Navigational Positioning Source Using Very Low Frequency Signals

Navy SBIR 21.1 - Topic N211-052
NAVSEA - Naval Sea Systems Command - Mr. Dean Putnam - dean.r.putnam@navy.mil
Opens: January 14, 2021 - Closes: February 18, 2021 (12:00pm EDT)

N211-052 TITLE: Navigational Positioning Source Using Very Low Frequency Signals

RT&L FOCUS AREA(S): General Warfighting Requirements

TECHNOLOGY AREA(S): Weapons

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop receivers and algorithms that employ Very Low Frequency (VLF) radio signals from existing United States Government (USG) ground stations to determine position and velocity information at sea on a United States Navy (USN) ship or submarine.

DESCRIPTION: The success of U.S. Navy missions depends on personnel and platforms having access to accurate and reliable position, velocity, attitude, and time information. Maritime platforms specifically need this information continuously to support safety of ship, weapons deployment and network communications, and geo-registration. The DoD developed a Global Positioning System (GPS) to provide accurate, worldwide, all-weather, continuous position and time information to warfighters. As a result, GPS is the primary positioning and time source for maritime surface platforms. However, GPS is susceptible to interference and may not be continuously available in a time of conflict. Consequently, backups to GPS are needed for positioning and timing information to meet mission support.

Many military platforms also deploy inertial navigation systems along with GPS. Inertial navigation systems (INSs) are continuous, all-weather sources of position, velocity, and attitude information. INSs are not susceptible to interference in the same manner as GPS. Also, many maritime platform missions can be met with a military grade INS. INSs drift over time and require periodic fixes to reset their position. Typically, an INS will be corrected by fixes to GPS or some other fix source, such as a visual source, a radar contact or some other navigational feature. In the event of a prolonged period of GPS not being available and no other usual sources being available, additional sources of position fixing are needed.

Using VLF signals to aid navigation has its origins from the middle of the 20th century with the OMEGA hyperbolic navigation system being the most widely used system by the U.S. (Russia had a comparable system known as ALPHA.) OMEGA had 8 ground-based transmitters strategically located around the world and provided 24-hour global coverage, operating in the 10-14 kHz range. In these hyperbolic navigation systems, transmitters were synchronized by using one of the transmitters as the trigger for the other to broadcast after a fixed known delay. A receiver measured the signals from the transmitters and a comparison was made between the known delay and the measured delay, and the location of the receiver was determined to lie on a curve that was a function of this delay. Using two or more pairs of transmitters allowed for an accurate horizontal position measurement.

The OMEGA navigation system had accuracy in the 1-4 nautical mile (nmi) range, which was dependent on a number of factors. Synchronizing of the two transmitters over transmitter distances of thousands of miles was challenging in the mid-20th century. This error source would later be overcome using atomic clocks at all transmitter sites; however, aligning clocks at multiple sites was still problematic. Additionally, the paths of VLF signals from transmitters to receivers are severely distorted by the ionospheric changes along the very long transmission paths. The OMEGA navigation system ceased transmissions in 1997 with the advent of alternative systems that had greater accuracy, such as GPS.

However, near the end of OMEGA operations, many of the technical challenges limiting VLF navigationís accuracy performance were solved, including improved ionospheric modeling and better signal processing.

Recently there has been renewed interest in positioning using VLF signals. A terrestrial-based position and timing source is desired as a backup to GPS, and an OMEGA-like VLF system can provide global coverage with just a few transmitters. VLF signals are very difficult to interfere with because of the high power with which they are transmitted. DARPAís Spatial, Temporal, and Orientation Information in Contested Environments (STOIC) program sought to achieve GPS-level or better performance in part using VLF signals. The STOIC program demonstrated much improved positioning over OMEGA by creating a stable VLF signal, developing high fidelity physics models of the ionosphere along the signal path and improved signal processing at the receiver.

The Navy seeks innovative technology that can mature the VLF navigation technology to support navigation resilience on U.S. Navy shipboard platforms. The focus of this SBIR topic is expected to center on improved receivers for processing the VLF signals, and algorithms to extract the signals that can be used to develop accurate position and velocity to estimate INS errors without a backchannel communications need for ionospheric corrections. Position fix accuracy should be within 0.5 nmi (dRMS) or better, with fixes available at least 12 hours per day. Short-term velocity output performance should be within 0.1 knots or less (rms, each horizontal axis) over 1 hour. An additional research focus will be on modeling the error characteristics of the VLF-derived position and velocity reference, as this model will need to be incorporated into real-time Kalman filter algorithms of an inertial navigation system. VLF antenna will be a contractor selection, but must not exceed 22" x 22" x 22" in volume. Electronics must fit within a standard 19" electronics rack and not to exceed four electronic rack units (RU). However, receiver and algorithms should be adaptable to both purpose-built and existing VLF shipboard antenna systems.

The technology sought will develop the algorithms and receiver technology that will deliver reliable, consistent, and predictable position and velocity information providing known error characteristics.

Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. Owned and Operated with no Foreign Influence as defined by DOD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence Security Agency (DCSA). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this contract as set forth by DCSA and NAVSEA in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advance phases of this contract.

PHASE I: Develop a concept for improved VLF system navigation algorithms and receivers. Demonstrate feasibility for obtaining accurate position and velocity from maritime platforms using existing Navy or purpose-built antennas. Demonstration will show that the concept meets the requirements as described in the Description and includes analysis, modeling, and simulation. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype solution in Phase II.

PHASE II: Develop and deliver a prototype of an improved VLF system navigation algorithm(s) and receiver(s). The prototype will show that it achieves the parameters described in the Description. Deliver the prototype to be independently evaluated by the Government to determine if the technology has the potential to meet the Navyís performance goals for position and velocity accuracy using VLF signals.

It is probable that the work under this effort will be classified under Phase II (see Description section for details).

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology to Navy use. Develop a mature prototype capable of testing on a maritime platform. Mature any key algorithms, software or hardware. Field test the system on a maritime platform to demonstrate performance of the mature system. Compare the systemís demonstrated performance with GPS to determine the usefulness and the applicability of this technology in GPS-challenged environments.

Potential commercial applications include navigation and positioning in mining, aviation, surveying, agriculture, marine, and recreation. Department of Navy could use the technology for multiple missions including surface, submarine, and air navigation.

REFERENCES:

  1. DARPA PNT Program Overview of 1 Aug 2017 b. Broad Agency Announcement Spatial, Temporal and Orientation Information in Contested Environments (STOIC) Strategic Technology Office DARPA-BAA-14-41 June 3, 2014. https://www.gps.gov/governance/advisory/meetings/2019-06/burke.pdf
  2. Sasmal, S., Palit, S. and Chakrabarti, S.K. "Modeling of long-path propagation characteristics of VLF radio waves as observed from Indian Antarctic station Maitri." J.Geophys. Res. Space Physics,120, 2015, pp. 8872Ė8883, https://doi:10.1002/2015JA021400
  3. Newman, Edward M. "The Biggest Little Antenna in the World." PowerPoint Presentation, AP-S, November 14, 2012. http://arlassociates.net/Newman%20AP%20Presentation.pdf
  4. "Omega." Skybary. https://www.skybrary.aero/index.php/Omega
  5. Barr, R., Jones, D. Llanwyn and Rodger, C.J. "ELF and VLF Waves." 14 June 2000, Journal of Atmospheric and Solar-Terrestrial Physics 62, 2000, pp. 1689-1718. https://www.sciencedirect.com/science/article/abs/pii/S1364682600001218

KEYWORDS: Very Low Frequency; Navigation; OMEGA; STOIC; Atmospheric Signal Propagation; RF Receivers and Antenna

** TOPIC NOTICE **

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