basic Telemetry functions to be provided are shown in Figure 2-8. Additional requirements relative to these functions are identified below.

  1. Telemetry Reception. The capability shall exist for reception of satellite telemetry data transmitted within the 2.2 to 2.3 GHz and 225 to 260 Mhz frequency bands. Signals within the 2.2 to 2.3 GHz frequency band will be in either the Space-Ground Link Subsystem (SGLS) or the non-SGLS mode.

    Provision shall be made for simultaneous reception and demodulation of:

    1. 2.2 to 2.3 GHz. Provision shall be made for

 

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