Jötunn Class
Basic Information:Propulsion:
- Role: Nuclear-Powered Arctic Cargo Hovercraft
- Mass: 5,000 t
- Payload 3,000 t
- 40x PzKpfw 151 MBT
- 50x HTTS 50.1000 10x10 Truck
- 200x KfZ 310 All-Terrain Carrier
- 1,000 TEU
- Complement: 40 + 160
- Length: 150 m
- Beam: 80.0 m
- Height 32.5 m
- 1x AEG 750 MWth Ultra-High Temperature Reactor
- 4x SDI 187.5 MWth fossil fired helium heater modules
- 6x 6.0 meter Variable geometry lift fans, 7.5 MW each
- 6x 9.0 meter Ducted propulsors, 30 MW each
Performance:Sensors & Processing Systems:
- Top speed (smooth ice): 145 knots
- Top speed (water, SS4): 120 knots
- Cruise speed: 105 knots
- Range: Unlimited (nuclear), 1,000 km @ 105 knots (conventional mode, full payload)
- Endurance: 90 days supplies
- SDI FMG 960 S band Surface Search & Navigation Radar
- SDI FMG 970 X band Surface Search & Navigation Radar
- SDI FMG 990 W band Ice Detection Radar
Overview:
The Jötunn class is a class of large nuclear air cushion vehicles designed by SDI Marine Systems. The Jötunn is a 5,000 tonne air cushion vehicles (ACV) that can carry up to 3,000 tonnes of cargo including heaay wheeled and tracked vehicles, containerized cargo, and various mission modules, at 100 knots over open water and at up to 140 knots over consolidated ice.
Design & Construction:The Jötunn class vessels have a length of 150.0 meters, beam of 80.0 meters, and a height of 24.0 meters from the keep to the aft rudder fin tips. Mass fully loaded is 5,000 tonnes. The hull is a single deep box-girder construction buoyancy raft 150 m × 78 m × 4.0 m deep running the full length and width of the vehicle forming the hull, the cushion pressure boundary, the cargo deck, and the reserve buoyancy. The hull upper flange is the cargo dec and the lower flange is the flotation tank bottom plating, and its webs are the two longitudinal bulkheads separating the central hold from the port and starboard side bays. Superstructure, fan ducts, ramps, fins and machinery foundations are carried on this box. Longitudinal strength is carried by two heavy outboard side girders forming the skirt attachment backbone, four inboard girders defining the cargo bay boundaries, and a centerline keel girder that also forms the longitudinal cushion divider. Transverse frames are at 2.0 m spacing, decreasing to 1.0 m under the cargo lanes and at ramp reaction points. The reactor citadel is a self supporting titanium box structure integrated into the raft and continuous with it through the full depth of the vehicle carrying its own loads independently of the cargo deck. Watertight subdivision comprises 48 compartments, the vehicle survives flooding of any three adjacent compartments. The reactor citadel is independently watertight and gastight. Girder depth amidships is 11.0 m including 9.2 m of cargo hold clear height, 1.8 m of flotation tank depth, and the deck and bottom plating. Transverse strength is provided by watertight bulkheads at 12.5 m spacing, dividing the vehicle into 20 longitudinal zones used by the zonal electrical, hydraulic and damage control systems. The reactor trunk is an 18 m square torsion box built integrally with both longitudinal bulkheads and with the transverse bulkheads. The flotation tanks are subdivided into 48 individually vented and sounded cells providing 200% reserve buoyancy. The vehicle floats on these cells with the cushion off and retains positive buoyancy and stability with any four cells open to the sea. A hardened ice belt 3.2 m deep encircles the flotation tanks at the design waterline, constructed to a Polar Class 6 glancing impact standard, allowing the vehicle to settle amongst broken ice in routine operation. Expansion joints are fitted at the four zone boundaries to accommodate through thickness thermal gradients between the heated interior and the external ambient temperature. The hull primary structure is constructed almost entirely of Ti-5111 (Ti-5Al-1Sn-1Zr-1V-0.8Mo) titanium alloy providing high specific yield strength, complete immunity to seawater galvanic corrosion, no magnetic signature, excellent fatigue performance, and adequate weldability with proven marine fabrication procedures. Ti-5111 is used for the cargo deck and bottom plating, all longitudinal and transverse bulkheads, the flotation tank shell and ice belt, the reactor trunk, the bow and side ramp primary structures with their hinges and locks, the resting pad legs and load paths, and all helium pressure boundary penetrations. The bow, stern, and outboard side girders incorporate a 1.5 m deep crushable zone of thin wall tubular titanium crush structure elements in a syntactic foam matrix, designed to absorb a 12 MN longitudinal impulse without any penetration of the cushion pressure boundary. The reactor citadel is set a minimum of 24 m inboard of any external boundary, which is the single largest contributor to its impact protection. The bottom of the hull is a three layer system with titanium faced titanium honeycomb structural layer, a UHMWPE ablative layer in replaceable 3 m × 3 m panels, and a skid layer. Six full length longitudinal landing skids at ±6, ±18, and ±30 m from centerline, each a titanium backed AR500 steel shoe 600 mm wide and 50 mm thick on a syntactic foam crush core, run the entire length of the hull bottom. Seawater heat rejection exchangers are integrated flush into the bottom plating between the inner skid lines. Twelve hydraulically extending landing pads, four per side and four across the stern extend and hold the raft 1.2 m clear of the surface for loading, discharge, servicing, and repair, and prevent the skirt from carrying vehicle weight when parked. Retracted they lie flush within the bottom contour. Each pad carries a 400 mm syntactic foam crush core sized for 2.0 g setdown and can be set on prepared support posts at a permanent berth. With the pads extended onto support posts the skirt carries no load and the complete skirt system is accessible from beneath.
The structure above the hull including the majority of the superstructure is fabricated from carbon fiber reinforced epoxy using a toughened resin system qualified for continuous service at −60 °C. Glass fiber laminates are used where radio frequency transparency is required. Composite construction covers the superstructure and bridge, all twelve fan ducts and bellmouths, the plenum walls, the two forward and two aft vertical fins and all four rudder surfaces, the side bay weather deck panels, and all external fairings. The forward end of the superstructure contains a bow ramp and access trunk with a clear width of 20 m. In the stowed position the bow ramp closes the hull, transmits bow slam loads into the box girder, and forms the aerodynamic nose. Behind it the access trunk runs aft into the central cargo hold. Crew and passenger citadels port and starboard flank the bow trunk. Each is a three deck accommodation block with independent life support, power feeds, escape routes and provisions. The enclosed pilthouse is located above the bow ramp upper closure with sight lines over the deployed bow ramp. The forward central hold measures 26 m wide by 36 m long, being fed directly from the bow ram and connects to both side bays through openings in the longitudinal bulkheads. The reactor trunk is located in the center of the ship, being an 18 m square armored trunk extending from the flotation tank structure to the weather deck. Immediately port and starboard of the reactor trunk are the two lift fan banks each consisting of three vertical fan trunks 7 m square, in line fore and aft on 11 m centers. Each fan trunk extends the full height of the vehicle from a louvred inlet structure on the weather deck down through the cargo deck level to the cushion plenum beneath. Above the cargo dec on either side of the reactor trunk the plenum deck carries the two louvred inlet structures. Each louvred inlet structure is a rectangular housing 25 m long and 9 m wide running fore and aft above one bank of three lift fan trunks and supplying all three from a common inlet plenum. The aft central cargo compartment is located immediately aft of the reactor trunk and measures 26 m wide by 35 m long, accessed through openings in the longitudinal bulkheads which connect it to both side bays and to the two aft side ramps. The side cargo bays are each 84 m long and 22 m wide and connect to both central bays through forward and aft openings in the longitudinal bulkheads. The propulsion fan bank is located behind the cargo deck with six ducted fans in line across the stern with their ducts blended into the aft fuselage, and the two vertical fins carrying the aft rudder pair.
The vehicle's air cushion is a peripheral jet cushion that supports the entire mass of the vehicle. Air is discharged downward and inboard at 30° from the vertical around the entire perimeter of the vehicle. The momentum of this curtain confines a cushion of air beneath the hull at a gauge pressure of 4,800 N/m² acting over 10,215 m² which supports the 5,000 tonne gross weight. The peripheral seal is a bag-and-finger skirt of 9.0 m total height: a pressurized peripheral bag of 3.6 m section height and 5.4 m fingers. The bag is fabricated from a fluorosilicone coated hybrid laminate of aramid and ultra-high-molecular-weight polyethylene fibers which retains flexural modulus below −50 °C. Fingers are molded elastomer with an ice phobic surface treatment and embedded sacrificial abrasion plies. Reject heat from the power cycle is bled into the bag plenum and maintains fabric temperature above −20 °C at all ambient conditions. Each of the individual skirt segments carries a 500 bar hydraulic actuator capable of retracting the segment 1.2 m in under 0.4 seconds. Segments are retracted on command from the forward looking ice profiler immediately before the segment reaches a pressure ridge crest and are released as it passes, the predictive retraction allowing continuous high speed operation over ridged ice. The cushion is divided into eight cells by internal skirt curtains arranged as two longitudinal rows of four. Each cell is fed through independently modulated louvres from the common plenum. Differential cell pressure provides attitude control at low speed, ride control at all speeds, and limits the lift loss from a single skirt breach to 12.5%. All skirt attachment hardware is inboard of the hull's outer surface and reached from heated peripheral galleries running the full circumference of the raft at plenum level. Fingers are changed from inside the vehicle through a gasketed access hatch. Resistive heating is included on all attachment rails and bag seams held above −5 °C whenever the vehicle is on cushion or on standby. After overwater operation a purge sequence drives cushion air through bag and finger drains at high flow while hovering, expelling free water before setdown. Each finger has three drains with non-return flaps. Six additional hydraulic actuators give ±1.0 m of longitudinal and transverse skirt displacement for static trim, cargo distribution compensation, and ice accretion compensation. The bag is divided into 32 independently fed sections. Loss of up to 24 consecutive fingers is tolerated at full speed and 60 at reduced speed.
Propulsion:The vehicle powered by a nuclear propulsion system consisting of a 750 Megawatt helium cooled ultra-high temperature reactor (UHTR) connected to a closed cycle bi-brayton power transmission system. The bi-brayron power cycle uses the reactor's helium coolant as the working fluid to drive a closed cycle gas turbine, with the resulting shaft power is used to recirculate the reactor's own coolant circuit and and circulate a set of physically separate secondary helium circuits which carry energy out to the six lift fans and six propulsion fans. The vehicle reactor is a helium cooled, graphite moderated ultra-high-temperature thermal reactor rated at 750 MWt thermal power. The core is annular with an outer diameter of 3.5 m, inner diameter of 1.5 m and active height of 3.5 m give an active volume of 27.8 m³ and a mean power density of 21 MW/m³. The annular geometry shortens the conduction path between the centerline of a fuel compact and the nearest coolant channel and limits the peak fuel temperature reached during a depressurized conduction cooldown. Fuel is in the form of tristructural isotropic coated particles. Each particle consists of a 425 µm diameter kernel of uranium oxycarbide enriched to 19.75 per cent in ²³⁵U surrounded by four coating layers. A 100 µm porous carbon buffer accommodates fission gas release and kernel swelling. A 40 µm inner pyrolytic carbon layer provides a bonding and diffusion barrier. A 35 µm silicon carbide layer forms the principal pressure boundary and the barrier to metallic fission product diffusion. A 40 µm outer pyrolytic carbon layer protects the silicon carbide during compact fabrication. Overall particle diameter is approximately 1.0 mm. Fuel particles are consolidated at a packing fraction of 35% into cylindrical compacts 12.5 mm in diameter and 25 mm long in a silicon carbide matrix. The silicon carbide matrix has a thermal conductivity approximately three times that of the graphite matrix used in earlier fuel forms, which reduces the temperature rise from compact centerline to compact surface. Compacts are loaded into axial fuel channels in hexagonal graphite blocks 360 mm across flats and 850 mm high. Each block contains 210 fuel channels and 108 coolant channels of 16 mm diameter on a triangular lattice. Four blocks stacked axially form one fuel column, and 72 columns form the annular core. The graphite blocks are nuclear grade near isotropic graphite, Blocks are keyed to their neighbors by dowels and located radially by a core barrel of silicon carbide fiber reinforced silicon carbide composite. The composite barrel retains strength at core outlet temperature, has a thermal expansion coefficient close to that of graphite, and contributes negligible parasitic neutron absorption. The core is qualified for the vehicle acceleration environment of 3.0 g vertical and 2.0 g longitudinal together with continuous cushion borne vibration in the 1 to 8 Hz band. The radial reflector is graphite and carries the twelve control drum channels. Axial reflectors 500 mm thick are fitted above and below the active core. The central column within the annulus is graphite and contains the six shutdown rod channels together with the core instrumentation thimbles. Twelve control drums are located in the radial reflector, each drum consisting of a graphite cylinder 400 mm in diameter carrying a 120° arc of boron carbide absorber on its outer face. Rotating the control rods presents the absorber toward or away from the core and provides the reactivity worth required for power operation, xenon override and temperature defect. Drums are driven by electric actuators mounted on the vessel head and operating in the cold helium space. Six shutdown rods employing boron carbide in a silicon carbide sheath are provided in the central column, held out of core by electromagnetic latches and inserted by gravity assisted by spring on loss of power or on trip signal. Either system alone has sufficient worth to bring the core to cold shutdown from any operating condition and to hold it subcritical with the most reactive element fully withdrawn. The reactor, its shield, its containment, the primary turbomachine and the four intermediate heat exchangers are assembled as a single removable module. Shielding consists of an actively cooledtungsten laminate inside the pressure vessel, Tungsten, beryllium oxide, and boron carbide plug shields with internal coolant passages, the t
thick wall steel containment vessel, ⁶Li-enriched lithium hydride external neutron shielding, and tungsten laminate and borated water jacket gamma shielding.
The primary circuit is a closed helium loop containing the heat source, the primary turbine, the primary compressor, the secondary compressor and the four intermediate heat exchangers. The primary turbine absorbs its entire output within the loop by driving the two compressors, and no shaft power leaves the primary circuit. Helium enters the core at 520 °C and 7.05 MPa at a flow rate of 250 kg/s. The helium passed through four inlet nozzles spaced at 90° where it passes downward through an annular downcomer between the vessel wall and the core barrel, which holds the vessel wall close to inlet temperature and permits construction of the vessel from modified 9Cr-1Mo ferritic steel. At the bottom of the downcomer the flow turns into the lower plenum, passes upward through the coolant channels of each fuel column, and collects in the upper plenum at 1,100 °C at 7.00 MPa. The upper plenum and the hot gas duct to the primary turbine are lined with silicon carbide composite tiles over an insulating layer of carbon fiber felt with the metal outside the insulation and cooled by inlet helium, holding all pressure boundary metal below 550 °C. The helium then passes through the primary turbine that absorbs energy to drive the two compressors. Helium expands through the primary turbine at a pressure ratio of 3.0, and develops 570 MW of power, 410 MW being absorbed by the primary compressor and 160 MW by the secondary compressor. The gas leaves the turbine at 660 °C and then passes through the four intermediate heat exchangers where exchanges 590 MW and leaves them at 205°C. The primary compressor then raises the helium to 7.05 MPa and 520 °C at where it returns to the reactor inlet plenum. The primary turbine, primary compressor and secondary compressor are mounted on a single shaft acting a single hermetically sealed machine within the reactor containment vessel. The machine has no dynamic seal to the exterior and no external lubrication supply. Rotational speed is 11,500 rpm. The turbine has four stages. Rotor and stator blading in the first two stages is carbon-carbon with CVD SiC/ZrC environmental barrier coatings with with silicon carbide reinforced composite shrouds, transitioning to SiC/SiC CMC blisks in the third and fourth stages. The primary compressor has fourteen axial stages and the secondary compressor has eleven stages, both with titanium alloy blading in the forward stages and TNM titanium aluminide alloy ( Ti–43.5Al–4Nb–1Mo–0.1B) n the rear stages where discharge temperature reaches 520 °C. The rotor is supported on gas foil bearings using the helium working fluid as the lubricating medium with catcher bearings for rundown. Power level is set by inventory control. Helium is bled to or admitted from storage tanks to change loop density and therefore mass flow at constant temperature and constant rotational speed. A purification plant treating a 1% bypass flow removes water, carbon oxides, hydrogen, methane and nitrogen through oxidizer, molecular sieve and cryogenic charcoal beds, holding total impurities below 10 ppmv. Impurity control at this level limits oxidation of the graphite core structures and carburization of heat exchanger surfaces. Total helium inventory is 4.5 tonnes across both circuits, with a 15 tonne reserve in a high pressure storage tank and an onboard recovery and purification plant.
Four intermediate heat exchangers (IHX) transfer heat from the primary circuit to the two secondary circuits. The units are arranged as two pairs, each pair serving one secondary circuit with all four are mounted within the containment vessel as part of the removable reactor module. Each IHX is printed circuit with flow passages are chemically etched into flat plates which are then diffusion bonded into a solid block. This construction provides a heat transfer surface density of approximately 1,200 m² per cubic meter and accommodates the 4.7 MPa differential pressure between primary and secondary sides within a core volume of 4.6 m³ per unit. The IHX are constructed from iAlloy 617 nickel-chromium-cobalt-molybdenum alloy selected for creep strength and for resistance to carburization in impure helium at 660 °C. Primary helium enters at 660 °C and leaves at 205 °C, secondary helium enters at 180 °C and leaves at 640 °C. The two independent secondary circuits are each supplied by two intermediate heat exchangers and serves three lift fans, three propulsion fans and two turbogenerators. Each circuit carries 125 kg/s of helium flow. The two circuits are cross connected at two points through normally closed isolation valves. With one circuit isolated the remaining circuit supplies its own six fans and two turbogenerators at full rating or supplies a selected subset of the isolated circuit's machines at reduced rating through the cross connects. The vehicle remains fully controllable on one secondary circuit at approximately half power, with lift and propulsion both retained on the same side and cushion cell modulation compensating for the resulting lift asymmetry. Secondary helium is compressed from 3.40 MPa to 7.00 MPa with a temperature rise from 55 °C to 180 °C. It gains 590 MW in the intermediate heat exchangers and leaves at 640 °C. Expansion through the power turbines to 3.55 MPa yields 245 MW at the twelve fan drive turbines and 25 MW at the four turbogenerator drive turbines, with the gas leaving at 450 °C. The precoolers return it to 55 °C, rejecting 510 MWt to the fan discharge streams. Helium is distributed from the containment penetrations to the machinery spaces through concentric piping. The hot supply line runs inside the cold return line, separated by a thin liner of Alloy 800H which traps a stagnant helium layer as insulation. The outer pipe is Ti-5111 and runs close to return gas temperature which permits conventional supports and removes hot external surfaces from the machinery spaces. Total secondary run is 520 m. Expansion is accommodated by bellows units at 40 m interval each restrained against pressure thrust by external tie bars.
Six lift fans are installed in two groups of three, one group on each side of the reactor trunk in line. Each fan is 6.0 m in diameter and delivers 1,200 m³/s at a total pressure rise of 5,750 Pa, absorbing 7.5 MW of shaft power. Air is admitted through two large louvred inlets on the weather deck, one on each side of the vehicle, each 25 m long and 7.5 m wide. Each inlet discharges into a longitudinal inlet plenum from which the three fans on that side draw. The common plenum equalizes inlet conditions across the three fans, permits any one fan to be shut down without disturbing the others, and provides a settling volume that reduces distortion at the fan face. The louvres are variable position airfoil sections of composite construction with electrically heated leading edges and reject heat trace heating in the pivots that modulate inlet area with fan demand, close completely for weather protection when the vehicle is settled, and close on the affected side in the event of fire or heavy spray ingestion. The fan rotor has 24 blades constructed from carbon fibre composite with titanium leading edge sheaths and titanium root fitting, mounted on a titanium alloy hub. The fan casing is filament wound carbon fiber with an integral titanium containment ring at the rotor plane. Downstream of the rotor a 32 vane composite stator recovers swirl and delivers axial flow to the discharge scroll. Fan discharge is collected in a scroll and delivered to the main plenum which runs the full perimeter of the vehicle within the hull box and supplies the bag and the cell curtains. The secondary circuit precoolers for that fan are installed in the discharge scroll, so cushion air is delivered approximately 10 K above ambient, raising skirt fabric temperature and reducing spray freezing on the inner skirt faces. Each fan is driven by a five stage helium power turbine through a reduction gearbox. The turbine operates at 9,000 rpm and the fan at 660 rpm. Fan speed follows from a tip speed limit of 180 m/s to control blade stress and noise. The gearbox is a two stage epicyclic unit rated at 10.0 MW with case carburized steel gearing and an aluminum alloy casing. It is pressure lubricated from a self-contained system with a heated reservoir and full flow filtration, independent of every other lubrication system in the vehicle. The power turbine has five stages with single crystal nickel base blading in the first two stages and conventional cast nickel base blading in the remaining three. The rotor runs in gas foil bearings on the working fluid. Casings are Alloy 617 with external insulation. Each turbine has an inlet isolation valve pair and a trim valve permitting individual shutdown and individual power setting.
Six propulsion fans are installed in line across the stern on a common transverse axis located 15.0 m above the keel. Each fan is 9.0 m in diameter and each duct is blended into the aft fuselage so that the aft hull surfaces that form the outer walls of the ducts form a single continuous faired structure across the stern, reducing the wetted area and interference drag associated with separate nacelles, shortening the load path between the fan thrust bearing and the hull box girder, and allowing the innerduct structure to carry the aft vertical fin loads. Air enters through a full width intake above the flight deck faired into the upper hull line with a boundary layer diverter and splitters forward of the fan faces. The intake lip and the splitters carry thermal anti-icing supplied from the reject heat loop. Each fan absorbs 30.0 MW of power and produces 350 kN of thrust at the 105 knot open water cruise condition, giving a total installed thrust of 2,100 kN. The rotor has 18 blades of carbon fibre composite with titanium leading edge sheaths mounted on a titanium alloy disc with titanium dovetail root fixings. The duct is filament-wound carbon fiber with a titanium containment ring at the rotor plane and a titanium bladeoff shield on the outboard face of each outer duct. A 40 vane composite stator downstream of the rotor recovers swirl and transmits rotor torque reaction into the duct structure. Fan diameter of 9.0 m provides low disc loading, which yields high propulsive efficiency. Each fan is driven by a six stage helium power turbine through a reduction gearbox. The turbine operates at 7,500 rpm and the fan at 450 rpm. Fan speed follows a tip speed limit of 230 m/s. The gearbox is a three stage epicyclic unit rated at 35 MW with case-carburized steel gearing, a nitride steel ring gear and an aluminum alloy casing. Lubrication is by a self-contained pressure system with a heated reservoir, full flow filtration and a chip detector. Turbine construction uses single crystal nickel-base blading in the first three stages. Each turbine has an inlet isolation valve pair and a trim valve. Any propulsion can may be shut down and its rotor allowed to windmill, or braked and locked, with the remaining five continuing at rated power.
Four turbogenerators are installed on the plenum deck, two supplied by each secondary circuit. Each unit comprises a four stage helium turbine driving a high speed permanent magnet generator directly on a common shaft. Each unit is rated at 7.5 MWe, giving 30 MWe of main generation. The turbine takes secondary helium at 640°C and 6.80 MPa and exhausts at 450 °C into the common precooler return in parallel with the fan drive turbines. Helium consumption is 6.5 kg/s per unit. Shaft speed is 25,000 rpm. The generator is a four pole machine with samarium-cobalt magnets retained by a carbon fiber containment sleeve. The stator is cooled by a closed glycol jacket connected to the reject heat loop. Output is rectified at the machine terminals and delivered to the 12 kV MVDC main ring through an integrated converter. Because the turbogenerators are supplied from the secondary circuits, electrical generation is identical in nuclear operation, conventional operation and combined operation. Backup power is provided by twin 3.0 MWe and twin 500 kWe diesel generators. Electrical distribution is via a a zonal Medium Voltage Direct Current (MVDC) electrical distribution system. The distribution voltage is 12kV DC on the main ring bus with local zone conversion to 1 kV DC for major loads, 800 V DC for medium loads, and 400 V AC (three-phase, 60 Hz) synthesized locally for legacy AC loads. Each of the twenty zones contains zonal converters, load centers, and cross connects to both sides of the main ring. Any one zone may be isolated with the remaining three carrying the full hotel and control load. The vessel includes four LFP Battery Energy Storage System (BESS) modules of 3 MWh usable energy storage each contained in fire rated pressure relieved enclosures vented overboard, liquid heated and cooled to hold cells between +5 °C and +35 °C. Charging is inhibited below 0 °C cell temperature. Battey functions include no-break power transfer, black start of the backup plant and the reactor, peak shaving, silent watch, and 90 minutes of essential loads including reactor instrumentation after total generation loss. The modules also absorb the load fluctuations of ridge crossing and heavy maneuvers.
Four fossil fired heater modules provide an alternative source of heat for the primary circuit. Each module is rated at 187.5 MWt and heats helium from 520 °C to 1,100 °C so that four modules operating together match reactor thermal power and reactor outlet temperature. The full performance envelope of the vehicle is therefore available with the reactor shut down or with the reactor module removed. The heater modules are installed on the plenum deck, two on each side, outboard of the reactor trunk. Each draws combustion air through a heated inertial separator intake on the weather deck and discharges through an uptake in the same location. In conventional operation, helium leaving the primary compressor is diverted through a bypass branch which carries it around the reactor through the four heater modules and back into the primary circuit immediately downstream of the reactor outlet and upstream of the primary turbine. Lift, propulsion, electrical generation, thermal services and ride control are identical in the two modes. Each module is a recuperated gas turbine core designed to produce a large mass flow of hot combustion gas which is used to heat the helium circuit through a helium heat exchanger. The turbine within the module drives the compressor and the recirculating gas fan and delivers no shaft power outside the module. Ambient air is drawn through the intake and compressed to 4.0 atm and 190 °C. It is then preheated to 250 °C in the air preheater against turbine exhaust. In the combustor the preheated air burns with arctic diesel or JP and is diluted by recirculated combustion gas returning at 560 °C, producing 225 kg/s of gas at 1,300 °C. This gas passes through the helium heater, transferring 187.5 MW to the helium stream and leaving at 560 °C. Of the cooled gas, 125 kg/s is returned to the combustor by the recirculating gas fan and 100 kg/s passes to the turbine where it expands to 500 °C, gives up further heat in the air preheater, and leaves through the uptake at 280 °C. The helium heater is a counterflow tube bank in with the two hottest tube rows constructed from silicon carbide fiber reinforced silicon carbide composite and the remaining rows Alloy 617. The composite tubes carry 7.0 MPa internal helium at metal temperatures approaching 1,200 °C. The air preheater is a plate-fin unit constructed from Alloy 800H. Combustor liners are silicon carbide composite with an yttria-stabilized zirconia thermal barrier coating. The compressor is titanium alloy in the forward stages and nickel-base alloy in the rear stages, the turbine and the recirculating gas fan are cast nickel-base alloy, both operating below 600 °C. Ducting and casings are Alloy 800H with external insulation. Each module carries a 2 MW permanent magnet machine mounted integrally on the compressor and turbine shaft, supplied from the 12kV DC zonal bus through a bidirectional converter. It motors the shaft to light-off speed and through to self-sustaining operation, achieving cold start to rated output in 90 seconds at −45 °C ambient. No air start supply, starting engine or hydraulic starter is fitted. In steady operation the same machine trims shaft speed against varying recirculation rate and helium side load, which decouples heater output from shaft speed and gives rapid and stable response to propulsion demand. At part load it recovers surplus turbine work to the bus. This system allows the vehicle to be started into full propulsion from stored energy alone. The energy storage modules motor one heater to self-sustaining operation, that heater raises the primary circuit to temperature, the primary circuit brings up both secondary circuits and the four turbogenerators, and the remaining three heaters are started from the resulting bus supply. The bypass circuit is a parallel branch of the primary circuit located outside the containment vessel. The circuit takes helium from the primary compressor discharge header, carries it through the four heater modules in parallel, and returns it to the primary turbine inlet header downstream of the reactor outlet. Isolation is by two high temperature helium shutoff valves in the reactor branch and two in the bypass branch. All fail to the safe (open) position which is reactor branch open and bypass closed. Valve bodies are Alloy 617 with silicon carbide composite internals and gas-purged bellows stem seals. During nuclear operation 2% helium bleed circulates continuously through the bypass and the four heater modules, holding the heat exchangers above 200 °C. This keeps the branch purged and leak monitored, prevents cold soak of the helium heaters, and removes thermal shock from the transfer sequence. Mode transfer is performed by walking the two valve positions against each other over approximately 90 seconds while the plant control system holds primary turbine inlet temperature on schedule. Propulsion is continuous through the transfer and fan speeds are unchanged.
Vehicle Management & Control:The vehicle's active closed loop ride control system is a closed-loop controller which regulates cushion cell pressures, lift fan power and skirt segment position to hold the vehicle attitude, clearance and vertical acceleration within limits over a surface which is neither flat nor rigid. Twelve servo accelerometers are mounted at the corners, quarter points and center of the hull box, measuring vertical acceleration. Three inertial measurement units supply pitch, roll, heading and their rates. Sixteen laser clearance sensors are mounted around the periphery inside the skirt line. Pressure transducers measure cushion pressure in each of the eight cells and plenum pressure at each of the six fan discharges. Load cells at the four resting pad attachments measure skirt reaction when settled. Surface elevation ahead is supplied by the radar at 2 Hz. The eight cushion cell feed louvres modulate cell pressure with a bandwidth of 5 Hz and an authority of ±35% of nominal cell pressure. The six lift fan turbine trim valves modulate total cushion airflow with a bandwidth of 2 Hz and an authority of ±20%. The 96 skirt segment actuators retract individual segments 1.2 m in 0.4 s. The six propulsion fan deflector pairs contribute pitching moment through thrust line offset. The controller runs at 200 Hz on triplex processors in the flight control cabinet, with a model predictive outer loop at 20 Hz. The outer loop takes the surface elevation model from the radar, projects the vehicle path 90 seconds ahead at commanded speed, and computes the cell pressure schedule and skirt retraction sequence required to clear the profiled terrain while holding the acceleration objective. The inner loop takes accelerometer, clearance and cell pressure feedback and regulates the louvre positions against the schedule. The controller operates in feedforward on the terrain ahead and in feedback on the response achieved which permits it to command a cell pressure change before the vehicle reaches a ridge instead of reacting to the resulting heave. The controller holds vertical acceleration below 0.15 g RMS at the crew stations in the design ice regime, maintains daylight clearance above 0.15 m at all points on the periphery, limits pitch to ±2.5° and roll to ±3.0°, and prevents hard skirt contact at speeds above 60 knots. Four modes are selectable. Transit mode optimizes for ride quality at constant commanded speed. Ridge mode raises the clearance objective and accepts higher acceleration for crossing heavily ridged fields. Hover mode holds attitude and height with zero forward speed for ramp operations. Settling mode manages the controlled descent onto water, ice or pads following a plant trip, using the bus level energy storage and holding attitude within 1° throughout.
The vehicle's control surfaces include twin pairs of rudders located forward and aft and by air deflectors in the propulsion fan slipstreams. The forward rudder pair is mounted on the upper hull on short vertical pylons which place the surfaces clear of the hull boundary layer. Each forward surface has an area of 42 m². The aft rudder pair is carried on the two vertical fins mounted outboard of the outer propulsion ducts, each surface having an area of 68 m². All four surfaces are composite with carbon fiber skins over a foam filled substructure, titanium hinge fittings, and leading edge abrasion strip with reject heat anti icing. Actuation of each rudder is by dual hydraulic actuators and an electro-hydraulic actuator. Deflecting both the fore and aft rudder pairs in opposition produces a yawing moment with small net sideforce which turns the vehicle while deflecting them together produces a sideforce with small yawing moment which translates the vehicle laterally and is the primary means of correcting drift in a crosswind. The flight control system blends the two modes according to speed and maneuver demands. Both rudder pairs become effective above 30 knots. Air deflectors are also fitted in the slipstream of each of the six propulsion fans. Each deflector consists of a pair of composite vanes which insert progressively into the duct exit flow, deflecting the jet in yaw by up to 30° or at full insertion of both vanes reversing a portion of the flow forward. Deflectors are individually controlled with differential insertion across the six ducts producing yaw at any forward speed (including zero) and symmetric insertion produces braking. The deflectors provide directional control below 30 knots and during all hover, docking and ramp alignment maneuvers. Roll and pitch trim at all speeds is by differential cushion cell pressure. Crosswind handling is by a combination of rudder sideforce, deflector sideforce, and cushion cell trim.
Cockpit:The Vehicle Pilothouse accommodates a pilot, copilot and two observer positions. The cockpit includes two night-vision-goggle compatible 40 x 30 degree FOV 1,280 x 1,024 pixel super XGA resolution heads up displays for both the pilot and co-pilot and eight 15 by 20 cm centimeter active matrix liquid crystal displays including two primary flight displays, two navigation displays, an engine display, a system display, and two multifunction displays which can be used to display information from the vehicle's other avionics systems. Each pilot station also includes a 20 x 13 centimeter 1024 x 768 pixel XGA touchscreen electronic flight bags (EFB). An SDI Digital Map Module (DMM) with 512 GB of removable memory is included in the cockpit which features dual channel digital map capability and supports DTED (Digital Terrain Elevation Data) level 2 (~30 m resolution) and controlled image base 10 meter (CIB-10) resolution satellite imagery maps which support color moving map display capability on the cockpit's multifunction AMLCD displays.
The pilothouse is equipped with an SDI combined vision system which fuses a synthetic vision system with the vehicle's own forward looking sensors and presents the result on head up and head down displays at both pilot stations. The synthetic vision system renders the surface ahead from the stored terrain and bathymetry database, the current ice chart, the drift model and the navigation solution, producing a continuous perspective view aligned to the vehicle's computed position and attitude. The enhanced vision element fuses data from the 95 GHz radar and from long wave infrared image the low light television imager and fuses them into one conformal scene. Database terrain provides the far field and the general form of the coastline with live sensor returns overwrite wherever available. Sea ice, which is absent from any database and changes hourly, is rendered entirely from live data. Four presentation layers are overlaid on the fused scene. The route corridor is drawn as a pair of ground referenced lines along the commanded track. The planned path from the ride control outer loop is drawn as a ribbon showing the 90 second projection, colored by the commanded clearance margin. Obstacles exceeding 4 m in profiled height are outlined and annotated with height and range. Leads, open water and thin ice identified by radar backscatter and infrared signature are shaded. The system runs a continuous integrity monitor which compares the database rendering against live sensor returns. Any persistent discrepancy in position or elevation raises a caution, suppresses the database layer in the affected sector, and flags the navigation solution for reversion to terrain referenced update.
Vehicle Decks & Cargo Handling:The vehicle's cargo hold includes forward and aft central hold and port and port and starboard cargo holds located around the ship's central reactor and lift fan compartment that provide a combined 9,500 m² of cargo deck space. The forward central compartment connects to the bow ramp directly and to both side bays through large openings in the longitudinal bulkheads. The aft central compartment connects to both side bays through large openings in the longitudinal bulkheads aft. The amidships machinery block separates the two central compartments over its full width and height, so all movement between the forward and aft central bays passes through the side bays. The cargo hold is divided into two levels including the lower main deck, located on the upper flange of the hull box girder, and upper deck located 5.6 meters above it. The main deck has a clear height of 5.6 m which accommodates two ISO containers stacked with 0.42 m of clearance and carries all heavy vehicle traffic. Main deck strength is rated at 12.5 t/m² uniform with 75 t axle capacity. The upper deck has a clear height of 3.0 m which accommodates a single ISO container and is intended for light wheeled and tracked vehicles and containerized cargo. Upper deck strength is 5.0 t/m² uniform with 25 t axle capacity. Six internal ramps connect the main deck to the upper deck, one installed in each central compartment and two in each side bay. Each ramp has a clear width of 6 m, a gradient of 7.5°, and a rated axle load of 25 tonnes. Ramp decking is composite over titanium primary structure with a non slip surfaces. Container capacity is two tiers on the main deck and one tier on the intermediate deck with a total total capacity of 1,000 TEU. The entire cargo hold is conditioned to +5 °C from the reactor reject heat loop with dehumidification on the return side. Lashing is on a flush 0.5 m grid of Ti-5111 sockets rated at 25 tonnes per point on the main deck and 10 tonnes per point on the upper deck.
The bow ramp is the main cargo access point and has a width of 20 m and a deployed length of 40 m (two sections of 24 m and 16 m) and can be deployed on up to a 12° slope. Rated axle load is 75 t tracked and 50 t wheeled. The outer section carries a self-levelling articulated toe which conforms to broken ice, beach gravel and tundra with traction matting stowed in the ramp structure for soft ground. The ramp face is deiced from the reject heat loop and a snow-melting circuit in the toe clears a working area before vehicle movement begins. The ramp is normally deployed with the vehicle resting on its pads but can also be deployed with the vehicle on cushion and the toe grounded, where the vehicle holds station on deflector sideforce and cushion cell trim while vehicles drive off, and lifts clear without settling. This technique is standard on thin ice and on tidal beaches. In the stowed position the ramp is primary structure and its locks are dimensioned by bow slam loads. Four side ramps are also fitted, two per side, serving the forward and after ends of each side bay/ Each has a clear width of 15 m, a deployed length of 25 m, and the same 75 t tracked and 60 t wheeled axle rating as the bow ramp. Deployment time is 120 seconds. The side ramps discharge directly onto unprepared ground. Each ramp stows flush within the flotation tank structure and forms part of the hull closure when retracted. Ramp decking is composite over a Ti-5111 primary structure with the same reject heat de-icing circuit as the bow ramp. In addition to the ramps the upper side bays each featute large gull-wing side doors, located between between the forward and after rear ramps. Each door is 54 meters long and 7.2 meters deep, hinged along the weather deck edge and driven to 78° above horizontal by four 550 bar actuators and provides pier side cranes direct access to the upper cargo deck to load and unload cargo, including oversize cargo too large for the internal ramps and for modular shelter and facility units in the mobile base and for machinery modules during maintenance periods. Opened the door forms a weather shelter over the working area and deploys a fabric curtain from its outer edge which permits cargo work to continue in blowing snow. A 2.5 merer wide personnel gallery with a folding rail runs the length of the door's inner face and gives access to the container tops for lashing and unlashing. Hinge rails, seals, and the sill are heated from the reject heat loop. The seal is an inflatable perimeter section pressurized from the cushion supply, backed by sixteen mechanical wedge locks which take the sea and slam loads. With the door closed and locked the side shell is continuous and the panel carries hull girder shear through its locks and hinge line. Both doors can be opened with the vehicle settled afloat alongside a quay, settled on its pads ashore, or resting on prepared ice.
Cargo is moved within the vehicle through a combination of overhead cranes and powered roller decks. Two 150 tonne overhead travelling cranes are installed one per side bay running the full length of the bay on rails, designed to lift heavy vehicles, machinery modules and container blocks. Each has a 22 m span covering the full bay width, a lifting height of 8.5 m, and a traverse speed of 1.0 m/s. Six 50 tonne overhead cranes are also fitted, two in each side bay and two in the central hold, running on the same rail system as the heavy cranes in the side bays and on dedicated rails in the central hold. These smaller handle individual containers, palletised cargo and stores at higher speed, with a traverse of 2.5 m/s and permit container movement to continue while a heavy crane is engaged elsewhere. Powered roller decks are fitted over 4,100 m² of the main deck and 3,200 m² of the upper deck. The rollers are arranged in longitudinal lanes on 1.2 m centers with transverse transfer stations at 12 m intervals which allow movement in both directions and transfer between lanes without a crane. Each roller section is individually driven by an integral electric motor and is controlled from the cargo control station or from local panels. The system moves containers and palletized loads along and across the holds without deck tractors, positions loads beneath the cranes, and feeds the bow and side ramps directly. Rollers are recessed flush with the deck and are covered by removable plates in the lanes designated for tracked vehicle traffic. A container arriving over the bow ramp is placed on the main deck roller lane, run aft and outboard into a side bay, and either stowed in the main deck tiers by a 50 tonne crane or lifted to the upper deck roller lane for stowage there. Discharge follows the reverse sequence. Heavy vehicles bypass the handling system and drive on and off under their own power over the five ramps. Cargo operations are directed from a cargo control station on the port side of the pilothouse which carries the crane and roller control displays, the ramp position and lock indications, the stowage plan, and the weight and balance computation. Weight and balance figures are fed continuously to the flight control system. Representative loads include 40 heavy tracked vehicles of 75 tonnes, 250 wheeled support vehicles, 120 flatracks with modular shelter units, a complete forward operating base with accommodation, power, fuel, water treatment, workshops and 60 days of stores for 500 personnel, or 1,000 TEU of general containerized freight.
The cargo compartments convert to a mobile operations base by the installation of standard facility modules. Base modules are built on ISO frames and secured on the standard lashing grid as contained cargo and connect to the vehicle through four service risers in each compartment carrying 400 VAC and 750 VDC power, potable and grey water, low pressure air, hot water from the reject heat loop, and data. Installation of a complete fit takes 24 hours with the vehicle's own cranes and roller decks with no shore support required at any point. The full base fit occupies 4,000 m² of the 9,500 m² available and weighs 2,200 tonnes, which leaves 800 tonnes of payload margin and the remaining deck area for embarked vehicles, project cargo and additional working space. The medical group provides a two table surgical suite, a six bed intensive care unit, a twenty four bed ward, an isolation suite of four beds, radiography and computed tomography, a laboratory, a dental surgery, a pharmacy, and a casualty reception bay sized for twelve stretcher cases. The accommodation group adds 300 berths in four berth cabins to the 200 fitted in the citadels resulting in 500 total with sanitary modules, a gym and two recreation spaces. Modules are stowed on the upper deck of both side bays where the 3.0 m clearance suits their height and the gull wing doors allow direct loading. The vehicle and plant workshop occupies the after central compartment beneath removed upper deck panels, giving 9.2 m of overhead under the coverage of both 50 tonne central compartment cranes. The vehicle workshop accepts trackedes vehicles for major repair, and includes a hydraulic bay, a track and undercarriage bay, a tire shop, and a heated wash and steam bay. The machine, weld and fabrication shops contain CNC lathes, mills, a plasma cutting table, and press and brake capacity for structural sections up to 12 m. The command group provides a planning space, a communications center, a survey and geospatial cell, and a project management office. The laboratory group supports ice, soil, aggregate and concrete testing. Power export of 20 MWe and process heat export of up to 100 MWth are taken from the four turbogenerators and the reject heat loop through the deck connection panels, sufficient to power and heat a construction camp of 500 personnel together with a batching plant, a crushing plant and a heated aggregate store. In this configuration the vehicle supports projects of the scale of a 3,000 m runway with its aprons and hangars, a long range early warning radar site with its power plant and accommodation, a small port facility, or a mining camp.
