Future Submarine Technology

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Future Submarine Technology Powered By Docstoc
					             Per-Ola Hedin/                           Future Submarine Technology
            Peter Hauschildt

T       oday and in the future, the subma-
        rine is more and more tasked to
perform a wide range of missions, rang-
                                                                                                                     mand of so me navies for a higher
                                                                                                                     amount of AIP energy stored on board.
                                                                                                                     Both systems mentioned are limited in
ing from counter-terrorism at sea, ASW,                                                                              this respect, the Stirling engine mainly
ASuW to supporting operations ashore.                                                                                due to the required amount of oxygen,
These missions will most likely be in the                                                                            the FC mainly by weight constraints
very difficult maritime environment of                                                                               of the hydrogen storage in metal hy-
the littorals, but combined with extend-                                                                             dride cylinders.
ed transits to the scenes of today’s ex-                                                                                To overcome the limitations of the
peditionary warfare. By integration of                                                                               FC system, TKMS is developing a
state of the art technology the subma-                                                                               methanol reformer. The methanol re-
rine will meet these new operational de-                                                                             former produces the hydrogen required
mands. On the basis of the synergy of                                                                                for the fuel cell plant onboard, replac-
the submarine design experience of Ger-                                                                              ing the metal hydride storage cylinders.
many and Sweden including the design                                                                                 The amount of AIP-energy stored on-
of the “Collins” class TKMS today is                                                                                 board can be easily enlarged, without
the solution provider for non nuclear                                                                                further increasing the submarines size.
submarines. This paper handles the                                                                                   Further advantages are the simplifica-
main aspects and recent developments                                                                                 tion of the reactant logistics because
in submarine platform technology                                                                                     Methanol is easily available worldwide
                                          The AIP Systems of TKMS, the Stirling Engine.                              at low prices The system being under
           Propulsion                                                                   Grafics/Pictures: Authors development is based on steam reform-
                                                                                                                     ing of Methanol, to produce a hydro-
                                                                                                                     gen-rich gas mixture inside the reformer.
  Air -IndependentPropulsion – AIP                                                                                               In a further step the major
                                                                                                                                    part of the hydrogen is sep-
   Non-nuelear submarines are highly                                                                                                 arated from the reformate
manoeuvrable and well suited for littoral oper-                                                                                      by using a membrane pu-
ations. With a modern air independent propul-                                                                                       rification unit. The off-gas
sion the submarine can remain underwater and                                                                                        of the membrane purifica-
on station throughout the time span of a major                                                                                    tion still contains some com-
military operation AIP is the key to “deniabil-                                                                                bustibles, which are oxidised
ity”: The submarine can do missions like intel-                                                                           utilizing pure oxygen to provide
ligence, surveillance and reconnaissance or                                                                     the heat that is required for the reforming
deployment of Special Forces with an extreme                                                                process.
low risk of interception. TKMS can today of-                                                                  The process is performed at elevated pres-
fer the only mature AIP systems: The Stirling                                                               sure, to realize a CO2-dissolution system with-
Engine, the AIP system which is operational                                             The Fuel Cell.      out the need for an additional compressor at
for the over twenty years and the PEM Fuel Cell                                                             most diving depths The hydrogen produced
system (FC), the most sophisticated AIP sys-                                                                by the reformer has a very high quality, suit-
tem which is today most widely used.                                                                        able to be used directly in the existing and
   There are still continuous devel-                                                                                   proven Siemens Fuel Cell Modules.
opments on both systems. For in-                                                                                       A functional demonstrator of a
stance in order to increase the system                                                                                 Methanol Reformer has been built up
efficiency of the Stirling engine even                                                                                 at HDW several years ago. At the mo-
more, the engine as such is fine-tuned                                                                                 ment HDW develops all components
at the same time as the efficiency of                                                                                  to be suitable for use onboard a sub-
other components, e.g. the electrical                                                                                  marine, which is very challenging
generator is increased. Excess heat                                                                                    having in mind the integration of a
will be used for different purposes on-                                                                                process engineering plant into the
board the submarine, e.g. for regener-                                                                                 closed atmosphere of a submarine.
ating a potential solid-amin system                                                                                    The Methanol Reformer itself will be
used for air purification.                                                                                             operated in an encapsulation compris-
   Both systems have been presented                                                                                    ing several safety features, to prevent
on former occasions and shall not be                                                                                   the crew from any harmful gases and
handled in this paper in detail, but is                                                                                liquids. With the development of the
there any mayor continuous develop-                                                                                    Methanol Reformer HDW combines
ment in the area of AIP? Driven by the                                                                                 the advantages of fuel cell AIP sys-
demand for prolonged mission times                                                                                     tems with the advantages of a liquid
and higher AI P speed there is a de- Functional Demonstrator of 240kW Methanol Reformer.                               fuel as energy carrier, offering the cus-

European Security and Defence 1/2009                                                                                                                         57
                                                   long time discharge and a factor
                                                   of four for a maximum speed dis-
                                                   charge compared to traditional
                                                   lead-acid technology. Further-
                                                   more the batteries are by far
                                                   lighter than lead acid cells and
                                                   are therefore ideal for combina-
                                                   tion with the metal-hydride hy-
                                                   drogen storage cylinders of Fe
                                                   AIP, giving the designer the free-
                                                   dom to increase the amount of
                                                   energy in AIP without signifi-
                                                   cantly changing the submarine
                                                      Besides the capacity Lithium
                                                   Polymer cells bring a lot more
                                                   advantages to the submarine:
                                                   • The cells can take very high
                                                      charging currents which can
                                                      enable lower indiscretion rates.
                                                   • The cell capacity can be used
                                                      by 100% which gives an even
                                                      lager capacity advantage com-
                                                      pared to lead acid batteries.
                                                      The batteries are maintenance
                                                   • They can be stored at any load-
                                                      ing condition
                                                   • They don’t consume distilled
                                                   • They don’t release gases             New Composite Propeller on a Class 212A Submarine.
                                                   • No water cooling is required
                                                   • The battery efficiency is very high due to low      ments on the attachment of the blades to the
                                                      internal resistance.                               hub are evaluated and TKMS is already offer-
                                                      The last advantage is at the same time the         ing the composite propeller as standard equip-
                                                   only disadvantage to the designer. The very low       ment on future submarines
                                                   internal resistance causes very high short cir-
                                                   cuit currents which have to be handled by ap-                    Flexible Payload
                                                   propriate measures in the design of the ship’s
New Lithium Battery for Submarines.
tomer a very promising alternative in the field       At present time TKMS and GAIA have test-              The torpedo has been the standard subma-
of AIP-Systems at TKMS.                            ed the first 500Ah cells and are testing the first    rine weapon for over half a century. Modern
                                                   full scale battery modules and partial batteries      torpedoes are quiet and locate their targets by
 High Energy Batteries                             including the battery monitoring system.              passive sonar, making not only the torpedo it-
                                                                                                         self but also the submarine difficult to locate.
   A further milestone in submarine design is        Composite Propeller                                 For a modern submarine, a flexible payload
about to enter the market in form of Lithium                                                             consists of much more than the heavy weight
based high energy batteries. In combination           A limiting factor of the typically used mate-      torpedo. A wide range of weapons is equally
with High Energy Batteries based on Lithi-         rial, bronze or sonoston, is their relatively low     essential for the submarine to exercise self-
um Polymer technology the future submarine         material damping to reduce propeller induced          defence and to act offensively. A modular sub-
will have increased capabilities not only in       noise, which becomes more and more impor-             marine can be fitted with a wide variety of
long term slow speed endurance but also in         tant due to new sensors which are able to de-
flank speed and transit. Since Lithium Poly-       tect also noise of very low frequency, another
mer Batteries have entered our daily life in-      material was needed.
side consumer electronics like mobile phones,         Anticipating big advantages in composites,
handhelds or laptops the safety problems of the    a development on composite propellers was
first days have become obsolete. Today mod-        started. As a first step, technical feasibility was
ern types of construction in combination with      demonstrated by building a CRP based pro-
polymer electrolyte and battery management         peller in exactly the same shape like the estab-
systems have solved these problems. A neces-       lished class 206a propeller. The long term tests
sary step is the up-scaling by one or two orders   on board an operational 206a class submarine
of magnitude. The challenges in production         of the German Navy showed feasibility, espe-
technology have been overcome in a joint de-       cially concerning the attachment of the CRP
velopment with the German company GAIA.            blades on the propeller hub made from metal.
   With these new battery modules it is possi-     As logical continuation a new propeller with a
ble to increase the battery capacity in the same   high material damping was build and is being          Test Firing of IDAS Missile through the Submarines
volume by a factor of approximately two for        tested on class 212a. At present time improve-        Periscope.

58                                                                                                                        European Security and Defence 1/2009
                                                         mines, divers as well          A new generation of lightweight fibre-optic
                                                         as heavy and light mis-     guided missiles for submarines is currently be-
                                                         siles and AUVs of ap-       ing developed The System IDAS (Interactive
                                                         propriate shape. To         Defence and Attack System). IDAS is connect-
                                                         have more flexibility       ed to the submarine by fibreoptic link during
                                                         some of the torpedo         its entire mission duration. The missile trans-
                                                         tubes can be replaced       mits a constant stream of images from its IR
                                                         by a large versatile        camera to the consoles of the submarine Com-
                                                         tube called Flexible        bat System. The missile is intended for use
                                                         Payload Lock (FPL),         against the modern submarine’s deadliest ene-
                                                         which enables the sub-      my: the ASW helicopter However, the degree

Flexible Payload Lock and Payload Compartment of

weapons, mines, sensors and other equipment,
depending on the likely mission profile. In the
last 30 years, increasing importance has been
attached to missiles as a submarine weapon for
use against surface ships or land-based targets.
Furthermore Special Operations Forces (SOF)
have become an important asset within many
forces, and the submarine would be the ideal
clandestine delivery system for sea borne SOF
missions. Therefore a modern submarine must
be able to deploy: Torpedoes, Ship to Ship Mis-
siles, Land Attack Missiles, Self Defence De-
coys and Weapons, Mines, Unmanned Vehicles,
Special Forces.
   Today the weapon tubes and reserve storage
can accommodate not only torpedoes but

                                                   marine to carry large and         of precision with which the missile can be con-
                                                   odd shaped UUVs or larger         trolled makes it suitable far operations against
                                                   groups of Special Forces          surface ships and coastal targets as well. The
                                                   with their equipment. The         IDAS missile is launched from a launching con-
                                                   FPL will be an important          tainer that can be loaded in a torpedo tube like
                                                   part of Sweden’s next sub-        any heavyweight torpedo. The system can
                                                   marine project A26.               therefore be retrofitted into an existing sub-
                                                      In addition to this the tra-   marine with relatively little difficulty
                                                   ditional reserve storage has,
                                                   in A26, been transformed                        Signatures
                                                   into a Flexible Payload
                                                   Compartment serving the
                                                   weapon tubes and the FPL             In recent decades a lot of effort has been
                                                   with storage and mainte-          spent by TKMS on minimizing all signatures
                                                   nance space for different         emitted by our submarines. The improvements
                                                   types of payloads, e.g. tor-      achieved during this period have been enor-
                                                   pedoes, mines, divers as          mous and, although they always have to be mir-
                                                   well as heavy and light mis-      rored against the similarly developing sensor
                                                   siles and UUVs of uncon-          technologies, it can clearly be stated that our
                                                   ventional shape. It can also      submarines are nowadays less detectable than
                                                   serve as living quarters for      ever since INW 11. In fact, today TKMS is pro-
                                                   Special Forces or other ad-       ducing the stealthiest submarines ever built.
                                                   ditional personnel. In addi-      These submarines are nowadays more or less
                                                   tion a vertical cylindrical       undetectable for opponents by passive means.
                                                   tube, penetrating the pres-          Consequently the opponents are forced to
                                                   sure hull could incorporate       think of active means of detection, even though
                                                   various payloads like cruise      this means giving away their own position first.
                                                   missiles, Special Forces          Against this background it is obvious that the
                                                   equipment, mines or simply        use of active means will become more and more
Vertical Payload Tube.                             additional fuel.                  common again.

European Security and Defence 1/2009                                                                                              59
                                                                                                       pression with increasing diving depth must be
                                                                                                       taken into account for the layout of the sub-
                                                                                                       marine’s compensating tanks.
                                                                                                          TKMS has developed and is using a reflec-
                                                                                                       tive coating to cover bow, stern and tilted sur-
                                                                                                       faces. The material is reflecting and scattering
                                                                                                       the incoming sound energy, thus preventing the
                                                                                                       sound energy from entering free flooded areas
                                                                                                       were structures which form excellent reflectors
                                                                                                       are situated. The shine line of the pressure hull
                                                                                                       itself can be covered with an absorbing mate-
                                                                                                       rial, which needs a significantly higher materi-
                                                                                                       al thickness for physical reasons. An absorbing
                                                                                                       material for this purpose is currently under de-
                                                                                                       velopment with TKMS.

                                                                                                          More and more changes in the geopolitical
                                                                                                       environment influence maritime strategies and
                                                                                                       result in alterations in operational demands and
                                                                                                       requirements – adding up to new technical and
Submarine signatures.                                                                                  non-technical challenges. Wherever such a
                                                                                                       challenge is identified there is on the one hand
   Having analyzed-this changed threat sce-        100m, the elevation angle stays below 6°.           a risk, but on the other hand there are chances
nario the attention is turned to an adequate       Since the probability of a threat at such short     for substantial renewals and developments.
defence. There are two main threats through        distances is negligible (and under most cir-           The non-nuclear submarine is currently un-
active detection for a submarine: in periscope     cumstances avoidable by the submarine’s             dergoing a dual transformation in development,
condition it is radar and in submerged condi-      crew), an optimization for elevation angles         design and production as well as in associated
tion it is active sonar. Especially for AIP sub-   of the incoming signal in the range between         technologies that expand the mission capabil-
marines, radar is a minor threat as compared       0° and approximately 6° is self-evident. The        ities of the submarine. Together, these transfor-
to surface ships due to the fact that modern       prevalence of these very low elevation angles       mations will make the conventional submarine
AI P submarines operate submerged (hid-            is further increased by the influence of salt       more robust, harder to detect, and more flexi-
den from radar below the sea surface) most                                                                           ble to allow for operations covering
of the time.                                                                                                                         the entire mission
   Nevertheless, as the demands concerning
stealth are much higher for submarines, some
effort is spent on minimizing the remaining risk
of being detected that way by application of
radar-absorbing materials to the masts. This
leaves the main threat for modern submarines,
                                                   Echo strength optimised submarine.
the opponent’s active sonar. In the following
sections it will be discussed what can be done
about shaping and what about coating in order
to minimize the target strength.                   and temperature layers resulting in horizontal      spectrum – from
                                                   acoustic channels.                                  peacetime to high-intensity war fighting.
                Shaping                               The first consequence is to avoid reflecting        Thus the evolution of non-nuclear sub-
                                                   vertical surfaces wherever possible. Since the      marines has to some extent overtaken their gi-
                                                   pressure hull has to withstand the diving pres-     ant nuclear sisters simply because they do not
   The first thing that is done about shaping is   sure at high depth, it is not possible to deviate   feature the manifold shortcomings of these
to make the submarine as small as possible This    from the circular cross-section. The side faces     boats, e.g. with regard to signature management
does not only help maneuverability but also de-    of the sail, superstructure and keel should also    and cost.
creases the size of sonar reflecting surfaces.     be inclined. The influences of all these modi-         The added capabilities and extended opera-
However, the related reduction of the target       fications on the submarine’s resistance, maneu-     tional endurance will make the submarine even
strength is not very pronounced, so that further   verability, ease of operation and flow noise have   more important in the twenty-first century as it
steps, ie. the optimization of geometrical de-     been studied by TKMS in detail. In the end a        was in the twentieth. The submarine has a va-
tails, also have to be taken.                      compromise between the different require-           riety of uses in the coming decades. While its
   In to do this, the direction of the approach-   ments posed on a submarine has to be found.         premier role as a first rate naval asset remains,
ing sonar signal with respect to the submarine                                                         the submarine will extend it usefulness into the
and the likelihood of certain directions have                       Coating                            arena of MOOTWs. This will ensure that the
to be considered. In case the opponent is far                                                          non-nuclear submarine will remain a premier
away, it is obvious for geometrical reasons that                                                       tool for world wide security policy.           ■
the sonar signal will impinge on the subma-          The second or additional option to reduce the
rine nearly horizontally (0°). Even at relative-   submarine’s target strength is the application        Per-Ola Hedin, Koekums AB and Peter
ly short distances, e.g. opponent 1000m away       of acoustic coatings. On principle all acoustic     Hauschildt, Howaldtswerke-Deutsche Werft
from the submarine submerged at a depth of         coatings are compressible materials. Their com-     AG,

60                                                                                                                      European Security and Defence 1/2009