It’s a lesson that we’ve all learned as children. Don’t put all your eggs in one basket. Why? Simple. If you drop the basket you lose everything. Essentially the lesson teaches us not to focus all [effort, resources, etc] into one thing. In engineering we might refer to this as a ‘single point of failure’ or a system with no ‘dissimilar redundancy.’

What is dissimilar redundancy? Well, a backup system can be referred to as a redundant system. However, if the backup system works exactly the same way as the primary system, then both are susceptible to what is known as a ‘common mode’ failure. Let’s take satellite-based navigation systems as the example in point for this post. The United States system is known as GPS and Europe is in the process of fielding a satellite system known as Galileo. Once Galileo is fully operational, it would be redundant to have both a GPS and a Galileo receiver (or a receiver that was able to process signals from both systems). This is a good thing. If there is a glitch in the systems that control the GPS satellites, for example, Galileo will be unaffected. However, GPS and Galileo are not dissimilarly redundant. A particularly massive solar storm (bursts of energy from the Sun that cause the Northern lights) could theoretically affect all satellite systems and thus GPS and Galileo service would be affected simultaneously.

In recognition of this, Britain has made operational a backup navigation system known as eLoran. eLoran is an ‘enhanced’ or modernized version of Loran (Loran was originally developed during WWII and was upgraded from the 1950s through the 1980s). Loran (LOng RAnge Navigation) is a system consisting of ground-based transmitters that operate at a very low frequency (100 kHz). GPS, in contrast, operates at an extremely high frequency (~1.6 GHz) in addition to operating with space-based transmitters. Since eLoran operates completely differently than satellite-based navigation systems, it is dissimilarly redundant. The error modes that adversely affect GPS will not affect eLoran and vice-versa. An operator that has both GPS and eLoran will have high confidence that they will be able to continue to navigate even if one system is degraded or even completely unavailable. Since the British eLoran system covers the North Sea area, vessels operating in this region will benefit. [It’s important to note that the five Loran transmitters used in the British eLoran system only provide coverage over Britain and parts of western Europe]

The synergistic natures of GPS and Loran were researched extensively in the United States back in the 1980s. Loran was pioneered in the United States and by the late 1980s Loran provided coast-to-coast coverage. However, the growing interest and utilization of GPS in the 1990s led to Loran being viewed as an unnecessary government expense. After various budget battles, the U.S. government decommissioned its Loran stations in 2010. Not long afterward, however, the threat to GPS by intentional interference and jamming (even in non-wartime, domestic situations) became undeniable. In an effort to save a relatively small amount of money, the U.S. government had turned off the only viable backup to GPS [note: the distance measuring equipment (DME) network is a backup that is applicable to aviation users only].

A recent media report indicates that Congress wants to put eLoran back on the table as a possible GPS backup. Britain is very wisely not waiting to see what the U.S. will do. More details can be found in reports by the Financial Times and by BBC News.