GNSS

Question 1

3 segments of the GPS

Answer 1

Space
User
Control

Question 2

The space segment

Answer 2

24 satellites in 6 orbits
20,000km in orbit
Inclination to the equator is 55*
1 orbit is roughly 24hrs

Question 3

How many atomic clocks

Answer 3

3/4

Question 4

Space segment sends 2 types of messages

Answer 4

L1 - 1500MHz Course acquisition with selected availability and P code

L2 - 1200MHz and P code

Question 5

Type of modulation and polarisation GPS

Answer 5

Phase modulated with circular polarisation

Question 6

Type of antenna for a GPS

Answer 6

Helical

Placed on top, close to CofG

Question 7

Selective availability- GPS

Answer 7

Deliberately introducing error to find course

Currently not used in civilian flying

Question 8

P-code

Answer 8

Precession for military a/c

Question 9

Data package - GPS

Answer 9

Nav message that inc

Satellite time when it was sent
Satellite ident using pseudo random noise (PRN code)
Type of encryption unique to that satellite
Ephemeris data - its own position in orbit for the individual satellite
Almanac for position of satellites

Question 10

Time to download data package

Answer 10

Around 12mins

Question 11

The control segment

Answer 11

Ground stations around the equator - main in the USA

Send revised data to satellites for nav message

Question 12

2 different types of receiver GPS

Answer 12

Sequential

Multiplexing

Question 13

Sequential receiver - GPS

Answer 13

Track only 1 satellite at a time

Not suitable for IFR flying

Question 14

Multiplexing receiver

Answer 14

Track multiple satellites simultaneously

Multi channel

Req for a/c doing IFR

Question 15

Min satellites and different pos fix

Answer 15

3 SAT = 2D fix
4 SAT = 3D fix
5 SAT = RAIM
6 SAT = RAIM and spare (incase of failure)

Question 16

RAIM

Answer 16

Receiver autonomous integrity monitoring

Self checking position
Req extra SAT
Have a mask angle below which satellites are excluded
Pick the best satellite for accuracy

Question 17

Pseudo range

Answer 17

System is time based

Calculate distance from satellite based on time of transit - compares time left to time received

Question 18

Receiver clock correction

Answer 18

Running deliberately slower
Req 3 satellites

Once established, an accurate position is given

Question 19

Receiver data - GPS

Answer 19

Position - WGS 84
Alt (above MSL)
Speed 
Track
Time

Question 20

Receiver error GPS

Answer 20

Ionospheric delay (most significant)
Receiver clock error
Dilation of position - non optimum satellite geometry
Selective availability

Question 21

RAIM with baro altimeter

Answer 21

May reduce to min 4 satellites

Question 22

GLONASS

Answer 22

Russian GPS

24 satellites 
3 orbits 
Inclination 64.8* - good for high lats 
1 orbit = 11hrs 15min 
Ref is PZ90 - equivalent to WGS84 
Freq 1100 - 1500MHz

Question 23

GALILEO

Answer 23

European civil GNSS but still in development 
30 Satellites 
23,222km orbit 
Inclination 56* to the equator
1 orbit = 14hrs 

2 atomic clocks - Rubidium, very accurate passive hydrogen master clock

Has the same L1 and L2 msgs

Question 24

ABAS

Answer 24

Airborne augmentation system

RAIM - does not improve accuracy only integrity

Question 25

SBAS

Answer 25

Satellite based augmentation system

EGNOS

Question 26

EGNOS

Answer 26

European geostationary navigation overlay system

Wide area augmentation
Req no extra equipment - only normal receiver
Improves accuracy

Question 27

GBAS

Answer 27

Ground based augmentation system

Local area augmentation system
Pretends ground station is satellite - uses VHF signal to transmit error correct to GNSS receiver
Needs extra equipment in a/c

Question 28

GBAS range

Answer 28

Standard range is 20miles, 30km

More accurate than SBAS and when close to station

CAT 1 minima req

GLS is made up by the FMC