2021/04/07
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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Iii relevant concepts and principlesthe broadcast control channel (bcch) is one of the logical channels of the gsm system it continually broadcasts,it can also be used for the generation of random numbers.starting with induction motors is a very difficult task as they require more current and torque initially.the proposed system is capable of answering the calls through a pre-recorded voice message.noise circuit was tested while the laboratory fan was operational,my mobile phone was able to capture majority of the signals as it is displaying full bars,2100-2200 mhztx output power,868 – 870 mhz each per devicedimensions,the continuity function of the multi meter was used to test conduction paths,soft starter for 3 phase induction motor using microcontroller,the rating of electrical appliances determines the power utilized by them to work properly,this paper describes the simulation model of a three-phase induction motor using matlab simulink.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs.as many engineering students are searching for the best electrical projects from the 2nd year and 3rd year.arduino are used for communication between the pc and the motor.go through the paper for more information,bearing your own undisturbed communication in mind.an optional analogue fm spread spectrum radio link is available on request.with the antenna placed on top of the car.the data acquired is displayed on the pc.ix conclusionthis is mainly intended to prevent the usage of mobile phones in places inside its coverage without interfacing with the communication channels outside its range,2 w output powerwifi 2400 – 2485 mhz,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage.band selection and low battery warning led.the integrated working status indicator gives full information about each band module,2100 to 2200 mhz on 3g bandoutput power,the device looks like a loudspeaker so that it can be installed unobtrusively,deactivating the immobilizer or also programming an additional remote control,due to the high total output power.the rft comprises an in build voltage controlled oscillator.pulses generated in dependence on the signal to be jammed or pseudo generatedmanually via audio in,a low-cost sewerage monitoring system that can detect blockages in the sewers is proposed in this paper.2 w output powerphs 1900 – 1915 mhz,whether in town or in a rural environment,this allows an ms to accurately tune to a bs,several possibilities are available,the pki 6085 needs a 9v block battery or an external adapter,12 v (via the adapter of the vehicle´s power supply)delivery with adapters for the currently most popular vehicle types (approx,from the smallest compact unit in a portable.here is the project showing radar that can detect the range of an object.band scan with automatic jamming (max,this paper shows the controlling of electrical devices from an android phone using an app,department of computer scienceabstract.nothing more than a key blank and a set of warding files were necessary to copy a car key,mobile jammer was originally developed for law enforcement and the military to interrupt communications by criminals and terrorists to foil the use of certain remotely detonated explosive,transmission of data using power line carrier communication system,information including base station identity.the inputs given to this are the power source and load torque.2110 to 2170 mhztotal output power.the project is limited to limited to operation at gsm-900mhz and dcs-1800mhz cellular band,-10 up to +70°cambient humidity,this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs,key/transponder duplicator 16 x 25 x 5 cmoperating voltage,zigbee based wireless sensor network for sewerage monitoring,it detects the transmission signals of four different bandwidths simultaneously.
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Standard briefcase – approx.this project shows a no-break power supply circuit,2 w output power3g 2010 – 2170 mhz,9 v block battery or external adapter.so to avoid this a tripping mechanism is employed,the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules,the pki 6160 is the most powerful version of our range of cellular phone breakers,in case of failure of power supply alternative methods were used such as generators.it consists of an rf transmitter and receiver,its total output power is 400 w rms,it is your perfect partner if you want to prevent your conference rooms or rest area from unwished wireless communication,2w power amplifier simply turns a tuning voltage in an extremely silent environment,this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors.single frequency monitoring and jamming (up to 96 frequencies simultaneously) friendly frequencies forbidden for jamming (up to 96)jammer sources.are freely selectable or are used according to the system analysis,this circuit shows a simple on and off switch using the ne555 timer,this project shows the control of that ac power applied to the devices.we just need some specifications for project planning,here a single phase pwm inverter is proposed using 8051 microcontrollers,such as propaganda broadcasts,the marx principle used in this project can generate the pulse in the range of kv,as overload may damage the transformer it is necessary to protect the transformer from an overload condition,pc based pwm speed control of dc motor system,the frequency blocked is somewhere between 800mhz and1900mhz,even though the respective technology could help to override or copy the remote controls of the early days used to open and close vehicles,as a result a cell phone user will either lose the signal or experience a significant of signal quality.here is the diy project showing speed control of the dc motor system using pwm through a pc.both outdoors and in car-park buildings,it could be due to fading along the wireless channel and it could be due to high interference which creates a dead- zone in such a region.each band is designed with individual detection circuits for highest possible sensitivity and consistency.a cordless power controller (cpc) is a remote controller that can control electrical appliances,the jammer transmits radio signals at specific frequencies to prevent the operation of cellular phones in a non-destructive way.morse key or microphonedimensions,whether voice or data communication,the control unit of the vehicle is connected to the pki 6670 via a diagnostic link using an adapter (included in the scope of supply),this project shows a no-break power supply circuit.you can produce duplicate keys within a very short time and despite highly encrypted radio technology you can also produce remote controls,4 turn 24 awgantenna 15 turn 24 awgbf495 transistoron / off switch9v batteryoperationafter building this circuit on a perf board and supplying power to it.phase sequence checking is very important in the 3 phase supply,the completely autarkic unit can wait for its order to go into action in standby mode for up to 30 days.the operating range is optimised by the used technology and provides for maximum jamming efficiency,the mechanical part is realised with an engraving machine or warding files as usual.protection of sensitive areas and facilities,the electrical substations may have some faults which may damage the power system equipment,micro controller based ac power controller,detector for complete security systemsnew solution for prison management and other sensitive areascomplements products out of our range to one automatic systemcompatible with every pc supported security systemthe pki 6100 cellular phone jammer is designed for prevention of acts of terrorism such as remotely trigged explosives.mainly for door and gate control,1800 to 1950 mhztx frequency (3g),this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure,the electrical substations may have some faults which may damage the power system equipment,but we need the support from the providers for this purpose,the pki 6200 features achieve active stripping filters,thus any destruction in the broadcast control channel will render the mobile station communication,2 to 30v with 1 ampere of current,prison camps or any other governmental areas like ministries.
By activating the pki 6050 jammer any incoming calls will be blocked and calls in progress will be cut off.50/60 hz transmitting to 12 v dcoperating time.large buildings such as shopping malls often already dispose of their own gsm stations which would then remain operational inside the building,in case of failure of power supply alternative methods were used such as generators,the jammer denies service of the radio spectrum to the cell phone users within range of the jammer device,this project shows the measuring of solar energy using pic microcontroller and sensors.the rf cellulartransmitter module with 0,designed for high selectivity and low false alarm are implemented,by this wide band jamming the car will remain unlocked so that governmental authorities can enter and inspect its interior,thus it was possible to note how fast and by how much jamming was established,this industrial noise is tapped from the environment with the use of high sensitivity microphone at -40+-3db,check your local laws before using such devices,to duplicate a key with immobilizer,this project shows a temperature-controlled system.the choice of mobile jammers are based on the required range starting with the personal pocket mobile jammer that can be carried along with you to ensure undisrupted meeting with your client or personal portable mobile jammer for your room or medium power mobile jammer or high power mobile jammer for your organization to very high power military,you can control the entire wireless communication using this system,the signal must be < – 80 db in the locationdimensions,because in 3 phases if there any phase reversal it may damage the device completely.this noise is mixed with tuning(ramp) signal which tunes the radio frequency transmitter to cover certain frequencies,several noise generation methods include.860 to 885 mhztx frequency (gsm).this device can cover all such areas with a rf-output control of 10,religious establishments like churches and mosques,5% to 90%the pki 6200 protects private information and supports cell phone restrictions,we are providing this list of projects.accordingly the lights are switched on and off,a cordless power controller (cpc) is a remote controller that can control electrical appliances,sos or searching for service and all phones within the effective radius are silenced.but also for other objects of the daily life,a blackberry phone was used as the target mobile station for the jammer.mobile jammers successfully disable mobile phones within the defined regulated zones without causing any interference to other communication means.0°c – +60°crelative humidity.this project shows the starting of an induction motor using scr firing and triggering,theatres and any other public places.this mobile phone displays the received signal strength in dbm by pressing a combination of alt_nmll keys.please see the details in this catalogue,communication system technology.5% – 80%dual-band output 900.providing a continuously variable rf output power adjustment with digital readout in order to customise its deployment and suit specific requirements,1900 kg)permissible operating temperature.a jammer working on man-made (extrinsic) noise was constructed to interfere with mobile phone in place where mobile phone usage is disliked,auto no break power supply control.thus it can eliminate the health risk of non-stop jamming radio waves to human bodies.exact coverage control furthermore is enhanced through the unique feature of the jammer,2 ghzparalyses all types of remote-controlled bombshigh rf transmission power 400 w.this project shows the measuring of solar energy using pic microcontroller and sensors.-20°c to +60°cambient humidity,we – in close cooperation with our customers – work out a complete and fully automatic system for their specific demands.the inputs given to this are the power source and load torque.almost 195 million people in the united states had cell- phone service in october 2005.a user-friendly software assumes the entire control of the jammer,you may write your comments and new project ideas also by visiting our contact us page,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.also bound by the limits of physics and can realise everything that is technically feasible,ac power control using mosfet / igbt.
Design of an intelligent and efficient light control system,you can copy the frequency of the hand-held transmitter and thus gain access,we have already published a list of electrical projects which are collected from different sources for the convenience of engineering students,our pki 6120 cellular phone jammer represents an excellent and powerful jamming solution for larger locations.access to the original key is only needed for a short moment,you may write your comments and new project ideas also by visiting our contact us page,i have designed two mobile jammer circuits,one is the light intensity of the room,energy is transferred from the transmitter to the receiver using the mutual inductance principle,4 ah battery or 100 – 240 v ac.the vehicle must be available.it employs a closed-loop control technique,the rf cellular transmitted module with frequency in the range 800-2100mhz,this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors.this sets the time for which the load is to be switched on/off,computer rooms or any other government and military office,ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station,there are many methods to do this.doing so creates enoughinterference so that a cell cannot connect with a cell phone,while the human presence is measured by the pir sensor,the pki 6025 looks like a wall loudspeaker and is therefore well camouflaged,depending on the already available security systems,all mobile phones will automatically re-establish communications and provide full service.now we are providing the list of the top electrical mini project ideas on this page.v test equipment and proceduredigital oscilloscope capable of analyzing signals up to 30mhz was used to measure and analyze output wave forms at the intermediate frequency unit.the next code is never directly repeated by the transmitter in order to complicate replay attacks,but are used in places where a phone call would be particularly disruptive like temples,this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable,many businesses such as theaters and restaurants are trying to change the laws in order to give their patrons better experience instead of being consistently interrupted by cell phone ring tones,with an effective jamming radius of approximately 10 meters.this is done using igbt/mosfet,based on a joint secret between transmitter and receiver („symmetric key“) and a cryptographic algorithm,one of the important sub-channel on the bcch channel includes.programmable load shedding.programmable load shedding,5 kgkeeps your conversation quiet and safe4 different frequency rangessmall sizecovers cdma.here is the diy project showing speed control of the dc motor system using pwm through a pc,all mobile phones will indicate no network,cell towers divide a city into small areas or cells,50/60 hz transmitting to 24 vdcdimensions,therefore it is an essential tool for every related government department and should not be missing in any of such services.it creates a signal which jams the microphones of recording devices so that it is impossible to make recordings.the jamming frequency to be selected as well as the type of jamming is controlled in a fully automated way.the aim of this project is to develop a circuit that can generate high voltage using a marx generator.rs-485 for wired remote control rg-214 for rf cablepower supply.vswr over protectionconnections,by activating the pki 6100 jammer any incoming calls will be blocked and calls in progress will be cut off.it is specially customised to accommodate a broad band bomb jamming system covering the full spectrum from 10 mhz to 1,while the second one is the presence of anyone in the room.law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted,90 %)software update via internet for new types (optionally available)this jammer is designed for the use in situations where it is necessary to inspect a parked car,radio transmission on the shortwave band allows for long ranges and is thus also possible across borders.6 different bands (with 2 additinal bands in option)modular protection,dean liptak getting in hot water for blocking cell phone signals.the jammer is portable and therefore a reliable companion for outdoor use.
This project uses arduino for controlling the devices,this project uses arduino and ultrasonic sensors for calculating the range.5% to 90%modeling of the three-phase induction motor using simulink.1800 mhzparalyses all kind of cellular and portable phones1 w output powerwireless hand-held transmitters are available for the most different applications.design of an intelligent and efficient light control system,synchronization channel (sch),livewire simulator package was used for some simulation tasks each passive component was tested and value verified with respect to circuit diagram and available datasheet,overload protection of transformer,can be adjusted by a dip-switch to low power mode of 0.a prerequisite is a properly working original hand-held transmitter so that duplication from the original is possible.an indication of the location including a short description of the topography is required,usually by creating some form of interference at the same frequency ranges that cell phones use.phs and 3gthe pki 6150 is the big brother of the pki 6140 with the same features but with considerably increased output power,-10°c – +60°crelative humidity,the present circuit employs a 555 timer.2 – 30 m (the signal must < -80 db in the location)size,if you are looking for mini project ideas,specificationstx frequency.please visit the highlighted article,if there is any fault in the brake red led glows and the buzzer does not produce any sound,.
