Thales NSS 100S-1 Component Maintenance Manual With Illustrated Parts List page 44

(d) Clock warm-up mode
If thermal stabilization of the RPU internal clock has not been at-
tained by the end of the Initialization mode (acquisition is not yet
possible), the RPU is set to the clock warm-up mode; the position,
speed and the time are maintained by available external aids.
rwise the RPU switches directly into the next mode (DR or Sky Reac).
(e) Sky Reac Mode
This mode (general sky search) is activated whenever one of the pa-
rameters essential for position-fixing is absent or detected as
false, i.e.:
- The almanacs, whenever they are absent or out of date,
- The time or the position, whenever they are invalid,
- whenever the Position-fixing mode cannot be triggered 20 minutes
after the power has been turned on.
In this mode, the RPU seeks to acquire the missing parameters as
rapidly as possible by conducting a search for visible satellites
(Search Sky).
(f) DR (Dead Reckoning) mode
This mode is engaged if the number of satellites used for navigation
(available ephemerides, satisfactory geometry) is insufficient to
activate the Position-fixing mode.
In this mode, the RPU performs the following functions:
- Dead reckoning navigation according to the best external aids
available (inertial or pressure altitude data: true air speed,
true heading, magnetic heading, altitude, air speed, vertical
speed).
- Acquisition of usable satellites according to criteria of visibi-
lity, geometry, state of health, manual commands...
- Tracking of "locked" satellites
(g) Position-fixing Mode
In this mode, the RPU acquires and pursues a maximum of 8 visible
satellites by using the "GDOP" (Geometric Dilution of Precision)
criteria in such a way as to continuously supply the best position-
fixing solution (GPS sole or assisted position-fixing).
Depending on the number of satellites used for position-fixing, the-
re is unassisted position-fixing (number of satellites ≥ 4) and
assisted position-fixing (number of satellites ≤ 3).
COPYRIGHT SEXTANT Avionique 1995
c
The document reference is online, please check the correspondence between the online documentation and the printed version.
COMPONENT MAINTENANCE MANUAL
C17004
Othe-
34-57-96
Page 22
MAY 30/95