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Gravity-Aided Navigation Technology for Reducing Ballistic Missile Submarines’ (SSBN) Dependence on the Global Positioning System (GPS)
Navy SBIR 2009.1 - Topic N091-092
SSP - Mr. Robert Thorne - robert.thorne@ssp.navy.mil
Opens: December 8, 2008 - Closes: January 14, 2009

N091-092 TITLE: Gravity-Aided Navigation Technology for Reducing Ballistic Missile Submarines’ (SSBN) Dependence on the Global Positioning System (GPS)

TECHNOLOGY AREAS: Information Systems, Ground/Sea Vehicles, Weapons

ACQUISITION PROGRAM: Strategic Systems Programs, DRPM, ACAT I

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Develop a gravity-aided navigation capability to reduce or eliminate SSBN dependence on GPS fixes.

DESCRIPTION: The positional accuracy of an inertial navigation system deteriorates over time unless periodic fixes from an absolute position reference are applied. In the case of the inertial navigation system supporting the Fleet Ballistic Missile (FBM) submarine, the position reference is primarily provided by GPS. However, GPS is susceptible to both natural and man-made interference, which if continued over time can lead to loss of navigation system availability. Therefore an unjammable, reliable, totally submerged and absolutely covert (passive) method of updating the inertial system is required. An alternative to GPS as an absolute position reference may be provided by correlation processing of gravity anomaly measurements with respect to gravity map data. Innovative techniques are sought for measuring and utilizing gravity anomaly signals in order to extend the GPS fix interval for SSBNs, Guided Missile Submarines (Submersible, Ship, Guided, Nuclear - SSGNs), and Fast Attack Nuclear Submarines (Ship, Submersible, Nuclear – SSN). Until now, gravity navigation has never been implemented and has been demonstrated only inconsistently in isolated cases. Previous GAINS efforts were directed at singular specific inertial system(s) and singular, confined operational scenarios. These inertial systems, platforms and operational scenarios are no longer directly applicable because they have and are changing. Further, the technology advances in gravity maps, inertial sensors and algorithms have significantly evolved opening new possibilities. Extending these new possibilities to the capabilities required will necessitate innovative R&D beyond the present state of the art. Specifically, the following factors need be investigated:

1. GAINS, as would be implemented on current and future INS, is highly sensitive to indexing, accelerometer stability due to thermal gradients and scale factor errors. Develop techniques and methods for reducing the sensitivity to these error sources to be less than 1.5 milligals rms.

2. For GAINS to be used on different platforms, adaptive algorithms will be required. Gravity field signatures and mission requirements can vary significantly, requiring that site selection signature recognition algorithms must be used for GAINS fixes. Develop algorithms which account for these factors. Provide fixability and availability algorithms with position fix accuracy as a parameter.

Because the work may be classified in Phase II, companies must have SECRET facility and personnel clearances.

PHASE I: Conduct a feasibility study of a gravity aided navigation capability for SSBNs, SSGNs and SSNs. Mechanization should include capability to compensate gravimetry for depth variation. Demonstrate feasibility by performing simulations using best available unclassified gravity anomaly maps provided by Strategic Systems Programs. Provide detailed plans for demonstrating capability using government supplied models for the ESGN Replacement navigator and gravimeter data from USNS Waters in Phase II. Provide test planning input for USNS Waters.

PHASE II: Design and demonstrate a gravity navigation capability by using data from an inertial navigator and gravimeter on the USNS Waters. Evaluate suitability of existing inertial navigator accelerometers for gravimetry by comparing with USNS Waters (BGM-5) data.

PHASE III: Transition the technology to the Strategic Systems Programs, SP24.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial inertial navigation systems commonly experience loss of GPS due to dense foliage, tunnels, multipath, geomagnetic activity, and solar flares. Geophysical navigation aiding techniques developed for this product have potential application to these scenarios. Further, using gravity anomalies would be advantageous for accurate underwater mapping of the sea floor for oil, gas and mineral exploration.

REFERENCES:
1. Vajda, S. and Zorn, A., Survey of existing and emerging technologies for strategic submarine navigation, IEEE PLANS 1998.

2. Lowrey, J.A. III and Shellenbarger, J.C., Passive navigation using inertial navigation sensors and maps, Naval Engineers Journal, May 1997.

3. May, M., Gravity navigation, IEEE PLANS 1978.

KEYWORDS: navigation; gravity; anomaly; map; SSBN/SSGN/SSN; GPS dependence

** TOPIC AUTHOR (TPOC) **
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