This column includes updates on the Global Navigation Satellite System (GNSS) scene, as well as an update on U.S. Global Positioning System (GPS) satellites. It has been announced in various publications that both China and India are making plans to create their own GPS equivalents. In related news, the oldest operating GPS satellite was recently decommissioned from active service.



Figure 1. Plot showing visibility times for all operational GPS satellites. Courtesy of Dr. Charles Ghilani.

China

As reported in POB’s “Newsline” in February and April 2007, China has been successfully launching more Beidou satellites. China’s Beidou-1 satellites are dual-way transmission satellites in geostationary orbits. A geostationary satellite is positioned twice as high as a GPS satellite, having an orbital period of 24 hours less 3m 56s; they are also referred to as being in a sidereal orbit. The orbital plane rotates at the same rate as the Earth’s rotation, never changing in longitude.

Last October, China announced it would build a full-fledged GNSS based on its current satellite navigation system, which has the Beidou-1 satellites on orbit. This new system, to be known as the Compass Navigation Satellite System (CNSS), will be able to provide navigation and positioning services to users in China and its neighboring countries by 2008. CNSS will be expanded into a system of five geostationary satellites and 30 medium Earth orbit satellites. Unlike the current Beidou Satellite Navigation Experimental System, the new CNSS will allow a ground receiver to calculate its position by determining the distance between itself and three or more satellites, similar to the method of operation of GPS and the Russian GLONASS system.

The first of these new satellites, named Beidou-2, was successfully placed into orbit earlier this year. An ACZ-3A three-stage space launch vehicle carrying the satellite lifted off from Xichang Satellite Launch Centre at 16:28 GMT on Feb. 2, 2007. The three existing Beidou-1 satellites are in geostationary orbital planes with positions 80o E, 110.5o E and 140o E. This new Beidou-2 satellite was positioned into another geostationary orbital plane at 58.75o E or 160o E. As reported in this month’s “Newsline” (see page 12), another Beidou-2 satellite is now on orbit in the last open geostationary orbital plane.

Next, China will begin launching the medium Earth satellites, which will be compatible with GPS and the European Union’s Galileo system. According to an October 2006 announcement, the system will transmit signals in the L1 band where GPS and Galileo military and public services are located.

In addition, I find it surprising that China is a partner in the Galileo project. China invested 200 million euros in Galileo under a 2000 agreement with the European Union.



India

There are currently a few reports circulating on India’s involvement in the GNSS scene. One is that India intends to use the Russian GLONASS navigation system. Another is that India will build an independent satellite navigation system. Also, like China, India has a financial stake in Galileo; this took place in 2005.

It has been reported that India and Russia will jointly develop the GLONASS-K satellite. GLONASS-K is the third satellite in the GLONASS series; it will have a third civil frequency and a longer design life. Additionally, six GLONASS-K satellites will be able to be launched at one time. According to a press release dated Sept. 1, 2006, Russian President Vladmir Putin signed space cooperation agreements during a visit to India.

In addition, other reports dating from July 2006 state the Indian government’s plans to build an independent satellite navigation system using homegrown components. The project, called the Indian Regional Navigation System, will be implemented over the next five or six years and will consist of a constellation of seven or eight satellites as well as a large ground segment. The space segment will be dual-frequency (L1 & L5) GPS-compatible on India’s GSAT-4 satellites. The ground segment will consist of eight reference stations, a master control center, a land uplink station, and associated navigation software and communication links.

Why are India and China now building their own systems? I think it’s because delays in Galileo development have caused a lot of frustration. There’s no way Galileo will be even partially operational by 2008 as reported.



GPS Update

The purpose of the GPS Block IIR satellites is to replenish the system when the older Block II and Block IIA satellites cease being operational.

GPS satellite PRN 15 (also named SVN 15) was decommissioned from active service on March 14, 2007. The satellite was launched Oct. 1, 1990, and put into operation Oct. 15, 1990. That’s a lifetime just one day short of 16 years and 5 months, but it had been unusable for a period of time before being decommissioned.

Satellite PRN 15 was in slot D5. The day after the satellite was decommissioned (March 15), I received a telephone call from a surveyor who said he was having a problem with PRN 24. On March 16, a report came out from the U.S. Naval Observatory stating that PRN 24 was unusable from 1703 to 2238 UT due to repositioning. PRN 24 is in slot D6, and with PRN 15 no longer usable, PRN 24 was moved to a different position in the D plane. This notice was posted before the satellite was unusable, allowing users to prepare for the occurrence. It pays to look at these daily reports from the U.S. Naval Observatory and the U.S. Coast Guard.

A new Block IIR-M satellite will replace PRN 15. As stated in my last column (March 2007), PRNs 12, 17 and 31 are operational Block IIR-M satellites. Figure 1 on page 48 shows satellite visibility from January 2007 generated by Dr. Charles Ghilani of Pennsylvania State University. If you look closely, you can see that only two Block IIR-M satellites are visible at the same time, and a minimum of four are needed to get a position. It may be quite some time before enough older satellites are replaced to make that portion of the system operational. There is one active satellite that was launched in 1991 and five launched in 1992--not too bad for satellites with a design life of seven and a half years.