Avionics MCQs – Stellar Inertial Navigation Theory
1 - Question
Which of the following are false with respect to stellar navigation?
a) Can be used in daylight and at night
b) Position and altitude can be measured
d) Cannot be jammed
Explanation: High precision stellar inertial navigation systems have been developed with automatic daylight and night star tracking system. These are highly useful for military aircraft in that they provide accurate position and attitude information, are autonomous, non radiation and are invulnerable to jamming.
2 - Question
Which of the following can be used to estimate the latitude in the northern hemisphere using the horizon as a reference?
a) North pole
b) Magnetic north
d) Orion’s belt
Explanation: The north star or Polaris can be used to estimate latitude in the northern hemisphere using the horizon as a local level reference at the observers position. This type of navigation was used by the ancient mariners.
3 - Question
What is it called when the position is determined by angles between a star and an accurate time reference?
a) Position fix
b) Celestial fix
c) Sun fix
d) Horizontal fix
Explanation: Navigators on early transoceanic flights used sextants to manually measure star angle with respect to their local vertical. Using the line of sights form two or more stars, along with a star catalog and accurate time reference, the position in Earth latitude and longitude can be deduced. This was known as celestial fix.
4 - Question
Why is the inertial navigation system combined with celestial navigation system?
a) Correction of drift error
b) Deriving true north
c) Deriving magnetic north
d) Correction for weather effects
Explanation: Inertial navigational suffer from drift after long hours of using. Since the position error growth of these free inertial navigation systems was excessive on long flights, it was natural to periodically update their position with position updates from manual star fixing.
5 - Question
The sensors that maintain a centered star image for celestial navigation is called as _________
a) Star fixer
b) Celestial fixer
c) Star tracker
d) Star searcher
Explanation: The star sensors have a narrow field of view and maintain a centered star image through the gimbal drive commands and are called star trackers. They have day and night tracking capability, given reasonable cloud cover conditions.
6 - Question
Which of the following is required to integrate stellar navigation and inertial navigation to get the best estimate navigation solution?
a) Kalman filter
b) Star fix
c) Celestial fix
d) Multisensor processing
Explanation: Navigational systems use Kalman filtering techniques to integrate all the sensed navigational data to obtain the best estimate navigation solution. The use of Kalman filter to integrate stellar measurements requires that star observations and errors be correctly modeled.
7 - Question
The observability problems are greatly intensified if the telescope is rigidly mounted to the IMU.
Explanation: Observability problems associated with the Kalman filter are greatly intensified in a stellar inertial navigation system if the telescope is rigidly mounted to the IMU even though the IMU is gimballed to provide star pointing.
8 - Question
The inertial LOS to any star is precisely given from _______
a) Star tracker
b) Star catalog
c) Air data computer
d) Celestial fix
Explanation: The application of Kalman filter begins with the precise mathematical definition of the star observation. The inertial line of sight to any given star is precisely known from the star catalog.
9 - Question
The angular error is the angular difference between computed LOS and the physical star sensor LOS.
Explanation: The angular error which is measured by a star sensor is the angular difference between the computed (error corrected) LOS to the star and the physical star sensor LOS.