USA-54, also known as GPS II-7 and GPS SVN-20, was an American

navigation satellite A satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). , four global systems are op ...

which formed part of the

Global Positioning System The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...

. It was the seventh of nine Block II GPS satellites to be launched, which were the first operational GPS satellites to fly.

Background

Global Positioning System (GPS) was developed by the

U.S. Department of Defense The United States Department of Defense (DoD, USDOD, or DOD) is an executive department of the U.S. federal government charged with coordinating and supervising the six U.S. armed services: the Army, Navy, Marines, Air Force, Space Force, t ...

to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces. Since its implementation, GPS has also become an integral asset in numerous civilian applications and industries around the globe, including recreational used (e.g., boating, aircraft, hiking), corporate vehicle fleet tracking, and surveying. GPS employs 24 spacecraft in 20,200 km circular orbits inclined at 55.0°. These vehicles are placed in 6 orbit planes with four operational satellites in each plane. GPS Block 2 was the operational system, following the demonstration system composed of Block 1 (Navstar 1 - 11) spacecraft. These spacecraft were 3-axis stabilized,

nadir The nadir is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direction opposite of the nadir is the zenith. Et ...

pointing using

reaction wheel A reaction wheel (RW) is an electric motor attached to a flywheel, which, when its rotation speed is changed, causes a counter-rotation proportionately through conservation of angular momentum. A reaction wheel can rotate only around its center ...

s. Dual solar arrays supplied 710 watts of power. They used

S-band The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave band of the electromagnetic spectrum covering frequencies from 2 to 4 gigahertz (GHz). Thus it crosses the convention ...

(SGLS) communications for control and telemetry and

Ultra high frequency Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...

(UHF) cross-link between spacecraft. The payload consisted of two

L-band The L band is the Institute of Electrical and Electronics Engineers (IEEE) designation for the range of Frequency, frequencies in the radio spectrum from 1 to 2 gigahertz (GHz). This is at the top end of the ultra high frequency (UHF) band, at t ...

navigation signals at 1575.42

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

(L1) and 1227.60 MHz (L2). Each spacecraft carried 2

rubidium Rubidium is a chemical element; it has Symbol (chemistry), symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have ...

and 2

Cesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals ...

clocks and nuclear detonation detection sensors. Built by Rockwell Space Systems for the U.S. Air force, the spacecraft measured 5.3 m across with solar panels deployed and had a design life of 7.5 years.

Launch

USA-54 was launched at 02:45:01 UTC on 26 March 1990, atop a

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...

launch vehicle A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...

, flight number D193, flying in the 6925-9.5 configuration. The launch took place from Launch Complex 17A (LC-17A) at the

Cape Canaveral Air Force Station Cape Canaveral Space Force Station (CCSFS) is an installation of the United States Space Force's Space Launch Delta 45, located on Cape Canaveral in Brevard County, Florida. Headquartered at the nearby Patrick Space Force Base, the sta ...

(CCAFS), and placed USA-54 into a transfer orbit. The satellite raised itself into

medium Earth orbit A medium Earth orbit (MEO) is an geocentric orbit, Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between above sea level.

using a Star-37XFP

apogee motor An apogee kick motor (AKM) is a rocket motor that is regularly employed on artificial satellites to provide the final impulse to change the trajectory from the transfer orbit into its final orbit (most commonly circular orbit, circular). For a ...

Mission

On 30 April 1990, USA-54 was in an orbit with a

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

of , an

apogee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

of , a period of 717.84 minutes, and 55.0° of

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

to the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

. The satellite had a mass of , and generated 710 watts of power. It had a design life of 7.5 years, however following problems with the satellite switching between timing standards, the satellite was declared unusable on 21 May 1996.

References

{{Orbital launches in 1990 GPS satellites USA satellites Spacecraft launched in 1990