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Product features
Output frequency up to 500 MHz
Can use the patented SmarTiming+ technology, disciplining an external SAASM or a non-SAAMS GPS or GNSS 1PPS reference up to 100,000 seconds with an auto-adaptive loop time operating at 1-ns resolution
State-of-the-art frequency and timing signal stability performance
Integration of an ultra-low-noise OCXO oscillator with optional low g-sensitivity and a single or dual vibration-isolated tray for the OCXO and/or the Rb oscillator to meet various dynamic application requirements.
It’s all physics. How things work, that is. You’ve heard me say that before in this column, but I suppose I’m a little biased (or realistic) as my first degree is in physics — applied physics, to be more precise. Mind you, some chemists might disagree that it’s all down to physics. But as Sheldon Cooper in the popular American TV sitcom The Big Bang Theory stated in a radio interview with real science journalist Ira Flatow following his apparent discovery of the first stable super-heavy element, “Yes, yes, I’d be a physicist with a Nobel in chemistry. Everyone laugh at the circus freak. You know, I don’t need to sit here and take this, Flatow. It is because of bullies like you, every day more and more Americans are making the switch to television.”
But in all seriousness, it really was physicists who first explained the physical phenomena associated with a range of technologies that had to be understood before global navigation satellite systems could become a reality. From orbital mechanics, to relativity theory, to semiconductors, to transatmospheric propagation of radio signals, to atomic clocks, the fundamental understanding of how these worked was provided by physicists.
This was particularly true for atomic clocks. An atomic clock, like any clock, consists of two basic components: a resonator or oscillator and a counter. The oscillator generates a stable frequency, whose cycles are counted, converted to units of seconds, minutes, hours and perhaps days, and continuously displayed. This is the case whether we are describing a wristwatch with a quartz crystal oscillator or an atomic clock whose oscillator is made up of atoms undergoing quantum energy transitions. A crystal oscillator is stimulated to vibrate at its design frequency and thereby generate a fluctuating electrical current with that frequency. The atomic oscillator works thanks to the principles of quantum physics. Atoms have energies, but the energies are quantized, meaning that only specific energy levels are possible. An atom may exist at a particular energy level and spontaneously transition to a lower energy level and in so doing emit electromagnetic radiation (such as radio waves or light) of a specific frequency equal to the change in energy divided by a fundamental physical constant called Planck’s constant, named after Max Planck, who introduced it in 1900. The atom can be stimulated to return to the higher energy level by exposing it to radiation of that same exact frequency. A practical atomic oscillator can be constructed by confining a collection of atoms in an enclosure and bathing them in electromagnetic radiation from a tunable generator. By automatically tuning the frequency of the generator to maximize the number of stimulated atoms through a feedback loop, a very pure and constant frequency will result.
The first clocks based on an energy transition of the cesium atom were developed in the mid-1950s. Later on, clocks based on energy transitions of the rubidium and hydrogen atoms were developed. By the 1960s, commercial rack-mountable cesium and rubidium clocks became available. But a need existed for miniaturized atomic clocks that could be easily embedded in equipment requiring a very stable frequency source. Funded in part by the Defense Advanced Research Projects Agency, the first chip-scale atomic clock was demonstrated by physicists in 2004, and by 2011, a chip-scale atomic clock based on a cesium atom transition became commercially available.
In this month’s column, we look at how chip-scale atomic clocks can help us navigate more safely by allowing a GNSS receiver to position itself more accurately even with only three satellites in view, and to protect itself by being able to detect a sophisticated spoofing attempt. Physics — isn’t it wonderful!
GNSS positioning and navigation are based on one-way range measurements. Synchronization of the receiver and satellite timescales is carried out with respect to a third time scale of higher stability, such as GNSS system time, by introducing so-called clock errors. To account for the time and frequency offsets of the satellites, the user can obtain appropriate corrections from the broadcast navigation message in real time. In post-processing, more accurate corrections are provided by various products of the International GNSS Service (IGS).
Due to the generally poor accuracy and limited long-term frequency stability of a quartz oscillator built into a GNSS receiver, the receiver clock error has to be estimated epoch-by-epoch. This is the typical case for single-point positioning (SPP) based on code (pseudorange) observations only. This comes with certain drawbacks:
The up-coordinate is determined two to three times less precisely than the horizontal coordinates,
Higher dilution of precision values are obtained than in the hypothetical case of trilateration,
High correlations of up to 99 percent between the receiver’s up-coordinate and clock error persist, and
At least four satellites are necessary for positioning.
Especially in the case of kinematic positioning, this situation can be significantly improved by using a more stable (atomic) clock for the receiver and introducing the information about its frequency stability into the estimation process. This approach is called receiver clock modeling (RCM), and basically requires that the integrated clock noise is smaller than the receiver noise during the modeling interval. Besides SPP, this method can also be applied in a common-clock setup in relative positioning using single-differenced observations (which, by their nature, contain more information) instead of typically used double-differenced observations, or precise point positioning.
The recent development of chip-scale atomic clocks (CSACs) offers the required frequency stability and accuracy, and opens up the possibility of using atomic clocks in real kinematic GNSS applications without any severe restrictions regarding power supply or environmental influences on the clocks. When connecting one of these clocks to a GNSS receiver, replacing or steering the internal oscillator accordingly, and modeling its behavior in a physically meaningful way instead of epoch-wise estimation, the navigation performance can be improved distinctly.
The receiver clock parameter absorbs signal delays common to all simultaneous line-of-sight signals whether these delays represent the physical clock or any other common delay. Thus, it is especially vulnerable to delays caused by jammers or spoofers. If the clock behavior is predictable, information about jamming or spoofing can be retrieved, and thus the integrity of the positioning solution can be improved.
Chip-Scale Atomic Clocks
For our test purposes, we used two different commercially available CSACs, dubbed CSAC A and CSAC B. To gain knowledge about their frequency stabilities, we compared them against an active hydrogen maser at the Physikalisch-Technische Bundesanstalt (PTB), Germany’s official metrology institute. We analyzed the raw fractional phase measurements and computed individual Allan variances for our devices. The resulting frequency stabilities are shown in FIGURE 1.
Clock Model
Basically, a clock is an oscillator generating a sinusoidal signal with a given nominal frequency coupled with a frequency counter. The deviation of the signal’s nominal frequency with respect to a reference time scale can be described by a frequency offset and drift plus random frequency fluctuations. In the time domain, the resulting clock error δt, that is, the difference between nominal time t and the time read simultaneously on the clock, can be approximated by the following equation:
(1)
with systematic time offset b0, frequency offset b1, frequency drift b2, and random noise x(t,t0). Thus, the main (deterministic) part of a clock model can be described by a quadratic polynomial.
The more interesting characteristics of a clock are contained in the underlying noise processes. The time-dependent Allan deviation (ADEV) enables the determination of a modeling or predicting interval τp over which receiver clock modeling is physically meaningful; that is, the integrated clock noise x(t,t0) is smaller than GNSS receiver noise:
(2)
The noise σrx of a typical commercial GNSS receiver can be assessed to approximately one percent of the chip or wavelength of the signal in use, such as 3 meters, 0.3 meter, or 2 millimeters for C/A-code, P-code, or L1 carrier-phase observations, respectively.
To apply the knowledge gained about the devices’ frequency stabilities, appropriate models for GNSS data analysis should be established. One prerequisite is that the clock noise has to be well below the GNSS receiver noise; that is, the integrated random frequency fluctuations of CSACs cannot be resolved by the GNSS observations in use. We assume typical values for code and ionosphere-free carrier-phase observations from modern geodetic GNSS receivers of 1 meter and 5 millimeters, respectively. Since these observations are phase-based measures, we can model the dominating underlying noise process as white-noise phase modulation (WPM) over time. The corresponding graphs are depicted in FIGURE 1 as dashed lines. The intersection points between these lines and the ADEV curves define maximal time intervals Δt for physically meaningful receiver clock modeling in our case study. Depending on the CSAC in use, RCM is applicable over time intervals of at least ten minutes and up to one hour in C/A-code-based applications, such as SPP.
GNSS Applications
We have tested and validated our receiver clock modeling approaches for GNSS navigation.
Kinematic Experiment
We carried out a real kinematic experiment on a cart track in farm fields with an approximately 500 × 800 square meter area with only a few natural obstructions in the form of a tree-lined lane (see FIGURE 2). The basic measurement configuration consisted of four GNSS receivers running the same firmware version connected to a GNSS antenna via an active signal splitter. Three of these receivers were fed by the 10-MHz signals of our CSACs. For comparison purposes, the fourth receiver was driven by its internal quartz oscillator.
Each test drive with our motor vehicle lasted approximately 8 to 10 minutes. We recorded GPS and GLONASS data with a sampling interval of one second. (Only GPS-based results are described herein.) That was also the case for our temporary local reference station, which consisted of a GNSS antenna mounted on a tripod and connected to another GNSS receiver. Hence, we were able to generate reference solutions for the vehicle trajectories in relative positioning mode with baselines of up to only some hundred meters, yielding 3D coordinate accuracies below 20 centimeters.
The RCM algorithms presented here were implemented in the Institut für Erdmessung GNSS Matlab Toolbox. To compute a typical real-time SPP navigation solution based on GPS C/A-code observations only, broadcast ephemerides were used. Tropospheric and ionospheric signal delays were corrected by the Saastamoinen and Klobuchar models, respectively. [Click on an image to enlarge it.]
FIGURE 1. Allan deviations of investigated atomic clocks and GPS ionosphere-free carrier and C/A-code observation noise modeled as white-noise phase modulation (WPM) over time.
FIGURE 2. Test track. The yellow ellipse marks a treed lane with signal obstructions.
Precision and Accuracy
Two of the most important GNSS performance parameters are the precision and accuracy of the coordinate solution. FIGURE 3 shows topocentric coordinate differences with respect to the reference trajectory and clock-error time series of the receiver driven by its internal quartz oscillator, estimated without RCM. This is typical for almost all end users. The (linearly detrended) receiver clock error exhibits values between roughly −100 and +200 nanoseconds, which is typical for a quartz oscillator.
The noise of the coordinates is in the range of 20–25 centimeters in the horizontal components and about 50 centimeters in the up-component, respectively. Furthermore, certain coordinate offsets are visible due to remaining systematic effects such as ionospheric delay and orbit errors. We could attribute these effects thanks to repeated analysis runs with different correction models such as precise IGS final orbits or by forming the ionosphere-free linear combination. Hence, the assessment of the accuracy of the results is difficult since it chiefly depends on the applied correction models, and it is less influenced by receiver clock modeling.
Without use of RCM, the three receivers connected to the CSACs show similar behavior in the coordinate domain. However, the clock residuals become very small compared to those of the internal oscillator and amount to only a couple of nanoseconds at most. As an example, FIGURE 4 depicts the results for CSAC A. Even over a relatively short period of time of approximately eight minutes, this oscillator shows a significant frequency drift, which we have to account for in RCM. Note that this is also true for the device’s oven-controlled crystal oscillator (OCXO) post-filtered signal.
When applying RCM, as expected, no changes in the time series of the north and east coordinates occur, but a strong decrease of the up-coordinate residuals is clearly visible. The noise level is up to 20–30 centimeters. Due to the applied polynomial clock model, the clock residuals are also reduced. Thanks to the increasing number of epochs/observations contributing to the estimation of the clock parameters, the course of these residuals gets smoother over time. Furthermore, spikes in the up-coordinate time series at around minutes five to seven caused by sudden signal obstructions are almost eliminated thanks to RCM. Also, when applying RCM, there are no improvements in the horizontal components, but the scatter of the up-coordinates is decreased in the range of 48 percent (CSAC B) to 58 percent (CSAC A).
Our second RCM approach based on an existing extended Kalman filter clock model shows comparable results. The most obvious difference to a sequential least-squares approach is that the spikes in the up-coordinate and clock residual time series at around minutes five to seven are not smoothed as strongly.
Reliability and Integrity
Reliability and integrity are very important GNSS performance parameters, especially for real-time and safety-of-life critical applications. In general, we distinguish between internal and external reliability, which are both measures for the robustness of the parameter estimation against blunders in the observation data. Thereby, good reliability makes it easier to identify and remove gross errors and outliers in GNSS data analysis.
Internal reliability is calculated in terms of so-called minimal detectable biases (MDBs) of the GNSS observations. These values determine lower bounds for gross observation errors so that these can still be detectable. External reliability describes the influence of these MDBs on the parameter estimates. In our experiments, we found reductions in the size of the MDBs of up to 16 percent.
As a consequence, the vertical protection level — a measure of integrity — is also improved.
Positioning with 3 Satellites
Generally, GNSS positioning requires at least four satellites in view to solve the equation system for the four unknowns. This can become a severe restriction in difficult environments such as urban canyons. Taking benefits of an oscillator of high accuracy, with known and predictable frequency stability, enables positioning using only three satellites. This approach enhances GNSS continuity and availability, and is called clock coasting.
Thanks to the stability of CSACs, the GNSS observations are corrected by an additional receiver clock term, which is computed from the latest clock-coefficient estimates. To show the effects of this method, we generated two artificial partial satellite outages so that only observations on only three satellites remain. The latter were chosen in such a way that typical situations in an urban canyon were simulated; that is, only satellites with high elevation angles were visible to the receiver.
The resulting coordinate and clock time series are depicted in FIGURE 5. When coasting through periods with only three satellites available, the horizontal coordinates become approximately two to three times noisier (1–2 meters). Due to the poor observation geometry, an additional offset of about 1 meter is induced in the north component during the first partial outage. However, the noise of the up-coordinate is only slightly increased in both of the outage periods, although a significant drift is visible during the first one. Most likely, this is because the coefficients used for clock coasting are only based on 60 epochs up until that time. During the second partial outage this drifting behavior vanishes independently of the satellite geometry. Due to the fact that the clock time series are linearly detrended and a linear clock polynomial is applied, the corresponding residuals shown in FIGURE 5 equal zero during the coasting periods.
The presented approaches for RCM and clock coasting are applicable in multi-GNSS positioning and timing data analysis, too, where we also have to consider inter-system biases. Thanks to the high temporal stability of these biases, they can be modeled by a polynomial in the same sense as the receiver clock error. [Click on an image to enlarge it.]
FIGURE 3. Topocentric coordinate deviations with respect to the reference trajectory and clock errors. The receiver is driven by its internal oscillator. No receiver clock modeling was applied in a sequential least-squares adjustment. Note the different y-axis scales.
FIGURE 4. Topocentric coordinate deviations with respect to the reference trajectory and clock errors for a receiver connected to the CSAC A signal. The results without receiver clock modeling are depicted in black and blue. The results applying a quadratic polynomial for clock modeling in a sequential least-squares adjustment are shown in red.
FIGURE 5. Topocentric coordinate deviations with respect to the reference trajectory and clock errors. The receiver is connected to CSAC B. The solution is obtained from a sequential least-squares adjustment with clock coasting from minutes one to two and five to seven.
Spoofing Detection
Jamming and spoofing of GNSS signals have become major threats to GNSS positioning and timing. Although these authentication issues have been well known since the beginnings of GPS, they have become more severe in recent years due to the greatly increased number of applications that rely on (highly) accurate GNSS positioning and timing.
Experiment
A spoofing attack’s goal is for the signal tracking loops of a target receiver to acquire the spoofing signal, and then pull its navigation solution away from the authentic position. So as not be detected by the target receiver, the common delay of the spoofing signals — which will be absorbed by the receiver’s clock-error estimate — must not deviate significantly from the receiver’s authentic clock error. This means that the injected delay has to be as small as possible so that it cannot be separated from the typical random frequency (and thus time) fluctuations of the oscillator driving the receiver.
To simulate a spoofing attack, we set up an experiment consisting of two GNSS receivers, one driven by its internal quartz oscillator, and one connected to CSAC B, both recording the same GNSS signals via a signal splitter. The input signal of the latter comes from an active coaxial switch, which allows us to switch between two different antennas in less than 1 second. Both antennas in our measurement configuration were mounted on tripods. However, one antenna was connected to a commercial GNSS repeater, which generates an additional delay, and its output signals were transmitted via cable to the coaxial switch (see FIGURE 6). When switched to the antenna without the repeater, the receivers recorded authentic signals. When switched to the repeater, they recorded spoofed signals. The location of the repeater antenna ranges from 2 to 25 meters away from the authentic antenna, thereby introducing different delays — in addition to the repeater delay — into the signal processing of the two receivers. We assume that a short delay of about 2 meters (7 nanoseconds) is more difficult for receivers to detect than a delay of about 25 meters (83 nanoseconds).
Whenever the signal path is switched from the authentic antenna to the repeater antenna, this should result in a jump in the clock-error time series. Combined with the known frequency stability of the receivers’ oscillators, we can establish a hypothesis test for the significance of such a clock-error jump.
For each new location of the repeater antenna, the measurement procedure was the same. We recorded authentic and spoofed data four times alternating for two minutes with a data rate of 1 Hz.
FIGURE 6. Measurement configuration of a spoofing detection experiment.
Results
FIGURES 7 and 8 show the original clock-time offsets for two different locations of the repeater antenna as recorded by the receivers, and the corresponding predicted clock states from the Kalman filter. The jumps in each clock-error time series are more or less clearly visible, especially in the case of the 2-meter distance. For the latter, the hypothesis test of the temperature-controlled crystal oscillator (TCXO) always accepts the alternative in favor of the null hypothesis; that is, from a statistical standpoint, no spoofing attack is detectable. This is because of the small signal delay attributable to the measurement geometry, which cannot be properly separated from random time deviations caused by the TCXO’s low frequency stability. On the contrary, even for this short distance between the spoofing and authentic antennas, every start and end of the four spoofing attacks were detected.
As an example, FIGURE 8 shows the results for a larger distance (around 14 meters). In this case, all spoofing attacks can be properly detected by both the TCXO- and the CSAC-controlled receivers. The seven-times-increased distance ensures that even the low-cost TCXO inside the receiver combined with a sophisticated receiver internal clock estimation is capable of spoofing detection by monitoring its clock states.
FIGURE 7. Original and predicted receiver time-offset states after a straight line fit for a receiver driven by its internal TCXO and connected to CSAC B, respectively. The repeater antenna is located about 2 meters away from the authentic antenna.
FIGURE 8. As for Figure 7 but with the repeater antenna located about 14 meters away from the authentic antenna.
Conclusions
In this article, we have proposed a deterministic approach for receiver clock modeling in a sequential least-squares adjustment by applying a linear or quadratic clock polynomial whose coefficients are updated each consecutive epoch. As a prerequisite, an individual characterization of the frequency stabilities of three miniaturized atomic clocks was carried out with respect to the phase of an active hydrogen maser showing an overall good agreement with manufacturers’ data.
A real kinematic experiment was carried out with two chip-scale atomic clocks, and typical code-based GPS navigation solutions were computed. We showed that the precision of the up-coordinate time series are improved by up to 58 percent, depending on the clock in use. Furthermore, internal and external reliability were significantly enhanced. Additionally, it was shown that our algorithm is capable of coasting through periods of partial satellite outages with only three satellites in view. This increases availability and continuity of GNSS positioning with poor satellite coverage caused by high shadowing effects or multipath, for example.
Finally, we investigated the benefits of an atomic clock in spoofing detection and showed first results. Our approach, based on a Kalman filter and a hypothesis test, enhances the detectability of a spoofer when using a CSAC instead of the receiver’s internal oscillator, especially in the case of small signal delays injected by the spoofing device, which helps to identify a sophisticated spoofer very quickly.
Manufacturers
We used two different CSACs: a Jackson Labs (jackson-labs.com) LN (CSAC A) and a Microsemi Quantum SA.45s (CSAC B). For the kinematic experiment, we used four JAVAD GNSS Delta TRE-G3T receivers connected to a NovAtel 703 GGG antenna via an active signal splitter. The local reference station consisted of a Leica (leica-geosystems.us) AX1202GG antenna connected to a Leica GRX1200+ GNSS receiver. A JAVAD Delta TRE-G3T was used in the spoofing experiment.
Disclaimer
The authors do not recommend any of the instruments tested. It is also to be noted that the performance of the equipment presented in this article depends on the particular environment and the individual instruments in use.
Acknowledgments
This article is based, in part, on the paper “Benefits of Chip Scale Atomic Clocks in GNSS Applications” presented at ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, held Sept. 14–18, 2015, in Tampa, Florida.
The authors would like to thank Andreas Bauch and Thomas Polewka, who are both with PTB, for their support during execution and analysis of the clock comparisons, and Achim Hornbostel from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt) for discussions on spoofing experiments.
We also thank IGS and its participating agencies for their GNSS products, which were a valuable contribution to our case study.
Our work was funded by the Federal Ministry of Economics and Technology of Germany.
Further Reading
• Authors’ Conference Paper
“Benefits of Chip Scale Atomic Clocks in GNSS Applications” by T. Krawinkel and S. Schön in Proceedings of ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, Tampa, Florida, Sept. 14–18, 2015, pp. 2867–2874.
“A Historical Perspective on the Development of the Allan Variances and Their Strengths and Weaknesses” by D.W. Allan and J. Levine in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 63, No. 4, April 2016, pp. 513–519, doi: 10.1109/TUFFC.2016.2524687.
Time – From Earth Rotation to Atomic Physics by D.D. McCarthy and P.K. Seidelmann, published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2009.
“Special Issue: Fifty Years of Atomic Time-Keeping: 1955 to 2005,” Metrologia, Vol. 42, No. 3, June 2005.
The Measurement of Time: Time, Frequency and the Atomic Clock by C. Audoin and B. Guinot, published by Cambridge University Press, Cambridge, U.K., 2001.
The Science of Timekeeping by D.W. Allan, N. Ashby and C.C. Hodge, Hewlett Packard (now Agilent Technologies) Application Note 1289, 1997.
“Time, Clocks, and GPS” by R.B. Langley in GPS World, Vol. 2, No. 10, Nov./Dec. 1991, pp. 38–42.
• Clock Modeling
Feasibility and Impact of Receiver Clock Modeling in Precise GPS Data Analysisby U. Weinbach, Ph.D. dissertation, Gottfried Wilhelm Leibniz Universität Hannover, Hannover, Germany, Wissenschaftliche Arbeiten der Fachrichtung Geodäsie und Geoinformatik der Leibniz Universität Hannover, Nr. 303, and Deutsche Geodätische Kommission bei der Bayerischen Akademie der Wissenschaften, Reihe C, Dissertationen Heft Nr. 692, 2013.
“Time and Frequency (Time-Domain) Characterization, Estimation, and Prediction of Precision Clocks and Oscillators“ by D.W. Allan in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. UFFC-34, No. 6, Nov. 1987, pp. 647–654, doi: 10.1109/T-UFFC.1987.26997.
“Relationship Between Allan Variances and Kalman Filter Parameters” by A.J. van Dierendonck, J. McGraw and R.G. Brown in Proceedings of the Sixteenth Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting, Greenbelt, Maryland, Nov. 27–29, 1984, pp. 273–292.
“Assessing the Spoofing Threat” by T.E. Humphreys, P.M. Kintner, Jr., M.L. Psiaki, B.M. Ledvina and B.W. O’Hanlon in GPS World, Vol. 20, No. 1, January 2009, pp. 28–38.
Sponsored by: Symmetricom Broadcast Date: Thursday, March 7, 2013 Speaker: Steve Fossi, Director of New Business Development, Symmetricom Panelist: Ravi Pragasam, Marketing Manager, Embedded Solutions, Symmetricom Summary: Atomic clocks have enabled a world where ultra-precise timekeeping is now mandatory for communications, navigation, signal processing and many other applications critical to a modern functioning society. Symmetricom has utilized leading-edge technology and multiple innovations in various disciplines such as semiconductor laser technology, silicon processing, vacuum-packaging and firmware algorithms to deliver the Quantum SA.45c CSAC (Chip Scale Atomic Clock). Attend this webinar and learn how the CSAC can address your requirements for a precise clock without consuming excessive power or taking up too much space in your application.
The Defense Advanced Research Projects Agency (DARPA) is holding a Proposers Day on Feb. 1 to inform potential contractors about the Atomic Clock with Enhanced Stability (ACES) program.
ACES is a potential $50 million program that seeks to develop battery-powered atomic clocks that work to provide warfighters with synchronization and precision timing capabilities during navigation, communications, electronic warfare and reconnaissance missions in the event of a GPS shutdown.
The registration deadline for the Proposers Day is 5 p.m. EST on Jan. 25. The Proposers Day will be held Feb. 1 from 9:30 a.m. to 5 p.m. EST at the DARPA Conference Center, 675 N. Randolph Street, Arlington, Virginia 22203.
The host is Robert Lutwak, ACES program manager at DARPA. In 2012, GPS World awarded Lutwak its Leadership Award for Products.
The meeting will provide information and promote additional discussion on the ACES program, address questions from potential proposers, and provide an opportunity for potential proposers to share their capabilities and ideas for teaming arrangements.
The ACES Proposers Day will include overview presentations by government personnel, technical presentations by potential proposers and collaborators, and an open poster session to facilitate interaction and teaming.
According to the Department of Defense (DoD), “Precision timing and synchronization is essential to DoD communications, navigation, reconnaissance, and electronic warfare systems. The requirements for timing precision and stability have grown increasingly demanding as DoD systems have evolved towards distributed engagement and surveillance architectures, and this trend is expected to continue for the foreseeable future.
“The ACES program aims to develop portable, battery‐powered atomic clocks with stability, repeatability, and environmental sensitivity approaching that of laboratory‐grade cesium beam frequency standards. This will be accomplished through research, development and integration of reduced SWaP components and technologies for advanced atomic physics interrogation techniques. These include, but are not limited to, laser‐cooled and magneto‐optically trapped atomic samples, and RF‐trapped ion samples, as well as interrogation of less environmentally‐sensitive microwave and optical transitions.”
40th Annual NIST Time and Frequency Metrology Seminar
There were four of us, mature males who all remember having a crush on Annette Funicello, were seated around a table avidly discussing deviant behavior with a sometimes rapt mixed-gender audience. The four of us, loudly discussing deviant, and only occasionally aberrant behavior, were doctors: David Allan the world renowned creator of Allan Deviation or variance fame, Judah Levine, world renowned nuclear physicist and Father Time of NIST (National Institute of Standards and Technology), Neil Ashby, former chair and currently Professor Emeritus of Physics at UC Boulder, also from NIST, along with yours truly representing GPS World magazine and the Institute for Defense Analyses. Our ever-changing audience was composed of the 40+ members from around the globe attending the 40th Annual NIST Time and Frequency (T&F) Metrology Seminar, held June 2-5 in stunningly beautiful Boulder, Colo.
Of course, the numerous deviant behaviors under discussion had more to do with the sometimes-fickle performance of various atomic reference systems than they did anatomy. And we were speaking loudly because that is what most men of our age do. Dr. David Allan frequently threw in quotes and anecdotes from his recently published book on time, It’s About Time, about which you will read more later.
The NIST T&F Metrology Seminar is truly one of a kind, easily the best in the world for time and frequency metrology. I have been fortunate enough to attend numerous times. I can truly say I have never found it repetitive or boring. There are so many exciting discoveries concerning time, which David Allan staunchly maintains is a purely human construct, and how time applies to our everyday lives, especially to GPS — all PNT systems actually — that it is impossible not to be constantly fascinated.
NIST Mission
NIST Boulder is all about research and development for timing standards, which is a benign way of saying NIST SMEs (subject matter experts) are the world’s foremost authorities on time and metrology. To wit, NIST has produced no less than four Nobel Prize winners in metrology, the last being awarded in 2012. The atmosphere at NIST and the University of Colorado Boulder campus is such that you can’t help but feel certain there are more Nobel Prizes for NIST on the horizon.
David Howe (Ph.D.), my NIST host and group leader of the Time and Frequency Metrology Division, explained that his organization, which sponsors the seminar, is an operating unit of the Physical Measurement Laboratory of the National Institute of Standards and Technology (NIST), an agency of the U.S. Department of Commerce. The NIST T&F Division is located in Boulder at the NIST Boulder Laboratories, just across from the street from the University of Colorado. Many of the NIST researchers are also University of Colorado professors, adjuncts or graduate students.
The NIST mission includes:
Maintaining the primary frequency standard for the United States
Developing and operating standards of time and frequency
Coordinating United States time and frequency standards with other world standards
Providing time and frequency services for United States clientele
Performing research in support of improved standards and services
Precise time and frequency information is required by electric power companies, radio and television stations, telephone companies, air traffic control systems, participants in space exploration, computer networks, scientists monitoring data of all kinds, and navigators of many types. These users need to compare their own timing equipment to a reliable, internationally recognized standard. NIST provides this standard for the United States.
Of course one of the largest distribution networks for timing data is through the Global Positioning System (GPS), which provides this data globally to more than 4+ billion users and millions of timing systems everyday, numerous times per day. The number of times GPS time is utilized per day is almost impossible to calculate, but most certainly resides in the trillions.
The NIST Time and Frequency distribution system delivers NIST Internet time over the Internet at the rate of 8 billion requests per day from servers at 25 locations across the United States.
The frequency stability provided by classic Cesium and Rubidium atomic reference systems onboard GPS payloads have historically been on the order of 1 x 10-14. While this is the stability provided by the GPS IIF rubidium clocks, currently the rubidium clocks being prepared for GPS III are achieving frequency stability on the order of 1 x 10-15 under laboratory conditions, an order of magnitude better than the current on-orbit clocks.
This is actually an amazing feat. For those of you who don’t deal in scientific notation on a daily basis, this means — since it is on a logarithmic scale — that the frequency stability of GPS III’s atomic clocks have the potential to be 10 times as stable as the IIF clocks, which are currently the most stable and accurate GPS clocks on orbit to date.
Where atomic reference systems are concerned, we routinely speak of frequency stability and not clock accuracy. It is the stability over measured epochs, short and long, that matters most. Indeed, it is the oft-misunderstood frequency stability uncertainty expressed as delta f/f = 1 x 10-16 that produces the clock accuracy to within one standard (SI) second in three hundred (yes, 300) million years — a statistic that is obviously not directly observable, but reasonably predictable. Hence, as Judah Levine often says, where stability is concerned you are an historian, but where accuracy is concerned you are a prophet. NIST defines an SI second as the duration of 9,192,631,770 cycles of the cesium hyperfine transition.
Tom O’Brian, the current chief of the NIST Time and Frequency Division, explained that this level of precision is equivalent to measuring the distance from the Earth to the Sun, a distance of 150 million kilometers, to the uncertainty of 15 microns or 1/10 the thickness of a human hair. While that is impressive, the best is yet to come. NIST is currently working on research-grade optical clocks, which we could reasonably expect to see on orbit one day in future GPS payloads, with an optical frequency stability equivalent to delta f/f = 2 x 10-18 or accuracy equal to 1 second in 15 billion years. Again this is the equivalent of measuring the distance from the Earth to the Sun to an uncertainty of 0.3 micron or the size of a virus.
So What?
Many of you may be asking why, as a GPS user, or merely as a user of technology, you should care about accurate and stable time reference systems. Marc Weiss, a long-time acquaintance and noted researcher at NIST (now in semi-retirement), very eloquently put his thoughts about time in an introduction to a recent timing white paper*, which has been slightly edited for length, current trends and readability. [Ed. So as to not be accused of putting words or opinions in the authors’ mouths, we have provided a reference for the unedited paper at the end of the referenced section]. Marc and several other metrology luminaries express their feelings concerning the future of time and why we should all care:
We stand at the advent of a revolutionary new economy fueled by the global Internet of Everything (IOE). The IOE is a combination of traditional telecom systems with a growing need for wireless technology, and the emerging Internet of Things (IOT) including Machine-to-Machine (M2M) technology. Several current technology providers predict there will be a trillion global endpoints connected to the Internet by 2022, with $14.4 trillion in value at stake.
One fundamental enabler of this revolution is a marriage of timing signals and data that breaks through existing barriers. Currently, optimal use of data in computing and networking is anathema to optimal use of timing signals. Computer hardware, software and networking all isolate timing processes, allowing the data to be processed with maximum efficiency due in part to asynchrony. Yet, the coordination of processes, the time stamping of events, latency measurements and optimal use of precious spectrum are all enabled by ever more accurate and stable timing.
Timing is critical for the future development of and improvements to several high-value applications. For example, in smart transportation systems the exchange of information between vehicles, highways, and civil authorities depends on a robust ubiquitous timing system to ensure the rapid, accurate synchronization and provenance of data. Similar requirements are found in the operation of power grids, especially now that wind farms, solar arrays and the like require different control strategies, which are a critical part of the system. Modern medical applications such as tele-surgery and real time integrative online medical conferences, as well as applications in financial systems are all important examples that require accurate and stable timing signals and may well affect us all.
There are three different types of timing signals for dependable synchronization: frequency, phase, and time. Frequency can be supplied by an individual clock, such as a commercial (atomic) Cesium or Rubidium standard, though practicality drives the use of local oscillators that require calibration and active reference signals. [Ed. Many of these local reference systems and oscillators are routinely updated by GPS signals.] By contrast, phase and time synchronization always require the transport of timing signals plus data. Timing signals are physical, they occur on the physical layer of networks. Indeed the IoT has many devices and applications that require frequency, time and/or phase synchronization. Frequency, time and phase all need to cross layers, boundaries, and networks from their sources in accurate clocks. Requirements for these transfer systems include parameters that create different, perhaps orthogonal, demands on systems. Accuracy, stability, integrity and even non-repudiability requirements are realized with varying demands on different systems….
To facilitate the massive growth of the IoE, data processing and networking require new designs at fundamental levels, allowing integration with precise and verifiable time, frequency and phase signals.
Timing performance is fundamentally dependent upon an underlying oscillator, or ensemble of oscillators and the clocks constructed based on these oscillators.
However, it is apparent to us that many of the researchers and developers of the various time aware systems operate independently of each other. They attend different conferences, read different literature, and in general do not interact sufficiently to achieve the breakthroughs needed. In our minds this calls for a dedicated and collaborative “across the stack” research collaboration focused on two or three comprehensive challenge problems.
Fortunately, this is what researchers, scientists, analysts and metrology experts do at NIST and what we learned about during the T&F Metrology Seminar. The bottom line is many perturbations affect timing signals from atomic reference systems and even local quartz oscillators (clocks). The more these perturbations are understood, the easier they are mitigated and the more stable and accurate our timing signals will be and the faster technology — PNT (position, navigation and timing), clock and otherwise — advances.
For many traditional timing applications and developing “post-timing” applications, stability is more important than accuracy; just as for most advanced technology applications, frequency is more important than time of day.
NIST clearly states its Time and Frequency Metrology Group has the world’s most advanced measurement and calibration facilities for characterizing noise components in oscillators and frequency synthesizers. NIST engages in numerous research and development activities to determine the cause of various types of noise for the purpose of isolating and reducing it, leading to improved components, instruments, techniques and results that are often critical in modern applications. In other words, you have to thoroughly understand a clock issue before you can begin to mitigate issues affecting it. NIST, a synecdoche for understanding time, does that better than any other metrology laboratory in the world today when it comes to atomic reference systems.
What Is Time and Why Does It Matter?
Accurate timing and synchronization are a crucial part of the world’s critical national infrastructure and of modern technology in general, especially the timing signals from GPS satellites, which are used by billions of users continuously every day — although most users remain unaware of the importance and impact that accurate and stable timing has on their everyday lives.
Tom O’Brian reminded us that even St. Augustine of Hippo wondered about time. In circa 400 he wrote:
“What then is time? If no one asks me, I know. If someone asks me to explain, I know not.”
Then, just 1500 years later in 1930, Albert Einstein had this to say about time:
“Space and time are modes by which we think, not conditions under which we live.”
Therefore, I agree with David Allan when he posits that time is a human invention with which only humans struggle. Be that as it may, it is still a condition we live under, and when you consider all the forces, minute to infinite, that affect atomic reference systems and clocks in general, it is amazing our clocks function as well as they do.
Consider that atomic clocks, and even quartz clocks to some extent, are affected by the following elemental and environmental forces and more in the laboratory:
Motion
Acceleration
Gravity – Earth, Moon and planetary
Changes in elevation
~23 different types of noise
Temperature
Magnetic fields
Earth’s Poles
Tides
Light (including lasers)
Electricity
General and Special Relativity
Radiation
The United States Air Force then takes these delicate clocks, atomic (Rubidium and Cesium) as well as quartz VCXOs and OXOs, and launches them (with violent maneuvers) into space in a Medium Earth Orbit that regularly intersects the Van Allen radiation belt. Once on orbit, the clocks routinely experience every one of the listed forces and more on both a regular and changing basis. Of course, we expect the GPS clocks to operate at the same standards and with the same stability and accuracy they displayed in the laboratory. Not asking much are we?
The amazing fact is that thanks to the dedicated scientists and physicists at NIST and other timing laboratories, the clocks work as advertised and continue to do so sometimes for more than 20 years. The current GPS III Rubidium clocks being tested and aged at NRL (Naval Research Laboratory) and other locations around the U.S .are posited to be the first 30-year Rubidium standards with nominal frequency stability of 1 x 10-15. This should provide GPS with another nanosecond of timing accuracy and another 12 inches of positioning accuracy. There will be three of these extremely stable Rubidium clocks on board each GPS III satellite — no Cesium clocks for this family of satellites. Horologists around the world are hoping it is truly a 30-year tube and that only one Rubidium will be required. Only time will tell.
Little Known Factoid (LKF): The first family of GPS satellites on orbit made use of a General and Special Relativity switch that could be set in one of three positions: neutral, plus or minus, depending on whether the universe was relatively static, expanding or shrinking in size. Guess where the switch was set initially and (hint, hint) it could be changed via software from the ground. Drop me a line @ [email protected] and let me know what you think — posit or know, as the case may be.
Thanks
My thanks to David Howe, Judah Levine, Neil Ashby, David Allan (Ph.D.s all) and Danielle Lirette, who made my visit to NIST such a wonderful experience.
It’s About Time
Earlier I mentioned physicist David Allan’s wonderful book, published in 2014. It’s About Time: Science Harmonized with Religion. Allan is about science harmonized with religion and where we are in God’s time. I am halfway through the 402-page tour de force on time, and it is a fascinating read. It is a 50-year biography and history of atomic reference systems, since the first atomic clock only came about in 1949. You’ll be amazed how that happened. Based on what I have read so far, I highly recommend this scientific tome, which is very readable and understandable even for the lay reader. I promise a full review in a future column.
Until then, Happy Navigating! I hope to see many of you at ION JNC (Institute of Navigation Joint Navigation Conference) in Orlando, Fla., June 21-26. There will be a classified day on Thursday, June 25, and a Warfighters Panel as well. Hope you can join us. Remember, GPS is brought to you courtesy of the United States Air Force.
A bi-partisan group of legislators led by Congressman John Garamendi (D-Calif.) has introduced a bill that would require the U.S. Secretary of Defense to establish a backup for GPS within three years using eLoran.
The National Positioning, Navigation, and Timing Resilience and Security Act of 2015, H.R. 1678, was co-sponsored by Congressmen Duncan Hunter (R-Calif.), Peter DeFazio (D-Ore.), and Frank LoBiondo (R-N.J). Garamendi is the ranking member of the House Transportation and uInfrastructure Subcommittee on the Coast Guard and Maritime Transportation.
H.R. 1678 would require the secretary of defense, in coordination with the commandant of the Coast Guard and the secretary of transportation, to establish and sustain a reliable, land-based positioning and navigation system that will complement and backup America’s GPS for military and civilian uses by using eLoran.
eLoran is the government’s existing and underused long-range navigation system infrastructure. The backup system would step in when GPS signals are corrupted, degraded, unreliable, or otherwise unavailable. A terrestrial-based system, eLoran wouldn’t be affected by atmospheric interruptions such as solar storms, or jamming or spoofing aimed at GPS.
The bill directs the secretary of defense to incorporate the expertise and contributions of the private sector to quickly establish system architecture, as well as build and operate the system.
“GPS is much more than a LCD screen on your dashboard. It’s a technology used for much of our nation’s critical infrastructure and by almost every major industry in America, as well as the military, law enforcement, and first responders,” Garamendi said in a press release. “We are increasingly reliant on the precision, navigation, and timing services that GPS provides. From land navigation on cell phones to a timing source for our national infrastructure, we need a reliable backup system to GPS.”
Garamendi said the bill would make the nation’s geopositioning infrastructure more resilient to “threats both natural and nefarious.” “A backup system could also reach places that GPS currently cannot, such as inside many buildings. This would help first responders and law enforcement more effectively protect the public,” he added.
Other members of Congress are expected to sign on as co-sponsors after Congress returns from its spring recess, according to Dana A. Goward, president and executive director, Resilient Navigation and Timing Foundation.
The eLoran PNT system would use enhanced long-range signals (eLoran) from 19 towers around the country, each with approximately a 1,000-mile range providing overlapping fields from which a device can derive its location. The back-up system would use the remaining Loran infrastructure and provide a secure and reliable cybersecurity insurance policy, said the press release.
The U.S. atomic clock, accurate to one second in 300 million years, also serves as the base timing source for this backup GPS capability. This exceeds the timing needs of modern cell phones, creating an infrastructure backbone that is prepared to handle the evolution of consumer and industry electronic communications in the years ahead, the press release said.
The bill sets out numerous requirements for the system, saying that it shall:
Be wireless, terrestrial, and wide area
Provide a precise, high-power 100 kilohertz signal
Be resilient and extremely difficult to disrupt or degrade
Be able to penetrate underground and inside buildings
Take full advantage of existing, unused Loran infrastructure
Work in concert with and complement any other similar positioning, navigation and timing systems, including eLoran.
Since 2004, the federal government has recognized that the absence of a reliable backup system for GPS is a glaring economic and security threat to the United States, and has reaffirmed its interest in developing an eLoran as a reliable, land-based backup for GPS signals, the press release said.
In January, the United States Army began soliciting information for eLoran receivers for the warfighter, either stand-alone or integrated with GPS, for use in Army and other Department of Defense maritime, aviation, or vehicular platforms, and for position and timing.
The United Kingdom began using eLoran in October 2014 to protect its shipping lanes, which carry 95 percent of UK trade, in case of GPS signal loss.
“Networks of correlated atomic clocks, some of them already in existence, such as the Global Positioning System, can be used as a powerful tool to search for topological defect dark matter, thus providing another important fundamental physics application for the ever-improving accuracy of atomic clocks,” write physicists Andrei Derevianko and Maxim Pospelov in the current issue of Nature Physics journal.
Derevianko teaches at the University of Nevada, Reno, and Pospelov at the University of Victoria and the Perimeter Institute for Theoretical Physics in Canada. Derevianko and Geoff Blewitt, director of the Nevada Geodetic Laboratory at the University of Nevada, Reno are testing this dark-matter detection theory by analyzing clock data from atomic clocks aboard GPS satellites, searching for instances where initially synchronized clocks might have become desynchronized. They expect time discrepancies between spatially separated clocks to exhibit a distinct signature, one that may reveal the nature of spatial dark matter.
The Geodetic Lab developed and maintains the largest GPS data processing center in the world, according to a University of Nevada statement, able to process information from about 12,000 stations around the globe continuously, 24/7.
“We know the dark matter must be there,” explains Blewitt, “because it is seen to bend light around galaxies, but we have no evidence as to what it might be made of. If the dark matter were not there, the normal matter that we know about would not be sufficient to bend the light as much as it does. That’s just one of the ways scientists know there is a massive amount of dark matter somewhere out there in the galaxy. One possibility is that the dark matter in this gas might not be made out of particles like normal matter, but of macroscopic imperfections in the fabric of space-time.”
“Despite solid observational evidence for the existence of dark matter, its nature remains a mystery,” said Derevianko. “Some research programs in particle physics assume that dark matter is composed of heavy-particle-like matter. This assumption may not hold true, and significant interest exists for alternatives.
“Modern physics and cosmology fail dramatically in that they can only explain 5 percent of mass and energy in the universe in the form of ordinary matter, but the rest is a mystery.”
Scientific evidence reportedly shows that dark energy constitutes about 68 percent of the mystery mass and energy. The remaining 27 percent may be dark matter, though it has never been detected or measured.
“Our research pursues the idea that dark matter may be organized as a large gas-like collection of topological defects, or energy cracks,” Derevianko added. “We propose to detect the defects, the dark matter, as they sweep through us with a network of sensitive atomic clocks. The idea is, where the clocks go out of synchronization, we would know that dark matter, the topological defect, has passed by. In fact, we envision using the GPS constellation as the largest human-built dark-matter detector.”
In consulting my notebooks for the spring of 2014, I find many remarkable cases that engaged the attention of my intimate friend Mr. Sherlock Holmes. Among them stand out the tragedy of the ancient British barrow, the disappearance of Pemblestoke the magician, and the curious facts associated with the giant rat of Sumatra, a tale for which the world is still not prepared. Perhaps none of these so well illustrate, however, the advanced technical insights and consultative powers of the great detective as did the intrigue into which we were drawn by the brilliant young American scientist, Geo. P. Hess.
“Watson, we have a new client,” Holmes announced over breakfast, “a friend, actually, upon whom I have depended for many years. He has always proved reliable, helping me navigate the highways and by-ways all across the land.”
“His name?” I inquired.
“The Right Honorable George Parkinson Hess from California, Colorado, Pennsylvania, Florida, and doubtless many other parts of the American nation. I have watched G.P. Hess grow these last 36 years into a prodigiously successful entrepreneur, known the world round for his ubiquity, openhanded generosity to all, and, equally, his devotion to his own country. Now it seems he needs my advice, and I cannot refuse him.“
“I wonder that an American should be able to find his way here this morning,” I replied. “There’s a beastly fog about, and London streets are no friendly environment under the best of conditions.”
“Have no fear, Watson,” Holmes chuckled. “I have never known G. P. Hess to be late for any function. Since a lad he was always on time, right to the second. You can set your watch by him, and as far as I know he has never been lost. He has an uncanny sense of direction and is indeed a fount of knowledge concerning maps and directions. I believe I hear his ring at the bell even now.”
Mrs. Hudson ushered in our American visitor, and Holmes introduced us. “It is always good to see you, G.P. How are you — in good health, I presume?”
“Indeed, Mr. Holmes, things are neither as well they may seem on the surface, nor as well as they could be. I am troubled of late, severely troubled by potential gaps in my future. Not to mention the seismic activity lately in Los Angeles. In the last 18 months, the magnitude of the tremors has grown from 3.1 to 5.1 on the Richter scale. I just can’t understand why they thought to have our major acquisition headquarters in a place that is constantly threatened by tremors, outright quakes, wild fires, floods, landslides, and tsunamis. Not to mention the traffic. It would have been much better to co-locate acquisition with the main headquarters in Colorado. All they have to worry about there are blizzards, high winds, and an occasional wildfire.
“While I could not agree with you more, G.P., I fail to see what I can do, try as I might, about Mother Nature.”
Fire in Florida
“Right you are, Mr. Holmes. I’ll get to the heart of the matter. I am deeply concerned about several of our business ventures: expansion and modernization efforts, if you will. You may have heard about a small but rather serious fire at the U.S. Air Force’s Cape Canaveral radar tracking facility and the subsequent launch delays. That small fire at a single tracking facility has already delayed a National Reconnaissance Office (NRO) launch, and a resupply mission to the International Space Station, currently manned by U.S. and Russian crews who, whether or not they are still speaking to one another, really need the replenishments. Now we aren’t allowed use Russian engine cores for space launch any more. A blessing, actually, as the Russians have put more malfunctioning GLONASS satellites into salt water lately than into the vacuum of space, when they aren’t simply blasting them to kingdom come.
“With all the troubles besetting Cape Canaveral, Elon Musk is burning figure eights in his Tesla, and SpaceX is a very happy company — in the right place at the right time, what? Able to launch its Falcons and Falcon Heavies from Vandenberg as well as Canaveral.
“Imagine, one little fire has caused the cancellation of several space launches, and those still on the manifest are moving to the right daily. We had hoped to put into orbit four new IIF models this year, but that looks next to impossible now. Plus it appears the GPS III payload has hit a snag. It is delayed six to nine months.”
GPS III Delay
“A delay in GPS III had not been looked for, had it?” queried Holmes.
“No sir, it had not. Everything was proceeding smoothly, but now the satellite payload is in question. Subcontractor Exelis has provided every GPS payload since 1978 and all have worked marvelously well, some of them for more than 23 years. But now — there is a problem. Some say it is signal crosstalk, some say it is with the new rubidium clocks. One thing for sure, it is demoralizing. I am given to understand the powers that be in Colorado Springs and Los Angeles are calmly but firmly looking for some competition or even an alternate payload provider.
OCX Delay
“And then there is the GPS ground segment. It has moved one month to the right for every month it has been in existence, it has gone over budget, and now is on its third program manager in three years. Whatever happened to the days when a capable leader conducted a program from beginning to end, knew it intimately from top to bottom, from soup to nuts? What is this world coming to? Where are our leaders?
“And don’t get me started on the effects of ‘seques-castration’!” fumed the young man.
“And the Chinese!” he continued, gathering steam. “Just who do they think they are? Do you know they called their regional system a PNT gold standard? Gold standard! Don’t make me laugh!”
“Now G.P., don’t despair,” soothed Holmes. “There are still excellent leaders out there, you just have to look a bit harder nowadays. In the space arena, Elon Musk, General William Shelton, Wild Bill Cooley, Frank Kendall, and Keoki Jackson are just five of many that come immediately to mind. Of course I would not want to play poker with any of them, but I digress.”
Solutions Appear
“I have been reading and thinking about the alternative payload issue,” the detective continued, “and I have other sources of information as well. Dr. Watson calls them my Baker Street Irregulars, and they are both resourceful and quite knowledgeable. These sources tell me there is another Colorado company, with excellent leadership, that is really on the ball, can move mountains (or huge boulders, anyway), and mark my words, they have top-notch crews, expertise, and even some past performance where an alternative GPS payload is concerned. They might be worth watching.
“As far as OCX goes, frankly I am hearing there are indeed backups and alternatives. My sources have confirmed the existence of a bracket of applicable technologies belonging to a small residual company, run by an Irish clan, believe it or not, with considerable past performance and expertise. Once officially launched to work on the real-time issues, they should be able to help the ground-segment team get back on the fast track.
“As for as the Chinese and their claims, all I can say is no one believes their gold standard rhetoric, although it obviously has a purpose.”
“Mr. Holmes, I hope you are right,” the American replied with an assuaged look. “I knew that if I talked with you I would feel better about these perplexing issues.
“I must resume my journey to Rotterdam, where I will hear a lot more about the Galileo program meeting its launch dates — or not — and the GLONASS outage. As rough a shape as we are in, we’re still far better off than the rest! In the meantime, I’ll pop over to Greenwich to synch up and universally coordinate with those folks before I move on to the Continent.”
G.P. Hess carefully scrutinized his pocket watch. “Now Mr. Holmes, Dr. Watson, I must depart. As you know I have a reputation to maintain: always precisely on time, never lost, and as far as I know, I have never blacked out. Cheerio!”
“What a remarkable fellow, Holmes!” I said after our client had left. “He is certainly full of energy.”
“Yes,” my friend replied, “energetic and very successful. If you had observed him more closely, Watson, you would have noticed his pocket watch. Ah, you did not remark upon it? Standard-issue, atomic-reference version, crafted of solid gold. You might say, and rightly so, that where time is concerned, G.P. Hess is the undisputed holder of the Gold Standard.”
So ends our brief visit with Holmes and the illustrious Watson. Stay tuned for further adventures, and until next time, Happy Navigating! G.P. Hess and I hope to see you all next week in Rotterdam, the Netherlands, at the European Navigation Conference, ENC-GNSS 2014. Drop by and say Hello!
If you can’t drop by and say hello in Rotterdam, the Netherlands, then please join me at the 30th Space Symposium, which is slated for May 19-22, 2014, at The Broadmoor Hotel in Colorado Springs. The Space Symposium is considered by many of us in the Space business to be the premier gathering of space professionals in the world.
In June, I will be attending the 39th NIST Time and Frequency Seminar. It has a great lineup of speakers this year to include: Judah Levine who is the NIST civilian time leader, David Allan who is the original creator of the famous Allan variance, and Neil Ashby, an expert in relativistic timing effects. The seminar takes place in Boulder, Colorado, June 3-6, 2014.
What Is Don Reading?
I had very little time for reading this month, or so I thought — then I had a brief but enlightening correspondence and conversation with local author George E. Nolly, who also lives in Colorado. George sent all four of his wonderful books direct to the Kindle app on my iPad. I had told George I was so swamped I would save his books to read on the airplane on my way to Rotterdam and report on them after the European Navigation Conference.
Then I read just one chapter of the first book and I was hooked. There was nothing for it but to devour all four volumes of the escapades of young Vietnam era USAF pilot, Hamilton “Hamfist” Hancock. Hamfist Out: The Chill Is Gone; Hamfist Over Hanoi: Wolfpack on the Prowl; Hamfist Down! Evasion, Survival and Combat in the Jungle; Hamfist Over The Trail: The Air Combat Adventures of Hamilton “Hamfist” Hancock
It will be like going back in time for many readers of a similar age. George Nolly writes with such an easy-going grace and fluidity that reading of these often stressful and life-threatening times, while sitting in my lounge chair, was, for me anyway, indeed a pleasure.
Certainly I can remember undergoing many of the same flying and ground ordeals, and Nolly tells his tales with such honesty and clarity that it brought back vivid memories. In fact I have never read such accurate descriptions of what it was like to fly the old T-29 with radial engines and all that entails. George actually brought back the unforgettable sound and smell of those two Pratt & Whitney R-2800 radial, air-cooled engines. They are from a long-forgotten era of aviation, but those of us who heard them will never forget them.
T-29A Aircraft, Vietnam era, restored. Courtesy of CONVAIR T29A.
George also makes wonderful plugs for GPS, possibly without knowing it, when he describes using LORAN maps under red lights in a cramped cockpit. This, along with all the time he spent just trying to figure out where he was or where the target was located, just screams for a GPS solution. In truth, in the Vietnam era we airmen spent a great deal of time trying to figure out exactly where we were, where our target was, and where the enemy was located, especially if he was shooting at us. Today all those tasks are made infinitely simpler with the use of GPS and modern electronics. However, this also highlights the amazing feats of airmanship accomplished in the Vietnam era, all while being constantly targeted by the enemy, all the more incredible.
Radial engine.
Just between us veteran airmen, the author relates the tales with such clarity and detail I suspect many of them are autobiographical. George E. Nolly, after graduating from the U.S. Air Force Academy here in Colorado Springs, served as a pilot in the United States Air Force, flying 315 combat missions on two successive tours of duty in Vietnam, winning three Distinguished Flying Crosses and 24 Air Medals, flying O-2A and F-4 aircraft, so he knows whereof he writes.
Even if you are a few generations younger than George Nolly and me, and don’t undergo a nostalgic experience as you read, you will certainly enjoy these fabulous books. Be sure to read them in order, as they are actually one running story that brings to life the trials, tribulations, and joys of Hamilton “Hamfist” Hancock for all of us and vividly recreates the way things were back in the 1960s and ’70s in the United States, the USAF, and what it was like flying in combat in Southeast Asia. I highly recommend these tales. I hope there are more to come.
Upcoming Conferences
If you can’t drop by and say hello in Rotterdam, the Netherlands, then please join me at the 30th National Space Symposium, which is slated for May 19-22, 2014, at The Broadmoor Hotel in Colorado Springs. The National Space Symposium is considered by many of us in the Space business to be the premier gathering of space professionals in the world.
In June I will be attending the 39th NIST Time and Frequency Seminar. It has a great lineup of speakers this year to include: Judah Levine who is the NIST civilian time leader, David Allan who is the original creator of the famous Allan variance, and Neil Ashby, an expert in relativistic timing effects. The seminar takes place in Boulder, Colorado, June 3-6, 2014.
Anritsu Company is launching an internal atomic clock option for its MS2720T Spectrum Master handheld spectrum analyzer that allows users to acquire excellent frequency accuracy, including in environments in which the GPS cannot be used.
Integrating the atomic clock inside the MS2720T provides field engineers and technicians with a durable, handheld spectrum analyzer that can deliver the extremely high accuracy necessary to prove regulatory compliance.
By using the atomic clock, users can acquire a very accurate frequency reference without the need of the GPS. Calibration accuracy of the atomic clock is 1×10-9. The MS2720T can be configured with the GPS receiver and the atomic clock to achieve both high-frequency accuracy and GPS location stamping of measurements.
Because the atomic clock module mounts inside the instrument, there are no loose cables that can potentially snag on branches, antennas or other extensions prevalent in the field environments in which the MS2720T is used, the company said. The atomic clock is automatically used once it is installed.
The Spectrum Master MS2720T series features the highest performance handheld spectrum analyzers on the market, the company said. Providing field technicians and engineers with performance that rivals a benchtop spectrum analyzer, the MS2720T features a touchscreen and best-in-class performance for dynamic range, DANL, phase noise, and sweep speed, providing unprecedented levels of spectrum monitoring, hidden signal detection, RF/microwave measurements, and testing of microwave backhauls and cellular signals.
Continuous frequency coverage from 9 kHz to 20 GHz is provided by the MS2720T with the option 1 internal atomic clock. An improved sweep mode allows users to set resolution bandwidth from 30 kHz to 10 MHz with minimal effect on sweep speed. Because the sweep speed with a 30 kHz bandwidth is nearly the same as a 10 MHz RBW, sensitivity can be selected without the need for long sweep times.
The MS2720T has dynamic range of > 106 dB in 1 Hz RBW, DANL of -163 dBm in 1 Hz RBW, and phase noise of -112 dBm @ 10 kHz offset at 1 GHz. These best-in-class specifications are complemented by unprecedented measurement capabilities. A burst detect sweep mode function allows emitters as short as 200 microseconds to be captured every time, allowing the MS2720T to detect bursty signals that can lead to finding intermittent or bursty emitters. The burst detect sweep mode increases sweep speed more than 1,000 times in a 15-MHz span.
The internal atomic clock has a U.S. price of $5,900 and is available in 6 to 8 weeks.
Orolia has finalized the contracts to supply Rubidium atomic clocks (Rubidium Atomic Frequency Standard, RAFS) and passive hydrogen masers to equip eight satellites for Galileo’s Full Operational Capability Phase II program. The two new contracts, totaling 14.5 million euros, follows the authorization to proceed received in June 2012 for the manufacture of these two types of high-precision clocks.
Orolia brands include Spectratime and Spectracom. The announcement was made through Orolia subsidiary Spectratime.
Each Galileo satellite carries two Rubidium atomic clocks and a passive hydrogen maser, the most stable clock in the world, according to Spectratime. Once completed, this new contract, in partnership with Astrium and Selex Galileo, will make Spectratime the leading supplier in the world for active atomic clocks in space, including 72 for the Galileo system.
Rubidium atomic clock, or RAF.
Atomic clocks are used in satellite navigation because of their stability, low weight and high reliability. Very accurate time is used to precisely measure the path of radio signals from the satellites to Earth, and by calculation, the distance between the satellites and the Galileo receiver. The stability of these clocks is enough to guarantee geo-location accuracy of one meter with a fully operational ground infrastructure.
Spectratime said it has the expertise and capability in designing advanced maser physics packages for high-performance, high-reliability space applications, where the clocks need protection in the hostile space environment from radiation, magnetic fields, shock, vibration, or thermal variations.
Spectratime, a provider of atomic clocks and a business of the Orolia Group, has announced it has been selected to provide the Rubidium atomic clocks and passive hydrogen masers for eight satellites for Europe’s Galileo GNSS. Spectratime expects this Authorization to Proceed will lead to a final contract for the manufacture of these two types of high precision clocks, estimated at 14 million euros, by summer 2012.
“This new authorization to proceed, just a year after the signing contracts totaling nearly 20 million euros for the supply of the clocks for the first 14 operational satellites for the Galileo satellite navigation system, confirms Spectratime’s position as a world leading supplier of space atomic clocks,” said Jean-Yves Courtois, CEO of the group. “Each satellite carries on board two rubidium atomic clocks and a passive hydrogen maser, the most stable type of atomic clock in the world. In a few years, after the execution of the contract, which will be implemented in partnership with Astrium and Selex Galileo, we will have the most currently active atomic clocks in space, including 72 for the Galileo system alone.”
I must govern the clock, not be governed by it.
— Golda Meir
The Question
A few months ago at a speaking engagement, I took questions from the audience after my presentation. The audience was made up of GPS enthusiasts, GPS equipment vendors, and evidently GPS neophytes as well, because the last question was asked by a young lady, from a large well known government user segment, who was intrigued by but obviously knew little about the inner workings of GPS. Her question so stunned me and the audience that it brought the questions to an abrupt end. Thank goodness no one actually laughed out loud, and frankly I was so incredulous that I almost gave an impertinent answer that would not have served any purpose other than to embarrass the young lady and expose some insensitivity on my part. No, fortunately, after recovering from the initial shock due to the naiveté of the question, I answered her with a straight face, because it seemed to be an honest and sincere question.
Allow me to set the stage. My talk was on the Perfect Handheld GPS Transceiver and how the PHGPST could be aided by a Symmetricom Chip Scale Atomic Clock (CSAC).
The young lady’s comment and eventual question was exactly as follows: “I came here this afternoon because I was intrigued by your columns in GPS World and I wanted to know more about the Perfect Handheld GPS Transceiver and possibly learn how I could even purchase one or more for my organization. However, most of your comments have been focused on the benefits of atomic clocks. Frankly, I am a bit disappointed. So where can I buy a PHGPST and what do atomic clocks have to do with GPS anyway?”
Retrospective
I have had a few months to think about that episode, and although all ended well, with no one being overly embarrassed, despite some good-natured ribbing, it was a little unsettling. It also takes me back to a previous theme in several of my columns concerning educating users about the Global Positioning System. Not just what GPS can do for you — certainly that is well covered in GPS World, other publications, and on the Internet. Indeed, just type the acronym “GPS” into any search engine and you will be rewarded with the rather daunting number of 1,670,000,000 hits — yes that’s 1 billion, 670 million hits.
A Daunting Perspective
Considering that the average person today, who has reached my advanced age, my will probably live to be approximately 80 years of age or more, the obvious question is does anyone actually have the time to peruse ~1.6B websites on GPS?
You don’t have to be a professional metrologist or an expert mathematician to determine the logical answer, but if you are really concerned about time it might help. Consider the following answers — yes, plural — to the question posed, which assumes that a person would spend one minute or 60 seconds at each website — which begs the question, just how many minutes are there in an 80-year life span anyway? Of course, this answer assumes the hopefully unlikely event that one would come out of the womb Googling “GPS.”
Calculations
By the nominal quartz clock on the wall, and using the Gregorian calendar, and not considering leap years, 80 human years equates to 42,048,000 minutes. If we utilize the Julian calendar and add leap years, it equates to 42,076,800 minutes. By a standard years definition it equates to 42,075,936 minutes. By SI, international system of units, or true metrology standards, 80 years equates to, 42,075,901.3 minutes. The differences have to do with metrology and atomic reference systems versus the nominal unaided quartz clock. And although we say GPS runs on atomic clocks, the true answer is GPS runs on highly stable (accuracy is not a relevant term to be used here) atomic reference systems — noble gases and all that.
Now stay with me and allow me to explain the 80-years-in-seconds answers (and you naively thought there was only one answer) in terms a metrologist (the guys and gals who really care about time and frequency) at NIST, the National Institute of Standards and Technology in Boulder, Colorado, would use:
80 Years by the Calendar and Clock
For an entire block of 80 years, containing 20 leap years, the number of minutes would be the same as in 80 Julian calendar years of 365.25 days.
The number of minutes as calculated by calendar and clock is 42,076,800 — 80 years x 365.25 days/year x 24 hours/day x 60 minutes/hour = 42,076,800.
Or 80 times the number of minutes in a year, which is calculated as 525,960.
SI or Leap Years
Now, when we approach the question from an SI perspective, the answer is slightly but significantly different. The definition of a year is 31,556,926 standard seconds, while the standard leap year calculation is equal to 365 days, 5 hours, 49 minutes, and 12 seconds (31,556,952 seconds). Instead of 525,960 clock minutes, you have 525,949.2 (standard) minutes. For 80 years, the results equal 42,075,936 minutes.
The variation between clock/calendar minutes and the measured length of the year only becomes important to those unfortunate enough to be born on the 29th of February. That’s when the two calculations and calendars diverge by enough to subtract an entire day from the normal leap year system, hence the varying length of February, on the Gregorian calendar, every four years. However, to metrologist and GPS experts, who define an SI second as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the Caesium 133 atom, the differences are astronomical (pun intended).
Caesium, Rubidium, Hydrogen…
At this point many GPS/PNT cognoscenti are probably saying, wait a minute, there are also Rubidium and hydrogen maser clocks on orbit today, so why use the Caesium standard for the SI second?
The Standard Tale
The Caesium standard for the SI second was established in 1960 when it was decided that it was time to abandon the astronomical or ephemeris, revolution of the Earth around the Sun, basis for the second. Indeed Louis Essen from the National Physical Laboratory (NPL in Teddington, England) and William Markowitz of the United States Naval Observatory (USNO in Washington, D.C.) determined the relationship between the hyperfine transition frequency of the Caesium atom and the ephemeris second. Using a common-view measurement method based on the received signals from radio station WWV (operated by NIST and broadcast continuously from Boulder, Colorado) they determined the orbital motion (ephemeris) of the Moon about the Earth. From this data they inferred the apparent motion of the Sun, in terms of time as measured by an atomic reference system, in this case Caesium. They determined a second of ephemeris time (ET) to be equal to 9,192,631,770 ± 20 cycles of the atomic Caesium frequency. Consequently, in 1967 the 13th General Conference on Weights and Measures formally defined a second of atomic time in the International System of Units as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the Caesium-133 atom.
So, since 1967 the Caesium atom has determined and supplied the atomic time reference for the globe. Caesium clocks have certainly undergone numerous refinements, and companies like Symmetricom in the U.S. still build Caesium reference systems that are used globally to determine the SI second and hence coordinate both International Atomic Time (IAT) and UTC or Coordinated Universal Time. And just how accurate is Caesium as a standard? The Swiss have built a continuous cold Caesium fountain atomic clock in Switzerland that started operating in 2004 at an uncertainty of one SI second in 30 million years.
Numbers Can Be Deceiving
Now while that sounds and is very impressive, the fact of the matter is one SI second is a long duration when it comes to atomic clocks — notice I avoided saying a “long time.” Indeed, today metrologists routinely speak in terms of 18 orders of magnitude less than an SI second. That is 18 places to the right of the decimal place, a very small number, destined to become even smaller.
We are speaking of incredibly short measures of duration (time) and they keep getting smaller.
So What?
Now many of you may be thinking, this is all very well and good, possibly even interesting, but so what? OK, here is the “so what.” Asking what GPS and all the incredible technology it enables has to do with atomic clocks is like asking what gas or electricity, as the case may be, has to do with my automobile. Atomic clocks, and the increasingly minute measurements of time they define, fuel our global economy today. And if you doubt the veracity of that statement, think about all that GPS/PNT enables in around the globe. All of our critical national infrastructure depends on a coordinated time, and the primary distribution system for that time for the last 20+ years has been GPS.
While there are academically numerous definitions of time and several so-called standards, primarily today the world runs on UTC (Universal Coordinated Time) distributed by GPS and other PNT systems with the requisite corrections.
System
Description
UT1
UTC
TT
TAI
GPS
UT1
Mean Solar Time
UT1
UTC = UT1 – DUT1
TT = UT1 + 32.184 s + LS – DUT1
TAI = UT1 – DUT1 + LS
GPS = UT1 – DUT1 + LS – 19 s
UTC
Civil Time
UT1 = UTC + DUT1
UTC
TT = UTC + 32.184 s + LS
TAI = UTC + LS
GPS = UTC + LS – 19 s
TT
Terrestrial (Ephemeris) Time
UT1 = TT – 32.184 s – LS + DUT1
UTC = TT – 32.184 s – LS
TT
TAI = TT – 32.184 s
GPS = TT – 51.184 s
TAI
Atomic Time
UT1 = TAI + DUT1 – LS
UTC = TAI – LS
TT = TAI + 32.184 s
TAI
GPS = TAI – 19 s
GPS
GPS Time
UT1 = GPS + DUT1 – LS + 19 s
UTC = GPS – LS + 19 s
TT = GPS + 51.184 s
TAI = GPS + 19 s
GP
Note: In June 2012, GPS will add another leap second.
NIST and Metrology
What then is time? If no one asks me,
I know what it is. If I wish to explain it to him who asks, I do not know.
— Saint Augustine
Now, just how do you learn about atomic time and frequency, GPS, UTC, clock errors, ephemeris errors, and all the other multitude of errors that affect the GPS time we all, meaning the world, depend on every day?
Obviously there are many routes to that knowledge, but for me, and I have been involved with GPS since 1978, the best resource I have experienced to date was the annual week-long Time and Frequency Metrology Seminar that has been held at NIST in Boulder, Colorado, for the last 37 years.
The seminar is billed as a course on understanding clocks, oscillators, atomic frequency standards, RF (radio frequency) and optical synchronization, optical oscillators, quantum information, optical cooling and heating (think lasers); making precise frequency, time, phase-noise, and jitter measurements; and establishing measurement accuracy and traceability. I am convinced the four-day course is the most comprehensive available anywhere today.
The June 2012 seminar included extremely informative presentations by Judah Levine, David Howe and David Allan (Ph.D.s all) — David Allan is the author of the Allan Variance — and 23 other presenters in subjects as diverse as direct-digital PM (phase modulation) noise measurements, how to specify frequency uncertainty, oscillator needs for new radars and surveillance systems, GPS vs. other global navigation satellite systems, photonic (laser-based) oscillators, chip-scale atomic clocks, femtosecond laser dividers, active PM-noise reduction techniques in oscillators, millimeter-wave applications and noise measurements, and ultra-low noise amplifier design techniques.
As the seminar descriptor says it is comprehensive in nature and there is no wasted time. One day the presentations lasted from 8 a.m. until 9 p.m. that evening. So it is an intensive metrology seminar filled with incredible learning opportunities. This year’s activities included an enjoyable and educational evening with Symmetricom, a forward-looking company that I sincerely view as the last true major commercial atomic reference builder in the United States. Symmetricom produces Hydrogen, Cesium (the ubiquitous 5071A), and Rubidium atomic reference standards, as well as high-end quartz oscillators with superior spectral purity and short-term frequency stability that support more military communications, satellite ground stations, and test and measurement applications than any other precision frequency references in the world today. Plus the incredible Symmetricom Chip-Scale Atomic Clock (CSAC), the world’s smallest atomic reference, has achieved historic breakthroughs in size, weight and power consumption — you can and I have balanced a CSAC on the end of my little finger. It is tiny yet powerful, and supports reference requirements as small as 1x10E-12 for specified periods of time. Indeed, this is the device that has the potential to revolutionize the Perfect Handheld GPS Transciever (PHGPST), but that is the subject for another column. As are the interviews I conducted with Judah Levine, who I refer to as “Father Time,” a Fellow at NIST, and David Allan, the originator of the Allan Variance and Allan Deviation, which allows the GPS Kalman Filter to work wonders and assures a GPS position accuracy of less than 1 meter possible for us all, with the right equipment of course.
The Right Equipment
Which leads me to my closing comments for this month’s column. While it is true that you can now routinely utilize GPS for real-time centimeter accuracy, since GPS does have the best atomic reference systems of any PNT system in orbit today, without monitoring systems and excellent GPS receivers you can’t depend on those parameters — the integrity is just not guaranteed without adequate signal monitoring, corrections, and augmentations.
Consequently, to ensure the best possible results, the receivers in the GPS global monitoring stations, of which there are hundreds more than those sanctioned by the U.S. government, tend to be high end and of stellar quality. And a majority of those receivers, according to my sources are, NovAtel receivers. Certainly NIST has a good number of NovAtel reference receivers, even though they are not allowed to specify or recommend a reference-grade receiver. I have also noticed large numbers of NovAtel receivers at FAA facilities around the U.S., and NovAtel’s reference receivers are at the core of national aviation ground networks around the world.
Recently NovAtel announced the development of a new receiver card known as the OEM625S Selective Availability Anti-Spoofing Module (SAASM) Global Navigation Satellite System (GNSS) receiver, which is actually a collaborative effort between NovAtel and L-3 Interstate Electronics Corporation (IEC). Since this is designated an OEM card, it is primarily for system integrators. However, since many users worldwide have come to rely on the centimeter-level positioning accuracy of real-time kinematic (RTK) GPS receivers, this may be a card you want to specify in your next high-end GPS receiver purchase or upgrade.
PPS Accuracy
Since defense users routinely rely on access to the Precise Positioning Service (PPS) for single-point positioning and this is certainly available with the OEM625S, it should be of special interest to those users. The card combines a commercial dual-frequency NovAtel GNSS receiver with an L-3 IEC XFACTOR SAASM in a single card solution, reducing overall size and power requirements for user applications. The new card maintains the OEMV-2 form factor, meaning it should be a drop-in replacement with backward compatibility for existing users.
NovAtel has promised to ship me a card to review in depth at the end of the third quarter of this year, so more on the new NovAtel/L3 card at that time. It promises real-time centimeter level accuracy and I can’t wait to see how it performs.
Make Your Reservation
Meanwhile, give Dr. David Howe a call at NIST and sign-up for the 38th Annual Time and Frequency Metrology Seminar — you will be glad you did.
I hope to see you all at ION JNC (Institute of Navigation – Joint Navigation Conference) in Colorado Springs, June 12-15, 2012! The classified Warrior Panel promises to be the hit of the show. Don’t miss it!
