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Assured PNT: A Path to Resilient Positioning, Navigation and Timing

Positioning, navigation and timing (PNT) has been at the foundation of military capability for centuries, required for functions ranging from navigating the seas to coordinating actions on the battlefield. Instruments such as the sextant, sundial, pocket watch and compass—using the reliable properties of celestial objects, mechanical springs and the Earth’s magnetic fields—have been critical in the battles that have shaped our history.

PositionedPOSITIONED FOR ACTION

A Fairchild Republic A-10 Thunderbolt II banks toward Air National Guard joint terminal attack controllers and Soldiers assigned to the 5th Squadron, 1st Cavalry Regiment, 1st Stryker Brigade Combat Team, U.S. Army Alaska, training at Yukon Training Area, AK, Aug. 20, 2014, during the Red Flag-Alaska 14-3 exercise. PNT SoSA is a key part of the Army strategy to achieve assured PNT, which underpins navigation and battlefield communication. (U.S. Air Force photo by Justin Connaher)

These instruments were ingenious discoveries that continue to prove useful today, with a certain degree of skill and training required to maintain proficiency. The sextant, first built in 1757 and still in use today on Navy warships, and the Davis quadrant, invented in 1594, allowed us to use the stars for navigation, the stars providing an extremely reliable positional reference. The map and compass, a staple of land navigation, are still used by some in the Army. The requirement is, and has always been, access to PNT information that you can trust—assured PNT.

A revolutionary change in PNT occurred with the invention and fielding of satellite-based navigation systems. Scientists at Johns Hopkins University, monitoring radio transmissions from Sputnik in 1957, ascertained a method to pinpoint an object’s location based on radio transmissions. Years of hard work ensued, and the first satellite navigation system, Transit, was tested by the Navy in 1959 and became operational in 1964. Transit eventually provided position accuracy of 200 meters and time accuracy of 50 microseconds—an amazing capability used by thousands of warships and seagoing vessels until 1991. This technology matured into the present-day GPS, one of the most complex technological innovations the world has ever seen. GPS, with a position accuracy of better than 1 meter and time accuracy better than 100 nanoseconds, has become a ubiquitous technology in consumer electronics and the U.S. critical infrastructure, from cellphones to the power grid, and is the PNT gold standard for military and civil users worldwide. GPS has become so prevalent and easy to use that most forget its underpinning enablers—and their vulnerabilities.

The next version of military GPS capability, known as Military Code (M-code), is presently in development, undergoing technology maturation and risk reduction. The M-Code signal is much improved over the present P(Y)-code precision military signal, offering additional signal power and a new signal structure. Under Public Law 111-383, Section 913, effective Jan. 7, 2011, procurement funds cannot be used after FY17 to purchase GPS receivers that are not capable of receiving the M-code signal, unless granted a waiver by the secretary of defense. The Chairman of the Joint Chiefs of Staff Instruction 6130.01E, “Master Position, Navigation, and Timing Plan (MPNTP),” effective May 1, 2013, requires the use of M-code-capable user equipment by the time the 24th M-code-capable GPS satellite is declared operational, which is estimated to occur in a five- to seven-year time frame.

In the Army, we have recognized that PNT is a critical enabler of our warfighting capability, and that GPS is the predominant materiel solution that we rely upon. The Army has integrated GPS receivers into most technology-based warfighting systems, such as Stryker, Nett Warrior, Rifleman Radio, the M777 howitzer and many others. These systems depend on PNT to varying degrees for some aspect of their functionality, from precise time to enable communications networks to precise positioning for targeting. The challenge presented to the product director for PNT (PD PNT), under the project manager for terrestrial sensors in the Program Executive Office for Intelligence, Electronic Warfare & Sensors (PEO IEW&S), is to ensure the integrity of PNT and access to it for these dependent systems. Thus the Army can be confident of a resilient PNT capability as technological threats continue to increase—in other words, assured PNT.

PNT SYSTEM-OF-SYSTEMS ARCHITECTURE

The establishment of the Army PNT System of Systems Architecture (SoSA) is a key part of the Army strategy to achieve assured PNT. The Hon. Heidi Shyu, the Army acquisition executive, directed the establishment of the PNT SoSA and the accomplishment of three objectives:

  1. Stay ahead of the PNT threat.
  2. Increase efficiencies and eliminate redundancies.
  3. Provide an affordable migration path to M-code.

The first objective is focused on enabling an affordable, open systems architecture that is flexible enough to accommodate additional capabilities without incurring expensive system or platform integration and certification costs—a framework that enables a pathway for future innovation. An analogy is the “IT box” concept, with a framework to add additional hardware and software in the future without impacting interfaces and end functionality. An example of this is the PNT Hub, under development in the Assured PNT program—a capability that allows the Army to control the level of PNT assurance through software and hardware configurations, seamless to the platform. The PNT Hub will enable integration of innovative technologies such as the Chip Scale Atomic Clock (CSAC), which harnesses the stable oscillations of the cesium atom to preserve precise time, even in the absence of GPS. In the future, when an engineer creates a novel means to determine positioning and timing, there will be an affordable pathway to insert this technology into a PNT SoSA compliant product.

Assurance levels
PRECISE PROTECTION
Assured PNT focuses on providing resilient, robust PNT in a scalable architecture that can span various levels of protection. (SOURCE: PD PNT)
Atomic Clock
TIMING IS EVERYTHING
The PNT Hub will integrate innovative technologies such as the Chip Scale Atomic Clock, which uses the oscillations of the cesium atom to provide precise timekeeping, even in the absence of GPS. (SOURCE: PD PNT)

The second objective—increase efficiencies and eliminate redundancies—is simple, using the Stryker platform as an analogy. Each of the 10 different functional variants of the Stryker employs a mix of supporting electronics, from the Force XXI Battle Command Brigade and Below/Blue Force Tracker to the AN/ PRC-155 HMS Manpack Radio. Some Stryker vehicles have up to eight GPS receivers, which means eight antennas and up to eight devices that require a cryptographic key for access to the secure military GPS signal. The PNT SoSA addresses this through the concept of platform distribution of PNT—providing the platform with a PNT source that is then distributed to each of the client systems requiring PNT data.

Data networks such as VICTORY (Vehicle Integration for Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance/ Electronic Warfare Interoperability) are great enablers of platform distribution. The benefits are a decreased burden on the Soldier, as there are fewer devices to manage, and decreased cabling and weight on vehicles. The consolidation also enables the platform to shift affordably to a single antijam antenna, and enables the next objective, an affordable migration path to M-code.

The benefits of M-code are best achieved when every platform and system for a warfighting element, such as a brigade combat team (BCT), uses M-code. The challenge is that this requires retrofitting and changing out the present receivers with M-code-capable receivers. Under the current approach, in which we lack a PNT SoSA, we have too many receivers to replace for this to be feasible. The third objective of the PNT SoSA addresses this by purposely reducing the number of GPS receivers and the number of formfactors of GPS receivers to a minimum.

LEADING THE CHARGE

The assistant secretary of the Army for acquisition, logistics and technology’s System of Systems Engineering and Integration Directorate is leading the charge to develop the architecture, supported by PD PNT, the HQDA chief information officer/G-6, the U.S. Army Training and Doctrine Command and many others, including participants in the Common Operating Environment (COE). Assured PNT spans each of the COE’s computing environments. Army programs will undergo a compliance assessment and evaluation as part of the entrance criteria for milestone decisions starting in FY16.

PNT
SETTING COURSE
SPC Christopher Quimbaya, a paratrooper assigned to 1st Battalion, 503rd Infantry Regiment, 173rd Infantry Brigade Combat Team (Airborne), uses the DAGR during a combined-arms live-fire exercise at Grafenwoehr, Germany, March 28, 2014. The DAGR D3, a replacement for the DAGR, is one of several solutions under development that incorporate the PNT SoSA. (U.S. Army photo by Markus Rauchenberger)

There are various materiel solutions under development that incorporate the PNT SoSA, including the Defense Advanced GPS Receiver (DAGR) Distributed Device (D3) and the Assured PNT program. The D3, a functional replacement for the DAGR, replaces up to eight GPS devices on a platform and is upgradable to M-code. The advantages of the D3 include both platform distribution and an affordable upgrade path to M-code. The D3 on Stryker, the Army’s lead platform for the Military GPS User Equipment program, is scheduled to be installed on multiple ground platforms, including the Stryker and Armored Knight.

The Assured PNT program focuses on providing resilient, robust PNT in a scalable architecture that can span various levels of protection, or PNT assurance levels. This scalable architecture enables the Army to avoid overbuying the capability, as a BCT can be scaled to the required level of PNT assurance; only certain units will require the highest levels of resilience. The Assured PNT program consists of four subprograms that comprise a family of systems required for resilience:

  • Pseudolites, or pseudo-satellites, which provide an alternate signal that can be used to increase resilience for area protection.
  • Mounted PNT, which provides a scalable architecture for mounted platforms, with technology enablers including GPS, CSAC for accurate time, inertial measurement units for self-referenced position, and an open architecture that allows the integration of other PNT enablers at any time.
  • Dismounted PNT, which follows the same concept, except for the Soldier platform.
  • Antijam, which includes technologies and devices that allow for blocking of threat signals while enabling a focus on valid PNT signals.

Each of these subprograms is leveraging competitive prototyping and structured testing to drive innovation as the Army shifts to assured PNT solutions.

CONCLUSION

Ingenuity and innovation are returning
to the forefront for PNT, from tapping into the dynamics of the atom with CSAC for self-referenced timing to financial economies from platform distribution of PNT information. The implementation of the PNT SoSA will provide a framework for efficiencies and resilience across Army systems, and the fielding of Assured PNT capabilities will provide the best PNT service to our most important customer—the Soldier.