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ATPL Radio Navigation > GPS > Flashcards

GPS Flashcards

1
Q

What are the 3 major segments of a satellite

A

Space segment = satellite

Control segment = ground monitoring station

User segment = GPS receiver

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2
Q

What does the ground control segment of the GPS satellites do

A

Monitors the satellites, calculates corrections and transmits them to satellites

1 master control and several monitors positioned close to the equator

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3
Q

How many satellites does NAVSTAR have

A

24 satellites

21 operational
3 spare

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4
Q

How many different orbital patterns does NAVSTAR have

A

6

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5
Q

What is the height of navstar orbits

A

20,200km

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6
Q

What incline is the NAVSTAR orbits to the equator

A

55°

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7
Q

How long is a NAVSTAR orbit

A

12 hours

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8
Q

What are the frequencies for NAVSTAR

A

Link 1 = 1575.42mhz

Link 2 = 1227.6mhz

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9
Q

Why is there 2 link frequencies for gps

A

Estimate ionosphere delay

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10
Q

What transmits the course acquisition code

A

Link one

Associated with sps service
Standard positioning service

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11
Q

What are the modes of operation for GPS

A

Standard positioning service (SPS) for civilian users = L1

Precise position service (PPS) for military users = L2

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12
Q

What is the reference datum for NAVSTAR

A

World geodetic system 1984

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13
Q

What is the user segment of a gps

A

Any capable satellite receiver

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14
Q

What gps is a civilian receiver capable of receiving

A

L1 = course acquisition / selected availability

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15
Q

What is a military GPS receiver able to receive

A

Both L1 and L2 signals with a P code (precision)

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16
Q

What is a satellite gps principle of operation

A

TIME

broadcast ranging codes and accurate times

Receiver measures signal transmit time to determine range from satellite

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17
Q

What gps location can a position from one satellite give you

A

A position on the surface of a sphere

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18
Q

What gps location can a position from two satellite give you

A

Produce a circular position line where the 2 spheres intersect

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19
Q

What gps location can a position from three satellite give you

A

Unambiguous position

20
Q

What gps location can a position from four satellite give you

A

Unambiguous fix with all timing errors resolved

21
Q

What is the max number of users on a gps satellite

A

Unlimited number of users

22
Q

How is pseudo range countered

A

Due to timing error = range error

Therefor

Resolved by receiver clocks being a little slower so that range is always overestimated

23
Q

How is receiver clock error corrected for gps

A

With signals from 4 satellites

24
Q

What does ephemeris data (almanac info) contain

A

Accurate satellite orbit info

25
Q

What is the optimum satellite position

A

One directly above

3 = 120° apart

26
Q 
How long does it take to download 
Ephemeris info
Ionosphere delay 
Timing info 
Satellite health
A

12.5 mins

27
Q

What is the time difference between Utc and satellite clock

A

13.5 seconds

28
Q

How accurate is the satellite atomic clocks

A

1 nanosecond

29
Q

What is the GPS receiver used in aircraft

A

Multi channel receivers

30
Q

What is the biggest error in gps

A

Ionospheric propagation delay IPD = 5m

31
Q

What is masking angle

A

Gps just disappears behind horizon

32
Q

What is RAIM

A

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

33
Q

What is GBAS

A

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

34
Q

What is GRAS

A

Ground regional augmentation system

GBAS with more pseudo satellites

Increases accuracy

35
Q

What is SBAS

A

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

36
Q

What is EGNOS

A

European geostationary navigation overlay system

Geostationary satellite

37
Q

What is WAAS

A

Wide area augmentation system

Operates by USA

Geostationary satellite

38
Q

What is MSAS

A

Multi function transport satellite augmentation system

Operates by japan

Geostationary satellite

39
Q

What is GAGAN

A

Gel and gps augmented navigation

Operated by India

Geostationary satellite

40
Q

What is ABAS

A

basically RAIM

41
Q

What is GLONASS

A

Old system resurrected by Russia

Fully operational by 2010

Uses Pz-90 datum

Been used since 2007

Integrity implemented by SBAS / GBAS

42
Q

What are the frequencies for GLONASS

A

L1 1.6GHZ

L2 1.2GHZ

43
Q

What is GALILEO

A

European system

Not operational yet

Estimated 2020

44
Q

What are the GALILEO clocks made out of

A

Rubidium frequency standard clock

Very accurate passive hydrogen master clock

45
Q

What does he signal generation section of GALILEO contain

A

Message comprises ephemeris and orbit info and clock references

46
Q

What are the GALILEO frequencies

A 
L1 = 1164-1215 MHZ 
L2 = 1260-1300 MHz 
L3 = 1559 - 1571 MHz

L3 shares with gps on a non interference basis

ATPL Radio Navigation (14 decks)

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