JAPANESE, EUROPEAN, & CHINESE NAVIGATION SATELLITE EFFORTS

* Both Japan and the European Space Agency (ESA) are now working on GPS augmentation systems, with the main function of both networks being air traffic control.

The Japanese system is known as "MTSAT (Multifunction Transport SATellite) Space-based Augmentation System" or "MSAS", and is being implemented by the Japanese Meteorological Agency and the Japanese Ministry of Transport, hence the name of the satellite. The MTSAT spacecraft are a combination meteorological and communications satellite, and are being placed in geostationary orbit over the eastern Pacific.

The satellites provide voice and data links between aircraft and ground controllers; hand off relay GPS augmentation and integrity data to aircraft; and provide ground controllers with precision aircraft location. They replace the long-standing Japanese "Himawari (Sunflower)" or "Geostationary Meteorological Satellite (GMS)" series in the weather surveillance role, using a observation payload to track clouds and storms, and a relay system to pass data from surface stations on to central weather analysis centers.

The first MTSAT was launched by a Japanese H-2 booster on 15 November 1999, but the spacecraft failed to reach orbit. A replacement spacecraft, designated "MTSAT-1R", was successfully launched by an H-2A booster on 26 February 2005, with a second satellite designated "MTSAT-2" following on 18 February 2006. MTSAT-1 and MTSAT-1R were built by Space Systems / Loral, are based on standard Loral satellite buses, and had a launch weight of 2,900 kilograms (6,400 pounds). MTSAT-2 was built by Mitsubishi Electric with assistance from Boeing Satellite Systems and Alcatel Space, and had a larger launch mass of 4,535 kilograms (10,000 pounds).

* The ESA network is known as the "European Geostationary Navigation Overlay System (EGNOS)". Like MSAS, EGNOS transmits augmentation and integrity data to aircraft through geostationary communications satellites. It went into service in July 2005, using the INMARSAT AOR-E and IOR commercial communications satellites, along with the European Space Agency Artemis experimental communications satellite. The satellites provide coverage of subpolar areas ranging from the east coast of the United States to Japan, using 43 ground stations in 22 countries. It is being used as an approach and landing system comparable to WAAS.

* There has been some effort towards building receivers that can obtain signals from both GPS and GLONASS, providing substantially greater accuracy than would be possible from either by itself. Use of two satellite systems also gives users a "backup" operational capability if one of the systems is disabled. The European Community is now implementing the "Global Navigation Satellite System 1 (GNSS-1)", which will integrate services from GPS, GLONASS, and various augmentation networks.

One of the problems in combining use of GPS and GLONASS is that they use different global coordinate systems. GPS uses a coordinate system named "WGS-84", in which the precise location of the North Pole (which drifts a bit) is fixed at its location in 1984. GLONASS uses a coordinate system named "PZ-90", in which the precise location of the North Pole is given as an average of its position from 1900 to 1905. Trying to link the two coordinate systems has proven difficult, particularly because there are far fewer GLONASS receivers than GPS receivers.

GNSS-1 is a stepping stone to a completely independent European "GNSS-2". GNSS-2, or "Galileo" as it has been named, will be based on an entirely new satellite constellation, consisting of 30 satellites, including three on-orbit spares, placed in three orbital planes at an altitude of 26,616 kilometers (16,530 miles). The orbital system will be integrated from the start with ground augmentation networks. The Galileo satellites will also carry COSPAS-SARSAT search and rescue payloads.

Unlike GPS, Galileo will be under complete civilian control. It is being implemented through a cooperative relationship between the ESA and the European Union (EU) organization. European military forces have expressed interest in making use of Galileo, but so far have not offered to help with funding. India bought into a share of the program in late 2003.

The Galileo group plans to offer four types of service packages: an "open" service available to all at no cost; a "safety of life" service that provides alerts when the system's accuracy or integrity is compromised; a commercial service using encrypted signals; and a public regulated service for government users. The Galileo system uses a different scheme from the US GPS system, but work was done to make sure the two systems dovetailed well enough to prevent mutual interference and allow users to pick up both systems with a single receiver.

Although the project bogged down in international squabbles for about a year, they were resolved and the green light for the demonstration-validation ("dem-val") phase was given in the summer of 2003. The squabbles were over very minor matters and proved extremely frustrating to the participants, and efforts are likely to be made to change the rules governing the effort to make sure trivial issues won't be roadblocks.

Current plans envision flight of two "Galileo Test-Bed Satellites (GTBS)", with the spacecraft known more specifically by the name of "Galileo In-Orbit Validation Element (GIOVE), followed by launch of four dem-val spacecraft.

The contract for the first testbed satellite, GIOVE A, was issued to Surrey Satellite Technology LTD in the UK in July 2003. GIOVE A was launched from Baikonur by a Soyuz-Fregat booster on 28 November 2005; the satellite had a launch mass of 600 kilograms (1,327 pounds). Galileo Industries, a European consortium led by Astrium, Alcatel Space, and Alenia, is developing the larger GIOVE B satellite, with this spacecraft to be launched by a Soyuz booster from Baikonur in the spring of 2006.

A contract for the four dem-val or "In-Orbit Validation (IOV)" spacecraft was signed in 2006 with Galileo Industries. Initial launch of an IOV satellite will be in 2008, with the full 30-satellite constellation in orbit by the end of 2010 and introduction to operational service in 2011. Galileo was designed to provide locations with a meter of error.

* China has now introduced their own first-generation satellite navigation system. The "Beidou Navigation Test Satellite 1", where "Beidou" is the "North Dipper", the Chinese name for the constellation of the Big Dipper, was launched by a Chinese Long March 3M booster from the Xichang space center on 31 October 2000, into a geostationary orbit. It was followed by "Beidou 1B" on 21 December 2000, and then "Beidou 3" on 25 May 2003.

The Beidou satellites were based on the Chinese DFH-3 geostationary communications satellite and had a launch weight of 1,000 kilograms (2,200 pounds) each. The three geostationary satellites provide navigational coverage over the entire country. There was some impression initially, partly because the spacecraft looked so much like communications satellites, that they provided error corrections of GPS signals much as did MTSAT, but as it turned out, they provided locations without use of other navsat systems.

The scheme is referred to as the "TwinStar" system; it was demonstrated using two DFH-2A communications satellites in 1989, leading to authorization of full development of the Beidou system in 1993. The developed system involves a ground-based control center sending an interrogation signal to a user's ground-based navigation receiver through the Beidou satellites, with the receiver then sending back a response through two satellites. The (usually different) "time delay of arrival (TDOA)" of the response signal back to each satellite allows the position of the receiver to be determined by triangulation, with the position estimate refined at the control center by cross-referencing to a China terrain altitude database. (TDOA is, incidentally, often used with military emitter location and targeting systems.) The position data is relayed back to the receiver using an encrypted channel -- of course, Beidou was designed with military applications in mind, just as were US and Soviet navsat systems -- and users can also send text messages with up to 120 Chinese characters through the spacecraft.

The system operates in a band around 2.491 GHz. Only two satellites are actually used, the third satellite being an on-orbit spare. There is am ambiguity in the use of two satellites, in that the position might be north or south of the Equator, but since all of China is well north of the Equator and Beidou was designed as a national system, that's not a problem. Accuracy is only about 100 meters (330 feet), though it can be improved to 20 meters (66 feet) or better using ground-based augmentation systems. Since two-way communications are required, the Beidou receivers are generally bigger than GPS / GLONASS receivers, and the maximum number of users runs to about 540,000 over the course of an hour.

Military users began to utilize the Beidou system in late 2001, with civilian users getting on board in April 2004. Beidou was clearly designed to provide a useful navsat system under Chinese control at much lower cost than fielding a full GPS / GLONASS-type global navsat constellation. The Chinese may be working on their own global navsat system, but they are also cooperating in development of the Galileo system.