NAVIGATION: BEIDOU

The United States and Soviet Union were the first two countries to introduce navigation satellites: the GPS and GLONASS, respectively, with Europe (Galileo, which includes China as a financial investor) and India (GAGAN) coming later. A Chinese system was approved in 1983 and, to save development costs, the Dong Fang Hong 3 communications satellite design was used, giving it a weight of 2,200 kg. China had developed sophisticated atomic clocks far in advance of Western ones. Under the guidance of Gua Guantan of the Chinese Science & Technology University, China had built a quantum computational center in 1999, learned how to use lasers to cool atoms, and conquered the problem of the atomic fountain [19]. These clocks, much more advanced than the old Western caesium clocks, reputedly had an accuracy of 1 sec in 30m years. Appointed chief designer of the system was Sun Jiadong, a natural choice granted his leadership of the DFH-2 and 3 series.

China’s first navigation satellite appeared on 31st October 2000. Following a midnight launch, a Long March ЗА placed the satellite at 140°E at 36,000 km with complete precision 10 days after leaving Xi Chang. It was given the name Beidou, the Chinese word for the Plough constellation, or the Big Dipper. Two months later, on 21st December, Beidou 2 followed. The last satellite to be launched that year, it reached its final destination at 80°E three days before the end of the old year and (strictly speaking) the millennium. With satellites at 80°E and 140°E, the Chinese

The Long March ЗА, used to lift the Beidou navigation satellite to orbit.

system appeared to follow a third way, quite different from the United States and Russia, providing a regional, rather than a global, system, using only two spacecraft, functional between the longitudes of Arabia and eastern Australia, centered on the Chinese landmass. Western analysts were puzzled by this system. Suspecting ulterior purpose, the suggestion was made that Beidou was a cunning way of providing accuracy measurements during the key over-the-horizon stages of the flight path of a nuclear strike when the DF-5A missiles curved over the North Pole en route to destroy the cities of the eastern United States [20].

China also booked an orbital location at 110.5°E. This was explained initially as the location for a spare, but then as the third element of a three-part system. A third Beidou, Beidou 3, duly arrived there on 24th May 2003. Like its predecessors, Beidou 3 reached the point following a 200-41,991 km super-synchronous orbit. Each satellite would fire thrusters every month to maintain its position in orbit to within 1°, or 150 km of its hover point. The system was first tested with Beijing’s 7,000-strong bus fleet in 1999, which had its own form of mission control room. Later, they said, Beidou would provide accurate navigational fixes for ships, road and rail transport, and presumably also for aircraft. It transpired that these were experimental tests for a later, operational system. They nevertheless served their makers well, for the first Beidou worked until October 2010, when it began to drift off station and reached 59°E. Beidou 1-2 and 1-3 were both retired on the same day: 21st November 2011.

China was ready to proceed with an operational system seven years after the first launch. The first intended operational Beidou took a super-synchronous orbit on 2nd February 2007 and arrived on station by the end of the month. There are quite contradictory reports as to what happened next. Orbital Debris Quarterly News quoted the US Space Surveillance Network as saying that there had been an engine explosion when it reached apogee on the first day of its mission, leaving 70-100 debris items – almost certainly a catastrophic explosion. China admitted that there were problems with the solar panels and, by mid-April, had moved the satellite to a stable orbit at 144°E, close to Beidou 1 at 140°E. There it stayed until it was maneuvered off station on 30th September and relocated to 147°E two weeks later, eventually retiring in February 2009. The 14th April 2009 launch also appears to have been even more problematical and it rapidly drifted off station.

The next Beidou followed in quick succession on 13th April 2007 and entered its final orbit on the 17th. To general amazement, it headed for a completely different type of orbit – 21,000 km, 55°, circling the Earth every 773 min or approximately every 12 hr. This was a type of orbit used by Russia for its GLONASS navigation satellites, although lower (19,000 km, period 675 min). It remained the only satellite of its type for five years when two were launched together in May 2012, this time using the CZ-3B for the first time in the series. The launch trajectory took the CZ-3B to the south-east, over Hainan Island, before heading over the Gulf of Tonking. They were given the designation MEO 3 and 4 (MEO for Medium Earth Orbit), even though MEO 2 was never listed. One explanation is that the medium-Earth – orbit version required a special type of clock. It is reported that China ordered 18-20 rubidium clocks from Spectratime in Switzerland, famed for a geographical accuracy

Beidou being fitted out.

of 10 m and a timing accuracy of 50 nanoseconds, and developing its application for this orbit took some time.

Ever incapable of leaving a numbering system alone, China now renumbered the series. First, these missions were called Beidou 2 (with 2-1, 2-2, and 2A, 2B subsequently, etc., being used). Then a new term, DW, also appeared, standing for Beidou Daohang Weixing, for Beidou Navigation Satellite, so this was DW1. This was further complicated by the announcement that Beidou would be subdivided into three sub-series: the G, the I, and the M, each with its own sub-designators. Sometimes the Chinese also applied the term “Compass”, referring to it as the “Compass System”. They defined the operational system as comprising 35 satelhtes by 2020:

• 5 satellites at GEO at the equator (0°), the G series, standing for geosynchronous;

• 3 satellites at GEO at 55°, the I series, Inclined Geo Synchronous Orbit (IGSO);

• 27 satellites at 21,000 km (GLONASS-type orbit), the M series (medium).

The 13th April 2007 launch was therefore called Beidou 2-1, or Compass Ml (1M was also used) or DW1. What appeared to be a simple, two-satellite regional navigation system had suddenly become more complicated. What the Chinese were

Beidou fitted into its launch shroud.

doing was using a constellation of three overlapping types of orbits (equatorial synchronous, inclined synchronous, and GLONASS) to ensure high accuracy. The signaling system varied from one type to the other, the G series using relays, the I series using caesium clocks, and the M series using rubidium clocks.

Beidou DW5 took an orbit that had never been seen before: the inclined synchronous. This was the first of the I or IGSO series, with two more and two

spares following in quick succession within the next 18 months (DW7, 8, 9, and 10). Satellites which circle the Earth every 24 hr had always been positioned over the equator but, this time, the Beidou was inclined in high orbit 55° above the equator, presumably to look down over the northern Chinese landmass.

After this, there was a return to the original Beidou model of 24-hr geosynchronous orbit over the equator (DW3, 4, 6, 11). By summer 2012, the system comprised 13 satellites – four GEO, six inclined synchronous, and three MEO – and was on course for completion of the full system, making it by any standards a significant national project.

The extent of use of the system was unclear. As was the case with GLONASS in Russia, the system was principally used by the public sector, where it had at least 40,000 customers. The value to the economy was estimated to be ¥50bn, scheduled to rise to ¥225bn (€25bn) by 2015. Most individuals continued to use the American GPS. Planned economies were notoriously slow to promote navigation satellites with ordinary consumers, with Russia only persuaded to do so when President Putin saw its value in relocating his lost dog to whom a receiver had been attached. One application was the fishing industry, where more than 30,000 receivers were installed on fishing boats. The lead had been taken by Hainan’s regional government, which began by installing 6,000 receivers at a cost of ¥79m (€10m), requiring the fishermen to pay 10% of the costs. China has over a million fishing boats, but hardly any of them had modem safety devices and the Beidou terminal could also be used to send distress calls. The series is summarized in Table 6.10.

Table 6.10. Beidou series.

Synchronous, 140°E Synchronous, 80°E Synchronous, 110.5°E Probable failure 55°, medium

Synchronous, 85°E, probable failure

Synchronous, 160°E, later 140°E

Synchronous, 84.6°E

55° inclined synchronous, 118°E

Synchronous, 160°E

55° inclined synchronous, 118°E

55° inclined synchronous, 118°E

55° inclined synchronous, 93°E, spare

55° inclined synchronous, 93°E, spare

Synchronous, 58.6°E

55°, medium

All from Xi Chang. Inclined orbits highlighted in italics.