- 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
- 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.)
- 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.
- 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
AUDIO TONE FREQUENCIES
Mode (bit) (kHz)
SGLS 1 95.0
Non-SGLS, 1 11.0
Mode A 0 13.5
Non-SGLS, 1 2.0
Mode B 0 2.9
- Secure Mode. Commands may be transmitted in either the secure or
- 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
- Command Verification and Authentication.
The capability shall exist for validating command
communication by evaluating telemetered vehicle
Basic Telemetry functions to be provided are shown in Figure 2-8. Additional
requirements relative to these functions are identified below.
- 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:
- 2.2 to 2.3 GHz.
Provision shall be made for