Global Navigation Satellite Systems Practice Flashcards

A set of vocabulary flashcards covering the components, signal structures, constellations, and technical specifications of the GPS, GLONASS, and Galileo navigation systems.

GPS Control Segment (CS)

The system component responsible for tracking and maintaining satellites, monitoring health and signal integrity, and updating satellite clock corrections and ephemerides.

Ephemeris Parameters

A quasi-Keplerian representation of GPS satellite orbits used to determine precise satellite position, typically valid for 3 to 4 hours.

Almanac

A reduced-precision subset of ephemeris parameters used to predict approximate satellite positions and aid in signal acquisition, typically valid for up to 60 days.

Dilution of Precision (DOP)

A parameter that measures the geometric contribution to navigation accuracy based on the observability of the satellite constellation.

RAAN

Right Ascension of the Ascending Node; the point where a satellite orbit intersects the equatorial plane while the satellite is traveling northward in inertial space.

Nominal GPS Orbital Radius

Approximately $26,600\,km$ from the Earth's center of mass.

GPS Orbital Period

One-half of a sidereal day, approximately $11\,hours\,58\,minutes$.

L1 Frequency

The primary GPS carrier frequency centered at $1,575.42\,MHz$ ($154 \times f_0$).

L2 Frequency

The secondary GPS carrier frequency centered at $1,227.6\,MHz$ ($120 \times f_0$).

L5 Frequency

A GPS frequency centered at $1,176.45\,MHz$, placed in a band protected for Aeronautical Radionavigation Services.

Master Control Station (MCS)

The central command facility located at Schriever Air Force Base (AFB) that provides continuous 24/7 mission control for GPS operations.

Selective Availability (SA)

A legacy capability that formerly denied full GPS accuracy to civilian users, discontinued on May 1, 2000.

WGS 84

The World Geodetic System 1984; the Earth-centered, Earth-fixed reference frame inherent in GPS broadcast orbits and clocks.

Binary Offset Carrier (BOC)

A spreading modulation used by modernized signals, such as the GPS M-code, to achieve spectral separation from civil signals.

FDMA

Frequency Division Multiple Access; the signal transmission technique used by GLONASS where different satellites transmit on distinct carrier frequencies.

PZ-90

The national coordinate system of the Russian Federation (Parametry Zemly 1990) used for geodetic support of GLONASS.

Galileo Open Service (OS)

The publicly accessible Galileo positioning, velocity, and timing service suitable for mass-market applications like smartphones.

Passive Hydrogen Maser (PHM)

An advanced atomic frequency standard used in the Galileo satellite timing subsystem to provide high-stability time references.

Galileo System Time (GST)

The continuous internal reference time scale for the Galileo system, synchronized to TAI with no leap second adjustments.

Search and Rescue (SAR) Payload

A secondary satellite payload used to relay 406-MHz distress signals from emergency beacons to rescue coordination centers.

AltBOC

Alternative Binary Offset Carrier; a wideband complex sideband modulation used for the Galileo E5 signal centered at $1,191.795\,MHz$.

Issue of Data (IOD)

A parameter in the navigation message that uniquely identifies a specific set of clock and ephemeris data batches.

User Range Error (URE)

The contribution of pseudo-range error stemming from the space and control segments, excluding errors from the user's environment.

Baseline GPS Constellation

The officially defined configuration consisting of 24 satellites positioned in 6 Medium Earth Orbit (MEO) planes.