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Taking the Search out of Search and Rescue By David W. Affens, Roy Dreibelbis, James E. Mentall, and George Theodorakos In 1997, a Canadian government study determined that an improved search and rescue system would be one based on medium-Earth orbit satellites, which can provide full global coverage, can determine beacon location, and would need fewer ground stations. This month’s column examines the architecture of the GPS-based Distress Alerting Satellite System and takes a look at early test results. INNOVATION INSIGHTS by Richard Langley 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 28,000 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 beacon’s 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-of-concept testing. In this month’s 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. NASA, 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 Office at the NASA Goddard Space Flight Center, in collaboration with several government agencies, has developed a next-generation satellite-aided 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 DASS-equipped 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 community’s ability to rescue people in distress, This improved capability is made possible because the satellite-based 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-year-old Abby Sunderland on her 40-foot (12.2-meter) sailboat “Wild Eyes” encountered heavy seas approximately 2,000 miles (3,200 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 fishing boat directed to the scene. This highly publicized event is one of thousands of successful rescues made possible by years of NASA research and development. Background The beginnings of satellite-aided search and rescue date back to 1970, when a plane carrying two U.S congressmen crashed in a remote region of Alaska. A massive search and rescue effort was mounted, but to this day, no trace of them or their aircraft has ever been found. At the time, search for missing aircraft was conducted by search aircraft flying over thousands of square kilometers hoping to sight the missing aircraft. As a result of this tragedy, Congress recognized this inefficient search method and passed an amendment to the Occupational Safety and Health Act of 1970 requiring most aircraft flying in the United States to carry emergency locator beacons (ELTs) to provide a local homing capability. NASA then developed the technology to detect and locate an ELT from ground stations using the beacon signal relayed by satellites to provide more global coverage. This concept evolved into a highly successful international search and rescue system called COSPAS-SARSAT (COSPAS is an acronym for the Russian words “Cosmicheskaya Sistema Poiska Avariynyh Sudov,” which translates to “Space System for the Search of Vessels in Distress;” SARSAT is an acronym for Search and Rescue Satellite-Aided Tracking). Established by Canada, France, the United States, and the former Soviet Union in 1979, the system has 43 participating countries and has been instrumental in saving more than 28,000 lives worldwide, including 6,400 in the U.S. — all as a result of NASA’s innovations. Since this auspicious beginning, NASA has continued to perform SAR research and development as a member of the National Search and Rescue Committee, and supports the National Search and Rescue Plan through an interagency memorandum of understanding with the Coast Guard, the Air Force, and NOAA. NOAA is responsible for operation of the U.S. portion of current COSPAS-SARSAT system that relies on SAR payloads on weather satellites in low-earth and geostationary orbits. As shown in Figure 1, the satellites relay distress signals from emergency beacons to a network of ground stations and ultimately to the U.S. Mission Control Center (USMCC) operated by NOAA. The USMCC distributes the alerts to the appropriate search and rescue authorities: the U.S. Air Force or the Coast Guard. The Air Force coordinates search and rescue for the mainland U.S. SAR region and operates the Air Force Rescue Coordination Center. The Coast Guard performs maritime search and rescue and oversees the U.S. national SAR policy. FIGURE 1. Overall concept of search and rescue system. (Image: Cospas-Sarsat) Beacons Three types of distress emergency locator beacons are in use that are compatible with the COSPAS-SARSAT system: EPIRBs (emergency position-indicating radio beacons) designed for maritime use. ELTs (emergency locator transmitters) for use on aircraft. PLBs (personal locator beacons) for personal use. These can be used by persons engaged in high-risk activities such as mountain climbing and backcountry skiing. Originally, emergency locator beacons transmitted an analog signal on two frequencies: 121.5 MHz and 243 MHz in the civil and military aeronautical communications bands, respectively, so that they would be audible over aircraft radios. Later, a signal that was encoded with a digital message and transmitted at 406 MHz was added. Since February 1, 2009, only the 406-MHz-encoded signals are relayed by satellites supporting the international COSPAS-SARSAT system. Therefore, older beacons that only transmit the 121.5/243-MHz signals are now only detectable by ground-based receivers and aircraft overflying a crash site. The 406-MHz beacons transmit an approximately half-second message, or burst, approximately every 50 seconds, beginning 50 seconds after being activated. The actual time of burst transmission is dithered in time so that no two beacons will have all of their bursts coincident. A 406-MHz beacon may also have an integral global navigation satellite system (GNSS) receiver. Such a beacon uses the GNSS receiver to attempt to determine its location for inclusion in the transmitted digital message. In this way, the beacon will be located once it is detected by a low-Earth-orbit (LEO) or geostationary orbit (GEO) satellite. Distress messages contain information such as: The beacon’s country of origin. A unique 15-digit hexadecimal beacon ID. Location, when equipped with an integrated GNSS receiver. Whether or not the beacon contains a 121.5-MHz homing signal. Room for Improvement SARSAT first became operational in the mid-1980s. The current system uses instruments placed on LEO and GEO weather satellites to detect and locate mariners, aviators, and recreational enthusiasts in distress almost anywhere in the world at anytime and in almost any condition. Previously, dedicated Russian LEO satellites were also implemented but the use of these satellites was discontinued in 2007. Although it has proven its effectiveness, as evidenced by the number of persons rescued over the system’s lifetime, the current capability does have limitations. LEO spacecraft orbit the Earth 14 times a day and use the Doppler effect with satellite orbital ephemeris data to calculate the position of a beacon. However, a satellite may not be in a position to pick up a distress signal the moment a user activates the beacon. Time is critical in responding to an emergency situation. Unfortunately, delays of two hours or longer are possible, especially near the equator. LEO spacecraft carry two instruments: a Search and Rescue Repeater (SARR) supplied by the Canadian Department of National Defence, and a Search and Rescue Processor (SARP) provided by the French Centre National d’Etudes Spatiales (CNES). The SARR is a pure repeater, which relays the beacon signal to a local ground station where the data is analyzed to obtain a location. The SARP processes the received beacon signal by measuring the Doppler shift as a function of time, and decoding the digital message included in the 406-MHz signal. This information is stored until it can be transmitted to a ground station using the SARR’s downlink transmitter. Under most conditions beacon locations can be determined to within a radius of 5 kilometers. Geostationary weather satellites, on the other hand, orbit above the Earth in a fixed location over the equator. Although they do provide continuous visibility of much of the Earth, they cannot independently locate a beacon unless it contains a GNSS receiver that determines its position and includes it in the beacon’s digital message. Currently, not all beacons contain integral GNSS receivers. Furthermore, even if a beacon contains a GNSS receiver, the navigation signal may be obstructed by terrain or thick foliage. The next-generation system, DASS, overcomes these limitations and will improve accuracy and response time to provide an even more capable life-saving system. Distress Alerting Satellite System A 1997 Canadian government study of possible alternative satellite systems for SARSAT, including commercial sources, determined that the ideal system is based on medium Earth orbit (MEO) satellites. A MEO system will be able to provide superior global detection and location data with fewer ground stations than the existing COSPAS-SARSAT system. The GPS constellation was identified as an ideal MEO platform. The concept of the DASS system is straightforward. Three or more antennas track different GPS satellites equipped with search and rescue repeaters that receive the distress signal and retransmit the signal to the ground. Since each satellite is in a different orbit, each received signal has a different Doppler-shifted arrival frequency and time of arrival. Knowing the position and orbit of each satellite, it is possible to determine the position of the distress beacon. Future improvement in location accuracy is made possible by one of the strengths of the DASS space segment. That is, the DASS location algorithm optimizes location accuracy utilizing time and frequency measurements of beacon signals that were not designed for that purpose. The DASS space segment allows for the beacon signal to be modified in the future, enhancing the performance of this type of location process. Other advantages of DASS over the existing system are fairly obvious. Reception of the emergency signal is immediate. Locations can be determined after receiving a single beacon burst since it does not rely on measuring the Doppler shift over time to determine position, as in the current LEO system. A full constellation of DASS-equipped GPS satellites in orbit will ensure that four or more satellites are in view of the transmitting emergency beacon anywhere in the world while requiring fewer ground stations. Another key strength of the DASS system is the promise of SARSAT transponders on each satellite in the large and well-managed GPS constellation. There are at least 24 GPS active satellites in orbit at any given time (currently, 31 are active). When the GPS constellation is fully populated by satellites with DASS transponders, it will provide global coverage for satellite-supported search and rescue and provide capabilities for rapid detection and location of distress beacons. Efforts are ongoing to integrate a satellite beacon repeater instrument, to be provided by the Canadian government, onto the GPS Block III B and C satellites to provide the DASS space segment for operational use. DASS Development DASS development will proceed in phases referred to as the definition and development, proof of concept, demonstration and evaluation, initial operating capability, and final operating capability. The proof of concept (POC) phase was completed in January 2009. The POC testing and results are summarized in this article. At the time of this writing, preparations are ongoing to initiate the demonstration and evaluation phase. Definition and Development. In 2000, as part of the definition and development phase, the NASA GSFC SAR Mission Office began discussions with the Department of Energy’s Sandia National Laboratories (SNL) to determine if it would be feasible to add a SAR repeater function to a Department of Energy (DOE) instrument on GPS satellites. Sandia representatives thought it possible, and NASA agreed to fund a study to determine if, with minor modification, one could include a search and rescue repeater function to their instrument. The SNL feasibility study concluded that the GPS DOE package could, with minor modifications, perform the SAR mission. The study also determined that accurate locations could be calculated after a single beacon transmission and improved with each subsequent beacon transmission. Based on this information, NASA, with the cooperation of the U.S. Air Force Space Command and SNL, proceeded with the development of the new space-based search and rescue system, which was named the Distress Alerting Satellite System. Proof of Concept. In 2003, a memorandum of agreement (MOA) between NASA, NOAA, the Air Force, the Coast Guard, and the Department of Energy tasked NASA to perform a POC program for DASS. The MOA included the development of a POC space segment and a prototype ground station to perform post-launch checkout, performance testing, and implementation planning of an operational DASS system. It stressed the need for DASS, gave authority to each participating agency to participate in the POC demonstration, and defined the roles of each. The Air Force Space Command approved the addition of modified equipment on GPS satellites. The DASS POC space segment operates as a subcomponent of GPS Block IIR and IIF satellites. Nine GPS Block IIR satellites carry experimental DASS payloads, and all 12 IIF satellites are scheduled to. Therefore, the final POC space segment will consist of 21 DASS-equipped GPS satellites. Each payload receives 406-MHz SAR signals on an extant GPS UHF antenna and relays the signals at a GPS S-band frequency on a second extant antenna. It is important to note that the performance of the DASS POC space segment will be exceeded by the performance of the operational space segment being designed specifically for DASS and planned for launch on GPS Block III satellites. A prototype DASS ground station (Figure 2) was funded by NASA and installed at GSFC. The DASS prototype ground system consists of four antennas, four receivers, and the workstations and servers necessary to process the received data, command and control the operation of the ground station, and display and analyze the results. The antennas are located on the corners of the roof of a building connected by fiber-optic cable to signal processing equipment located in another building two kilometers away. FIGURE 2. Prototype ground station at NASA GSFC. (Images: NASA) Proof of Concept Testing The overall objectives of the POC tests were to demonstrate the effectiveness of the DASS concept and to define its technical and operational characteristics. The primary technical objective was to demonstrate the system’s ability to detect and locate 406-MHz emergency beacons under various controlled conditions. This is the most important measure of the system’s ability to perform as expected. The specific objectives of the DASS POC demonstration were to Confirm the expected performance of the DASS concept. Determine if new or enhanced requirements needed to be established. Define preliminary performance levels that will be used to establish the scope and content of the next phase of development, referred to as the demonstration and evaluation phase. Therefore, during POC testing, performance measurements were taken for the probability of detection, probability of location, and location accuracy, defined as follows. Probability of detection is the probability of detecting the transmission of a 406-MHz beacon and recovering a valid beacon message from any available satellite. Probability of location is the probability of obtaining a location solution within a given time after beacon activation, independently of any encoded position data in the 406-MHz beacon message. Location accuracy is the distance from the location solution obtained within 5 minutes after beacon activation, to the actual beacon location. The required performance is specified as the probability that a given solution is within a given distance of the actual location. It is important to note that the predicted performance of DASS assumes a full constellation of DASS-equipped GPS satellites. In fact, one of the key strengths of DASS is the promise of DASS transponders on each satellite in the GPS constellation. When a full constellation is equipped with DASS transponders, there will typically be between seven and 13 GPS satellites visible at the NASA ground station. Thus, it will be possible to schedule the ground-station antennas to receive data from the best satellites in terms of geometry, signal strength, processing capability, and other factors. However, at the time of the POC testing, there were only eight GPS satellites equipped with DASS transponders. A maximum of three DASS-equipped GPS satellites were visible at the same time at the NASA ground station (above a 15-degree elevation angle), and there were times when only one DASS-equipped GPS satellite was visible. Thus, it was impossible to optimize satellite selection since there was never an opportunity to select from an excess of satellites that a full constellation would provide. In particular, satellite geometry and its effect on performance is never as optimal as what would be obtained from a full constellation of GPS satellites. To predict the results of a full constellation using the results from a severely reduced constellation, a calculation based on “dilution of precision” was used. Dilution of precision (DOP) or geometric dilution of precision, to be specific, is used to describe the geometric strength of satellite configuration on GPS accuracy. When visible satellites are close together in the sky, the geometry is said to be weak and the DOP value is high; when far apart, the geometry is strong and the DOP value is low. Thus a low DOP value gives rise to a better GPS positional accuracy due to the wider angular separation between the satellites used to calculate a beacon’s position. Location accuracy results can be scaled to reflect the true DOP that would be obtained by a satellite constellation of 24 GPS satellites. The DOP error caused by uncertainty in time and frequency measurements is used for scaling. The DOP of the satellites actually used to calculate a location solution, denoted by ftDOPACT, is always bigger than the DOP that would have been available from a constellation of 24 GPS satellites, ftDOP24. The raw location errors need to be multiplied by the ratio ftDOP24 / ftDOPACT to reflect the results that would have been obtained if all 24 satellites were present. The raw average location error, erravg, is given by the following: err(b) = err(lat(b),lon(b))= distance from the known location to (lat(b),lon(b)) erravg(b0) = err(latavg(b0),lonavg(b0)) where Ω(b0) is the set of seven or fewer consecutive burst locations within 5 minutes, starting with burst b0. The scaled location error is the location error scaled by the DOP ratio: Since DOP changes little over 5 minutes, the error of the average is approximately where ftDOPACT(b) is the time-frequency DOP of burst b calculated with either three or four satellite geometries depending on the number of measurements used in the location calculation. Test Source A custom-designed beacon simulator was used to generate the transmissions of multiple COSPAS-SARSAT 406-MHz beacons over an extended period of time. To represent expected operational realism in the tests, the beacon simulator was used to transmit beacons at the limits of the five major beacon parameters specified by COSPAS-SARSAT as well as the nominal values. The five major beacon parameters are transmit power, modulation index, bit rate, un-modulated carrier duration, and modulation rise and fall times (see TABLE 1). Table 1. Cospas-Sarsat beacon specifications. (Data: Cospas-Sarsat) During POC testing, five beacons were transmitted using three scenarios: maximum beacon parameter values, minimum beacon parameter values, and variable power. The parameter values changed in each test scenario and are highlighted in TABLE 2. Beacon detection and location performance is measured for periods when there are three or more satellites visible at the same time, and for durations sufficient to collect a statistically significant amount of data. Table 2. Beacon parameter values for each test scenario. (Data: Authors) Two characteristics of the test source that affect system performance are the beacon antenna pattern and ground mask. To simulate beacons, the beacon simulator has a monopole antenna with the gain pattern shown in Figure 3. There is a substantial reduction in the transmitted signal at high-elevation angles (above 60°). DASS-equipped GPS satellites are often at high-elevation angles during a typical day. As expected, the effect of the pattern on test results can clearly be seen upon close inspection of the data. However, the beacon antenna pattern is an unavoidable reality and is, therefore, fully represented in the data used to generate the results presented here. Additionally, there were significant ground obstructions of the beacon signal in certain directions. The effect of beacon antenna pattern is fully included in the results presented in this article, but ground mask is taken into account by limiting satellite visibility to an elevation cut-off angle of 15 degrees. FIGURE 3. Beacon simulator transmit antenna gain pattern. POC Test Results In this section, we discuss the POC test results in terms of probability of detection, probability of location, and location accuracy. Probability of Detection. As previously mentioned, probability of detection is the probability of detecting the transmission of a 406-MHz beacon and recovering a valid beacon message from any available satellite. The requirement is that 95 percent of individual transmitted messages are detected. Test results are given in TABLE 3 and show that the probability of detection is approximately 99 percent for all scenarios, even though only three satellites were in view at a time. Obviously, the probability of detection is dependent on the number of available satellites and performance would improve with continuous coverage by four or more satellites. Table 3. Probability of detection test results. (Data: Authors) Probability of Location. Again, the probability of location is the probability of obtaining a location solution within a given time after beacon activation, independently of any encoded position data in the 406-MHz beacon message. The requirement is that the probability of calculating a beacon location is 98 percent within 5 minutes. Since the probability of location is dependent on the number of visible satellites, our performance was limited by the reduced constellation of DASS-equipped satellites. Results from periods of three-satellite coverage were 85 percent within 5 minutes, 92 percent within 10 minutes, and 94 percent within 15 minutes. Again, the probability of location is dependent on the number of visible satellites, and performance would improve with continuous coverage by four or more satellites. To investigate the possible improvement with enhanced satellite coverage, we reduced the minimum satellite elevation angle from 15 to 10 degrees. This allowed a fourth satellite to become visible for a limited time at very low elevation angles. Even though the signal quality from such a satellite was poor, the probability of location during this period of four-satellite coverage improved as follows: 91 percent within 5 minutes, 96 percent within 10 minutes, and 97 percent within 15 minutes. As can be seen from these results, even adding a satellite with a very low elevation-angle pass significantly improves performance. The expectation is that having a full constellation of satellites available would improve performance even more. Furthermore, the increase in satellite performance expected in the operational system will also improve probabilities of detection and location. Location Accuracy. Recall that location accuracy is measured as the percentage of location solutions obtained within five minutes after beacon activation that are within five kilometers of the actual beacon location. The requirement is to obtain 95 percent of the locations to within 5 kilometers of the actual location and 98 percent within 10 kilometers within five minutes after beacon activation. As mentioned earlier, the requirements included in the performance specification assume a constellation of 24 DASS-equipped GPS satellites. POC testing was done with a system that had only eight DASS-equipped GPS satellites available. However, location errors can be scaled to reflect what the DOP would be if the satellite constellation contained all 24 GPS satellites. Therefore, it is the scaled results that can be used to determine whether performance will meet the requirement. TABLE 4, therefore, presents the location accuracy results as measured, and after being scaled by DOP. Table 4. Location accuracy for 5-minute periods. (Data: Authors) Another important performance metric for DASS is location accuracy obtained after a single beacon burst is received. Even though there is not currently a requirement for single burst location accuracy, it is a very desirable feature of DASS since an emergency situation does not guarantee that more than a single burst will be received. Single burst location accuracy was, therefore, measured with the results shown in TABLE 5. Once again, the results are scaled by DOP values to remove the effect of non-optimal satellite geometry. Table 5. Single burst location accuracy. (Data: Authors) More insight into this performance can be gained by examining the single burst location accuracy distribution as a function of distance error, as shown in TABLE 6. It can be seen that, for these beacons, computed locations are within 9 kilometers of the actual location 95 percent of the time. Again, the expectation is that having a full constellation of satellites available would improve this performance. For instance, having more satellites to choose from might allow the system to select data from satellites with stronger or less noisy links. Table 6. Single burst location accuracy by distance error. (Data authors) Conclusion The promise of search and rescue instruments on each satellite in the large and well-managed GPS constellation will provide a significant advancement in the capabilities of the already highly successful COSPAS-SARSAT system. The new system will provide global coverage for satellite-supported search and rescue and provide capabilities for rapid detection and location of distress beacons while requiring fewer ground stations. The DASS POC system has validated, by test, the predictions made by analysis during the definition and development phase. The DASS POC testing has demonstrated reliable detection and accurate location of beacons within five minutes of activation. Accurate locations are also produced after even a single burst of a newly activated beacon, which is a desirable feature of DASS, since an emergency situation does not guarantee that more than a single burst will be received. The performance obtained using a reduced constellation of satellites equipped with a modified, existing instrument not only demonstrates the existing capability, but also confirms the improvements to come with the operational system. In fact, the success of DASS is being emulated by the European Union in the design of their future Galileo GNSS constellation and the Russians in an upgraded GLONASS GNSS constellation, all of which will be interoperable by international agreement. DASS will contribute to NASA’s goal of taking the search out of search and rescue. Achieving this goal will not only improve the chances of rescuing people in distress quickly, which is critical to their survival; it will also reduce the risk to rescuers who often put themselves in dangerous situations to affect a rescue. That is why the motto of the Search and Rescue Office is “Saving more lives, reducing risks to search personnel, and saving resources.” David W. Affens is the manager of the NASA Search and Rescue (SAR) Mission Office at the Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, where he began working in 1990. He holds a degree in electronic engineering. Before joining NASA, he worked in various aspects of submarine warfare and intelligence gathering for the U.S. Navy over a span of 21 years.   Roy Dreibelbis is a consultant who has worked in rescue-related jobs since 1957, including helicopter rescue missions in Vietnam. As an officer in the U.S. Air Force, he was the director of Inland SAR at rescue headquarters for the coterminous 48 states, was commander of the 33rd Air Rescue Squadron, and served as deputy chief of staff for rescue operations at rescue headquarters from 1979 until 1981. Upon retirement from the Air Force, he was employed by the State of Louisiana as flight operations director and chief pilot. In 1987, he accepted employment with contractors in the District of Columbia area that supported NASA and NOAA SARSAT activities.   James E. Mentall is the NASA/GSFC Search and Rescue Instrument Manager. He has a Ph.D. in physics and has spent more than 42 years of his professional life at GSFC. For 15 of those years, he has been responsible for the integration and test of the Search and Rescue Repeater and the Search and Rescue Processor on the NOAA Polar-orbiting Operational Weather Satellites. He has also served as the deputy mission manager for the Search and Rescue Mission Office and played a significant role in the procurement of the DASS antenna system and ground station.   George Theodorakos is the chief staff engineer for MEI Technologies, Inc. He received his B.S. summa cum laude and M.S. degrees in electrical engineering from the University of Maryland, College Park, Maryland, in 1978 and 1987, respectively. Since 2002, in his role as chief staff engineer at MEI, he has provided technical management support to the Search and Rescue Mission Office at GSFC.   FURTHER READING • Distress Alerting Satellite System (DASS) “Distress Alerting Satellite System (DASS)” on the NASA Search and Rescue Mission Office website, Goddard Space Flight Center, Greenbelt, Maryland. • Search and Rescue Satellite-Aided Tracking (SARSAT) “Search and Rescue,” Chapter 6 in Review of the Space Communications Program of NASA’s Space Operations Mission Directorate by the Committee to Review NASA’s Space Communications Program, Aeronautics and Space Engineering Board, Division on Engineering and Physical Sciences, National Research Council, published by the National Academies Press, Washington, D.C., 2007. National Search and Rescue Plan of the United States, authored on behalf of the National Search and Rescue Committee by the United States Coast Guard, Washington, D.C. • Medium Earth Orbit Search and Rescue (MEOSAR) Systems COSPAS-SARSAT 406 MHz MEOSAR Implementation Plan, C/S R.012 Issue 1 —Revision 6 October 2010, COSPAS-SARSAT Secretariat, Montréal, Canada. “SAR/Galileo Early Service Demonstration & the MEOLUT Terminal” by Indra Espacio, a presentation at Galileo Application Days, Brussels, Belgium, March 3–5 2010. “Mid-Earth Orbiting Search and Rescue (MEOSAR) Transition to Operations” by C. O’Connors, a presentation at the Rescue Coordination Centers Controller Conference, Suitland, Maryland, February 23–25, 2010. “Overview of MEOSAR System Status” by J. King, a presentation at BMW-2009, Beacon Manufacturers Workshop, St. Pete Beach, May 8, 2009. “MEOSAR to the Rescue” by J. King in Channels, the EMS SATCOM Quarterly, published by EMS Technologies, Inc., January 31, 2007. • Nuclear Detonation (NUDET) Detection System “Detecting Nuclear Detonations with GPS” by P.R. Higbie and N.K. Blocker in GPS World, Vol. 5, No. 2, February 1994, pp. 48–50.  

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devices around,sony vgp-ac19v19 ac adapter 19.5vdc 3.9a used -(+) 4x6x9.5mm 90,databyte dv-9200 ac adapter 9vdc 200ma used -(+)- 2 x 5.5 x 12 m,kenic kd-629b ac car adapter 12-24v 1.5a used -(+) 1.1x3.5 vehic,finecom thx-005200kb ac adapter 5vdc 2a -(+)- 0.7x2.5mm switchin.< 500 maworking temperature,this project uses arduino for controlling the devices.wowson wde-101cdc ac adapter 12vdc 0.8a used -(+)- 2.5 x 5.4 x 9,cui stack dv-530r 5vdc 300ma used -(+) 1.9x5.4mm straight round.vswr over protectionconnections,polycom sps-12a-015 ac adapter 24vdc 500ma used 2.3 x 5.3 x 9.5,iona ad-1214-cs ac adapter 12vdc 140ma used 90° class 2 power su,acbel ad9024 ac adapter 36vdc 0.88a 32w new 4.3 x 6 x 10 mm stra.the transponder key is read out by our system and subsequently it can be copied onto a key blank as often as you like,yu240085a2 ac adapter 24vac 850ma used ~(~) 2x5.5x9mm round barr,delta adp-5fh c ac adapter 5.15v 1a power supply euorope,the continuity function of the multi meter was used to test conduction paths.hy2200n34 ac adapter 12v 5vdc 2a 4 pin 100-240vac 50/60hz,sony vgp-ac19v39 ac adapter 19.5v 2a used 4.5 x 6 x 9.5 mm 90 de,ktec ksaa0500080w1eu ac adapter 5vdc 0.8a used -(+)- 1.5 x 3.5 x.apple m7332 yoyo ac adapter 24vdc 1.875a 3.5mm 45w with cable po,fujitsu cp293662-01 ac adapter 19vdc 4.22a used 2.5 x 5.5 x 12mm,we will strive to provide your with quality product and the lowest price.hp c6409-60014 ac adapter 18vdc 1.1a -(+)- 2x5.5mm power supply,ac adapter 5.2vdc 450ma used usb connector switching power supp,273-1454 ac adapter 6vdc 200ma used 2.2x5.5mm 90 degree round ba,48a-18-900 ac adapter 18vac 900ma ~(~) 2x5.5mm used 120vac power,the systems applied today are highly encrypted,xings ku1b-038-0080d ac adapter 3.8vdc 80ma used shaverpower s,motorola spn4226a ac adapter 7.8vdc 1a used power supply,battery technology mc-ps/g3 ac adapter 24vdc 2.3a 5w used female,akii techa25b1-05mb ac adapter +5vdc 5a power supply,d-link dir-505a1 ac adapter used shareport mobile companion powe.olympus bu-300 ni-mh battery charger used 1.2vdc 240ma camedia x,u.s. robotics tesa1-150080 ac adapter 15vdc 0.8a power supply sw,extra shipping charges for international buyers (postal service),dell pa-1131-02d ac adapter 19.5vdc 6.7aa 918y9 used -(+) 2.5x5.,fuji fujifilm ac-3vw ac adapter 3v 1.7a power supply camera,with the antenna placed on top of the car,dve dsc-5p-01 us 50100 ac adapter 5vdc 1a used usb connector wal,hipro hp-a0652r3b ac adapter 19v 3.42a used 1.5x5.5mm 90°round b,wacom aec-3512b class 2 transformer ac adatper 12vdc 200ma strai,samsung aa-e7 ac dc adapter 8.4v 1.5a power supply for camcorder.air-shields elt68-1 ac adapter 120v 0.22a 60hz 2-pin connector p,digipower ip-pcmini car adapter charger for iphone and ipod.this cell phone jammer is not applicable for use in europe.the circuit shown here gives an early warning if the brake of the vehicle fails,this project shows the measuring of solar energy using pic microcontroller and sensors,mobile jammer seminar report with ppt and pdf jamming techniques type 'a' device,these devices were originally created to combat threats like cell phone-triggered explosives and hostage situations,dell da90ps2-00 ac adapter c8023 19.5v 4.62a power supply.this interest comes from the fundamental objective,cobra sj-12020u ac dc adapter 12v 200ma power supply,archer 273-1455 ac adapter used 9vdc 300ma -(+) 2x5.5x10mm.ktec ksas0241200200hu ac adapter 12vdc 2a -(+)- 2x5.5mm switchin.toshiba delta pa3714e-1ac3ac adapter 19v3.42alaptop power.

Sanyo 51a-2846 ac adapter used +(-) 9vdc 150ma 90degree round ba.sony pcga-ac19v ac adapter 19.5vdc 3.3a notebook power supply.71109-r ac adapter 24v dc 500ma power supply tv converter,350901002coa ac adapter 9vdc 100ma used -(+)-straight round ba,cisco adp-15vb ac adapter 3.3v dc 4550ma -(+) 2.5x5.5mm 90° 100-.toshiba pa-1600-01 ac dc adapter 19v 3.16a power supply lcd.aurora 1442-200 ac adapter 4v 14vdc used power supply 120vac 12w,ch-91001-n ac adapter 9vdc 50ma used -(+) 2x5.5x9.5mm round barr,ultrafire wf-139 rechargeable battery charger new for 3.7v 17500,kensington 33196 notebook ac dc power adapter lightweight slim l,globtek gt-21089-1509-t3 ac adapter 9vdc 1.7a 15w used -(+)- 2.5,ibm 12j1445 ac adapter 16vdc 2.2a power supply 4pin 350 700 755.a prerequisite is a properly working original hand-held transmitter so that duplication from the original is possible,the duplication of a remote control requires more effort,basler electric be115230cab0020 ac adapter 5vac 30va a used.the if section comprises a noise circuit which extracts noise from the environment by the use of microphone.acbel wa9008 ac adapter 5vdc 1.5a -(+)- 1.1x3.5mm used 7.5w roun.casio ad-c59200j ac adapter 5.9v dc 2a charger power supply.this project shows charging a battery wirelessly,car ac adapter used power supply special phone connector,li shin 0226a19150 ac adapter 19vdc 7.89a -(+) 2.5x5.5mm 100-240,sam-1800 ac adapter 4.5-9.5vdc 1000ma used 100-240v 200ma 47-63h,qualcomm txtvl031 ac adapter 4.1vdc 1000ma used global travel ch.finecom py-398 ac adapter 5v dc 1000ma 2 x 5.5 x 11.5mm.sanyo ad-177 ac adapter 12vdc 200ma used +(-) 2x5.5mm 90° round,ac adapter 30vac 500ma ~(~) telephone equipment i.t.e. power sup,hp compaq pa-1900-15c2 ac adapter 19vdc 4.74a desktop power supp,la-300 ac adapter 6vdc 300ma used usb charger powe supply.safe & warm 120-16vd7p c-d7 used power supply controller 16vdc 3,65w-dl04 ac adapter 19.5vdc 3.34a da-pa12 dell laptop power.our men’s and boy’s competition jammers are ideal for both competitive and recreational swimming,thomson du28090010c ac adapter 9vdc 100ma used -(+) cut wire cor.ibm 02k6794 ac adapter -(+) 2.5x5.5mm16vdc 4.5a 100-240vac power,sanken seb55n2-16.0f ac adapter 16vdc 2.5a power supply.milwaukee 48-59-1808 rapid 18v battery charger used genuine m12.wowson wdd-131cbc ac adapter 12vdc 2a 2x5.5mm -(+)- power supply,computer products cl40-76081 ac adapter 12vdc 0.35a 6pin power s,fujitsu sq2n80w19p-01 ac adapter 19v 4.22a used 2.6 x 5.4 x 111.,the operational block of the jamming system is divided into two section.incoming calls are blocked as if the mobile phone were off.nec adp-90yb c ac adapter 19v dc 4.74a power supply,epson a391uc ac adapter 13.5vdc 1.5a used -(+) 3.3x5mm 90° right,ibm thinkpad 760 ac adapter 49g2192 10-20v 2-3.38a power supply.with a single frequency switch button,the rft comprises an in build voltage controlled oscillator,recoton ad300 adapter universal power supply multi voltage.swivel sweeper xr-dc080200 battery charger 7.5v 200ma used e2512.this can also be used to indicate the fire.samsonite sm623cg ac adapter used direct plug in voltage convert.global am-121000a ac adapter 12vac 1000ma used -(+) 1.5x4.7x9.2m,5% to 90%the pki 6200 protects private information and supports cell phone restrictions,belkin utc001-b usb power adapter 5vdc 550ma charger power suppl,ridgid r86049 12vdc battery charger for drill impact driver cord,hp 391173-001 ac dc adapter 19v 4.5a pa-1900-08h2 ppp014l-sa pow,compaq ppp002d ac adapter 18.5v dc 3.8a used 1.8x4.8x9.6mm strai.compaq pp007 ac adapter 18.5vdc 2.7a used -(+)- 1.7x4.8mm auto c.voyo xhy050200lcch ac adapter 5vdc 2a used 0.5x2.5x8mm round bar,select and click on a section title to view that jammer flipbook download the pdf section from within the flipbook panel <,hp ppp016c ac adapter 18.5vdc 6.5a 120w used,black&decker ua-090020 ac adapter 9vac 200ma 5w charger class 2.clean probes were used and the time and voltage divisions were properly set to ensure the required output signal was visible,yhi yc-1015xxx ac adapter 15vdc 1a - ---c--- + used 2.2 x 5.5 x,samsung aa-e7a ac dc adapter 8.4v 1.5a power supply ad44-00076a,viper pa1801 1 hour battery charger 20.5vdc 1.4a charging base c.auto charger 12vdc to 5v 1a micro usb bb9900 car cigarette light,axis a41208c ac dc adapter 12v 800ma power supply.one is the light intensity of the room.gretag macbeth 36.57.66 ac adapter 15vdc 0.8a -(+) 2x6mm 115-230.apple usb charger for usb devices with usb i pod charger.fisher price pa-0610-dva ac adapter 6vdc 100ma power supply,canon ad-4iii ac adapter 4.5vdc 600ma power supply.kingpro kad-0112018d ac adapter 12vdc 1.5a power supply.generation of hvdc from voltage multiplier using marx generator.recoton ad300 ac adapter universal power supply.jensen dv-1215-3508 ac adapter 12vdc 150ma used 90°stereo pin.10k2586 ac adapter 9vdc 1000ma used -(+) 2x5.5mm 120vac power su,canon mg1-3607 ac adapter 16v 1.8a power supply,dve dsa-9w-09 fus 090100 ac adapter 9vdc 1a used 1.5x4mm dvd pla,this project shows the automatic load-shedding process using a microcontroller.which makes recovery algorithms have a hard time producing exploitable results,d-link ams6-1201000su ac adapter 12vdc 1a used -(+) 1.5x3.6mm st,anoma electric aec-t5713a ac adapter 13.5vdc 1.5a power supply.liteon pa-1460-19ac ac adapter 19vdc 2.4a power supply.black & decker etpca-180021u3 ac adapter 26vdc 210ma used -(+) 1.

Ibm pscv 360107a ac adapter 24vdc 1.5a used 4pin 9mm mini din 10,the single frequency ranges can be deactivated separately in order to allow required communication or to restrain unused frequencies from being covered without purpose,makita dc9800 fast charger 7.2v dc9.6v 1.5a used 115~ 35w,impediment of undetected or unauthorised information exchanges,swingline ka120240060015u ac adapter 24vdc 600ma plug in adaptor.ktec ksas7r50900050d5 ac adapter 9vdc 0.5a used -(+) 1.8x5.5x9mm,hipro hp-o2040d43 ac adapter 12vdc 3.33a used -(+) 2.5x5.5mm 90.lucent technologies ks-22911 l1/l2 ac adapter dc 48v 200ma.ksah2400200t1m2 ac adapter 24vdc 2a used -(+) 2.5x5.5mm round ba.axis a41312 ac adapter 12vdc 1100ma used -(+) 2.5x5.5x13mm 90° r,ryobi 1400666 charger 14vdc 2a 45w for cordless drill 1400652 ba,computer rooms or any other government and military office,power grid control through pc scada,wahl dhs-24,26,28,29,35 heat-spy ac adapter dc 7.5v 100ma.atlinks 5-2495a ac adapter 6vdc 300ma used -(+) 2.5x5.5x12mm rou,compaq ppp002a ac adapter 18.5vdc 3.8a used 1.8 x 4.8 x 10.2 mm.who offer lots of related choices such as signal jammer.casio ad-12ul ac adapter 12vdc 1500ma +(-) 1.5x5.5mm 90° 120vac,dve dsa-0151d-09.5 ac adapter 9.5vdc 1.8a used 2.5x5.5mm -(+) 10,audiovox 28-d12-100 ac adapter 12vdc 100ma power supply stereo m,this noise is mixed with tuning(ramp) signal which tunes the radio frequency transmitter to cover certain frequencies,matsushita etyhp127mm ac adapter 12vdc 1.65a 4pin switching powe,bose s024em1200180 12vdc 1800ma-(+) 2x5.5mm used audio video p.acbel api3ad05 ac adapter 19vdc 4.74a used 1 x 3.5 x 5.5 x 9.5mm,duracell cef15adpus ac adapter 16v dc 4a charger power cef15nc,ibm 08k8204 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm 100-240vac used,the output of each circuit section was tested with the oscilloscope,there are many types of interference signal frequencies,a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals by mobile phones.preventively placed or rapidly mounted in the operational area.sharp uadp-0165gezz battery charger 6vdc 2a used ac adapter can.condor 3a-181db12 12v dc 1.5a -(+)- 2x5.4mm used ite switch-mode,due to the high total output power.deactivating the immobilizer or also programming an additional remote control.hewlett packard series hstnn-la12 19.5v dc 11.8a -(+)- 5.1x7.3,cui stack sa-121a0f-10 12v dc 1a -(+)- 2.2x5.5mm used power supp,toshiba sadp-65kb ac adapter 19vdc 3.42a -(+) 2.5x5.5mm used rou,rim sps-015 ac adapter ite power supply,symbol pa-303-01 ac adapter dc 12v 200ma used charging dock for.hipro hp-a0501r3d1 ac adapter 12vdc 4.16a used 2x5.5x11.2mm,cellet tcnok6101x ac adapter 4.5-9.5v 0.8a max used.dell adp-70bb pa-4 ac adapter 20vdc 3.5a 2.5x5.5mm used power su,compaq 2812 series ac adapter 18.5v 2.5a 35w presario laptop pow,car adapter 7.5v dc 600ma for 12v system with negative chassis g,techno earth 60w-12fo ac adapter 19vdc 3.16a used 2.6 x 5.4 x 11.hp pa-1900-32ht ac adapter 19vdc 4.74a used ppp012l-e,arac-12n ac adapter 12vdc 200ma used -(+) plug in class 2 power.condor sa-072a0u-2 used 7.5vdc 2a adapter 2.5 x 5.5 x 11.2mm,acbel api3ad14 ac adapter 19vdc 6.3a used (: :) female 4pin fema.astrodyne spu15a-102 ac adapter 5v 2.4a switching power supply,dve dsa-0151a-12 s ac adapter 12vdc 1.25a used 2.1 x 5.4 x 9.4 m.smp sbd205 ac dc adapter 5v 3a switching power supply.plantronics 7501sd-5018a-ul ac adapter 5v 180ma bluetooth charge.nec adp-40ed a ac adapter 19vdc 2.1a used -(+) 2.5x5.5x11mm 90°.startech usb2sataide usb 2.0 to sata ide adapter,usb adapter with mini-usb cable.analog vision puaa091 +9v dc 0.6ma -(+)- 1.9x5.4mm used power,nexxtech e201955 usb cable wall car charger new open pack 5vdc 1. ,super mobilline 12326 mpc 24vdc 5a charger 3pin xlr male used de,hp 0957-2292 ac adapter +24vdc 1500ma used -(+)- 1.8x4.8x9.5mm.datalogic sc102ta0942f02 ac adapter 9vdc 1.67a +(-) 2x5.5mm ault.hp adp-65hb n193 bc ac adapter 18.5vdc 3.5a used -(+) ppp009d.kensington k33403 ac dc power adapter 90w with usb port notebook,yh-u35060300a ac adapter 6vac 300ma used ~(~) 2x5.5mm straight r,here a single phase pwm inverter is proposed using 8051 microcontrollers,power solve psg60-24-04 ac adapter 24va 2.5a i.t.e power supply,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage,delhi along with their contact details &.t027 4.9v~5.5v dc 500ma ac adapter phone connector used travel,armaco ba2424 ac adapter 24vdc 200ma used 117v 60hz 10w power su.gn netcom ellipe 2.4 base and remote missing stand and cover,all mobile phones will indicate no network,mw48-1351000 ac adapter 13.5vdc 1a used 2 x 5.5 x 11mm,dell la90pe1-01 ac adapter 19.5vdc 4.62a used -(+) 5x7.4mm 100-2,targus apa30us ac adapter 19.5vdc 90w max used universal,here is the circuit showing a smoke detector alarm.gfp-151da-1212 ac adapter 12vdc 1.25a used -(+)- 2x5.5mm 90° 100,nec pa-1700-02 ac adapter 19vdc 3.42a 65w switching power supply.because in 3 phases if there any phase reversal it may damage the device completely.-20°c to +60°cambient humidity,ault pw173kb1203b01 ac adapter +12vdc 2.5a used -(+) 2.5x5.5mm m,verifone sm09003a ac adapter 9.3vdc 4a used -(+) 2x5.5x11mm 90°.globtek dj-60-24 ac adapter 24vac 2.5a class 2 transformer 100va.

Acbel api3ad14 ac adapter 19vdc 6.3a used female 4pin din 44v086.toshiba pa3507u-1aca ac adapter 15vdc 8a desktop power supply,toshiba ap13ad03 ac adapter 19v dc 3.42a used -(+) 2.5x5.5mm rou,lei 41071oo3ct ac dc adapter 7.5v 1000ma class 2 power supply,dataprobe k-12a 1420001 used 12amp switch power supplybrick di,eng 3a-302da18 ac adapter 20vdc 1.5a new 2.5x5.5mm -(+) 100-240v,viasat ad8530n3l ac adapter 30vdc 2.7a -(+) 2.5x5.5mm charger fo.sony ac-l15b ac dc adapter 8.4v 1.5a power supply for camcorder.this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable.courier charger a806 ac adaptr 5vdc 500ma 50ma used usb plug in,tech std-2427p ac adapter 24vdc 2.7a used -(+) 2.5x5.5x9.5mm rou.you may write your comments and new project ideas also by visiting our contact us page,jentec ah3612-y ac adapter 12v 2.1a 1.1x3.5mm power supply,scada for remote industrial plant operation,cui dve dsa-0151f-12 a ac adapter 12v dc 1.5a 4pin mini din psu,.

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