"In a break with recent US design philosophy, Electric Boat
sees its future revolutionary submarine as employing a double-hull arrangement
in which the pressure hull is enveloped by a free-flooding outer hull. This
follows the lead set by the VLS for Tomahawks adopted for the Los Angeles- and
Virginia-class submarines, which is installed outside the pressure hull. As a
result, the weapon payload of these boats has been increased by 50% without
extending their length.
The baseline double-hull design is shorter than the Virginia class (just under
100m, compared with 115m), but has a greater displacement (8,600t submerged,
rather than 7,830t), while retaining the same pressure-hull diameter of 10.35m.
The Chief of Naval Operations'
Strategic Study Group has also examined a double-hulled behemoth, 156m long by
12.8m in diameter, displacing 10,200t. This could carry up to 280 weapons of
21in diameter, or 1,056 of 10in, or 2,400 5in munitions. Other postulated
payloads include 20 UUVs attached to external clips, 20 micro-UAVs, and six
unmanned combat air vehicles in vertical tubes.
A double-hull design also allows the traditional shape of a right circular
cylinder -which is inherently inexpensive to build - to be retained for the
pressure hull, while at the same time exploiting an outer shape that is
optimized for hydrodynamic efficiency and maneuverability.This latter aspect
becomes more important as submarines are required to operate at or near the
surface for long periods in shallow waters, where maneuverability is at a
premium.
The shaping that is possible with an external fairing additionally contributes
to signature reduction. A double-hull arrangement provides two external surfaces
for acoustic coatings, and the space between the hulls can be filled with
absorbent materials. Further advantages come from the ability to recess sonar
arrays. A combination of these approaches may allow a reduction in isolation
measures such as complex mountings, permitting the use of commercially available
auxiliary equipment.
Versatile payloads
Standardization on 533mm (21in) torpedo tubes and 635mm (25in)
hatches constrains not only the payloads available, but also determines which
should even be considered Accordingly, designers are turning to alternative
solutions. The Submarine Payloads and Sensors effort has spawned many futuristic
ideas. This began as a study, sponsored jointly by the USN and the Defense
Advanced Research Projects Agency (DARPA), focusing on potential applications
running from variants of the Virginia class through to radically new designs
that could enter service in about 2020.
Two groups - Forward PASS (Payloads And Sensors for Submarines) and Team 2020 -
conducted the initial 18-month studies. Many of the members have not
historically been associated with submarine technology, allowing the teams to
consider non-traditional approaches more easily. Electric Boat is a member of
both consortia, enabling it to contribute its design expertise and to ensure
that all proposed solutions are technically feasible.
The studies, completed between August and November 2000, continued into early
2001 under bridge contracts. The USN has since assumed responsibility for
follow-on risk-reduction efforts, which involves demonstrations lasting about
two-and-a-half years.These include analytical work, augmented by testing, to
pave the way for development of selected systems. These could potentially enter
service as early as 2007-10, although the USN has not yet allocated funding to
implement the results.
The goal of the program is to avoid ever having to develop another specialized
payload for submarines. By adopting different methods of packaging and delivery,
payloads from a variety of sources - including those originally developed for
other services - can be employed without 'submarinizing' them. This greatly
expands the number of roles that a submarine can perform, while also reducing
payload costs. A modular approach permits reconfiguration of the devices to be
deployed, according to the tactical situation, without returning to port.
The Forward PASS consortium consists of 12 member organizations from industry,
academia and government research laboratories. Raytheon acts as team leader,
although each has equal status in terms of its design inputs and
recommendations. The other member companies are BBN Technologies, Boeing, ERIM
International, Foster-Miller, General Dynamics, Oceaneering, Sarcos, Sensis, and
Systems Planning and Analysis.
These are complemented by the Applied Research Laboratory at Penn State
University, and by the NUWC Newport Division. Forward PASS is developing
technologies in two main areas: a Broaching Universal Buoyant Launcher (BUBL) to
accommodate payloads in a capsule that can be released from a submerged
submarine or other vehicle, then rise to the surface; and a Multi-Payload UUV (MPUUV),
together with the interfaces that would enable it to be launched from (and
recovered back into) a submarine and deploy a variety of payloads.
BUBL is intended to be cheaper than present methods of encapsulation, and to be
capable of launch at greater speeds and depths. It could be mounted externally
in 'clips, stored in a free-flooding cargo bay, or carried within the pressure
hull. Control of the ascent would allow the submarine to leave the area before
the encapsulated weapon is launched. The demonstration program includes
construction of prototype items for the capsule structure, electronics/sensor
and power subsystems, and is expected to involve launches of representative
missile airframes.
The other main approach being pursued by Forward PASS is one of 'cascading'
delivery vehicles and their payloads, thereby providing the greatest
flexibility. Cascading permits the gradual step-down in size from the submarine,
via a smaller vehicle, to payloads that may be as small (and therefore stealthy)
as UGVs, UGSs and 'meso' UAVs. At the center of this chain is the MPUUV, which
the Forward PASS team sees as a lengthened derivative of the OSIRIS commercial
vehicle being developed by Boeing.
The MPUUV is stored within the boat, allowing it to be loaded with the
appropriate payload and fueled before a mission. It is then deployed into the
water via a 'flexible ocean interface', following which it transits to the
payload-delivery area either autonomously or under control from the parent
submarine or another platform.
The baseline MPUUV design is 10.7m long by 2m on each side. An adaptive
interface allows it to accommodate standard payload modules in a free-flooding
bay, each with a cross-section of 1.2x1.8m and in various lengths: 60cm for
electronic-warfare or information-warfare payloads, and for energy packages;
1.2m for underwater maintenance devices; 1.8m for deployable caches; and 6m for
torpedoes or cruise missiles. These would be assembled in different
combinations, according to the mission. For example, a package intended for
long-term ISR would devote some 90% of the available volume to energy storage.
One allocated to deployment of an undersea network, however, would typically
divide the space almost equally among a cache of communications nodes, a cable
reel and a manipulator.
An SSN outfitted in such a way could stand off by up to 200nm from an enemy
coastline, controlling both its own MPUUVs and those launched from other
platforms. It could also be replenished by UUVs delivered from surface ships up
to a further 400nm to the rear. Alternatively, upgrading earlier SSNs with ARCI
'Phase X' capabilities would allow them to assume the responsibility for
longer-term operation of payloads and sensors that have been put in place by
new-generation boats.
The Forward PASS team believes that its overall system concept would expand the
reach of a submarine's weapons and sensors by a factor of 10 to 100, permitting
a concept of operations that emphasizes monitoring rather than search. The
ability to carry at least twice the payload percentage of current designs is
predicted to double the number of kills achieved against TCTs while reducing
damage to friendly forces by 33%.
Cost benefits
Non-traditional ways of engaging targets can also bring cost benefits. A
submarine performing a strike mission against a land-based anti-access threat to
naval forces could employ a combination of weapons. Directly launched TacToms
carrying penetrating warheads (at a unit cost of approximately US$500,000) would
attack hardened and/or deeply buried targets, with the remaining 80% of the
total being engaged by 250nm-range.
Loitering Attack Munitions (LAMs) costing less than US$50,000 each. The LAMs,
which are being developed under the joint US Army/DARPA NetFires program, could
be launched from MPUUVs that had traveled to within 5nm of the enemy's
coastline.
Team 2020, headed by Lockheed Martin, is developing a Flexible Payload Module
(FPM) and a Stealthy Affordable Capsule System (SACS) that together perform a
similar function to the BUBL design being pursued by Forward PASS. The FPM is a
box, 2.4m square and 7.6m deep, that could be stacked in free-flooding areas or
in a missile tube. Towed modules could accommodate additional facilities, such
as cruise or ballistic missiles, a hub for acoustic and electronic sensors, a
habitat for special forces, and a UUV refueling station. Team 2020 is also
working on the information-management aspects of such an approach, and on UAV
applications.
The Manta Unmanned Undersea Vehicle Initiative that NUWC Newport Division has
been pursuing since 1996 employs self-contained vehicles that can be carried
externally by a submarine, then released to perform their own missions. Each can
accommodate a variety of weapons and sensors, augmenting those of the parent
vessel. This allows the submarine itself to have a smaller torpedo room,
reducing the cost of the boat.
A typical arrangement would involve four Mantas grouped around the parent
submarine's forward hull, being semi-recessed into divot-shaped depressions in
the outer casing. While attached, they could fire their own weapons to augment
the submarine's defensive or offensive armament. Following release, they would
operate independently or under control from a remote platform (which may include
the parent vessel). Various sizes of Manta have been studied, with lengths
ranging from approximately 15m to more than 25m and typically weighing 50t. A
90t 'Super Manta' would have a range of 1,000nm.
In support of its initiative, NUWC has built a Manta Test Vehicle (MTV) at
approximately one-third scale. The center has worked with industry partners -
including Boeing, Draper Labs, BAE Systems, Raytheon, General Dynamics, Kearfott,
SenSyTech and Sensors Unlimited - to install and tes subsystems aboard the MTV.
Trials during August and September 2000 included operation of a basic ISR and
communications payload consisting of a visual imager employing inexpensive
commercial cameras (one forward-looking and two side-looking), a radio-frequency
direction-finder, and a communications link. The last of these allowed the MTV,
running in shallow water off Newport, to transmit imagery to the submarine USS
Providence docked at Groton. In return, the SSN was able to control the UUV's
sensors.
Testing of the MTV during 2001 included operation of a thermal imager provided
by Threshold Unlimited, a SenSyTech Bobcat radar intercept receiver, a bottom
bathymetric mapping package for 'non-traditional' navigation, and a modified
commercial wireless Ethernet link able to handle data at 11Mb/s. The MTV has
also deployed REMUS mini-UUVs from its wingtips.
Submarines will increasingly act as nodes within a network that also includes
other surface and underwater platforms, both fixed and mobile, which will
require sufficient communications bandwidth for them to function as an equal
player in joint and combined operations.
This demands a comprehensive fit of radio-frequency and acoustic communications
equipment for use in different tactical situations, including new capabilities
such as expendable buoys that accommodate modems for acoustic and satellite
communications.
USS Providence was the first boat to be fitted with the Submarine High Data Rate
(SubHDR) system, which it received in mid-2000. SubHDR, which replaces the
current periscope-mounted Navy EHF System, uses a significantly larger antenna
(the OE-562/BRC) and additional radio-room equipment to provide high bandwidth
(up to 256kb/s) for EHF transmission and reception. It also provides SHF
satellite communications and can receive the Global Broadcast Service. At the
other end of the frequency scale, the ELF On-Hull Antenna system is intended to
provide full access to ELF broadcasts, with a significant increase in
maneuverability and flexibility, while conducting stealthy operations at depth
in littoral waters.
In April 2000, a prototype Submarine Super High Frequency (SHF) Phased Array
Antenna demonstrated two-way communication over the Defense Satellite
Communications System, using an electronically scanned phased-array antenna that
is designed for use in submarines. Data rates of up to 256kb/s were achieved by
the array, which incorporates the first transmit/receive modules derived from
DARPA's High Density Microwave Packaging technology.
NUWC's Communication at Speed And Depth program is examining technology
developed by industry, including that funded by DARPA, in the areas of buoyant
cable systems, towed bodies and tethered arrangements. Equipment under study
includes the BAE Systems AVXD antenna, which can handle a wide variety of
traffic, as a potential back-up to the present BR-34 or OE-538 aboard Los
Angeles-class SSNs. DARPA has directed the Massachusetts Institute of
Technology's Lincoln Laboratory to demonstrate an advanced UHF Buoyant Cable
Antenna (BCA) that will fit within space now occupied by the OE-315 BCA. The
Retrievable Tethered Optical Fibre (RTOF) buoy developed in the UK is a
candidate for UHF, SHF, ESM and video links."
Hope you enjoyed it. Now "Drink your dolphins."