This year the Queen Elizabeth Prize for Engineering has gone to the team behind the Global Positioning System (GPS).
The prestigious prize was today awarded to Professor Bradford Parkinson, Dr James Spilker, Hugo Fruehauf and Richard Schwartz.
Professor Parkinson is known for his GPS applications such as the first automatic landing of a commercial aircraft and the first fully automatic control of farm tractors on a field to an accuracy of two inches (5 cms).
Dr Spilker is responsible for the GPS signal structure known as CDMA (code division multiple access). That structure is now used by 4 billion receivers. His delay lock loop process for tracking CDMA signals is the key component that enables the system and is essential to GPS accuracy.
Dick Schwartz has led many of successful space and satellite programs, including the first flights of GPS and the NASA Space Shuttle. Dick worked for the Rockwell corporation and became its GPS Satellite Program Manager. He commissioned Hugo Fruehauf, as Rockwell’s chief engineer, to produce a satellite design that could withstand intense radiation and have antennas that ensured uniform power.
What is GPS?
Today billions of people around the world rely on the GPS system and its huge engineering infrastructure that extends across our planet and into space.
GPS enables anyone with a smartphone to pinpoint exactly where they are on Earth, as well as the precise time, and is also used in applications that range from aviation safety and banking to locating and rescuing ships in distress.
It was the American Global Positioning System (GPS) – the world’s first global satellite radio navigation system – helped make this possible.
While GPS can provide location data for Google Maps and SatNav users the system is also used in a huge number of industries. The tech can be applied to everything from precision farming with GPS-guided tractors to the guidance of humanitarian supplies into conflict zones.
How does GPS work
GPS works using a constellation of orbiting satellites, ground stations (that operate and manage the spacecraft) and a receiving device.
Each satellite broadcasts a radio signal containing information about its location and the time from an extremely accurate onboard atomic clock.
It is because of this precision timing, accurate to within billionths of a second, that the system has become critical for financial transactions, cellular networks and power grids.
The system was first developed for military applications for Position, Navigation and Timing services, civilian GPS is now freely available for peaceful, commercial and scientific use.
Today billions of people now rely on this engineering infrastructure and, in 2011, the International Astronautical Federation selected GPS as the revolutionary space system that most benefited humanity during the first 60 years of human spaceflight.
The full GPS system requires a network of at least 31 operational satellites flying in Medium Earth Orbit at around 20,200 km (12,550 miles) above the Earths surface. With a baseline number of satellites of around 24 – 12 in each half of the globe.
Each GPS satellite makes a nearly circular orbit around the globe twice a day, equally spaced around the equator.
This means a user from virtually any place on Earth can access the system.
To get a GPS position you need access to a signal from at least four satellites, using a process called trilateration, are required for latitude, longitude, altitude and time. Each GPS satellite broadcasts on the same signal frequency and carries extremely accurate atomic clocks. It transmits both the spacecraft’s position and its time signal.
The radio signal broadcast is actually weaker than those from a light bulb and travel by line of sight. While the signal can pass through clouds, glass and plastic but are blocked by solid objects such as mountains or buildings.
When a GPS receiver on the ground picks up these radio signals and the exact time that the signal was broadcast, it can then measure the time delay (radio waves travel at the speed of light) and can then determine the its own distance from the satellite and location on Earth to within two metres, for civilian use, and – if on a moving vehicle – velocity.
GPS actually provides two signals. A Standard Positioning Service (SPS) for civilian use and a Precise Positioning Service (PPS) primarily for military use.
Who manages the GPS network?
The US Air Force (USAF) manages the GPS constellation and each satellite is in one of six orbits in order to provide continuous worldwide coverage.
Twenty-four satellites were launched between 1978 and 1994 and, because the satellites have a lifespan of 7.5-11 years, next-generation satellites began launching in 2005 onwards.
The satellites network is tracked by six USAF monitor stations around the world. Each of these stations has two caesium atomic clocks to check GPS system time.
