Req. 5.3.4.3: "GPS Message from SC"

Between 500 msec and 800 msec before the GPS time hack, the SIU FSW shall receive and process a 1 Hz GPS time message from the SC, via the CTDB. This message provides information on the relationship between the GPS time hack and external time (UTC).

Basis (help)

[2] (3.2.6.3)

2: "LAT Instrument - Spacecraft Interface Requirements Doc." (NASA 433-IRD-0001)

3.2.6.3: "Time Messages"

3.2.6.3.1: "Distribution Format"

The SC shall issue to the LAT, a time message that gives a "time at the tone will be" message in Global Positioning System (GPS) format.

3.2.6.3.2: "Distribution Timing"

The Time Mark Message shall be issued between 500 ms and 800 ms before the transition of the 1 PPS time mark signal.

Context (help)

Test(s)

010b: LAT Time Signal Processing

This test verifies that the LAT FSW correctly processes the 1 Hz GPS time message from the SC to provide a mapping of external time to the LAT internal 20 MHz clock, and that the resulting mapping allows event time measurements to be accurate to within 10 usec of SC time.