63 GPS

Question 1

GPS Unique capabilities

8

Answer 1

Provides highly accurate 3D position
Provides velocity vector and time
Global coverage
Continuous availability
Passive service (receiver)
Unlimited number of users
Somewhat resistant to interference (spread spectrum)
Allows common grid reference

Question 2

System segments GPS

Answer 2

Space segment
Final constellation baseline provides 31 satellites for world-wide coverage
6 orbital planes of 4 satellites (non-uniform)
6 to 11 satellites are always in view
Orbit period is 12 hours (approx)
Orbit altitude is approximately 20200km
Control segment
User segment: receiver/computer of the vehicle using GPS consisting of
Antenna
Signal processing equipement
Computer
Oscillator

Question 3

GPS Policy

Answer 3

GPS provides 2 navigation services
1. Standard positioning service (SPS)
civil users and some military
coarse acquisition (C/A) on L1
Interim use of L2 for carrier phase
Degraded accuracy or SA (Selective availability) for non DoD users
7.8m error
Civil accuracy degraded further when national policy dictates

2. Precise positioning service (PPS)
   Military
   C/A on L1 and P/Y on L1 and L2
   ≤5.9m accuracy
   Anti-jam (spread spectrum) and anti-spoof (Y code) all block 2
   Requires decryption to access full capabilities