GPS BIIR-11 (PRN 19)

GPS BIIR-11 (PRN 19), catalogued by NORAD as object 28190 and carrying the international designator 2004-009A, is an American navigation satellite operating as part of the Global Positioning System constellation. Launched on March 19, 2004, it is operated by the United States Air Force and was manufactured by Lockheed Martin. Known also by its military designation USA-177, this satellite represents one component of the sustained infrastructure that underpins satellite-based positioning, navigation, and timing services relied upon by civilian and military users worldwide. As of the most recent catalog data, the satellite remains in orbit.

Mission and Purpose

GPS BIIR-11 is a member of the Block IIR ("Replenishment") series of GPS satellites, a generation designed to sustain and replenish the operational GPS constellation as earlier Block II and Block IIA satellites aged out of service. The Block IIR satellites were conceived to carry on the fundamental mission of the Global Positioning System: broadcasting precise timing and ranging signals that allow receivers on the ground, at sea, in the air, and in space to determine their location with high accuracy.

The Global Positioning System was originally developed under the auspices of the U.S. Department of Defense and has since grown into an essential global utility. GPS satellites continuously transmit signals on multiple radio frequencies; receivers calculate their position by measuring the time it takes signals from several satellites to arrive simultaneously. The integrity of this service depends on maintaining a sufficient number of healthy satellites in well-distributed orbital slots at all times, which is precisely the role the Block IIR series was designed to fulfill.

GPS BIIR-11 was the eleventh of thirteen Block IIR satellites launched in the original, unmodified configuration — sometimes referred to as the "baseline" IIR variant — and ranked twenty-first among all GPS satellites launched up to that point in the program's history. The satellite is also identified within the GPS system by the designations GPS IIR-11 and GPS SVN-59, with PRN code 19 assigned to it for signal identification purposes. PRN (Pseudo-Random Noise) codes are the unique spreading sequences used to distinguish the signals of individual GPS satellites from one another; PRN 19 identifies this satellite's broadcast channel within the constellation's signal architecture.

Although the mission type and current operational status are not formally recorded in the public satellite catalog, Block IIR satellites as a class were designed with extended on-orbit operational lifetimes and included autonomous navigation capabilities — meaning they could, under certain conditions, maintain accurate time and position data without continuous contact from ground control stations, a significant resilience improvement over earlier GPS generations.

Orbit and Tracking

GPS BIIR-11 occupies a Medium Earth Orbit (MEO), the orbital regime characteristic of the entire GPS constellation. The satellite's tracked orbital parameters place its apogee at 20,498 km and its perigee at 19,882 km above Earth's surface, yielding a nearly circular orbit with only modest eccentricity. Its orbital inclination is 54.8°, and it completes one full revolution of the Earth approximately every 718.0 minutes — just under twelve hours.

This roughly twelve-hour orbital period is a defining feature of GPS satellites. Because the period is almost exactly one-half of a sidereal day, a GPS satellite returns to nearly the same position in the sky relative to a fixed point on Earth's surface after approximately 24 hours, producing a highly repeatable ground track. This characteristic simplifies the planning of ground-station contacts and contributes to the constellation's predictable geometry as seen by users around the globe.

The GPS constellation is organized into orbital planes distributed around the Earth at evenly spaced longitudes, with multiple satellites in each plane. The 54.8° inclination of the Block IIR satellites ensures coverage extends to high latitudes, giving users in the Arctic and Antarctic regions reasonable access to GPS signals for significant portions of each day, while the MEO altitude provides each satellite with a wide field of view that allows a single spacecraft to serve users across a large swath of Earth's surface simultaneously.

NORAD tracks GPS BIIR-11 under catalog number 28190. Its orbital elements are regularly updated through the U.S. Space Surveillance Network and published in the form of Two-Line Element sets, which form the basis for the tracking data displayed on this page. The satellite's orbit is relatively stable at MEO altitudes, where atmospheric drag is negligible, though long-term perturbations due to solar radiation pressure, lunar and solar gravitational influences, and Earth's non-uniform gravitational field must be periodically managed by ground controllers.

Design and Operator

GPS BIIR-11 was built by Lockheed Martin on the AS-4000 satellite bus, a platform Lockheed Martin developed specifically to support the GPS Block IIR program. The AS-4000 bus was designed with robustness and longevity in mind, providing the structural, power, thermal, and attitude-control subsystems necessary to sustain navigation payloads through extended operational lifetimes in the relatively harsh MEO radiation environment. Medium Earth Orbit exposes satellites to elevated levels of energetic particle radiation, particularly from the Van Allen belts, placing demanding requirements on the radiation hardening of onboard electronics.

The Block IIR design introduced several improvements over the Block IIA generation it followed, most notably the autonomous navigation (AutoNav) capability mentioned earlier, as well as crosslink ranging — the ability for satellites to measure distances to one another directly, further enhancing the constellation's independence from continuous ground contact. These features gave the IIR series enhanced operational resilience compared to predecessor satellites.

The operator of record is the United States Air Force, which historically managed the GPS constellation through its Space and Missile Systems Center. Operational control of the constellation is exercised from the GPS Master Control Station. In subsequent years, organizational responsibility for military space systems, including GPS operations, has transitioned within the U.S. defense establishment, but the Air Force remains the owner-operator on record for satellites of this generation. The owning country is the United States. No mass figure for this specific satellite is publicly recorded in the catalog.

Significance and Status

GPS BIIR-11's place in the Block IIR series situates it at an important juncture in the long-term evolution of the GPS program. The Block IIR satellites, launched between 1997 and 2004, bridged the transition between the program's early operational phases and the subsequent Block IIR-M and Block IIF generations, which introduced modernized signals including new civilian and military frequencies. The thirteen baseline IIR satellites, of which GPS BIIR-11 is one, carried the traditional GPS signal set.

The launch in March 2004 came at a period of active GPS modernization planning, when the U.S. government was expanding civilian access to GPS and investing in signal improvements that would eventually be implemented on later satellite blocks. Satellites like GPS BIIR-11 maintained constellation availability during this transition, ensuring service continuity for the growing global base of GPS users — which by the mid-2000s had expanded dramatically into consumer electronics, precision agriculture, aviation, maritime navigation, surveying, and emergency services.

The satellite's longevity is notable. Block IIR satellites were designed with operational design lives intended to sustain the constellation across planned replenishment cycles, and GPS BIIR-11 remains in orbit more than two decades after its launch, a testament to both the engineering durability of the Lockheed Martin AS-4000 bus and the careful stewardship of the constellation by U.S. Air Force operators. Its current operational status within the GPS constellation — whether actively transmitting navigation signals, held in reserve, or decommissioned — is not reflected in the public catalog data available to this site, and users seeking up-to-date constellation health information should consult official GPS status resources published by the U.S. government.

As a navigational asset at medium Earth orbit, GPS BIIR-11 is not observable to the naked eye under normal circumstances and does not appear in lists of optically bright satellites. Its contribution is invisible to users — embedded in the nanosecond-level timing pulses that connect smartphones, aircraft navigation systems, and precision instruments to a common, highly accurate frame of reference — yet it represents one durable node in an orbital network that has become foundational to modern life.