TITLE: MK 48 Torpedo Composite Fuel Tank
PROGRAM: PMS 404, Undersea Weapons Program Office
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.
Develop a composite fuel tank that meets the MK 48 torpedo system requirements
and increases torpedo in-water performance.
The current MK 48 torpedo fuel tank is manufactured primarily from aluminum.
Due to the material properties of aluminum and the resulting product, the
current fuel tank has a number of limitations: higher than ideal weight,
internal reinforcing structures required for strength reducing internal volume
that could otherwise be used for fuel, and a high susceptibility to corrosion.
Due to numerous weapon system requirements, no current commercial off-the-shelf
(COTS) solution is available for immediate use by the MK 48 torpedo. Any COTS
approach would need to be adapted for MK 48 use and be designed to survive at
the maximum operating depth of the torpedo (>1200’) and significant torsional
loads when putting a composite structure in the middle of a metal torpedo.
Additionally, there are high load stresses due to the rapid depth changes, high
speed and high turn rates inherent to a torpedo dynamic that other COTS ocean
products would not experience.
The Navy is interested in improving the MK 48 torpedoes’ performance through an
objective of a 20% increase in range and better utilization of more of the Otto
fuel in the tank by decreasing or eliminating seawater/Otto fuel mixing during
high-speed maneuvers. A secondary goal is to decrease the opportunity for
corrosion in the tank, and reducing maintenance and life cycle costs of the
fuel storage solution for the weapon. This upgrade for the MK 48 torpedo is
important in furthering the Strategic Approach to ‘Build A More Lethal Force’.
Additionally, topics for improvement include:
Decreased weight: The total weight of the MK 48 torpedo has an effect on the
buoyancy of the weapon that affects the torpedo’s performance. By utilizing
materials with high strength to weight ratios, the weight of the fuel tank can
be decreased. The goal for weight reduction is 10% for the fuel tank section.
This allows additional fuel or hardware to be installed inside the MK 48
torpedo without affecting the torpedo’s performance.
Increased fuel tank internal volume: The current fuel tank has internal ribs
and separators that allow the fuel tank to survive the pressure requirements of
the torpedo (NAVSEA Drawing 5893767) as well as decreasing the current designs
Otto Fuel/Seawater mixing during high-speed maneuvers. By utilizing stronger
materials, these ribs can be removed, which would allow for additional fuel
storage. Other innovative methods and solutions for creating additional
internal volume inside the fuel tank without impacting system requirements are
of interest as well. The goal is to increase the usable fuel by 15% or more,
which would yield a tactical significant improvement to the weapon.
Better separation of Otto fuel and seawater: Otto Fuel II is the propellant
used in the MK 48 torpedo. It has a density greater than water and is
immiscible with water, which allows the fuel delivery system to displace
consumed fuel with seawater during operation. This reduces the sidewall
differential pressure requirement that would be significantly higher if
required to operate at the full operational depth of the weapon. However, the
seawater displacement system creates the opportunity for mixing during
high-speed maneuvers and the ingestion of seawater into the torpedo power plant
during operation, which results in shutdowns before fuel exhaustion. The
current fuel tank has internal structures to mitigate this potential. However,
fuel and seawater separation can be improved by designing improved separation
or a better fuel management scheme. This would allow additional fuel to be
consumed prior to seawater ingestion. The goal is to increase fuel utilization
by 10% by increased Otto fuel/seawater separation.
Reduced fuel tank corrosion: The current fuel tank and internal components are
inherently subject to corrosive materials (reactants and seawater), which can
cause extensive corrosion damage to high replacement cost items. By increasing
the utilization of corrosion-inert materials and decreasing areas that are hard
to flush or clean, corrosion damage can be reduced or eliminated along with
associated hardware repair and replacement cost. The goal is to reduce fuel
tank maintenance between runs and the maintenance required between storage
turns by 30%. It is also a goal to reduce the need for replacement of the fuel
tanks by 15% over the normal 20-year or greater life of the weapon.
The awardee will have to apply research in the field of composites to design
and manufacture a composite pressure vessel that meets all of the MK 48 fuel
tank requirements. Additionally, the awardee will have to determine a method to
ensure adequate bonding at the interfaces between a composite fuel tank and
existing MK 48 torpedo metal components. Fuel tank requirements include
pressure loads; axial and radial force loading; temperature, vibration, shock,
impact, and corrosion resistance; atmospheric control requirements; and hazards
to electromagnetic radiation on ordnance requirements. The awardee will need to
demonstrate that the design approach will withstand the maximum differential
pressure that the fuel tank is expected to experience, which is the design test
depth of the submarine plus the launch from a torpedo tube. The exact numbers
are classified but it is >1200 feet of Seawater. Once these requirements are
satisfactorily met, the application of composite pressure vessels can be
applied to other cases where pressure vessels are required by the Navy or
industry in Undersea Unmanned Vehicles, Naval Mines, and potentially manned
submersibles. Fuel separation systems improvements will also require research
and development and can be applicable to other fuel handling systems that are
In order to qualify the design for Navy use, qualification testing will occur
during Phase II. The Government will furnish test services for all testing
required specific to qualification of the design for the Torpedo (i.e.,
hydrostatic, land-based propulsion testing with the fuel tank, in-water
testing, shock, vibration, thermal). Contractor testing may include bond
testing of the composite to metal interface and coupon testing. Government
testing will take place primarily at Naval Undersea Warfare Center Division
Newport (NAVUNSEAWARCENDIVNPT), Naval Undersea Warfare Center Division Keyport
(NAVUNSEAWARCENDIVKPT), or other sites where the Government has unique test
Full Rate Production of the existing aluminum fuel tank begins in FY21 and is
projected to go through FY30. Once this new composite fuel tank design is
qualified and determined to have cost benefits and/or performance improvement,
the Navy anticipates the new tank will be phased into production for replacing
the aluminum fuel tank. Replacement of the current inventory of aluminum fuel
tanks will also be considered as the MK 48 torpedo is expected to remain in
service for at least 30 more years. 700 new fuel tank procurements are planned
for the MK 48 Production program and for insertion into a large number active
inventories of the U.S. Navy, and/or to be sold through foreign military sales.
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 be
implemented and approved by the Defense Security Service (DSS). 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 DSS 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.
Determine the technical concept and feasibility of manufacturing and fielding
composite fuel tanks that meet the current requirements including deployment
life. Work with the Government to ensure applicable requirements are
understood, so that the awardee can develop a design proposal that will address
all requirements. Address areas of weight reduction; improved fuel separation/management;
technology improvements; and risk reduction of the metal to composite
interfaces. Perform analysis on the concept to determine the ability of the
concept to meet requirements, including exposure to environments from the
stockpile to the target sequence and long-term exposure to Otto fuel. Assess
the durability of the composite material to the shipboard handling and storage
environment, and damage inspection techniques. Investigate manufacturing
processes required to manufacture a prototype fuel tank. Perform a cost
analysis to estimate the procurement costs and maintenance cost per 5-year
period. Assess the improvements of the MK 48 torpedo’s tactical use. The Phase
I Option, if exercised, will include the initial design concepts and plan to
build a prototype in Phase II.
Design prototype fuel tanks with a minimum of one prototype manufactured to
evaluate the proposed design approach. Evaluate the prototypes to determine if
the design approach will accomplish the goals of this project concerning cost
reduction, increased performance and decreased maintenance as well as the final
design’s ability to meet the weapon’s environmental requirements. Conduct
testing with the Navy to evaluate the increased fuel volume and fuel separation.
When Navy specific assets are required for testing, the Navy will provide the
assets or conduct the test for the performer. Refine the prototype until it can
successfully transition to the Navy. Upon successful validation of a prototype,
deliver the prototype(s) to the Government for the completion of MK 48 torpedo
integration testing and in-water testing.
It is probable that the work under this effort will be classified (see
Description section for details). If the Phase II Option is exercised, the performer
will produce production representative prototypes (minimum of 6) that will be
used to validate the design requirements against the MK48 torpedo’s design.
DUAL USE APPLICATIONS: Phase III will finalize the design and manufacturing
processes into final products and production drawings. The production of fuel
tanks or license the technology to produce operational fuel tanks for the Navy
will also be awarded in this Phase. The Phase III awardee will provide
production drawings to the Government for configuration management and
maintenance of the fuel tanks. The Phase III awardee will document and provide
the Government assembly and disassembly procedures, inspection procedures,
maintenance procedures, and repair procedures that will be used to support
composite fuel tanks for the duration of their service life.
Technology and manufacturing methods developed on this SBIR topic could be
transitioned to other military and commercial submersibles and industry for
manned or unmanned applications. Commercial application include oil and gas
exploration; deep-sea salvage and recovery operations; and deep-sea
exploration, as examples.
“MIL-DTL-901E, 20 June 2017. Shock Tests H.I. (High Impact) Shipboard Machinery
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6 August 1986. MIL SPEC OTTO FUEL II.” http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-O/MIL-O-82672A_13078/
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ISSN 0976-6340. https://www.academia.edu/20772591/WEIGHT_REDUCTION_OF_PRESSURE_VESSEL_USING_FRP_COMPOSITE_MATERIAL
5. MK 48 MOD 7 Heavyweight Torpedo Industry Day Presentation, MK 29 MOD 0 Warshot Fuel Tank. https://navysbir.com/n20_1/REF-5-N201-048.pdf
Composite Fuel Tank; Composite Pressure Vessel; High Strength Material Use in
Fuel Tanks; Seawater Ingestion; Displacement of Fuel with Seawater; Corrosion
in Fuel Systems