The Global Positioning System (GPS) Block II Replenishment (IIR) space vehicle (SV) has made up at least one-half of the GPS constellation since 2006. This consists of the 12 original 'classic' IIR SVs and the eight 'modernized' IIR-M SVs. As a stepping-stone toward the IIR-M modernization, Lockheed Martin developed and deployed an updated version of the satellite antenna panel for the L-band broadcast signal. This is the signal used by the worldwide GPS user population. This paper describes both antenna panel versions, their broadcast signal patterns, the performance observed in factory testing, and their on-orbit performance. This is the initial publication of these antenna panel patterns. Ground and on-orbit measurements of both versions of the antenna show that all specification requirements are exceeded. They also reflect the increased antenna gain for the new IIR antenna. The L1 signal shows an increase of 1 dB in received power at edge of Earth, and L2 shows an increase of 2 dB in received power. All users, both terrestrial and on-orbit, benefit from this enhanced power profile.
There are now at least six new Block IIR space vehicles in the GPS constellation. Five were made active in a relatively short span of 13 months from early 2000 through 2001. The oldest now has a track record of over 5 years of quality performance. An additional 14 have been built for launch over the next 5 years. Has navigation accuracy been any better as a result? What will it be like with the rest of the IIRs available? Have there been as many outages? Examination of the constellation performance with the Block IIRs added to date shows both increased navigation accuracy and increased availability of a healthy signal. This paper analyzes this improved performance in detail. It also examines the expected trend toward even greater accuracy and availability in the future as more IIRs become the backbone of the constellation. Finally, the new Block IIR modernization features are highlighted.
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