What is navigation? |
getting a person or craft from one place to another |
How |
eyes, common sense, landmarks |
navigation aids for accuracy |
Tools |
clocks |
odometer |
electronic aids |
"radio navigation aids" |
ground-based |
space-based |
who processes |
user's system that calculates position |
user's system processes some of information |
latitude and longitude what are they |
high accurate systems -> short wavelength |
-> LOS |
less accurate long wavelength |
-> not LOS |
early space-based systems |
U.S. Navy Navigation Satellite System "Transit" (1964) |
Russian "Tsikada" |
2-D |
High accuracy |
frequency of fixes vary with lat |
once very 30 minutes to once every 110 minutes |
History |
1960's fragmentation |
DOD |
NASA |
DOT |
all working on 3-D systems |
goals |
global coverage |
continuous/ all weather operation |
serve high-dynamic systems |
high accuracy |
Transit |
low dynamic systems |
New systems proposed |
Tranist variant Johns Hopkins Univiserty APL |
NRL working on Timation |
Air Force working on "System 612B" |
Army working on candidates in |
1969 |
DNSS Defense Navigation Satellite System formed |
Various systems were integrated into "NAVSTAR GPS" |
Became just "GPS" |
run by GPS Joint Program Office in El Segundo CA. |
Current GPS |
fully operational |
accurate, continuous, global, 3-D position and velocity |
also distributes coordinated universal time (UTC) time |
24 satellites |
6 orbital planes |
4 satellites per plane |
not geosynchronus |
world-wide network of monitoring stations |
Based on TOA |
Satellites have atomic clocks on board |
Two frequencies |
L1 1575.42 MHz |
L2 1227.6 MHz |
All satellites broadcast with psuedo random codes that don't correlate |
Two codes |
C/A course acquisition |
P(Y) precision code |
navigation data -> ephemeris data |
ranging data -> Time of Flight |
Receivers must have a local clock |
3-D position requires four satellites (clock error) |
time or height reduces this |
TOA based localization (example) |
Beacon based system |
signal propogation time |
speed of signal |
Fog horn example |
Assume an accurate clock |
Speed of sound 335 m/s, 5 s, 1675 m |
draw one circle |
Two fog horn example |
assume pretty good previous estimate - solved |
Three foghorn example |
Let them do an example |
Errors |
Atmospherics |
Foghorn offset |
Interfering sounds |
introduce epsilon |
draw new circles |
introduce uncertain epsilon |
draw new circles |
Go through 3-D analog |
assume knowledge of satellite position |
one range -> sphere |
two range -> circle |
three range -> two points |
one is probably on the earth |
four ranges -> one point |
Back to GPS |
GaliLeo |
Eventually details on satellites |