2021/04/08
Experimenting with GPS on Board High-Altitude Balloons
By Peter J. Buist, Sandra Verhagen, Tatsuaki Hashimoto, Shujiro Sawai, Shin-Ichiro Sakai, Nobutaka Bando, and Shigehito Shimizu
In this month’s column, we look at how a team of Dutch and Japanese researchers is using GPS to determine the attitude of a payload launched from a high-altitude balloon.
INNOVATION INSIGHTS by Richard Langley
IT IS NOT WIDELY RECOGNIZED that relative or differential positioning using GNSS carrier-phase measurements is an interferometric technique. In interferometry, the difference in the phase of an electromagnetic wave at two locations is precisely measured as a function of time. The phase differences depend, amongst other factors, on the length and orientation of the baseline connecting the two locations. The classic demonstration of interferometry, showing that light could be interpreted as a wave phenomenon, was the 1803 double-slit experiment of the English polymath, Thomas Young. Many of us recreated the experiment in high school or university physics classes. A collimated beam of light is shone through two small holes or narrow slits in a barrier placed between the light source and a screen. Alternating light and dark bands are seen on the screen. The bands are called interference fringes and result from the waves emanating from the two slits constructively and destructively interfering with each other. The colors seen on the surface of an audio CD, the colors of soap film, and those of peacock feathers and the wings of the Morpho butterfly are all examples of interference.
Interference fringes also reveal information about the source of the waves. In 1920, the American Nobel-prize-winning physicist, Albert Michelson, used an interferometer attached to a large telescope to measure the diameter of the star Betelgeuse. Radio astronomers extended the concept to radio wavelengths, using two antennas connected to a receiver by cables or a microwave link. Such radio interferometers were used to study the structure of various radio sources including the sun. Using atomic frequency standards and magnetic tape recording, astronomers were able to sever the real-time links between the antennas, giving birth to very long baseline interferometry (VLBI) in 1967. The astronomers used VLBI to study extremely compact radio sources such as the enigmatic quasars. But geodesists realized that high resolution VLBI could also be used to determine — very precisely — the components of the baseline connecting the antennas, even if they were on separate continents.
That early work in geodetic VLBI led to the concept developed by Charles Counselman III and others at the Massachusetts Institute of Technology in the late 1970s of recording the carrier phase of GPS signals with two separate receivers and then differencing the phases to create an observable from which the components of the baseline connecting the receivers’ antennas could be determined. This has become the standard high-precision GPS surveying technique. Later, others took the concept and applied it to short baselines on a moving platform allowing the attitude of the platform to be determined.
In this month’s column, we look at how a team of Dutch and Japanese researchers is using GPS to determine the attitude of a payload launched from a high-altitude balloon.
The Japan Aerospace Exploration Agency (JAXA) is developing a system to provide a high-quality, long duration microgravity environment using a capsule that can be released from a high-altitude balloon. Since 1981, an average of 100 million dollars is spent every year on microgravity research by space agencies in the United States, Europe, and Japan. There are many ways to achieve microgravity conditions such as (in order of experiment duration) drop towers, parabolic flights, balloon drops, sounding rockets, the Space Shuttle (unfortunately, no longer), recoverable satellites, and the International Space Station. The order of those options is also approximately the order of increasing experiment cost, with the exception of the balloon drop. Besides being cost-efficient, a balloon-based system has the advantage that no large acceleration is required before the experiment can be performed, which could be important for any delicate equipment that is carried aloft.
In this article, we will describe JAXA’s Balloon-based Operation Vehicle (BOV) and the experiments carried out in cooperation with Delft University of Technology (DUT) using GPS on the gondola of the balloon in 2008 (single baseline estimation) and 2009 (full attitude determination and relative positioning). The attitude calculated using observations from the onboard GPS receiver during the 2009 experiment is compared with that from sun and geomagnetic sensors as well as that provided by the GPS receiver itself.
Nowadays, GNSS is used for absolute and relative positioning of aircraft and spacecraft as well as determination of their attitude. What these applications have in common is that, in general, the orientation of the platform is changing relatively slowly and, to a large extent, predictably. Here, we will discuss a balloon-based application where the orientation of the platform, at times, varies very dynamically and unpredictably.
Balloon Experiments
Scientific balloons have been launched in Japan by the Institute of Space and Astronautical Science (ISAS), now a division of JAXA, since 1965, and it holds the world record for the highest altitude reached by a balloon — 53 kilometers. Recently, balloon launches have taken place from the Multipurpose Aviation Park (MAP) in Taiki on the Japanese island of Hokkaido. The balloons are launched using a so-called sliding launcher. The sliding launcher and the hanger at MAP are shown in FIGURE 1.
Balloon-Based Operation Vehicle. As previously mentioned, JAXA’s BOV has been designed for microgravity research. The scenario of a microgravity experiment is illustrated in FIGURE 2. The vehicle is launched with a balloon, which carries it to an altitude of more than 40 kilometers, where it is released.
Figure 2. Microgravity experiment procedure.
After separation, the BOV is in free fall until the parachute is released so that the vehicle can make a controlled landing in the sea. The BOV is recovered by helicopter and can be reused. The capsule has a double-shell drag-free structure and it is controlled so as not to collide with the inner shell. The flight capsule, shown hanging at the sliding launcher in Figure 1, consists of a capsule body (the outer shell), an experiment module (the inner shell), and a propulsion system. The inner capsule shown in FIGURE 3 is kept in free-falling condition after release of the BOV from the balloon, and no disturbance force acts on this shell and the microgravity experiment it contains.
Figure 3. Balloon-based Operation Vehicle overview.
The outer shell has a rocket shape to reduce aerodynamic disturbances. The distance between the outer and inner shells is measured using four laser range sensors. Besides the attitude of the BOV, the propulsion system controls the outer shell so that it does not collide with the inner s
hell. The propulsion system uses 16 dry-air gas-jet thrusters of 60 newtons, each controlling it not only in the vertical direction but also in the horizontal direction to compensate disturbances from, for example, wind.
Flight experiments with the BOV were carried out in 2006 (BOV1) and in 2007 (BOV2), when a fine microgravity environment was established successfully for more than 7 and 30 seconds, respectively.
Attitude Determination. Balloon experiments are performed for a large number of applications, some of which require attitude control. Observations from balloon-based telescopes are an example of an application in which stratospheric balloons have to carry payloads of hundreds of kilograms to an altitude of more than 30 kilometers to be reasonably free of atmospheric disturbances. In this application, the typical requirement for the control of the azimuth angle of the platform is to within 0.1 degrees.
JAXA is developing the Attitude Determination Package (ADP, see TABLE 1) for a future version of the BOV, which contains Sun Aspect Sensors (SAS), the Geomagnetic Aspect Sensor (GAS), an inclinometer, and a gyroscope. Each SAS determines the attitude with a resolution of one degree around one axis and the ADP has four of these sensors pointing in different directions. Inherently, this type of sensor can only provide attitude information if the sun is within the field of view of the sensor. The GAS also determines one-axis attitude. The resolution of magnetic flux density measured by the GAS and applied to obtain an attitude estimate is 50 parts per million. This results in an attitude determination accuracy of the GAS of 1.5 degrees with dynamic bias compensation. The inclinometer determines two-axis attitude with a resolution of 0.2 degrees.
Table 1. Sensor specifications.
Background GPS Experiment. DUT is involved in a precise GPS-based relative positioning and attitude determination experiment onboard the BOV and the gondola of the balloon. Not only is the BOV a challenging environment, but so is the gondola itself, because of the rather rapidly varying attitude (due to wind and — especially at takeoff and separation — rotation) and the high altitude. For a GPS experiment, the altitude of around 40 kilometers is interesting as not many experiments have been performed at this height, which is higher than the altitude reachable by most aircraft but below the low earth orbits for spacecraft. An altitude of about 40 kilometers is a harsh environment for electrical devices because the pressure is about 1/1000 of an atmosphere and the temperature ranges from –60 to 0 degrees Celsius. Furthermore, the antennas are placed under the balloon, which affects the received GPS signals. Later on, we will describe in detail two experiments performed in 2008 and 2009, respectively.
The GPS receivers on the first flight in 2008 were a navigation-type receiver, not especially adapted for such an experiment. The data was collected on a single baseline with two dual-frequency receivers. The receivers were controlled by, and the data stored on, an ARM Linux board using an RS-232 serial connection.
For the second flight in 2009, we used a multi-antenna receiver, for which the Coordinating Committee for Multilateral Export Controls altitude restriction was explicitly removed. This receiver has three RF inputs that can be connected to three antennas, so the observations from the three antennas are time-synchronized by a common clock. The receiver has the option to store observations internally, which simplified the control of the GPS experiment. We used three antennas: one L1/L2 antenna as the main antenna and two L1 antennas as auxiliary antennas.
Theory of Attitude Determination
In this section, we will provide background information on the models applied in our GPS experiment. More details can be found in the publications listed in Further Reading.
Standard LAMBDA. Most GNSS receivers make use of two types of observations: pseudorange (code) and carrier phase. The pseudorange observations typically have a precision of decimeters, whereas carrier-phase observations have precisions up to the millimeter level.
Carrier-phase observations are affected, however, by an unknown number of integer-cycle ambiguities, which have to be resolved before we can exploit the higher precision of these observations. The observation equations for the double-difference (between satellites and between antennas/receivers) can be written for a single baseline as a system of linearized observation equations:
(1)
where E(y) is the expected value and D(y) is the dispersion of y. The vector of observed-minus-computed double-difference carrier-phase and code observations is given by y; z is the vector of unknown ambiguities expressed in cycles rather than distance units to maintain their integer character; b is the baseline vector, which is unknown for relative navigation applications but for which the length in attitude determination is generally known; A is a design matrix that links the data vector to the vector z; and B is the geometry matrix containing normalized line-of-sight vectors. The variance-covariance matrix of y is represented by the positive definite matrix Qyy, which is assumed to be known.
The least-squares solution of the linear system of observation equations as introduced in Equation (1) is obtained using from:
. (2)
The integer solution of this system can be obtained by applying the standard Least-Squares Ambiguity Decorrelation Adjustment (LAMBDA) method.
Constrained LAMBDA. In applications for which some of the baseline lengths are known and constant, for example GNSS-based attitude determination, we can exploit the so-called baseline-constrained model. Then, the baseline-constrained integer ambiguity resolution can make use of the standard GNSS model by adding the length constraint of the baseline, ||b|| = , where is known. The least-squares criterion for this problem reads:
.(3)
The solution can be obtained with the baseline-constrained (or C-)LAMBDA method, which is described in referred literature listed in Further Reading. Later on, we will refer to the attitude calculated by this approach simply as C-LAMBDA.
For platforms with more than one baseline, the C-LAMBDA method can be applied to each baseline individually, and the full attitude can be determined using those individual baseline solutions. For completeness, we also mention a recently developed solution of this problem, called the multivariate-constrained (MC-) LAMBDA, which integrally accounts for both the integer and attitude matrix. Both approaches are applied in the analyses of the BOV data.
Onboard Attitude Determination. In this article, we also use the onboard estimate of the attitude as provided by the multi-antenna receiver. The method applied in the receiver is based on a Kalman filter and the ambiguities are resolved by the standard LAMBDA method. The baseline length, if the information is provided to the receiver a priori, is used to validate the results. For baseline lengths of about 1 meter, the receiver’s pitch and roll accuracy is about 0.60 degrees, and heading about 0.30 degrees according to the receiver manual. We will refer to the attitude as provided by the receiver as KF.
Flight Experiments
In this section, we will discuss our analyses of the GPS data from two of the BOV experiments.
Gondola Experimental Flight 2008. In September 2008, we performed a test of the ADP for a future version of the BOV and a GPS system containing two navigation-grade GPS receivers. The goal of the experiment was to confirm nominal performance in the real environment of the ADP sensors and GPS receivers on the gondola; therefore, the BOV was not launched. The data from the single baseline was used to determine the pointing direction of the gondola, an application referred to as the GNSS compass. The receivers and the controller were stored in an airtight container (see FIGURE 4) and the antennas were sealed in waterproof bags. The location of the two GPS antennas on the gondola is indicated in Figure 4. The baseline length was 1.95 meters. Both receivers used their own individual clocks, so observations were not synchronized. The trajectory (altitude) of this flight is shown in the right-hand side of Figure 4, with the longitude and latitude shown in FIGURE 5. This is a typical flight profile for our application. The flight takes about three hours and reaches an altitude of more than 40 kilometers.
Figure 4B. Single baseline experiment performed in September 2008, the flight trajectory (altitude).
First, the balloon makes use of the wind direction in the lower layers of the atmosphere, which brings it eastwards. During this part of the flight, the balloon is kept at a maximum altitude of about 12 kilometers. After about 30 minutes, the altitude is increased to make use of a different wind direction that carries the balloon back in the westerly direction toward the launch base in order to ease the recovery of the capsule and/or the gondola.
At the end of the flight, there is a parachute-guided fall over 40 kilometers to sea level, for both the gondola and the BOV (if it is launched), which takes about 30 minutes. In this experiment, we could confirm the nominal operation of some of the sensors and reception of the GPS signals on the gondola under the large balloon.
Gondola Experimental Flight 2009. In May 2009, the third flight of the BOV was performed. The three GPS receiver antennas and the other attitude sensors were placed on an alignment frame for stiffness, which was then attached to the gondola. Furthermore, we used a ground station to demonstrate the combination of GPS-based attitude determination and relative positioning between the platform and the ground station. As the motion of the system is rather unpredictable, we used a kinematic approach for both attitude determination and relative positioning.
Preflight static test: Before the flight, we did a ground test using the actual antenna frame of the gondola (see FIGURE 6). The roll, pitch, and heading angles for this static test are shown on the right-hand side of this figure. Due to the geometry of the baselines, the heading angle is more accurate. For this static test, we can calculate the standard deviation of the three angles to confirm the accuracy achievable for the flight test. These results are summarized in TABLE 2. For the baselines with a length of about 1.4 meters, we achieved an accuracy of about 0.25 degrees for the roll and pitch angles and 0.1 degrees for heading, which is as expected from the lengths and geometry of the baselines. Using single-epoch data, we could resolve the ambiguities correctly for more than 99 percent of the epochs (see TABLE 3). Also, the standard deviation of the receiver’s Kalman-filter-based attitude estimate (KF) is included in the table. The accuracy is, after convergence of the filter, similar to our C-LAMBDA result, although the applied method is very different. The Kalman filter takes about 10 seconds to converge for this static experiment, whereas the C-LAMBDA method provides this accuracy from the very first epoch. For completeness, the instantaneous success rate of the standard LAMBDA and MC-LAMBDA methods are also included in Table 3.
Figure 6. Static experiment: C-LAMBDA-based attitude estimates.
Table 2. Standard deviation of attitude angles for static test.
Table 3. Single-epoch, overall success rate for baseline 1-2 (static experiment).
Gondola nominal flight: Next, we applied the same GPS configuration on the gondola. An important difference with respect to the static field experiment is that the antennas were now placed under the balloon and inside waterproof bags (see the picture on the left-hand side of FIGURE 7). The right-hand side of Figure 7 shows the flight trajectory (altitude) of the experiment. At 21:05 UTC (07:05 Japan Standard Time), the balloon was released from the sliding launcher (Figure 1). In 2.5 hours, the balloon reached an altitude of more than 41 kilometers from which the BOV was dropped. At 23:55, the BOV was released from the Gondola, and at 23:59 the gondola was separated from the balloon. After the release of the BOV, the balloon and gondola ascended more than 2 kilometers because of the reduced mass of the system. For this flight, the attitude determination package and the GPS system were installed on the gondola to confirm the nominal performance of all the sensors.
Figure 7A. Full attitude experiment performed in May 2009, sensor configuration.
Figure 7B. Full attitude experiment performed in May 2009, flight trajectory (altitude).
Using the new GPS receiver with three antennas, we are able to calculate the full attitude of the gondola. The roll and pitch estimates, from both C-LAMBDA and KF, are shown in FIGURE 8. The heading angle from the GPS-based C-LAMBDA and KF, and that from the GAS and SAS sensors are shown in FIGURE 9. As explained in a previous section, the four SAS sensors will only output an attitude estimate if the sun is in the field of view of a sensor. Therefore we can distinguish four bands in the heading estimate of the SAS, corresponding to the individual sensors (indicated in Figure 7 as SAS1 to SAS4).
Figure 8A. GPS results for roll angles during nominal flight.
Figure 8B. GPS results for pitch angles during nominal flight.
Figure 9A. GPS results for heading angle during nominal flight.
Figure 9B. GAS and SAS results for heading angle during nominal flight.
The number of locked GPS satellites at the main antenna is shown on the right-hand side of Figure 7. Before takeoff, we saw that the number of locked channels varies rapidly due to obstructions, but after takeoff the number is rather constant until the BOV is separated from the gondola. Before takeoff, the GPS observations are affected by the obstruction of the sliding launcher and therefore ambiguity resolution is only possible on the second baseline (see Figure 8). Also, the GPS receiver itself does not provide an attitude estimation during this phase of the experiment. During takeoff, we see large variations in orientation of the gondola (up to 20 degrees (±10 degrees) for both roll and pitch), which can be estimated well by both C-LAMBDA and KF. Again, the Kalman filter takes a few epochs to converge (in this case, 15 seconds from takeoff), whereas the C-LAMBDA method provides an accurate solution from the very first epoch. After takeoff, the attitude of the gondola stabilizes and the C-LAMBDA and KF attitude estimates are very similar.
We investigated the difference between the attitude estimation from the different sensors during nominal flight. The mean and standard deviations of the differences are shown in TABLE 4. If we compare the C-LAMBDA and KF attitudes, we observe biases for all angles. This is something we have to investigate further, but the most likely cause for this bias is the time delay of the Kalman filter in response to changes in attitude, as we observed in the static experiment in the form of convergence time.
Table 4. Attitude differences (offset/standard deviation) for flight test of 2009.
The standard deviation for the difference in the estimates of roll, pitch, and heading is as expected. For the comparison with the other sensors, we use the C-LAMBDA attitude as the reference. Between C-LAMBDA and GAS/SAS, we observe a bias, most likely due to minor misalignment issues between the sensors. The standard deviations in Table 4 are in line with expectation based on the sensor specifications. During this part of the flight, we achieved a single-epoch, single-frequency empirical overall success rate for ambiguity resolution on the two baselines of 95.09 percent. As a reference, we also include in TABLE 5 the success rate for standard LAMBDA using observations from a single epoch. If we make use of the MC-LAMBDA method, the success rate is increased to 99.88 percent as shown in the table. The success rate is higher as the integrated model for all the baselines is stronger.
Table 5. Single-epoch, overall success rate for baseline 1-2 (flight experiment).
Gondola flight after BOV separation: After the separation of the BOV from the gondola, the gondola starts to ascend and sway. FIGURE 10 contains roll and pitch estimates for this part of the flight until the gondola separation. In the figure, we see large variations in the orientation of the gondola (up to 40 (±20) degrees for roll and 20 (± 10) degrees for pitch). It is interesting that after BOV separation, during the large maneuvers of the gondola caused by the separation, both KF and C-LAMBDA estimates are available but to a certain extent are different. Table 4 also contains standard deviations and biases between C-LAMBDA and KF for this part of the flight.
Figure 10A. GPS results for roll angles during nominal flight.
Figure 10B. GPS results for pitch angles during nominal flight.
We conclude that the differences (standard deviation but also bias) between C-LAMBDA and KF — both for roll and pitch — are increased compared to the nominal part of the flight. This confirms our expectation that the Kalman-filter-based result lags behind the true attitude in dynamic situations, whereas the C-LAMBDA result based on single-epoch data should be able to provide the same accurate estimate as during the other phases of the flight.
Future Work
For the final phase of the experiment program, we would like to collect multi-baseline data from a number of vehicles. The preferred option for the experiment is three antennas (two independent baselines) on the BOV, and two antennas (one baseline) on the gondola. Furthermore, similar to our 2009 experiment, a number of antennas at a reference station could be used. The goal of the final phase of the program is to collect data for offline relative positioning and attitude determination, though real-time emulation, between a number of vehicles that form a network.
Acknowledgments
Peter Buist thanks Professor Peter Teunissen for support with the theory behind ambiguity resolution and, including Gabriele Giorgi, for the pleasant cooperation during our research. The MicroNed-MISAT framework is kindly thanked for their support. The research of Sandra Verhagen is supported by the Dutch Technology Foundation STW, the Applied Science Division of The Netherlands Organisation for Scientific Research (NWO), and the Technology Program of the Ministry of Economic Affairs. This article is based on the paper “GPS Experiment on the Balloon-based Operation Vehicle” presented at the Institute of Electrical and Electronics Engineers / Institute of Navigation Position Location and Navigation Symposium 2010, held in Indians Wells, California, May 6–8, 2010, where it received a best-paper-in-track award.
Manufacturers
The Attitude Determination Package’s Sun Aspect Sensor is based on photodiodes manufactured by Hamamatsu Photonics K.K.; the Geomagnetic Aspect Sensor is based on magnetometers manufactured by Bartington Intruments Ltd.; the inclinometer is based on a module manufactured by Measurement Specialties; and the gyro is manufactured by Silicon Sensing Systems Japan, Ltd. For the 2009 experiment, we used a Septentrio N.V. PolaRx2@ multi-antenna receiver with S67-1575-96 and S67-1575-46 antennas from Sensor Systems Inc. Details on the receivers and antennas used for the 2008 experiment are not publicly available. A Trimble Navigation Ltd. R7 receiver and two NovAtel Inc. OEMV receivers were used at the reference ground station. The ARM-Linux logging computer is an Armadillo PC/104 manufactured by Atmark Techno, Inc.
Peter J. Buist is a researcher at Delft University of Technology in Delft, The Netherlands. Before rejoining DUT in 2006, he developed GPS receivers for the SERVIS-1, USERS, ALOS, and other satellites and the H2A rocket, and subsystems for QZSS in the Japanese space industry.
Sandra Verhagen is an assistant professor at Delft University of Technology in Delft, The Netherlands. Together with Peter Buist, she is working on the Australian Space Research Program GARADA project on synthetic aperture radar formation flying.
Tatsuaki Hashimoto received his Ph.D. in electrical engineering from the University of Tokyo in 1990. He is a professor of the Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA).
Shujiro Sawai received his Ph.D. in engineering from the University
of Tokyo in 1994. He is an associate professor at ISAS/JAXA.
Shin-Ichiro Sakai received his Ph.D. degree from the University of Tokyo in 2000. He joined ISAS/JAXA in 2001 and became associate professor in 2005.
Nobutaka Bando received a Ph.D. in electrical engineering from the University of Tokyo in 2005. He is an assistant professor at ISAS/JAXA.
Shigehito Shimizu received a master’s degree in engineering from Tohoku University in Sendai, Japan, in 2007. He is an engineer in the Navigation, Guidance and Control Group at JAXA.
FURTHER READING
• Authors’ Proceedings Paper
“GPS Experiment on the Balloon-based Operation Vehicle” by P.J. Buist, S. Verhagen, T. Hashimoto, S. Sawai, S-I. Sakai, N. Bando, and S. Shimizu in Proceedings of PLANS 2010, IEEE/ION Position Location and Navigation Symposium, Indian Wells, California, May 4–6, 2010, pp. 1287–1294, doi: 10.1109/PLANS.2010.5507346.
• Balloon Applications
“Development of Vehicle for Balloon-Based Microgravity Experiment and Its Flight Results” by S. Sawai, T. Hashimoto, S. Sakai, N. Bando, H. Kobayashi, K. Fujita, T. Yoshimitsu, T. Ishikawa, Y. Inatomi, H. Fuke, Y. Kamata, S. Hoshino, K. Tajima, S. Kadooka, S. Uehara, T. Kojima, S. Ueno, K. Miyaji, N. Tsuboi, K. Hiraki, K. Suzuki, and K. M. T. Nakata in Journal of the Japan Society for Aeronautical and Space Sciences, Vol. 56, No. 654, 2008, pp. 339–346, doi: 10.2322/jjsass.56.339.
“Development of the Highest Altitude Balloon” by T. Yamagami, Y. Saito, Y. Matsuzaka, M. Namiki, M. Toriumi, R. Yokota, H. Hirosawa, and K. Matsushima in Advances in Space Research, Vol. 33, No. 10, 2004, pp. 1653–1659, doi: 10.1016/j.asr.2003.09.047.
• Attitude Determination
“Testing of a New Single-Frequency GNSS Carrier-Phase Attitude Determination Method: Land, Ship and Aircraft Experiments” by P.J.G. Teunissen, G. Giorgi, and P.J. Buist in GPS Solutions, Vol. 15, No. 1, 2011, pp. 15–28, doi: 10.1007/s10291-010-0164-x, 2010.
“Attitude Determination Methods Used in the PolarRx2@ Multi-antenna GPS Receiver” by L.V. Kuylen, F. Boon, and A. Simsky in Proceedings of ION GNSS 2005, the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation, Long Beach, California, September 13–16, 2005, pp. 125–135.
“Design of Multi-sensor Attitude Determination System for Balloon-based Operation Vehicle” by S. Shimizu, P.J. Buist, N. Bando, S. Sakai, S. Sawai, and T. Hashimoto, presented at the 27th ISTS International Symposium on Space Technology and Science, Tsukuba, Japan, July 5–12, 2009.
“Development of the Integrated Navigation Unit; Combining a GPS Receiver with Star Sensor Measurements” by P.J. Buist, S. Kumagai, T. Ito, K. Hama, and K. Mitani in Space Activities and Cooperation Contributing to All Pacific Basin Countries, the Proceedings of the 10th International Conference of Pacific Basin Societies (ISCOPS), Tokyo, Japan, December 10–12, 2003, Advances in the Astronautical Sciences, Vol. 117, 2004, pp. 357–378.
“Solving Your Attitude Problem: Basic Direction Sensing with GPS” by A. Caporali in GPS World, Vol. 12, No. 3, March 2001, pp. 44–50.
• Ambiguity Estimation
“Instantaneous Ambiguity Resolution in GNSS-based Attitude Determination Applications: the MC-LAMBDA Method” by G. Giorgi, P.J.G. Teunissen, S. Verhagen, and P.J. Buist in Journal of Guidance, Control and Dynamics, accepted for publication, April 2011.
“Integer Least Squares Theory for the GNSS Compass” by P.J.G. Teunissen in Journal of Geodesy, Vol. 84, No. 7, 2010, pp. 433–447, doi: 10.1007/s00190-010-0380-8.
“The Baseline Constrained LAMBDA Method for Single Epoch, Single Frequency Attitude Determination Applications” by P.J. Buist in Proceedings of ION GPS 2007, the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation, Fort Worth, Texas, September 25–28, 2007, pp. 2962–2973.
“The LAMBDA Method for the GNSS Compass” by P.J.G. Teunissen in Artificial Satellites, Vol. 41, No. 3, 2006, pp. 89–103, doi: 10.2478/v10018-007-0009-1.
“Fixing the Ambiguities: Are You Sure They’re Right?” by P. Joosten and C. Tiberius in GPS World, Vol. 11, No. 5, May 2000, pp. 46–51.
“The Least-Squares Ambiguity Decorrelation Adjustment: a Method for Fast GPS Integer Ambiguity Estimation” by P.J.G. Teunissen in Journal of Geodesy, Vol. 70, No. 1–2, 1995, pp. 65–82, doi: 10.1007/BF00863419.
• Relative Positioning
“A Vectorial Bootstrapping Approach for Integrated GNSS-based Relative Positioning and Attitude Determination of Spacecraft” by P.J. Buist, P.J.G. Teunissen, G. Giorgi, and S. Verhagen in Acta Astronautica, Vol. 68, No. 7-8, 2011, pp. 1113–1125, doi: 10.1016/j.actaastro.2010.09.027.
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phone jammer london uk
With an effective jamming radius of approximately 10 meters.2 w output powerphs 1900 – 1915 mhz.pc based pwm speed control of dc motor system.here is the diy project showing speed control of the dc motor system using pwm through a pc,additionally any rf output failure is indicated with sound alarm and led display.large buildings such as shopping malls often already dispose of their own gsm stations which would then remain operational inside the building,a mobile phone jammer prevents communication with a mobile station or user equipment by transmitting an interference signal at the same frequency of communication between a mobile stations a base transceiver station,all mobile phones will indicate no network incoming calls are blocked as if the mobile phone were off,zigbee based wireless sensor network for sewerage monitoring,this mobile phone displays the received signal strength in dbm by pressing a combination of alt_nmll keys,this break can be as a result of weak signals due to proximity to the bts,this project shows charging a battery wirelessly,pki 6200 looks through the mobile phone signals and automatically activates the jamming device to break the communication when needed.while the human presence is measured by the pir sensor.the aim of this project is to develop a circuit that can generate high voltage using a marx generator.>
-55 to – 30 dbmdetection range,the single frequency ranges can be deactivated separately in order to allow required communication or to restrain unused frequencies from being covered without purpose.and frequency-hopping sequences,the integrated working status indicator gives full information about each band module.5% – 80%dual-band output 900,230 vusb connectiondimensions,binary fsk signal (digital signal).even temperature and humidity play a role,this project shows the system for checking the phase of the supply,the data acquired is displayed on the pc.generation of hvdc from voltage multiplier using marx generator,i can say that this circuit blocks the signals but cannot completely jam them.auto no break power supply control.protection of sensitive areas and facilities,the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,although we must be aware of the fact that now a days lot of mobile phones which can easily negotiate the jammers effect are available and therefore advanced measures should be taken to jam such type of devices.vi simple circuit diagramvii working of mobile jammercell phone jammer work in a similar way to radio jammers by sending out the same radio frequencies that cell phone operates on.this sets the time for which the load is to be switched on/off,this paper shows the real-time data acquisition of industrial data using scada,wireless mobile battery charger circuit,by activating the pki 6100 jammer any incoming calls will be blocked and calls in progress will be cut off.this is as well possible for further individual frequencies.with its highest output power of 8 watt.providing a continuously variable rf output power adjustment with digital readout in order to customise its deployment and suit specific requirements,860 to 885 mhztx frequency (gsm).2 w output powerwifi 2400 – 2485 mhz,1800 mhzparalyses all kind of cellular and portable phones1 w output powerwireless hand-held transmitters are available for the most different applications.0°c – +60°crelative humidity.
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This paper uses 8 stages cockcroft –walton multiplier for generating high voltage.here a single phase pwm inverter is proposed using 8051 microcontrollers,transmission of data using power line carrier communication system,key/transponder duplicator 16 x 25 x 5 cmoperating voltage,religious establishments like churches and mosques,10 – 50 meters (-75 dbm at direction of antenna)dimensions.nothing more than a key blank and a set of warding files were necessary to copy a car key,there are many methods to do this,energy is transferred from the transmitter to the receiver using the mutual inductance principle.three circuits were shown here,provided there is no hand over,the jammer transmits radio signals at specific frequencies to prevent the operation of cellular and portable phones in a non-destructive way.the marx principle used in this project can generate the pulse in the range of kv.this project uses arduino and ultrasonic sensors for calculating the range,a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals,4 turn 24 awgantenna 15 turn 24 awgbf495 transistoron / off switch9v batteryoperationafter building this circuit on a perf board and supplying power to it.with our pki 6670 it is now possible for approx.the rf cellulartransmitter module with 0.2100 to 2200 mhz on 3g bandoutput power.control electrical devices from your android phone.the first circuit shows a variable power supply of range 1.standard briefcase – approx,-10 up to +70°cambient humidity,which broadcasts radio signals in the same (or similar) frequency range of the gsm communication.a blackberry phone was used as the target mobile station for the jammer.it employs a closed-loop control technique,i have designed two mobile jammer circuits.please visit the highlighted article.this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed.this project shows the starting of an induction motor using scr firing and triggering,such as propaganda broadcasts,but we need the support from the providers for this purpose,2 w output powerdcs 1805 – 1850 mhz,it is specially customised to accommodate a broad band bomb jamming system covering the full spectrum from 10 mhz to 1,soft starter for 3 phase induction motor using microcontroller.this also alerts the user by ringing an alarm when the real-time conditions go beyond the threshold values,ac power control using mosfet / igbt.programmable load shedding.2100-2200 mhzparalyses all types of cellular phonesfor mobile and covert useour pki 6120 cellular phone jammer represents an excellent and powerful jamming solution for larger locations,this system also records the message if the user wants to leave any message,925 to 965 mhztx frequency dcs,a cell phone works by interacting the service network through a cell tower as base station,the device looks like a loudspeaker so that it can be installed unobtrusively.
3 x 230/380v 50 hzmaximum consumption,the proposed design is low cost.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,power grid control through pc scada.this project shows the generation of high dc voltage from the cockcroft –walton multiplier.the aim of this project is to achieve finish network disruption on gsm- 900mhz and dcs-1800mhz downlink by employing extrinsic noise,the electrical substations may have some faults which may damage the power system equipment,therefore the pki 6140 is an indispensable tool to protect government buildings,at every frequency band the user can select the required output power between 3 and 1.whether copying the transponder.cell phone jammers have both benign and malicious uses.most devices that use this type of technology can block signals within about a 30-foot radius,it can also be used for the generation of random numbers,2100 – 2200 mhz 3 gpower supply,mobile jammers successfully disable mobile phones within the defined regulated zones without causing any interference to other communication means.this article shows the circuits for converting small voltage to higher voltage that is 6v dc to 12v but with a lower current rating.an optional analogue fm spread spectrum radio link is available on request,power amplifier and antenna connectors.it is possible to incorporate the gps frequency in case operation of devices with detection function is undesired,phase sequence checker for three phase supply.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,please see the details in this catalogue,ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station.the effectiveness of jamming is directly dependent on the existing building density and the infrastructure,some people are actually going to extremes to retaliate.-20°c to +60°cambient humidity,here is the project showing radar that can detect the range of an object,this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors.zigbee based wireless sensor network for sewerage monitoring,this project uses arduino for controlling the devices,department of computer scienceabstract.this project shows the control of home appliances using dtmf technology,design of an intelligent and efficient light control system,rs-485 for wired remote control rg-214 for rf cablepower supply,all these project ideas would give good knowledge on how to do the projects in the final year.government and military convoys,automatic power switching from 100 to 240 vac 50/60 hz,programmable load shedding,the cockcroft walton multiplier can provide high dc voltage from low input dc voltage,you may write your comments and new project ideas also by visiting our contact us page,the present circuit employs a 555 timer,its great to be able to cell anyone at anytime,-10°c – +60°crelative humidity.
When the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition,5 kgadvanced modelhigher output powersmall sizecovers multiple frequency band.the pki 6200 features achieve active stripping filters.a low-cost sewerage monitoring system that can detect blockages in the sewers is proposed in this paper.whether voice or data communication,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.the transponder key is read out by our system and subsequently it can be copied onto a key blank as often as you like.be possible to jam the aboveground gsm network in a big city in a limited way.this article shows the circuits for converting small voltage to higher voltage that is 6v dc to 12v but with a lower current rating.the first types are usually smaller devices that block the signals coming from cell phone towers to individual cell phones,the jammer is portable and therefore a reliable companion for outdoor use.dean liptak getting in hot water for blocking cell phone signals.the frequency blocked is somewhere between 800mhz and1900mhz,load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit.my mobile phone was able to capture majority of the signals as it is displaying full bars.the mechanical part is realised with an engraving machine or warding files as usual,this project uses a pir sensor and an ldr for efficient use of the lighting system.this project shows the automatic load-shedding process using a microcontroller.a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals,this noise is mixed with tuning(ramp) signal which tunes the radio frequency transmitter to cover certain frequencies,can be adjusted by a dip-switch to low power mode of 0,its built-in directional antenna provides optimal installation at local conditions.in common jammer designs such as gsm 900 jammer by ahmad a zener diode operating in avalanche mode served as the noise generator,automatic changeover switch,this project shows the controlling of bldc motor using a microcontroller,starting with induction motors is a very difficult task as they require more current and torque initially.so that pki 6660 can even be placed inside a car,the data acquired is displayed on the pc,the unit is controlled via a wired remote control box which contains the master on/off switch.military camps and public places,the circuit shown here gives an early warning if the brake of the vehicle fails,this system uses a wireless sensor network based on zigbee to collect the data and transfers it to the control room.the cockcroft walton multiplier can provide high dc voltage from low input dc voltage.this project shows charging a battery wirelessly,the frequencies are mostly in the uhf range of 433 mhz or 20 – 41 mhz,placed in front of the jammer for better exposure to noise,this project shows the measuring of solar energy using pic microcontroller and sensors,jamming these transmission paths with the usual jammers is only feasible for limited areas,when the mobile jammers are turned off,the jammer works dual-band and jams three well-known carriers of nigeria (mtn.the third one shows the 5-12 variable voltage,computer rooms or any other government and military office,the complete system is integrated in a standard briefcase.
Conversion of single phase to three phase supply,a potential bombardment would not eliminate such systems,vehicle unit 25 x 25 x 5 cmoperating voltage,sos or searching for service and all phones within the effective radius are silenced,temperature controlled system,bearing your own undisturbed communication in mind,it consists of an rf transmitter and receiver,the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules,the jammer denies service of the radio spectrum to the cell phone users within range of the jammer device,arduino are used for communication between the pc and the motor.this device is the perfect solution for large areas like big government buildings,this project shows the automatic load-shedding process using a microcontroller.prison camps or any other governmental areas like ministries,preventively placed or rapidly mounted in the operational area,overload protection of transformer.2100-2200 mhztx output power,the multi meter was capable of performing continuity test on the circuit board,soft starter for 3 phase induction motor using microcontroller,the third one shows the 5-12 variable voltage.it should be noted that operating or even owing a cell phone jammer is illegal in most municipalities and specifically so in the united states,this system is able to operate in a jamming signal to communication link signal environment of 25 dbs,1800 to 1950 mhztx frequency (3g),law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted,control electrical devices from your android phone,dtmf controlled home automation system.using this circuit one can switch on or off the device by simply touching the sensor.so that we can work out the best possible solution for your special requirements,this article shows the different circuits for designing circuits a variable power supply.this project uses arduino and ultrasonic sensors for calculating the range,for technical specification of each of the devices the pki 6140 and pki 6200,this project shows a no-break power supply circuit.this project shows the control of appliances connected to the power grid using a pc remotely,our pki 6085 should be used when absolute confidentiality of conferences or other meetings has to be guaranteed.this project shows the measuring of solar energy using pic microcontroller and sensors,impediment of undetected or unauthorised information exchanges.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,1920 to 1980 mhzsensitivity.this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure,it creates a signal which jams the microphones of recording devices so that it is impossible to make recordings.a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals.this system considers two factors,the first circuit shows a variable power supply of range 1,this jammer jams the downlinks frequencies of the global mobile communication band- gsm900 mhz and the digital cellular band-dcs 1800mhz using noise extracted from the environment.
In case of failure of power supply alternative methods were used such as generators,the jammer transmits radio signals at specific frequencies to prevent the operation of cellular phones in a non-destructive way,this project creates a dead-zone by utilizing noise signals and transmitting them so to interfere with the wireless channel at a level that cannot be compensated by the cellular technology..
