Emergency Locator Signal Detection and Geolocation Small Satellite Constellation Feasibility Study

Aircraft Emergency Locator Transmitters (ELTs) are vital in helping search and rescue (SAR) teams in locating downed aircraft. Currently there are two types of ELTs available; one transmits at 121.5 MHz and the other at 406 MHz. The transmitters operating at 121.5 MHz have since been abandoned by satellite tracking systems even though these beacons are still available for non-commercial aviation use. Space based receiver decommissioning of 121.5 MHz systems was largely due to an inefficiency of the Very High Frequency (VHF) transmitter beacons; which have a 97% false alarm rate and only provide aircraft location within approximately 20 km of the transmitter. 406 MHz ELTs replaced the old VHF system but many do not broadcast GPS location data. While the Federal Aviation Administration (FAA) mandates all commercial air traffic use the 406 MHz transmitters, many privately owned aircraft still utilize 121.5 MHz and non-GPS 406 MHz ELTs. Small satellites have the capability of providing global coverage for a geolocation SAR constellation due to their low-cost and easily duplicated platform. This study assesses several identifying factors and risks regarding the implementation of such a small satellite SAR system that supports ELTs. Results from this study show that the need for an emergency locator signal detection and geolocation constellation can be seen as a low-cost solution to the current need for a 121.5 MHz and 406 MHz ELT detection system. BACKGROUND AND OBJECTIVES The current search and rescue satellite system, known as Cospas-Sarsat, provides support for not only aircraft ELTs but Emergency Position-Indicating Radio Beacons (EPIRB) for maritime distress as well as Personal Locator Beacons (PLB). Legacy hardware for each of the three beacons formerly operated at 121.5 MHz and has since moved to the new frequency of 406 MHz. All Cospas-Sarsat satellites’ on-board receivers for the 121.5 MHz frequency were turned off in February of 2009, discontinuing any further support of older beacons from a space-based platform. This system still provides support for all three types of beacons operating at 406 MHz and was used as an initial baseline in this study. Cospas-Sarsat consists of both geostationary and polar orbiting spacecraft, designated LEOSAR and GEOSAR. NOAAs Polar Orbiting Environment Satellites (POES) make up most of the LEOSAR portion and are most relevant to this study. Both LEOSAR and GEOSAR systems combine with local user terminals to allow Cospas-Sarsat to be able to provide global coverage for all three types of ultra high frequency (UHF) emergency transmitters operating at 406 MHz. A shortfall of this system is that the satellite segment contains large and very expensive spacecraft. Because of this cost gap, LEOSAR can only provide coverage based on the limited number of satellites in orbit. If replacement satellites are needed they will have to be much lower cost while still providing the same functionality. A lower cost also enables more satellites to be placed in orbit. Subsequently increasing global coverage and revisit times, allowing SAR teams a quicker response while not solely relying on the GEOSAR portion of Cospas-Sarsat; the CubeSat platform is ideal in fulfilling these criteria. In terms ELTs, it is estimated that over 170,000 aircraft around the world still operate older 121.5 MHz beacons. This causes an increase in the time it takes SAR and civil air patrol teams to respond to an aircraft emergency involving older beacons; further showing a need for legacy transmitter support. The objectives of this study are to first ensure need for a small satellite constellation supporting legacy 121.5 MHz as well as non-GPS capable 406 MHz emergency beacons. This is a key mission risk as the legacy beacons may be completely replaced when newer beacons become cheaper, more readily available, and