Navy Sticks With Current LCS Synthetic Aperture Sonar Minehunters After Review

The U.S. Navy is sticking with the Littoral Combat Ship (LCS) Mine Countermeasures (MCM) Synthetic Aperture Sonar (SAS) program of record after finding no alternates provide adequate performance, according to a report to Congress.

A provision of the FY ’18 National Defense Authorization Act (NDAA) required the Defense Department to submit a report explaining SAS technologies and evaluating those suitable for the LCS MCM Mission Package (MP). The report was released by assistant Secretary of the Navy for Research, Development, and Acquisition (ASN-RDA) James Geurts on May 21.

The Raytheon AN/AQS-20 minehunting sonar system. (Artist’s concept: Raytheon).

The Raytheon AN/AQS-20 minehunting sonar system. (Artist’s concept: Raytheon).

The report explained the service is transitioning to unmanned and modular SAS systems to counter various mine threats and these SAS systems make up much of the LCS MCM MP. SAS technology “provides improved minehunting performance for the side scan sonar, thereby saving the Navy time and money,” the report said.

The report underscored while it has evaluated options beyond those chosen, they “do not provide a fully integrated minehunting system, have inadequate performance for the MCM MP, would require significant funding to integrate and test, and/or would result in increased schedule risk to achieving MCM MP Initial Operational Capability (IOC) in FY 2021.”

The report notes Navy minehunting sonar systems have to search, locate, and identify mines in various water column regions and depths at an adequate search rate, image resolution, and with one pass while minimizing false positives.

These requirements led the Navy to focus on side scan sonar, “which primarily searches for bottom mines on the sea floor, combined with a fully-integrated volume search sonar, which primarily searches for volume mines floating below the surface, and mine identification capability.”

In its review of allied SAS technologies, the report said “although several promising in-production commercial and allied Navy SAS systems have been assessed, none are able to meet all of the challenging area search rate, resolution, and single pass requirements of the LCS MCM MP.”

Depth performance for allied options are adequate, but the Navy found shortfalls in lower search area rates, lack of volume search and identification capabilities, and each would require a “significant amount of additional integration and testing to be fully-incorporated into the LCS MCM MP."

The report mentioned the Thales Towed Synthetic Aperture Sonar (T-SAS), an upgraded of the Seamapper 2054 side scan sonar in service by the Dutch Navy and procured by the French and Singapore navies; the KATFISH by Kraken, which has been procured by Israel while a UUV version was procured by Australia and Canada; HISAS 1030/HUGIN 1000 by Kongber, which has been used by the Royal Norwegian navy for years and was procured by the Dutch and Spanish navies; and the PROSAS Surveyor by Raytheon [RTN], which has been procured by the Naval Oceanographic Office, Naval Undersea Warfare Center (NUWC) Division Newport & other commercial organizations.

Requirements for the LCS MCM MP SAS systems include being capable of conducting bottom search and volume search within a single pass; adequate sonar image resolution; suitable operating depth and area search rate; integration with an identification capability like laser line scan or electro-optical; able to operate from a vessel of opportunity (VOO); and embarkable within the LCS criteria of size, weight, etc.

The report described the status of the four main SAS systems undergoing demonstration and validation operations by the designated initial operational capability (IOC) in FY ’21.

A rendering of the Knifefish unmanned underwater vehicle which will be deployed from the littoral combat ship to sweep mines. Illustration: General Dynamics.

A rendering of the Knifefish unmanned underwater vehicle which will be deployed from the littoral combat ship to sweep mines. Illustration: General Dynamics.

Raytheon’s AN/AQS-20C will be towed from a MCM unmanned surface vessel (USV) and is currently in the vendor test phase. It is set to finish developmental testing in FY ’18 and reach IOC by the end of that year. The Navy plans to deploy 2 AN/AQS-20Cs and two MCM USVs for each LCS with the mine countermeasure mission package.

Northrop Grumman’s [NOC] AN/AQS-24 is used in the fleet today as a device towed by the MH-53E Sea Dragon helicopter. It supports optical identification, but not volume search. The Sea Dragons are expected to perform Airborne Mine Countermeasure missions until at least 2025 and to extend the minehunter’s life past the helicopter retirement the Navy is developing the AQS-24C variant as a deploy and retrieve system integrated into USVs. It is currently undergoing vendor developmental testing and integration with MCM USVs is planned to end by the fourth quarter of FY ’18. The Navy noted this supports volume search but not optical identification.

Hydroid’s MK18 MOD 2 is a UUV-based system used by explosive ordnance disposal units and is meant to provide minehunting for seaports of debarkation, sea lines of communications, amphibious operations, and maritime homeland defense. This system can be deployed independently from various VOOs like rigid-hull inflatable boats and Military Sealift Command ships. The MOD 2 variant will use a prototype dual-frequency small synthetic aperture minehunter (SSAM-2) sonar arrays for higher resolution bottom search capability. They are currently undergoing developmental, testing, and suitability assessments by the U.S. Fifth Fleet.

Lastly, the Navy is developing General Dynamics’ [GD] Knifefish UUV to hunt volume, bottom, and buried mines. It aims to achieve IOC in FY ’20. It uses a low frequency broadband SAS system to find mines in high clutter and burial environments. It can be deployed from either an LCS or VOO. Each system includes two 21-inch diameter, 23-foot long untethered vessels. Last October the system underwent contractor trials off the coast of Boston, Mass. It is intended to replace the dolphins and sea lions currently used for some mine detecting missions and the company expects sea acceptance trials this year (Defense Daily, Oct. 26, 2017).

The Navy also defended its acquisition strategy (AS) that describes required capabilities and quantities, rather than specific systems.

“The AS provides a mechanism to continue to introduce mature, leading-edge technologies through pre-planned product improvements (P3I) that meet the capability requirements of the MCM MP.  The system of systems approach to MCM was successfully demonstrated during the MCM technical evaluation in 2015 onboard LCS 2 employing the Airborne Laser Mine Detection System, Airborne Mine Neutralization System, and the Remote Minehunting System, consisting of the Remote Multi-Mission Vehicle and the AN/AQS-20 sonar,” the report said.





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