Question: Alternate position, navigation timing, APNT? Answer: ELORAN

The issue of a backup system for GPS has been discussed for years. This is particularly so when GPS became the backbone for so many systems which includes much more than just navigation. A U.S. presidential order issued in 2003 [1], required the Department of Homeland Security, DHS, in cooperation with the Department of Transportation, DOT, to develop an alternative position, navigation, and timing (APNT) system to use in case of loss or degradation of GPS. A year later the White House again addressed the problems with GPS degradation. [2] In 2012 DHS produced a report; “GPS National Risk Estimate”, NRE. (This document is for “official use only and not publically available.) The US Government Accountability Office, GAO, was tasked by Congress to assess the NRE and provide a report which was delivered in November 2013. [3] The GAO was critical of the NRE and offered several suggestions for a more accurate assessment. The United States, the owner and developer of GPS is not alone in its concern over an APNT, for global navigation satellite systems, GNSS. South Korea has experienced what appears to be deliberate jamming from the north over a period of three years, [4]. The jamming incidents lasted from 4 days to 16 days and have prompted South Korea to build an enhanced LORAN, eLORAN, system. [5] The use of GPS jammers to evade tracking by drivers, in particular of commercial vehicles, has been a problem in the United Kingdom, [6] and a man was fined US $32K for illegal use of a GPS jammer causing daily interference with Newark's Liberty Airport experimental ground-based augmentation system; GBAS. [7] Widespread jamming both deliberate and unintentional is expected to increase worldwide. Beyond jamming, electronics in space are subjected to a harsh environment from the sun. Solar radiation causes long term damage to electronics but this is accounted for in the design of spacecraft. However, sudden, intense radiation from the sun and energetic particles that occur during solar flares can cause temporary and permanent damage often requiring computers to be reset to restore normal operation. Some failures have been attributed to human error. In April 2014 the Russian GLONASS system was down for over 11 hours because of the uploading of ”bad ephemerides”. Two weeks later, another significant outage occurred. [8] Not all failures are due to satellite signals in space but GPS receivers. Again, in April 2014, the U. S. Coast Guard Navigation Center, USCG NAVCEN, received numerous reports of malfunctions associated with two pseudonoise sequences, PRNs. The Air Force GPS Operations center traced the problem to two recently-launched non-operational satellites that were undergoing testing. These satellites were set “unhealthy” in the almanac but certain model receivers attempted to include their data in the navigation solution producing significant errors.