Navigation Systems

9/30/2014: GPS Satellite background and update

The Coast Guard’s Navigation Center announced that the seventh GPS-IIF satellite, SVN-68/PRN-09, launched on 02 August 2014, was set to healthy and usable as of September 17, 2014. This brings the number of satellites transmitting the L2C signal to 14 and those transmitting the L5 signal to seven. The next GPS-IIF satellite, IIF-8/SVN-69 is tentatively scheduled for launch on October 29, 2014.

In an effort to put this into context for our readership, Maritime Commons reached out to the Civil GPS Service Interface Committee ’s, or CGSIC, Executive Secretariat for explanation.

Written by Rick Hamilton

The Coast Guard Navigation Center, or NAVCEN, is assigned duties, legacy from the Department of Transportation, as liaison between the world’s users of GPS and the U.S. GPS program authorities. The Federal Aviation Administration represents the aviation sector, the Air Force GPS Operations Center represents military users and NAVCEN represents maritime and terrestrial users of GPS signals. NAVCEN is assigned as Deputy Chair and Executive Secretariat for the U.S. government’s Civil GPS Service Interface Committee, essentially the operation arm of the Committee. As Executive Secretariat, I provide general information of interest to the members of the CGSIC.

This Notice Advisory to Navstar Users, otherwise known as NANU, notifies the public that the latest GPS satellite, a new Block IIF, launched on the 2nd of August -that’s Zulu time, 01 August local time- has completed its operational testing and has been set healthy to users. The NANU type is USABINIT, or Usable/Initial. The satellites are delivered in “Blocks,” Block I, Block II Block III, etc. Block IIF is the newest version of the satellites and this is how the satellite designations are broken down:

• IIA: These were the first operational constellation
• IIR: Replacement
• IIR-M: Replacement-modernized
• IIF: Follow-on, really the second generation of GPS satellites

The third generation is being developed and the first GPS-III satellite is tentatively scheduled for sometime in 2016.

All the satellites broadcast the L-band civil signal L1, the one you might use in your car or on the bridge of a Coast Guard cutter. Civilian users only use part of the L1 signal, the Coarse Acquisition Code, or CA Code, but maybe that is another story for another time. Beginning with the IIR-M satellites, a second civil signal (than L2C) began operation. This will give the civilian community the ability to use two-frequency operations like the military does, essentially solving for the atmospheric degradation of the accuracy. Beginning with the IIF satellites, the third civil signal started, L5, a signal intended to be used by aviation and located in a highly protected Aeronautical Radio Navigation Service band. GPS-III will bring the fourth civil signal, L1C, to civilian users around the world.

Much of the world is eagerly awaiting these new signals. L2C and L5 have only recently had their operational navigation messages activated in an experimental mode. The management of GPS satellites includes daily uploads, to steer the clocks for instance et al., but the Air Force is only doing uploads for L2C and L5 twice a week for now. Beginning in December, daily uploads will commence making these new civil signals fully operational like the legacy L1 and L2 signals. It is generally accepted that 18 GPS satellites on orbit transmitting a given signal are needed to consider it an initial operating capability, or IOC, and 24 will equal full operational capability, or FOC. The language I used to accompany the official NANU that came out for satellite vehicle number sixty-eight, or SVN-68, is merely an attempt to provide an ongoing tally of the number of satellites that carry the new signals as we progress toward an IOC/FOC.

This blog is not a replacement or substitute for the formal posting of regulations and updates or existing processes for receiving formal feedback of the same. Links provided on this blog will direct the reader to official source documents, such as the Federal Register, Homeport and the Code of Federal Regulations. These documents remain the official source for regulatory information published by the Coast Guard.