GLOBAL POSITIONING SYSTEM (GNSS) QUESTIONS
& ANSWERS
Describe the GPS satellite system: - Answer -■ The constellation consists of a
minimum of 24 satellites (with some spares)
■ They orbit above the earth at 10,900 NM
■ The system is designed so that at least 5 satellites are in view at any given location
on earth
How does a GPS receiver calculate distance to a GPS satellite? - Answer -Based on
the time lapse since the broadcast timestamp (obtained from an atomic clock onboard
the satellite) and the time it received the signal.
How does the GPS receiver calculate the aircrafts geographical position? - Answer -■
The GPS receiver uses the intersection of spheres, from multiple satellites, to calculate
the aircraft's geographical position.
■ Course and speed data are computed from aircraft position changes.
How many satellites are required for a 2d position? How many for 3d? - Answer -■ At
least 3 satellites are required for 2d position. (latitude and longitude)
■ At least 4 satellites are required for 3d position. (latitude, longitude and altitude).
What is RAIM? - Answer -Receiver Autonomous Integrity Monitoring (RAIM)
RAIM is a function of GPS receivers that monitors the integrity of the satellite signals.
▷ RAIM (fault detection) requires a minimum of 5 satellites, or, 4 satellites + an
altimeter input (baro-aided RAIM)
▷ To eliminate a corrupt satellite (fault exclusion), RAIM needs an additional satellite
(total of 6 or 5 + baro-aid)
What is Great Circle Navigation? - Answer -Great circle navigation is the practice of
navigating a vessel (a ship or aircraft) along a great circle. Such routes yield the
shortest distance between two points on the globe.
Does a GPS CDI deflection show distance, or angular distance off course like a VOR? -
Answer -Distance, unlike VOR
What is WAAS? - Answer -WAAS (Wide Area Augmentation System)
■ WAAS is a Satellite Based Augmentation System (SBAS) used in the United States
(EGNOS in EUROPE)
■ Ground stations (Wide-area Reference Stations and Wide-area Master Stations)
measure GPS errors and produce correction signals.
& ANSWERS
Describe the GPS satellite system: - Answer -■ The constellation consists of a
minimum of 24 satellites (with some spares)
■ They orbit above the earth at 10,900 NM
■ The system is designed so that at least 5 satellites are in view at any given location
on earth
How does a GPS receiver calculate distance to a GPS satellite? - Answer -Based on
the time lapse since the broadcast timestamp (obtained from an atomic clock onboard
the satellite) and the time it received the signal.
How does the GPS receiver calculate the aircrafts geographical position? - Answer -■
The GPS receiver uses the intersection of spheres, from multiple satellites, to calculate
the aircraft's geographical position.
■ Course and speed data are computed from aircraft position changes.
How many satellites are required for a 2d position? How many for 3d? - Answer -■ At
least 3 satellites are required for 2d position. (latitude and longitude)
■ At least 4 satellites are required for 3d position. (latitude, longitude and altitude).
What is RAIM? - Answer -Receiver Autonomous Integrity Monitoring (RAIM)
RAIM is a function of GPS receivers that monitors the integrity of the satellite signals.
▷ RAIM (fault detection) requires a minimum of 5 satellites, or, 4 satellites + an
altimeter input (baro-aided RAIM)
▷ To eliminate a corrupt satellite (fault exclusion), RAIM needs an additional satellite
(total of 6 or 5 + baro-aid)
What is Great Circle Navigation? - Answer -Great circle navigation is the practice of
navigating a vessel (a ship or aircraft) along a great circle. Such routes yield the
shortest distance between two points on the globe.
Does a GPS CDI deflection show distance, or angular distance off course like a VOR? -
Answer -Distance, unlike VOR
What is WAAS? - Answer -WAAS (Wide Area Augmentation System)
■ WAAS is a Satellite Based Augmentation System (SBAS) used in the United States
(EGNOS in EUROPE)
■ Ground stations (Wide-area Reference Stations and Wide-area Master Stations)
measure GPS errors and produce correction signals.
