GPS World, January 2011

INNOVATION GNSS Design Test N ASA which pioneered the technology used for the satellite aided search and rescue capability that has saved thousands of lives worldwide since its inception nearly three decades ago has developed new technology that will more quickly identify the locations of people in distress and reduce the risk to rescuers The Search and Rescue SAR Mission Offi ce at the NASA Goddard Space Flight Center in collaboration with several government agencies has developed a next generation satelliteaided search and rescue system called the Distress Alerting Satellite System DASS NASA the National Oceanic and Atmospheric Administration NOAA the U S Air Force the U S Coast Guard and other agencies are now completing the development and testing of the new system and expect to make it operational in the coming years after a complete constellation of DASSequipped satellites is launched When completed DASS will be able to almost instantaneously detect and locate distress signals generated by emergency beacons installed on aircraft and maritime vessels or carried by individuals greatly enhancing the international communitys ability to rescue people in distress This improved capability is made possible because the satellitebased instruments used to relay the emergency signals will be installed on the GPS satellites A recent satellite aided rescue started on June 10 2010 when 16 yearold Abby Sunderland on her 40 foot 122 meter sailboat Wild Eyes encountered heavy seas approximately 2000 miles 3200 kilometers west of Australia in the Indian Ocean Her sailboat was dismasted and an emergency situation resulted Ms Sunderland activated her two emergency beacons whose signals were picked up by orbiting satellites Using coordinates derived from the signals a search plane spotted Ms Sunderland the next day and a day later she was rescued by a fi shing boat directed to the scene This highly pub The Distress Alerting Satellite System Taking the Search out of Search and Rescue David W Affens Roy Dreibelbis James E Mentall and George Theodorakos IT IS NOT COMMONLY KNOWN that the GPS satellites carry more than just navigation payloads Beginning with the launch of the sixth Block I satellite in 1980 GPS satellites have carried sensors for the detection of nuclear weapons detonations to help monitor compliance with the Non Proliferation Treaty The payload is known as the Nuclear Detonation NUDET Detection System NDS and is jointly supported by the U S Air Force and the Department of Energy And now a third task is being assigned to the GPS satellites that of search and rescue Since the mid 1980s a combination of low Earth orbit LEO and geostationary orbit GEO satellites have been used to detect and locate radio beacons activated by mariners aviators and others in distress virtually anywhere in the world and at any time Some 28000 lives have been saved worldwide since the search and rescue satellite aided tracking or SARSAT system was implemented But the current system has some drawbacks LEO satellites can determine a beacons position using the Doppler effect but their field of view is limited and one of them may not be in range when a beacon is activated Furthermore a large number of ground stations is needed to relay data from these satellites to search and rescue authorities GEO satellites on the other hand have a large field of view although missing parts of the Arctic and Antarctic but they cannot position a beacon unless its signal contains location information provided by an integral satellite navigation receiver In 1997 a Canadian government study determined that a better SARSAT system would be one based on medium Earth orbit MEO satellites A MEO system can provide full global coverage determine beacon location and do this with fewer ground stations GPS was identified as the ideal MEO constellation And so was born the Distress Alerting Satellite System DASS that will become fully operational on Block III satellites But already nine GPS satellites are hosting prototype hardware that is being used for proof ofconcept testing INNOVATION INSIGHTS with Richard Langley GPS is the ideal constellation for SARSAT In this months column we examine the architecture of DASS including its relationship with the NDS and take a look at some of the very positive test results already obtained results that support the claim that DASS will take the search out of search and rescue GPS World January 2011 www gpsworld com 72