The System: eLoran Operational on Eastern UK Coast - GPS World

The System: eLoran Operational on Eastern UK Coast

December 1, 2014  - By
Bridge of the Galatea, a GLA vessel that carries a eLoran receiver and conducted tests of the new system.

Bridge of the Galatea, a GLA vessel that carries a eLoran receiver and conducted tests of the new system. Photo: GLA

Back-up to Vulnerable GPS Signals Required for Busy Shipping Lanes

The General Lighthouse Authorities (GLAs) of the UK and Ireland announced October 31 the initial operational capability of UK maritime eLoran. Seven differential reference stations now provide additional position, navigation, and timing (PNT) information via low-frequency pulses to ships fitted with eLoran receivers. The service will help ensure they can navigate safely in the event of GPS failure in one of the busiest shipping regions in the world, with expected annual traffic of 200,000 vessels by 2020.

Ships carry 95 percent of UK trade, accounting for its strongly expressed concerns regarding GPS vulnerability to jamming and spoofing, and the leadership role it has taken in eLoran research and testing. The UK is the first country in the world to deploy the technology along its coastline, thronged with both passenger and cargo services. Deployment involved replacing the existing radio receiver equipment in two prototype reference stations at Dover and Harwich, and the creation of five new reference stations in the Thames, Humber, Middlesbrough, and Firth of Forth and Aberdeen in Scotland, on the North Sea where oil-laden vessels come from deep-sea drilling rigs.

Entirely independent of GPS, eLoran can provide navigation information for vessels as well as the timing data necessary to maintain the power grid, cell phones, financial networks, and the Internet in the event of an outage. Unlike space-based navigation, eLoran signals can also reach inside buildings, underground, and underwater.

Captain Ian McNaught, deputy master of Trinity House, commented, “eLoran provides a signal around 1 million times more powerful than those from satellite signals, providing resilience from interference and attack. The achievement of initial operational capability for the system at Dover and along the east coast of the UK is a significant milestone, providing for improved safety aboard appropriately equipped vessels. The maritime industry would now benefit from the installation of eLoran receivers on more vessels to take advantage of improved navigational safety.”

“Telecoms, finance, energy, and other industries, which are subject to significant issues caused by the loss of timing signal provided by GPS, are recommended to take advantage of the enhanced reliability now available to address the over-dependence of key national infrastructure on vulnerable satellite systems,” McNaught said.

eLoran technology is based on longwave radio signals and is independent and complementary to GPS.

Several other nations are consulting with the UK GLAs on eLoran. South Korea wants to establish an eLoran alliance with the UK while it pursues its own rollout of differential eLoran reference stations and new eLoran transmitters based on the latest technology. In 2012, South Korea was the victim of a 16-day GPS jamming attack by North Korea.

Full operational capability covering all major UK ports is expected by 2019.

Galileo Roving High

The fifth Galileo navigation satellite, one of two left in the wrong orbit in August, made a series of November maneuvers as a prelude to its health being confirmed. The aim was to raise the lowest point of its orbit — its perigee — to reduce the radiation exposure from the Van Allen radiation belts surrounding Earth, as well as to put it into a more useful orbit for navigation purposes.

Should the two-week operation prove successful, the sixth Galileo satellite will follow the same route, according to the European Space Agency (ESA).

The Galileo pair, launched together on a Soyuz rocket on August 22, ended up in an elongated orbit traveling out to 25,900 kilometers (km) above Earth and back down to 13,713 km. The target orbit was a purely circular one at an altitude of 23,222 km. Also, the orbits are angled relative to the Equator less than originally planned.

The two satellites have only enough fuel to lift their altitude by about 4,000 km — insufficient to correct their orbits entirely. But the move will take the fifth satellite into a more circular orbit than before, with a higher perigee of 17,339 km.

“The new orbit will fly over the same location every 20 days,” said Daniel Navarro-Reyes, ESA Galileo mission analyst. “The standard Galileo repeat pattern is every 10 days, so achieving this will synchronize the ground track with the rest of the Galileo satellites.”

“In addition, from a user receiver point of view, the revised orbit will reduce the variation in signal levels, reduce the Doppler shift of the signal, and increase the satellite’s visibility,”  Navarro-Reyes said. “For the satellite, reducing its radiation exposure in the Van Allen radiation belts will protect it from further exposure to charged particles. The orbit will also allow Galileo’s Earth Sensor to hold a stable direction for the satellite’s main antenna to point at Earth. Right now, when the satellite dips to its lowest point, Earth appears so large that the sensor is unusable. The satellite relies on gyroscopes alone, degrading its attitude precision.”

The recovery is being overseen from the Galileo Control Centre in Oberpfaffenhofen, Germany, with the assistance of ESA’s Space Operations Centre, ESOC, in Darmstadt, Germany. France’s CNES space agency is providing additional ground stations so that contact can be maintained with the satellite as needed, ESA said.

Welcome IIF-8

The U.S. Air Force launched the eighth GPS IIF satellite on October 29, aboard an Atlas V 401 rocket. With this new arrival on orbit, only four more Block IIF satellites remain to be placed aloft. Three are in storage awaiting launch, and one is in production.

The Boeing-built GPS IIF-8 (SVN-69/PRN-03) will replace SVN-51 in the E plane slot 1. SVN-51 will be re-phased from E1 to an auxiliary node at E7 somewhere around SVN-54 currently on station at E4, according to the Air Force Second Space Operations Squadron (2 SOPS).  SVN-38/PRN-08 will be taken out of the operational constellation prior to SVN-69 payload initialization and sent to Launch, Anomaly Resolution and Disposal Operations (LADO).  PRN-08 will be assigned initially to SVN-49 and set to test.

SVN-51 will remain in an auxiliary node once it completes its re-phase journey. The SVN-51 re-phase will take about six months after the initial burn occurs.

About the Author: Alan Cameron

Alan Cameron is the former editor-at-large of GPS World magazine.