COMMAND RANGING & TELEMETRY UNIT CORTEX
Is.Rev.
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Page 33
1.6.9.
Time Code & Reference Clock Interface
The CORTEX CRT Quantum must be connected to an external timing system in the following cases:
If the equipment is to be used for satellite ranging or accurate Doppler measurement. Due to the high level
of performance of the unit, an external reference clock (GPS-based for example) is required to ensure
phase shift and frequency measurement with the required accuracy.
If the equipment must be used for launch or transfer orbit support or control of LEO satellites (high
Doppler). In that case, it may be necessary to connect the chassis to an external time reference (GPS-
based IRIG-B code generator for example) for accurate time-tagging of the ranging, Doppler and telemetry
data.
The internal 10-MHz clock accuracy and stability on the Main Signal Processing board allows the CORTEX CRT
Quantum to fulfill its mission in most other station keeping scenarios.
The external reference clock frequency is either 5, 10 or 100 MHz and is received on two ports in active
redundancy. Clock selection (internal clock, external clock from port 1 or port 2) is programmable and offers
several priority scenarios. Frequency selection (5, 10 or 100 MHz) is automatic, at boot. However, performances
of the unit cannot be guaranteed if the external reference clock signal is corrupted or if the frequency is not
exactly 5, 10 or 100 MHz.
1.6.9.1.
Time Code Decoding & Data Time-tagging
Input code
IRIG-B, NASA-36 or NTP
Amplitude
6 Vpp max
Impedance
1 M
Ω
Polarity and direction
Positive and forward
Error by-pass
7 frames
1-PPS input
Yes. TTL. Maximum rise and fall time: 20 ns
Time tagging accuracy
± 50 µs (without external 1-PPS), ± 100 ns (with external 1-PPS)
Flywheel mode
Yes
Leap second & leap year management: Yes
