USA-175: The Legacy of the GPS Block IIR-10 Satellite
The Global Positioning System (GPS) relies on a precise constellation of satellites to provide accurate positioning and timing data worldwide. One such critical component was USA-175, also identified as GPS IIR-10 and GPS SVN-47. As the tenth Block IIR satellite launched, it played a vital role in the American navigation infrastructure for nearly two decades.
Key Facts
- Operator: US Air Force
- Manufacturer: Lockheed Martin
- Launch Date: December 21, 2003
- Mission Duration: 18 years (exceeding the 10-year design life)
- Orbit Type: Medium Earth Orbit (Semi-synchronous)
- Deactivation Date: January 18, 2022
Technical Specifications and Construction
USA-175 was built by Lockheed Martin using the AS-4000 satellite bus, which serves as the structural and electrical framework of the spacecraft. With a launch mass of 2,032 kilograms (4,480 lb), the satellite was engineered for durability and precision in the harsh environment of space.
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Launch and Deployment
The satellite was launched at 08:05:00 UTC on December 21, 2003, from Space Launch Complex 17A at the Cape Canaveral Air Force Station. It was carried into space by a Delta II 7925-9.5 rocket (flight number D302). After reaching a transfer orbit, the spacecraft utilized a Star-48 apogee motor to raise itself into its final operational orbit.
Orbital Parameters and Operation
By February 22, 2004, USA-175 had achieved its target Medium Earth Orbit (MEO), a semi-synchronous regime where the satellite's orbital period matches a fraction of the Earth's rotation. This positioning is essential for maintaining consistent coverage of the Earth's surface.
The satellite operated in slot 2 of plane E within the GPS constellation, broadcasting the PRN 22 signal. Its orbital characteristics included a perigee (the lowest point of the orbit) of 20,043 kilometres and an apogee (the highest point) of 20,319 kilometres, with an inclination of 55.1 degrees relative to the equator.
| Parameter | Detail |
|---|---|
| COSPAR ID / SATCAT | 2003-058A / 28129 |
| Launch Mass | 2,032 kg |
| Orbital Period | 717.92 minutes |
| Inclination | 55.1 degrees |
| Planned Life | 10 years |
| Actual Life | 18 years |
Mission Conclusion
While originally designed for a mission duration of 10 years, USA-175 demonstrated remarkable longevity. It remained operational for 18 years before being decommissioned on January 18, 2022, as per the USCG Nanu 2022001 directive.
Frequently Asked Questions
What was the primary purpose of USA-175?
USA-175 was a navigation satellite used as part of the Global Positioning System (GPS) to provide accurate timing and positioning signals to users on Earth.
Who manufactured the USA-175 satellite?
The satellite was manufactured by Lockheed Martin using the AS-4000 satellite bus.
How long did USA-175 remain in service?
Although it had a planned design life of 10 years, the satellite achieved a total mission duration of 18 years before being deactivated in January 2022.
What rocket was used to launch USA-175?
USA-175 was launched using a Delta II 7925-9.5 carrier rocket (flight D302) from Cape Canaveral.
What is the significance of the PRN 22 signal?
The PRN (Pseudo-Random Noise) 22 signal is the specific identification code broadcast by USA-175, allowing GPS receivers to distinguish it from other satellites in the constellation.