Japan - Geodetic and Navigation Systems
The success of the US and French geodetic satellites launched in the mid-1970's influenced Japan's national space agency, NASDA, to sponsor a similar, yet complementary, geodetic satellite. Under the auspices of the Hydrography Department of the Maritime Safety Agency and the Geographical Survey Institute of the Ministry of Construction, the objectives of the Experimental Geodetic Satellite (EGS, also known as Ajisa) are to:
- correct the geodetic triangulation nets in the country,
- determine the location of isolated islands (improve the marine geodetic network) and
- establish Japan's geodetic datum.
EGS was launched 12 August 1986 on the inaugural mission of the H-l launch vehicle. The 685 kg satellite is spherical with a diameter of 2.15 m, but, unlike other geodetic satellites of its class, EGS is covered with both laser reflector assemblies (120 with 1436 corner cubes) and solar reflecting mirrors (318). The mean altitude of EGS is slightly less than 1,500 km with an orbital inclination of 50.0 degrees.
The Electronic Navigation Research Institute (ENRI) is responsible for research and development in the field of electronic navigation in Japan. Our research activities cover the basic technologies of avionics such as electronic navigation, air traffic control and satellite navigation, and the related field supporting governmental needs and social demands.
Research on the use of satellites at ENRI began 38 years ago, immediately after the establishment of the institute in 1967, with the creation of the Satellite Technology Division. Later, during a 9-year period from 1983 to 1991, ENRI developed basic technologies such as satellite positioning, ranging techniques, and satellite data communications, etc. through work on the large subject of “Developmental Research on Navigation Technologies” using the Engineering Test Satellite No. 5 (ETS-V). Based on this, ENRI expanded its work to research on satellite navigation augmentation systems (SBAS, GBAS), and research related to the ionosphere, which controls the accuracy and integrity of GPS and other satellite signals.
The present aeronautical navigation methods are limited in various respects, including their coverage and accuracy. To overcome these limitations, the International Civil Aviation Organization (ICAO) decided to introduce a global navigation satellite system (GNSS) using GPS and other technologies. However, in order to use the existing GPS, it will be necessary to improve its integrity, positioning accuracy, and availability. The satellite-based augmentation system (SBAS) and ground-based augmentation system (GBAS) were conceived to improve these properties.
JAXA has developed an integrated navigation system that uses GPS and INS (inertial navigation system) to compensate for each other's shortcomings, and is continuing research of the following two technologies to improve that technology. One is the technology for improving signal tracking performance in the GPS receiver by supplementing aircraft motion information measured with INS. By eliminating phase fluctuations caused by aircraft movement, it is expected that an even larger signal tracking margin can be ensured and signal interruptions will be reduced.
The second is the technology for alleviating surges in the protection level (accuracy ensured by a high degree of reliability) when the number of usable satellites is reduced due to reception interruptions or satellite exclusion by the CCD monitor, by switching to coasting (continuing inertial navigation without compensation by GPS), using INS to take over for the previous protection level of GPS.
In 2008 Prof Akio Yasuda of the GPS Society of the Japan Institute of Navigation suggested that “the Asia-Oceania region is the best place to receive the earliest benefit from this new multi-GNSS era”. Asia contains the manufacturing hubs of the global GNSS downstream industry, producing almost all current mobile handsets and navigation devices. Japan in particular is an industrial and science/technology powerhouse with a well-developed space industry and a highly advanced GNSS-related sector.
“Many Japanese firms have been early adopters of GPS and have thus developed 20-plus years of experience in building and running navigation systems, particularly for car navigation and maritime shipping,” says Germany-based Rainer Horn, managing partner of SpaceTec Capital Partners and project coordinator of GNSS.asia. While many mobile networks and electricity network systems in Japan are now synchronised using GPS signals, with Galileo in place Japanese firms will have a wider choice of satellites on which to base their systems, both for export as well as for domestic use.
Japan, China and India are developing their own navigation satellite systems, all to be operational in the next few years. Japan’s Quasi-Zenith Satellite System (QZSS), for example, is based on a planned constellation of seven satellites covering a north-south corridor above the Pacific Ocean. It will be compatible with, and enhance the accuracy of, the existing GPS and GLONASS. EU officials also hope QZSS will be interoperable with Galileo.
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