(CH. 3) Major test A Study Guide - SRVY 2331

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Minitrack

is a system within the satellite “an oscillator of minimum size and weight … to illuminate pairs of antennas at a ground station which measures the angular positions of the satellites.

Wheels

are devices that stabilize each satellite. In GNSS satellites, attitude and rotational rates are controlled with momentum wheels. Two rotations are necessary during the satellite’s orbit to ensure the solar panels are pointing at the Sun.

Laser retro-reflector arrays (LRA)

are small optical instruments that provide a target that reflects laser signals from ground Satellite Laser Ranging stations back to their source to provide tracking data for precise orbit determination.

Ballistic cameras

are used in the photogrammetric tracking of artificial Earth satellites often against the background of fixed stars.

Legacy Navigation Message

navigation message comprised 5 subframes.

S-band

Defined by IEEE as a frequency band in the range of 2 to 4 GHz

satellite laser ranging (SLR)

Direct unambiguous distance measurement of the round-trip time-of-flight from ground stations to the retroreflectors on orbiting satellites using very short pulsed lasers

Interferometry

The measurement of the interference between the phases of signals that originate at a common source but travel different paths to the receivers.

DOD

U.S. Department of Defense

Kalman filter

In GNSS, a numerical data combiner used in determining an instantaneous position estimate from multiple statistical measurements on a time-varying signal in the presence of noise.

NGA

It is an agency that produces geospatial intelligence in support of national security.

Joint Program Office (JPO)

The U.S. Department of Defense office that managed GPS system from 1973 to 2006.

Legacy Accuracy Improvement Initiative, L-AII

A National Geospatial-Intelligence Agency (NGA)-led project completed in 2008 that increased the data available to the GPS Master Control Station.

Sputnik

The first artificial satellite to orbit the Earth, launched by the Soviet Union

Kalman filter

In GNSS, a numerical data combiner used in determining an instantaneous position estimate from multiple statistical measurements on a time-varying signal in the presence of noise.

Omega

A radio navigation system that can provide global coverage with only 8 ground-based transmitting stations.

very long baseline interferometry (VLBI)

by measuring the arrival time of the front of microwaves emitted by a distant quasar at two widely separated Earth-based antennas, the relative position of the antennas is determined

sidereal day

is the time it takes the Earth to rotate once about its axis relative to the stars instead of the sun. The distant stars appear in the same positions in the sky at the end of a sidereal day that they had at the beginning. At a meridian, a sidereal day is the period between two successive upper transits of the vernal equinox.

Sidereal time

is also known as star time. The time measured relative to the stars instead of the sun.

Dilution of precision (DOP)

in GNSS positioning, an indication of geometric strength of the configuration of satellites in a particular constellation at a particular moment and hence the expected reliability of the results.

Which requirement for the ideal military navigational system does GPS not currently satisfy?

Not dependent on externally generated signals

GDOP is a combination of which DOP factors?

PDOP and TDOP

Which GPS satellite identifier is most widely used?

PRN number

Which GPS-related concept listed has been around the longest?

The Doppler shift

Which statement concerning the L-band designation is not true?

The frequencies broadcast by the TRANSIT satellites were within the L-band.

Why does a GPS satellite appear to return to the same position in the sky about 4 minutes earlier each day?

The apparent regression is due to the difference between sidereal time and solar time over a 24-hour period.

The concept of measuring distance with what type of signals had one of its earliest practical applications in RADAR?

Electromagnetic signals

What was the most attractive aspect of early civilian GPS surveying in the 1980s?

Accuracy

What NAVSTAR GPS improvement was not found in the retired TRANSIT system?

Atomic frequency standards

Which GNSS satellites are equipped with Laser Retro-reflector Arrays (LRA), and what is their purpose?

Nearly all new GNSS satellites have LRAs. They allow Satellite Laser Ranging for precise orbit determination and help separate satellite clock errors from ephemeris errors.

Which GPS satellite category listed is currently providing signals for positioning and navigation?

Block III

How many Control Segment stations track each GPS satellite at all times?

Tracks at all times and with at least three stations