GNSS

Question 1

What are the elements of the GPS system?

Answer 1

Space segment
Control segment
User segment

Question 2

What are the properties of the space segment of GPS?

Answer 2

• Orbits at 20,200km
• At least 24 satellites
• 6 Orbital planes
• 12 hours to complete one orbit
• Each orbital plane is at 55˚ to the equator

Question 3

What is contained on the navigation message obtained form the GPS satellites? What is each?

Answer 3

• Ephemeris: present position of the satellite in orbit
• GPS time reference: Atomic clock time of the satellite
• Clock corrections: Self explanatory
• Almanac data: parameters for the orbital data of the entire constellation
• System maintenance status: Self explanatory

Question 4

What is RAIM?

Answer 4

Receiver autonomous integrity monitoring

Receiver will monitor the integrity of the position solution,, and the number of reliable satellites data is being taken from

Question 5

What are the modes of GPS receiver operation?

Answer 5

Navigation with RAIM
2D or 3D navigation without RAIM
Dead reckoning

Question 6

What are the errors of the GPS?

Answer 6

• Ephemeris error
• Multi-path error
• Ionospheric propagation effects
• Tropospheric propagation effects
• Receiver error
• Clock error
• Interference

Question 7

What human factor considerations/ errors are there when using the GPS?

Answer 7

• Mode Error
• Data entry error
• Cross checking
• Automation induced complacency
• Non standard displays
• Control knobs and switch designs
• Compulsive fiddling
• Loss of situational awareness