24 satellites Selective Availability turned off May 2000 30 meter accuracy Can be jammed (denial of service) Can be spoofed

1. Global Positioning System
• 24 satellites
• Selective Availability
turned off May 2000
• 30 meter accuracy
• Can be jammed
(denial of service)
• Can be spoofed

2. GPS Frequencies
L1: 1575.42 MHz: Coarse Acquisition (C/A) code
L2: 1227.60 MHz: Precise (P) or Y (encrypted) code
L3: 1381.05 MHz: Nuclear burst detectors
L4: 1841.40 MHz: Ionospheric correction (under study)
L5: 1176.45 MHz: Civilian safety-of-life signal (proposed)

3. GPS Enhancements
The new architecture also requires new user equipment and an
upgraded ground control segment, as well as M-Code. All of those
elements should be in place by 2008, when 18 satellites with M-Code
- 12 IIRs and 6 IIFs - will be up.

4. GLONASS
• Global Orbital Navigation Satellite System
• 1606 to 1616 MHz
• Full operational status achieved once

5. Satellite Failures
• PanAmSat Galaxy 4
– Attitude control and backup failed
– Major supplier of service to paging towers
• AT&T Telstar 401
– launched 1993, failed 11 January 1997
– abrupt failure, solar activity? (large solar flare 6 January 1997)
• Galaxy 7
– Primary control processor failed June1998. Secondary processor failed
November 2000.
– Suspected electrical shorts in spacecraft control processor (SCP).
• Solidaridad 1
– Primary SCP failed May 1999. Secondary SCP failed August 2000.
• Anik E1
– 1996, Power Subsystem Failure, Partial Loss
• EchoStar 4
– 1998, Solar Array Failed to Deploy, reduced electrical power available

6. Satellite Glossary
BEACON
Modulated oscillator, usually containing telemetry. Sometimes referred to
as a “pilot.” Used to locate a satellite and determine received signal strength.
BEAM
Uplink or downlink channel to or from the satellite. May cover a wide area, or be
focused on a particular location (“spot beam”).
BENT PIPE
Big repeater in the sky. Simply repeats uplinked signal on downlink side, with
amplification. Also called non-processing.
DOWNLINK, UPLINK
Downlink is signal from satellite to ground station.
Uplink is signal from ground station to the satellite.

7. Satellite Glossary (con’t)
EOL
End of Life. Satellite lifetimes, barring accident or other damaging
incident, are determined by the amount of maneuvering fuel (typically
hydrazine) on-board. When the fuel runs out the satellite can no longer
be maneuvered to stay in it's assigned orbital location. The orbit then
becomes inclined. Current satellites have an expected life of 10 - 15 years.
ECLIPSE
Satellite's solar panels are blocked by the earth (22 days before and after spring
and autumn equinox, maximum of 70 minutes) or the moon (irregular).
EIRP
Effective Isotropic Radiated Power. A measure of satellite transmitter strength,
usually in dBw (decibels above one watt).

8. Satellite Glossary (con’t)
FDMA, TDMA, CDMA, DAMA
Modulation schemes to allow resource (bandwidth) sharing.
Frequency Division Muliple Access: standard for video.
Time Division Multiple Access: standard for telephone, most data.
Code Division Multiple Access: spread spectrum, originally military.
Demand Assign Multiple Access: shared data systems, including VSAT.
FEEDERLINK
Communications link between the ground station and the satellite.
This link is distinct from the user links.
FOOTPRINT
Geographic area on the earth covered by a particular satellite beam.

9. Satellite Glossary (con’t)
INCLINED ORBIT
When maneuvering fuel runs out. Requires tracker at ground station.
Traces a figure-eight pattern above and below the equator over 24 hours.
INMARSAT
International Maritime Satellite Organization.
Covers Atlantic (AOR East and West), Pacific (POR) and Indian (IOR) Oceans.
Has spares in orbit, not always in contact with TT&C.
LOOK ANGLE
Elevation from a given location to a satellite. 90 degrees is directly overhead,
0 degrees is on the horizon.
PSEUDOLITE
Pseudo-satellite. Ground-based or airborne transmitter emitting satellite-like signals.

10. Satellite Glossary (con’t)
TRANSPONDER
Discrete frequency slot assigned to an uplink/downlink.
TT&C
Telemetry, Tracking and Command. Ground Station monitoring and controlling
satellite operation.
TWT
Traveling-Wave Tube amplifier. Has nearly flat response across a wide bandwidth.
Newer satellites are using solid state amplifiers.
VSAT
Very Small Aperture Terminal. Usually dedicated data links in a star configuration.
Popular with gas stations for credit card verification; car dealers for sales information.