Ciaran Murphy, QinetiQ
Ciaran explained that GPS started following the launch of the Russian artificial satellite ‘Sputnik’ back in 1957. To connect with us mortals on earth it gave out a regular signal and due to the ‘Doppler’ effect it was possible to learn its position above earth. The wavelength or ‘signal’ is shorter and the frequency higher when close and longer and lower when further away. Hence you are able to judge when emergency vehicles are coming closer to you.
GPS however really only came into effect in 1995. It cost the Americans $20bn to develop and their system costs $1bn to run every year. In the first instance they thought that perhaps 10k ordinary people may find the technology useful. Well here we are in the 21st Century and GPS is ubiquitous - where would we be without it. Our phones, our cars and our lives rely on the technology.
To run the global navigation satellite system (GNSS) the Americans have GPS, the EU has Galileo, the Russians have Glonass and the Chinese have BeiDou (BDS).
There are three satellite orbits with the Low Earth Orbit being between 99-1,243 miles out and the furthest away being the Geostationary orbit at 22,236 miles.
Medium Earth Orbit (MEO) satellites represent only 10% of the satellites orbiting the earth, however they are the ones that are used almost exclusively for GPS and related services. These orbit at 5,000miles (8,000km) to 12,500 miles (20,000km) out. There are 31 of them however only 24 are needed to provide the service.
Ground stations correct the satellites position or time, to the nanosecond. Correct time is the key to the positioning system. Without the invention of the clock in the mid 1720’s by John Harrison none of this would have been possible. ‘Time is of the essence’.
How does this relate to me and my life? Well, if you use a mobile phone for navigation or use satellite navigation in your car your position will be accurate to around 5 metres. There is also the Inertial Measurement Unit or (IMU) which enables your car’s position to be known through motion analysis when you are not able to receive a signal from a satellite. For example when you are driving through a tunnel.
Naturally there are threats to these systems and GPS ‘spoofing’ is the main one. This is using a radio transmitter to interfere with the actual GPS signal being transmitted.
In today’s world of most concern would be ‘spoofing’ autonomous vehicles however as safety is at the forefront the human behind the wheel currently has to be present to intervene. With no driver present however, if there was ‘spoofing’, the car would stop if in danger though the route the car was programmed to take could be changed. We are entering an era when there is much to be learned about our way forward with self-driving vehicles.
Once again we had an excellent attendance and Mike concluded the evening after Ciaran had answered the questions that were not company sensitive. He thanked Ciaran for his insight into the world of GPS.
Finally, Mike reminded members that our next meeting on Tuesday 20 May is a presentation by Max Hunt on Shelsley Walsh, the hill climb venue and its surrounding history.
