Global Positioning System (GPS) Flashcards
What is GNSS?
Global Navigation Satellite System
A generic term for satellite navigation
The United States Global Positioning System is one form of?
GNSS
Satellite Navigation offers what?
a level of precision that no other system can provide
Each GPS satellite carries at least:
two atomic clocks, which measure the movement of elements like rubidium or cesium.
The GPS clock onboard the aircraft is what style?
simple quartz style
The accuracy of this clock is controlled by:
signals it receives from the GPS satellite
Clocks are the key to providing:
an accurate fix of position for the aircraft
Navstar Satellite System is known as what?
Time Delay Navigation
The position of the Navstar Satellite System can be determined by:
estimating when the LOPs cross
What does LOP stand for?
Lines of Position
The crossing points of the LOPs can be converted to:
the coordinate system of latitude, longitude, and altitude
In GNSS the navigation transmitters are the:
satellites or Space Vehicles (SV)
The more Space Vehicles (SV) that the receiver can “see”, the more what?
accurate the position fix
GPS consists of:
24 satellites in 6 orbital planes
There are three segments to the GPS system:
The Control Segment
The Space Segment
The User Segment
What does the Control Segment monitor?
satellite operation
Controls the SV’s and uploads information
What is the Space Segment?
the SV’s
What is the User Segment?
the pilots (receivers) who use the GPS to navigate
The L1 frequency is 1574.20 MHz and is used by:
the civilian user segment for position determine
The L2 frequency is 1227.60MHz and is currently used by:
the US military to measure errors caused by the ionosphere
The third frequency is the L5 or 117.45MHz and is protected worldwide for aeronautical radio navigation use. The addition of L5 will make GPS:
a more robust radio navigation service for many aviation applications as well as all ground based users
C/A code is also called:
a Pseudo Random Noise (PRN) code and repeats 1,023 bits each millisecond
The PRN is unique to:
each SV and is used for its identification
The L1 frequency also carries a navigation message containing bits of data. The navigation message builds the:
Almanac
The Almanac contains data about:
errors and ephemerides
What is an Ephemerid?
a small distortion in the orbit of an SV which can cause errors in position
A GPS receiver must have what?
a current almanac, including ephemeris data, to navigate properly
Exact distance between the GPS SV’s and the receiver is:
impossible to determine
The GPS receiver is able to best calculate position when?
the SV’s are widespread
Error based on lines of position angles is known as:
Geometric Dilution of Precision or GDOP
In worst case situation, GPS accuracy is:
100m laterally and 156m vertically
GPS accuracy can be increased by using:
a ground based augmentation system (GBAS)
When did the Wide Area Augmentation System (WAAS) come into use?
2003
A typical specification for a WAAS corrected GPS position is:
1m lateral and 2m vertical
WAAS provides an accuracy for aircraft to conduct precision approaches bearing or at:
minimum altitudes CAT I approaches
LAAS service is focused within 20-30 miles of the airport and has an accuracy of:
less than 1m, CAT I, II, III
GPS receivers without GBAS use the:
Receiver Autonomous Integrity Monitoring (RAIM)
RAIM monitors the:
pseudo range measurements of at least 6 SV’s
If one or more of the pseudo range measurements does not agree, what happens?
a RAIM alarm will be sent
WAAS and LAAS eliminate RAIM requirements by:
allowing the system to alert the pilot within 6 to 8 seconds of fault detection
What does Fault Detection Exclusion (FDE) do?
Analyzes the RAIM alarm to determine which SV is causing the problem. Once analyzed it automatically excludes the faulty SV from the navigation calculations
A crucial element of the system is the:
GPS database
The database may be contained in a:
user replaceable memory card, or be updated via a data port
What is Galileo?
the European GNSS
What is GLONASS?
the Russian abbreviation for GNSS
GPS Flight Line Testing must be accomplished outside so that:
the receiving antenna can “see” the SV’s
How can you test the GPS if the aircraft cannot be moved or the sky is not clear enough for a good signal?
there are ramp test simulators to test the receiver
