gps constellation pdf

gps constellation pdf插图

How many satellites orbit the Earth for GPS?

The Global Positioning System (GPS) is a constellation of about 24 artificial satellites. The GPS satellites are uniformly distributed in a total of six orbits such that there are four satellites per orbit. How do I know if my laptop has GPS? Yes, GPS tracking works for missing laptops too.

How high up is a GPS satellite?

U.S. space shuttles are manned satellites of Earth. They usually fly at altitudes around 200 miles above Earth. Rarely, they fly near 400 miles altitude. Russia’s orbiting space station Mir is another manned satellite.

How far are the GPS satellites from Earth?

The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above the earth. They are constantly moving, traveling at speeds of roughly 7,000 miles per hour, making two complete orbits in less than 24 hours.

How many times does GPS satellite orbit Earth?

This number of satellites and spatial distribution of orbits insures that at least eight satellites can be simultaneously seen at any time from almost anywhere on Earth. The GPS satellites circle the Earth at an altitude of about 20,000 km (13,000 miles) and complete two full orbits every day.

What was the purpose of the prototype board?

A prototype board was developed to compare the performance of both solutions, single and multi-GNSS time reference based clocks.

What is satellite data?

This technique consists of using satellite data from different navigation systems and combining them as if it was a single system providing one time reference. Such a solution, besides not being expensive or difficult to implement, offers great advantages over using

How many satellites are in orbit?

Conceived for military purposes in 1973 by the United States, the system was declared totally operational in 1995. Today it counts with 31 satellites that were launched to orbit for years, starting in 1978. Despite of the total, only 24 satellites are available simultaneously; the other ones are operational only in case of a failure or for data checks. The satellites orbit Earth at 20200 kilometers up in the sky and complete two full turns around the globe per day. They have a longitudinal trajectory with different angles for each satellite.

What is the demand for accurate time synchronization?

The demand for accurate time synchronization available 24/7 increases with the growth of critical substation applications, such as phasor measurement, merging units , traveling-wave fault location and current differential protection schemes . In order to yield the best accuracy and granularity from such applications, the use of a common, reliable and precision-time reference is essential.

When was the Russian navigation system developed?

The Russian navigation system GLONASS started to be developed in 1976 also for military purposes. The project was interrupted for many years after the end of the Soviet Union but it was reestablished and gained notoriety during the last decade, driven by the Russian president Vladmir Putin.

Is a single GNSS time reference?

Using a single GNSS as a time reference is the most used solution, commonly relying on the GPS, but using a single solution introduces some vulnerabilities and limitations to the system

What are non-correctable errors in GPS?

Sources of non-correctable errorsinclude receiver noise, which is unavoidably inherent in any receiver, andmultipath errors, which are environmental. Multi-path errors are caused bythe receiver “seeing” reflections of signals that have bounced off of surroundingobjects. The sub-meter antenna is multipath-resistant; its use is required whenlogging carrier phase data. Neither error can be eliminated with differential,but they can be reduced substantially with position fix averaging. The errorsources and the approximate RMS error range are given in the Table 5.Table 5. Error Sources

What are the two types of positioning errors?

There are two types of positioning errors: correctable and non-correctable.Correctable errors are the errors that are essentially the same for two GPSreceivers in the same area. Non-correctable errors cannot be correlated betweentwo GPS receivers in the same area.

What is differential positioning?

Differential positioning is technique that allows overcoming the effects ofenvironmental errors and SA on the GPS signals to produce a highly accurateposition fix. This is done by determining the amount of the positioning errorand applying it to position fixes that were computed from collected data.

How does DGPS work?

Most DGPS techniques use a GPS receiver at a geodetic control site whoseposition is known. The receiver collects positioning information and calculatesa position fix , which is then compared to the known co-ordinates. Thedifference between the known position and the acquired position of the controllocation is the positioning error.

What is a sensitive antenna?

Sensitive antenna of the GPS receiver detects the electromagnetic wavesignal transmitted by GPS satellites and converts the wave energy to electriccurrent] amplifies the signal strength and sends them to receiver electronics.

When was the T1 4100 GPS made?

Detailed description of code dependent T1 4100 GPS Navigator and codefree Macrometer V1000 is given here:T1 4100 GPS Navigator was manufactured by Texas Instrument in 1984.It was the first GPS receiver to provide C/A and P code and L1 and L2 carrierphase observations. It is a dual frequency multiplexing receiver and suitablefor geodesist, surveyor and navigators. The observables through it are:

Do GPS receivers use batteries?

First generation GPS receivers consumed very high power, but modernreceivers are designed to consume as little energy as possible. Most receivershave an internal rechargeable Nickel-Cadmium battery in addition to anexternal power input. Caution of low battery signal prompts the user to ensureadequate arrangement of power supply.

How many satellites are in the Galileo GNSS?

When fully deployed, the European Galileo GNSS will consist of 30 satellites (27 operational and 3 spares) in three orbital planes at an altitude of 23,222 kilometers.

What is GNSS tracking?

GNSS satellite tracking with SLR can provide improved GNSS satellite orbit information, modeling of satellite orbits and clocks , and improvement in the long-term stability of the ITRF. All GLONASS satellites have retroreflector arrays; two previously operational GPS satellites carried arrays.

What is a GNSS receiver?

GNSS receivers detect, decode, and process signals from the GNSS satellites. The satellites transmit the ranging codes on two radio-frequency carriers, allowing the locations of GNSS receivers to be determined with varying degrees of accuracy, depending on the receiver and post-processing of the data.

How many satellites are observable from any point on Earth?

The satellites are positioned so that six are observable nearly 100 percent of the time from any point on Earth. Two of the original GPS satellites flew laser retroreflector arrays for SLR tracking.

What is QZSS in Japan?

Japan’s Quasi-Zenith Satellite System (QZSS) QZSS will consist of three satellites in multiple orbital planes for regional positioning and time transfer. QZSS will enable a high accuracy satellite positioning service for nearly all of Japan, including urban areas and mountainous terrain.

How many satellites are in the GPS constellation?

The current GPS constellation includes 24 satellites, each traveling in a 12-hour, circular orbit, 20,200 kilometers above the Earth. The satellites are positioned so that six are observable nearly 100 percent of the time from any point on Earth. The current GLONASS constellation includes 24 satellites, each traveling in a circular orbit, 19,140 kilometers above the Earth. The satellites are positioned so that four are observable nearly 100 percent of the time from any point on Earth.

Which satellites have laser ranging?

Galileo, BeiDou, QZSS, and IRNSS satellites have (or will have) these arrays. The International Laser Ranging Servic (ILRS) actively supports laser ranging to many, if not all, GNSS satellites equipped with laser retroreflector arrays.