Global Positioning System Reference
In-Depth Information
ballistic missile program of 1956 . 58 Over several decades, the Delta rocket,
with subsequent upgrades, has been used extensively for both military and
commercial payloads. Between February 14, 1989, and August 17, 2009, Delta
II rockets carried forty-eight gps Block ii satellites into orbit.
The second block of gps satellites consists of four generations or groups of
updated and revised designs, with the following designations: 59
iia (“A” for advanced)—Nineteen satellites developed by Rockwell Interna-
tional were launched between November 1990 and November 1997.
Although designed to last seven and a half years in space, two have oper-
ated more than twenty years.
iir (“R” for replenishment)—Thirteen satellites built by Lockheed Martin
were launched between July 1997 and November 2004 to replace previ-
ous Block ii and iia satellites that had outlived their design life span. A
key improvement in these satellites was onboard clock monitoring, which
boosted accuracy and allowed longer intervals between ground station
updates.
iir(m) (“M” for modernized)—Eight satellites developed by Lockheed Mar-
tin were launched between September 2005 and August 2011. This design
added a second civilian signal (l2c) for better commercial performance
and two new, more powerful military signals with enhanced jam resis-
tance.
iif (“F” now stands for follow-on; earlier references used the word future )—
The first of twelve iif satellites, developed by Boeing (which acquired
Rockwell International's aerospace and defense businesses in 1996),
launched on May 27, 2010, with subsequent launches scheduled through
2013. These satellites boast a twelve-year life expectancy, more accurate
atomic clocks, and a third civilian signal (l5) for improved transportation
safety, especially aviation. (A new generation of satellites, Block iii, will
begin launching in 2015. See chapter 10.)
During the delay in gps satellite launches resulting from the Challenger disas-
ter, surveying equipment sales kept the commercial market growing and fueled
research and development of new gps applications at a faster rate than would
have occurred through defense contracts alone. 60 To address problems in the
field, advanced techniques and equipment evolved, such as the development
of complex interconnected receivers that correct for errors by calculating the
 
 
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