GPS Flashcards
What are the 3 major segments of a satellite
Space segment = satellite
Control segment = ground monitoring station
User segment = GPS receiver
What does the ground control segment of the GPS satellites do
Monitors the satellites, calculates corrections and transmits them to satellites
1 master control and several monitors positioned close to the equator
How many satellites does NAVSTAR have
24 satellites
21 operational
3 spare
How many different orbital patterns does NAVSTAR have
6
What is the height of navstar orbits
20,200km
What incline is the NAVSTAR orbits to the equator
55°
How long is a NAVSTAR orbit
12 hours
What are the frequencies for NAVSTAR
Link 1 = 1575.42mhz
Link 2 = 1227.6mhz
Why is there 2 link frequencies for gps
Estimate ionosphere delay
What transmits the course acquisition code
Link one
Associated with sps service
Standard positioning service
What are the modes of operation for GPS
Standard positioning service (SPS) for civilian users = L1
Precise position service (PPS) for military users = L2
What is the reference datum for NAVSTAR
World geodetic system 1984
What is the user segment of a gps
Any capable satellite receiver
What gps is a civilian receiver capable of receiving
L1 = course acquisition / selected availability
What is a military GPS receiver able to receive
Both L1 and L2 signals with a P code (precision)
What is a satellite gps principle of operation
TIME
broadcast ranging codes and accurate times
Receiver measures signal transmit time to determine range from satellite
What gps location can a position from one satellite give you
A position on the surface of a sphere
What gps location can a position from two satellite give you
Produce a circular position line where the 2 spheres intersect
What gps location can a position from three satellite give you
Unambiguous position
What gps location can a position from four satellite give you
Unambiguous fix with all timing errors resolved
What is the max number of users on a gps satellite
Unlimited number of users
How is pseudo range countered
Due to timing error = range error
Therefor
Resolved by receiver clocks being a little slower so that range is always overestimated
How is receiver clock error corrected for gps
With signals from 4 satellites
What does ephemeris data (almanac info) contain
Accurate satellite orbit info
What is the optimum satellite position
One directly above
3 = 120° apart
How long does it take to download Ephemeris info Ionosphere delay Timing info Satellite health
12.5 mins
What is the time difference between Utc and satellite clock
13.5 seconds
How accurate is the satellite atomic clocks
1 nanosecond
What is the GPS receiver used in aircraft
Multi channel receivers
What is the biggest error in gps
Ionospheric propagation delay IPD = 5m
What is masking angle
Gps just disappears behind horizon
What is RAIM
Receiver autonomous integrity monitoring
Checks integrity of what is displayed
Required for GNSS aviation
Required min of 5 usable satellites to allow swapping to maintain a 3D fix
RAIM with spare facility would require 6 satellites
What is GBAS
Ground based augmentation systems
Also known as local area differential gps (LADGPS)
Employs a local augmentation system (LAAS)
Allows;
Precision approach service
GBAS position service
Uses satellite close to airfield to adjust correction errors from gps and send these corrections to aircraft via VHF
What is GRAS
Ground regional augmentation system
GBAS with more pseudo satellites
Increases accuracy
What is SBAS
Satellite based augmentation systems
Wide area differential gps (WADGPS)
At best can give CAT 1 approach
Has control stations on the ground which asses the errors in gps positions which is sent to the satellites to correct
What is EGNOS
European geostationary navigation overlay system
Geostationary satellite
What is WAAS
Wide area augmentation system
Operates by USA
Geostationary satellite
What is MSAS
Multi function transport satellite augmentation system
Operates by japan
Geostationary satellite
What is GAGAN
Gel and gps augmented navigation
Operated by India
Geostationary satellite
What is ABAS
basically RAIM
What is GLONASS
Old system resurrected by Russia
Fully operational by 2010
Uses Pz-90 datum
Been used since 2007
Integrity implemented by SBAS / GBAS
What are the frequencies for GLONASS
L1 1.6GHZ
L2 1.2GHZ
What is GALILEO
European system
Not operational yet
Estimated 2020
What are the GALILEO clocks made out of
Rubidium frequency standard clock
Very accurate passive hydrogen master clock
What does he signal generation section of GALILEO contain
Message comprises ephemeris and orbit info and clock references
What are the GALILEO frequencies
L1 = 1164-1215 MHZ L2 = 1260-1300 MHz L3 = 1559 - 1571 MHz
L3 shares with gps on a non interference basis
