The GPS Observer: Changes are coming ... Eventually.
November 1, 2008
We constantly hear about the speed of technological innovation in today’s society. But changes in GPS satellite technology come slowly. Unlike the auto industry, it’s not necessary to come out with a different model each year.
Over the last 30 years, 60 GPS satellites have been built. The Block I satellites were launched from 1978 to 1985; of the 11 satellites built, one failed to reach orbit. The Block II and IIA satellites were launched from 1989 to 1998; 28 satellites were built, and all were successfully launched. Twenty-one Block IIR/IIR-M satellites were built; the first was launched in 1997 but failed to achieve orbit. Eighteen of the remaining 20 are on orbit, while two are on the ground ready for deployment.
In total, 58 GPS satellites have been launched; 56 of these satellites launched successfully, while two failed to reach orbit. Two additional satellites are awaiting launch. Thirty-one satellites are still on orbit--and one has been in operation for 17 years. Considering that the original design life for the satellite was seven and a half years, this has been a successful project.
Launch Failures and Delays
Originally scheduled for June 2008, the launch of the next GPS satellite, GPS IIR-20(M), has been delayed because of a faulty component in the Delta II rocket. At press time, the launch was scheduled for 2009. The Air Force reported that the questionable component is the 40-second timer that triggers separation of the third stage booster from the GPS space vehicle. The problem was detected in prelaunch testing at the Kennedy Space Center in Florida. On a side note, the 40-second timer problem has also delayed the launch of GPS IIR-21(M).
GPS IIR-20(M) is a crucial satellite because it has a civil L5 test signal in the navigation payload. At 1176.45 MHz, the L5 signal, which will be the third frequency on all Block IIF satellites, is a protected aeronautical radio-navigation service band. The signal needs to be transmitted from a satellite on orbit by Aug. 26, 2009, to meet the International Telecommunications Union (ITU) deadline for the L5 frequency allocation. In my July column, I discussed the same launch delay problem with the Galileo constellation. Because of these delays, the first Galileo satellite launched, GIOVE-A, had an onboard signal generator that allowed the satellite to successfully broadcast the Galileo signals allocated by ITU.
The last thing the Air Force needs is another failed launch; a single failed launch is a loss of more than $100 million. For the two satellites that failed to reach orbit previously, the rockets were determined to be the cause of the failure. With any luck, resolving the Delta II rocket problem will simply be a matter of ordering some new parts.
Block II Updates
Block IIR satellites perform a variety of tasks that are different from Block I and Block II/IIA satellites. The letter “R” stands for replenishment; when an on-orbit satellite is to be taken out of service, a IIR is launched and positioned in the same orbital plane. On Sept. 26, 2005, IIR-13 was launched with the L2C signal to be broadcast on L2. This was the first of the IIR-M (military) satellites, and it began broadcasting on Dec. 16, 2005.
Since then, five more IIR-M satellites have been launched. The two satellites on the ground, IIR-20(M) and IIR-21(M), will also broadcast L2C in preparation for the launch of the Block IIF constellation. GPS receiver manufactures are already producing receivers that can receive L2C. The L2C signal only works (efficiently) with the C/A code, and the C/A code will be on L1 on all Block IIF satellites.
Surveyors must keep in mind that L2C and L5 are primarily for the civil community, which uses point positioning (e.g., hobbyists, car navigation, 911, etc.). In the future, the codes will help in relative positioning since all that’s required for relative positioning is to receive codes on two different frequencies. After there are enough satellites with L2C and/or L5, my crystal ball tells me receiver manufacturers will cease working with the encrypted P-code on L1 and L2 and use L2C and/or L5 for the second code. The difference between the codes is that L2C is modulated on L2 and L5 is a separate frequency.
When will the first Block IIF satellite be launched? The first schedule I heard was February 2009, but the 40-second timer problem on the Delta II launch vehicle may postpone the Block IIF launch until May 2009. New rockets will be used on Block IIF launches. The first block IIF satellite will be aboard a Delta IV launch vehicle; the Air Force says the IIF spacecraft is capable of launching on both Atlas and Delta IV boosters.
Looking to the Future
As of this writing, only two Galileo satellites have been launched. The program objective is to have 30 satellites on orbit and the ground facilities operational by 2013. An interesting side note is that the tender agreement for prime contracts is limited to natural or legal persons established in one of the member states of the European Union. If you read this agreement in more detail, Canada is considered part of this group. Novatel, located in Calgary, Alberta, was awarded a contract by the Canadian Space Agency to extend the GIOVE-A monitoring ground network into Canada, and it is part of a team developing a reference receiver for the Galileo ground-control network.
Even though only two Galileo satellites have been launched, an interesting research project conducted at Germany’s University FAF Munich researched indoor positioning using the signals from Galileo. Dr. Gunter Hein and Andreas Teuber worked on this project and published a three-part series on it in Inside GNSS. I have met Hein; he is a geodesist by education, a member of the European Commission’s Galileo Signal Task Force and an organizer of the annual Munich Satellite Navigation Summit. Hein and Teuber simulated the Galileo satellite with a helicopter and positioned six receivers at different locations inside a building. Their major conclusion is that a lot more time and effort will be needed before the indoor performance of GNSS will be comparable to its outdoor performance.
Block II/IIA, Block IIR, Block IIR-M, Block IIF, Galileo, Glonass, perhaps satellites from China and India--someday we may need receivers as big as the dashboard of a car. Changes are coming but not that fast. GPS Block III is on the far horizon. On GPS III, the C/A code will disappear and be replaced with a modern code. But for surveyors, most of the receivers in use will work for some time, although that period of time is impossible to define.
1 “Faulty Booster Component Delays IIR-M Launches,” Inside GNSS, July/August 2008.
2 “GNSS Indoors: Fighting the Fading,” Inside GNSS, Part 1 (March/April 2008), Part 2 (May/June 2008) and Part 3 (July/August 2008).