Positioning, Navigation, and Timing (PNT) Satellites
In 2014, China had paused in its BeiDou PNT satellite launch activities with its BeiDou satellites making up 20.5% of the global PNT satellite fleets. There were 16 BeiDou satellites orbiting the Earth in medium or inclined geosynchronous Earth orbits providing regional PNT service to China during 2014. By the end of 2015, China had added another four BeiDou satellites, bringing the constellation strength to more than half of the 35 satellites China anticipates to have in operation by 2020.
India’s share of the world’s operational PNT satellites hovered around 4% for 2014 and 2015. Launching one Indian Regional Navigation Satellite System (IRNSS) satellite in 2015, the country continued to make progress toward its goal of operating seven regionally focused PNT satellites by 2016. All of the IRNSS constellation’s satellites will orbit the Earth in geosynchronous orbit, with four of the seven moving about in inclined orbits while the remaining three stay in a steady geostationary path.
The European Union’s space-based PNT efforts began in 2005, making 2015 the tenth anniversary for its PNT efforts. Galileo, the European PNT satellite system, is scheduled to be complete by 2020. For 2014, Europe owned 5% of the total global operational PNT satellites in orbit that. During 2014, Europe had succeeded in launching six Galileo PNT satellites. However, two of the Galileo satellites were launched into an incorrect orbit in August 2014, effectively reducing the number of operational European PNT satellites orbiting the Earth in 2014 to four.
As of December 2015, Russia’s Global Navigation Satellite System (GLONASS), comprised 24% of the operational global PNT constellations. Like the U.S. GPS milestone, 2015 marked the 20th anniversary of Russia’s deployment of GLONASS. The initial full deployment of 24 GLONASS satellites occurred in 1995. Completion of testing activities allowed the Russians to consider GLONASS fully operational in early 1996.
The U.S. Global Positioning System (GPS) satellite fleet made up 34% of the operational global positioning, navigation, and timing fleets orbiting the Earth in 2015. Originally developed for military use, GPS became fully operational in the spring of 1995, marking 2015 as the 20th anniversary for the constellation. This meant the satellite constellation consisted of a minimum of 24 GPS satellites in their assigned medium Earth orbits after the completion of several tests. Since it became fully operational, the constellation number annually exceeds the baseline requirement by a good margin, not including eight backup GPS satellites.
The number of positioning, navigation, and timing (PNT) satellites orbiting the Earth increased by 15% from the end of 2014 through 2015. Of the six nations fielding space-based PNT satellites or systems, the biggest contributors to the number of satellites in 2015 were the European Union and China. India continued a steady growth of its PNT constellation, while established…
Note: The exhibit in this section is from The Space Report 2015. Please refer to this year’s exhibits for the most current data as numbers may have been revised since this edition was published.
The Japan Aerospace Exploration Agency (JAXA) launched the ## satellite of its Quasi-Zenith Satellite System (QZSS) in September 2010, and continued to operate and run tests on it during 2014. Japan’s urban canyons and mountainous regions present challenges for receiving the relatively weak signals from PNT satellites such as GPS. The inclined orbit of QZSS, in combination with its dwell time over Japan, gives PNT receivers in Japan a better chance of receiving a PNT signal.
China was uncharacteristically inactive in terms of PNT satellite launches during 2013 and 2014. A new navigation test satellite the Chinese were expected to launch for phase 3 of the BeiDou2 constellation in 2014 was delayed to 2015. ## BeiDou2 satellites are already in medium Earth orbit, ## are in geostationary orbit, and another ## are in an inclined geosynchronous orbit. All ## are aimed at providing PNT service to China and areas surrounding it. China plans to have about ## BeiDou satellites in the constellation by 2020 for global coverage.
India continued with plans for its regional PNT constellation, the Indian Regional Navigational Satellite System (IRNSS), launching ## more IRNSS satellites in 2014. With a total of ## PNT satellites in geosynchronous orbit, India is nearly halfway toward completing its ##-satellite IRNSS constellation. Even with ## IRNSS satellites, the Indians will continue to rely on GPS for their GPS-Aided Geo Augmented Navigation (GAGAN) system, which became operational in 2014.