When GPS goes out, the chip-scale atomic clock may be coming to the rescue.
by Mr. John Delcolliano and Mr. Paul Olson
Accurate time is crucial to our military. It enables all the warfighting functions of an expeditionary force: radio communications, network synchronization, information gathering, weapon systems, manned and unmanned systems, maneuvers, fires, electronic warfare and all types of sensors.
In addition to relying on the positioning capabilities of the Global Positioning System (GPS), many Army systems use GPS, which was developed by the U.S. military, for its highly accurate time. That’s because if you know where you were 10 seconds ago, you can determine where you are now based on very sophisticated calculations.
CLOSING THE 12,000-MILE GAP
GPS satellite receivers like the one used by this Soldier are vulnerable to conditions that impede the signal transmission. The chip-scale atomic clock provides the Soldier a backup source of accurate time and a quicker recovery when the GPS signal is restored. (U.S. Army photo)
Timing is everything. GPS satellites, which have atomic clocks on board, send out signals at precisely timed intervals. On Earth, a GPS receiver calculates exactly how long it took to get the signal from the satellite to the ground. One measurement enables the receiver to determine the precise time of day, and three more triangulate the position of the GPS receiver on Earth.
However, more than 12,000 miles separate the Earth from the GPS satellites, leading to a fragile signal by the time it reaches the receiver. This makes GPS unreliable in some environments, such as dense forests or urban areas with large skyscrapers, and vulnerable to jamming from enemies. Today GPS receivers use ordinary quartz clocks. During signal drop-outs, the clock drifts during short intervals, making reacquisition of the signal difficult. If a receiver had an additional source of accurate time—such as its own atomic clock—that would allow for easier and quicker GPS recovery.
VERY ACCURATE, VERY BIG
Atomic clocks are recognized for their accuracy. But the typical atomic clock is rack-mounted, weighs 50 to 60 pounds and requires lots of power. They’re great for fixed-base tactical operation centers and large platforms such as ground and air vehicles, but not for dismounted Soldiers.
WHICH WOULD YOU RATHER CARRY?
Full-scale atomic clocks are the most accurate, telling time to the nanosecond, but they weigh 50 pounds or more, not including the weight of the power supply. At a very portable 15 cubic centimeters, the chip-scale clock tells time in microseconds or better. (Photos by U.S. Army CERDEC)
At the U.S. Army Communications-Electronics Research, Development and Engineering Center (CERDEC), the Positioning, Navigation and Timing (PNT) Division strives to enable true navigation, timing and total situational understanding for the dismounted Soldier and commander in varying conditions, including degraded or GPS-challenged or -denied environments. The division is part of the Command, Power and Integration Directorate (CP&ID) of CERDEC, home to the Army’s experts for Soldier and manned-unmanned ground platforms.
The CP&ID drives PNT innovation so that Soldiers will have an optimal solution regardless of the circumstances they might encounter; these innovations span the areas of identifying potential threats, anticipating future needs and making science and technology investments that will help the Soldier beyond 2025.
SEEKING ATOMIC CLOCK CAPABILITIES
In 2002, the National Institute of Standards and Technology demonstrated a rudimentary physics package that proved the feasibility of a miniature-scale atomic clock. CERDEC and the Defense Advanced Research Projects Agency (DARPA) set out to mature this proof of concept and provide complete atomic clock capabilities for weapons, weapon systems and the dismounted Soldier.
This collaboration resulted in the chip-scale atomic clock (CSAC), a microchip-sized prototype that would support highly accurate location and battlefield situational awareness, even in the temporary absence of GPS.
SMALL WONDER
CSAC is a microchip-sized prototype that can support highly accurate location and battlefield situational awareness, even in the temporary absence of GPS. Since it’s both very accurate and very small, it is highly relevant to the Army’s expeditionary vision.
CSAC is one of the most game-changing PNT technologies developed in a long time, and DOD has just begun to scratch the surface of its potential. CSAC enables a device to hold accurate time at sub-microseconds for hours after losing access to GPS. At 15 cubic centimeters, about the size of two books of matches, CSAC can be integrated into a platform, weapon or handheld device while being transparent to the user.
While CSAC’s precision is not that of a full-scale atomic clock, which is accurate to about a nanosecond or less, its accuracy is acceptable, making it a trusted source of time with advantages in size, weight and power. If GPS is degraded or disrupted, a CSAC could provide precise time to the GPS receiver to enable rapid recovery.
Such a device is considered game-changing because CSAC provides 100 to 1,000 times better accuracy than clocks of the same size and format, enabling new capabilities in radios, GPS receivers and other military electronics. But it was saddled initially with labor-intensive manufacturing processes that produce small quantities at high cost. CSAC was highly impractical at $8,700 per item, and the manufacturing capability was enough to turn out just tens of devices a month in a laboratory environment. These manufacturing challenges had to be addressed to ensure consistent, repeatable quality at a lower cost per unit.
CALLING IN MANTECH
In an effort to reduce production costs, CSAC transitioned to the U.S. Army Manufacturing Technology (ManTech) Program in 2010.
TIME IS OF THE ESSENCE
The Army relies on GPS not only for navigation but also for timing. Orchestrating the variety of weapon systems, information- and intelligence-gathering systems and communication technologies that support the modern Army’s operations requires highly accurate time. Thus GPS vulnerabilities make the entire Army vulnerable.
ManTech, under the deputy assistant secretary of the Army for research and technology (DASA(R&T)), works closely with the defense industrial base to provide affordable and timely solutions in a low-risk production environment for high-priority Army acquisition projects that face manufacturing challenges.
Upon funding a project, the ManTech office tracks cost, schedule, performance and implementation planning. Thus it enables the efficient transition of these critical technologies to the warfighter on a large scale.
Initiated by DARPA, the CSAC Manufacturing Technology Objective was jointly funded by the Army, the Air Force GPS Directorate and the Office of the Secretary of Defense. CERDEC served as the lead by managing the program and supporting the technical development, requirements verification and testing.
Through ManTech, CERDEC worked with three industry vendors to reduce the cost of parts for CSAC to $300 per unit in production lots of 20,000 or more per month.
As interest in CSAC grows across DOD, the U.S. Department of Homeland Security and the Federal Aviation Administration, the ManTech effort may enable mass production of CSAC in thousands of units per month, allowing for a significantly lower unit cost for DOD. Additionally, the lower cost could lead to the availability of CSAC in the commercial sector.
In September 2013, the CSAC effort transitioned to the program manager for positioning, navigation and timing (PM PNT), who reports directly to the Army acquisition executive. In support of PM PNT, CERDEC is continuing to look at how to integrate CSAC into various systems as well as mounted and dismounted platforms; how the environment will affect it; and how it could be an asset to various programs of record. CSAC’s continued improvements in power, size and accuracy will lead to new applications with benefits reaching beyond DOD.
PRECISION NAVIGATION AND TIMING
The goal of CERDEC’s PNT Division is complete situational awareness for Soldiers in all circumstances, eliminating their vulnerability to GPS jamming or disruption by environmental conditions. A CSAC on board could provide precise time to the GPS receiver to enable rapid recovery or to protect receivers from interference. (Photo by U.S. Army CERDEC)
CONCLUSION
The small size, low power consumption and low cost of CSAC will enable its use within small devices—handheld radios and GPS receivers, for example—in which atomic clocks would not have been practical, thereby enabling atomic timing precision for a whole new host of applications. Maintaining accurate time when GPS is not available will be important to the warfighter to maintain communications, network synchronization, electronic warfare and GPS reacquisition once the GPS signal is available again. Our warfighters will achieve overmatch as a result.
For more information on CERDEC or to contact the authors, go to www.cerdec.army.mil.
MR. JOHN DELCOLLIANO is the PNT Integrated Systems Branch chief in the PNT Division at CERDEC, Aberdeen Proving Ground, Maryland. He holds a B.S. in electrical engineering from the Stevens Institute of Technology. He is Level III certified in engineering and is a member of the Army Acquisition Corps (AAC).
MR. PAUL OLSON is the chief engineer of the PNT Division. He holds an M.S. in electrical engineering from Fairleigh Dickinson University and a B.S. in electrical and computer engineering from Clarkson University. He is Level III certified in engineering and is a member of the AAC.
This article was originally published in the July – September 2016 issue of Army AL&T magazine.
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