Gps
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The document outlines the functionalities and aspects of the Global Positioning System (GPS) and GLONASS satellite systems, including their operational specifications, frequencies, and potential vulnerabilities. It also provides insights into the satellite glossary, such as definitions related to signal transmission, modulation schemes, and satellite lifetimes. Furthermore, enhancements and requirements for updated GPS architecture are discussed, highlighting the expected improvements by 2008.
Gps
- 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.