GPS World, March 2015

SYSTEM THE Policy and system news and developments GPS Galileo GLONASS BeiDou Leap Second Confusion T he United States Civil GPS Service Interface Committee CGSIC has issued a notice about a problem some receivers are having implementing the correct time The U S Coast Guard Navigation Center has received reports of synchronization issues since the implementation of a leap second on Jan 21 Users experiencing this problem should contact the receiver manufacturer for a firmware or software update Here is the text of the CGSIC notice All CGSIC 2015 GPS Future Leap Second Implementation The GPS 50 bit per second navigation message transmitted by each GPS satellite specifically Page 18 subframe 4 includes the parameters needed to relate GPS time to UTC Coordinated Universal Time That relationship is maintained through leap second implementation transitions by IS GPS 200 compliant user equipment For leap second transition user equipment must utilize the notice regarding a scheduled future delta time due to leap seconds ÄtLSF together with the week number WNLSF and the day number DN at the end of which the leap second becomes effective On or about Jan 21 2015 those GPS navigation messages began to include futurevleap second data which indicates an increase in the leap second to become effective at the end of June 2015 IS GPS 200 revision H dated 24 Sep 2013 paragraph 2033524 Coordinated Universal Time UTC documents the appropriate algorithm details to ensure correct utilization of the parameters above including all potential truncated week number transitions and variations in time of processing relative to satellite upload timing near the future leap second effectivity The data upload for the June 30 leap second initiated with SVN48 PRN07 at 18 33 56z on Jan 21 was correctly executed However there are several receivers brands models that seem to be mishandling this information and applying the leap second now This is creating a negative one second offset in faulty receivers The U S Coast Guard Navigation Center has reports of these receivers causing synchronization issues with radios computer systems and data logging equipment Users experiencing issues with GPS receivers that began on Jan 21 should contact the receiver manufacturer to determine if the latest firmware or software patch can correct the issue Air Force Orders Two More GPS III Satellites The third and fourth Galileo Full Operational Capability FOC satellites are a confirmed fit for their Arianespace Soyuz launch March 27 having made initial contact with the missions dualpayload The United States Air Force plans to order two more GPS III satellites from contractor Lockheed Martin Lockheed Martin is under contract to build eight GPS III satellites with the first planned to be launched in 2016 The contract includes options for up to four more satellites However the Air Force plans to open up construction of subsequent GPS satellites for competitive bidding with GPS III space vehicle 11 The satellites are part of the Air Forces 1673 billion budget request for fiscal 2016 up from 1528 billion provided by Congress for fiscal 2015 The Air Force also intends to buy only one GPS satellite from Lockheed Martin or a different contractor in 2017 rather than the three included in the current budget blueprint Galileo FOC Three and Four Fit to Fly dispenser in French Guiana according to Arianespace The fit check was completed over a two day period inside the Spaceports S1A payload preparation building The two satellites were installed separately with the Flight Model 3 FM3 spacecraft integrated on and subsequently removed from the dispenser on Feb 9 Flight Model 4 FM4 underwent the same process the following day The payload dispenser for Galileo was developed by RUAG Space Sweden for Arianespace and carries one satellite on each side It will deploy the spacecraft during the Soyuz launch by firing a pyrotechnic separation system to release them in opposite directions at the orbital insertion point Final integration on the dispenser will be performed during upcoming processing at the spaceport and will be followed by the completed units installation on Soyuz The March 27 mission designated Flight VS11 in Arianespaces numbering system will be the companys fourth launch carrying spacecraft for the Galileo constellation More System News Online See www gpsworld com GPS World March 2015 www gpsworld com 8