A Vision for Directed Energy and Electric Weapons In the Current and Future Navy

Captain David H. Kiel, USN

Commander Michael Ziv, USN Commander Frederick Marcell USN (Ret)

Introduction In this paper, we present an overview of potential Surface Navy Directed Energy and Electric Weapon (DE&EW) technologies being specifically developed to take advantage of the US Navy’s “All Electric Warship”. An all electric warship armed with such weapons will have a new toolset and sufficient flexibility to meet combat scenarios ranging from defeating near-peer competitors, to countering new disruptive technologies and countering asymmetric threats. This flexibility derives from the inherently deep magazines and simple, short logistics tails, scalable effects, minimal amounts of explosives carried aboard and low life cycle and per-shot costs. All DE&EW weaponry discussed herein could become integral to naval systems in the period between 2010 and 2025.

Adversaries Identified in the National Military Strategy The 2004 National Military Strategy identifies an array of potential adversaries capable of threatening the United States using methods beyond traditional military capabilities. While naval forces must retain their current advantage in traditional capabilities, the future national security environment is postulated to contain new challenges characterized as disruptive, irregular and catastrophic. To meet these challenges a broad array of new military capabilities will require continuous improvement to maintain US dominance. The disruptive challenge implies the development by an adversary of a breakthrough technology that supplants a US advantage. An irregular challenge includes a variety of unconventional methods such as terrorism and insurgency that challenge dominant US conventional power. A catastrophic challenge couples unconventional actors or rogue states with weapons of mass destruction (WMD) or WMD-like effects that would be employed against the US or its allies. The war on terrorism encompasses both the irregular and catastrophic categories. The Department of Defense (DOD) Joint Operations Concept, in accordance with the National Security Strategy, the Quadrennial Defense Strategy and the Transformational Planning Guidance (TPG) describes planning for Joint Force operations over the next 15 to 20 years in terms of creating and sustaining pressure and attacking enemies with lethal and non-lethal means. It enumerates the strategic pillars of force transformation namely, strengthening joint operations, exploiting intelligence advantages, experimenting with new concepts and developing transformational capabilities. Unique and tailor-able effects offered by various DE&EW can provide the operational flexibility that makes these technologies suitable to the expanded set of national security challenges. Directed energy weapon systems offer a viable means to meet the defensive capabilities criteria established for the Navy through 2025 in the TPG. These systems span an array of capabilities employing lasers as weapons and sensors, and the electro-magnetic rail gun (EMRG). Deterrent high power microwave weapons will not be discussed in this paper.

Integrated Power Systems (IPS) – A Key Enabler for Electric and Directed Energy Weapons Systems Traditional US naval vessels have dedicated and separate prime movers to drive shipboard propulsion and electrical service loads. On a typical warship, nearly 50% of the installed shipboard propulsive power (on the order of 40 MW) is only used to power the ship through the final 5 knots to a ship’s maximum flank bell. Based on a typical operational profile, a ship will only use this power less than 5% of its underway time. These propulsion prime movers are typically mechanically coupled to the propeller or water jet via a shaft and reduction gear box.

The significant levels of unused propulsive power capacity have been addressed in the DDG-1000 “Zumwalt” class land attack destroyer. DDG-1000 is the first US warship to employ a sophisticated electrical distribution system to direct the total available installed power (approximately 80 MW) for use in both the electric propulsion motors and to support the full range of shipboard electrical loads. This system, known as the IPS, is a key enabler of a full range of novel shipboard directed energy and electric weapon systems including speed-of-light high energy laser systems and electromagnetic rail guns.

Laser Weapons and Sensors The Navy has an increasing interest in laser development and use to improve war-fighting capabilities in all facets of its operational scope. While funding for these programs must be weighed against other Navy priorities, funding requests for laser Science and Technology (S&T) programs, including transformational opportunities, are consistent with a long-term development path. Since other nations are aggressively developing advanced Directed Energy (DE) capabilities, the Navy’s current cautious laser development path increases the likelihood of technological surprise from near-peers and also jeopardizes achieving potential advantage that could be realized by laser systems currently under development.

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Chart Courtesy of Neil Baron Figure 1: The evolution of Naval Weapons (Chart courtesy of Neil Baron)

Why Lasers? Why Now? Laser weapon systems comprise a set of technologies that offer unique new capabilities. Unlike earlier weapon systems driven by the threats of the cold war era, those of today are driven by capability requirements because the threat is not dogmatically shaped. Figure 1 depicts the evolution of weapons in the surface Navy. Broad response capacity must be available to cope with the unexpected, innovative, low-tech surprise. The potential for use of directed energy in weapons, sensors and deterrent systems takes on new importance in this scenario especially when juxtaposed with the promise of multi-megawatt power availability from the shipboard electric plant. When placed in the context of the electric ship, electrically pumped laser weapons and their associated laser-based sensors, offer the potential for blinding sensors, providing protection against ballistic missiles and an ability to handle hard-to-discern, short-timeline anti-ship cruise missiles (ASCM).

More generally, laser weapons enable delivery of scalable levels of energy at both tactically and strategically relevant distances enabling the accomplishment of new missions and generating entirely new classes of effects during naval battle engagements and on the battlefield. They also offer unique solutions to many of the most serious threats and enable safer accomplishment of hazardous missions. Compared to traditional weapons, laser weapons offer significant benefits including: non-lethal, long-range force application capabilities, lethal target effects, potentially unlimited magazines and significantly smaller logistics footprints than non-DE weapon systems; although some specialized support equipment will be required. Furthermore, there are advantages of reduced operational costs and lower manpower requirements because of automated battle management systems using state-of-the-art electronics. Laser weapons destroy a target either by heating the target surface to the weakening point and causing it to fail under operating stress, or by burning through the skin to destroy underlying critical components and/or subsystems. Additionally, the laser may be used to attack energetic material in a target and cause low-order detonation, a primary destruction method. In all military applications, laser weapons, laser sensors and laser deterrence and communications systems proffer significant force multiplication and thus can enable future commanders to accomplish greater numbers of missions more effectively and in less time, consistent with Force Net and Sea Strike strategies.

•OTH Platform TAMD & Soft Target Strike*

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• EO IR Counter Measures • Optical Augmentation, EO Sensor Detection & Disruption • Laser Designator / Range Finder • (Laser Radar) & Periscope Detection • Dazzler / Non-Lethal • Visual ID / Non-Cooperative Target Recognition

• Counter Rocket Artillery Mortar (CRAM)• Asymmetric Threat• EO Sensor Damage• Counter MANPAD

FEL with Good BQ; High Power; Beam Director ~1m

FEL with Good BQ; Modest Power, Beam Director ~ 1m

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Block 1 + Improved Power Unphased Single Mode Low BQ Laser with Sensor Jamming Capability

Unphased, Single Mode, Low BQ, Low Power Fiber Laser with 30-50cm Beam Director

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Surface Navy Laser Development Vision

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Figure 2: A Laser Development Path.

Laser Development Roadmap Figure 2 shows a long-term laser development path for the DE&EW Program in terms of block segments. Goals must include overcoming socialization issues, assessing the utility of, developing and eventually integrating a megawatt-class, hard-kill laser weapon system into the very stressing shipboard environment. In terms of weaponization, the FEL is the laser device of choice and “holy grail” for weaponization in the 2020 time frame. However, there exist many nearer-term potential naval applications for kilowatt-class solid-state laser (SSL) and high-power microwave (HPM) weapons. The development of SSLs is of particular interest to the naval aviation and to the surface naval communities, while the free electron laser is of interest to and is being developed for surface shipboard use in the “navy of the future”. HPM weapons, being developed for employment as deterrent systems will not be discussed here.

Referring to figure 2 above, Block 1 and the improved Block 1A laser weapon systems, employing unphased, ganged, single-mode fiber lasers operating at modest average power levels with a beam director of 30-50cm aperture, could be useful ranges for enhancing mission capabilities on a variety of naval platforms. Activies within these missions could include counter-rocket artillery mortar (CRAM), asymmetric threats and destroying electro-optic sensors at tactically significant ranges. The Block 1A listing would improve capabilities of Block 1 laser systems by taking advantage of updated beam control and optical technologies as they come to fruition. It is interesting to note that, in commercial applications, solid-state lasers with output power of order 5kW are used to weld and cut metals. Modularized fiber lasers, with output power up to 1 kW and capable of being ganged, are currently available commercially. Many other types of low power SSLs are currently in use in such military systems as laser pointers, sensor blinders and deception devices. Block 2 capabilities listed in figure 2 depend on technical improvements to fiber lasers of Blocks 1 and 1A to achieve better beam quality and greater output power with improved beam control to buy greater power delivered to targets at increased range. Blocks 3 and 4, in figure 2, show the long-term development paths for the free electron laser (FEL). The FEL is currently very much a research device largely in the hands of the Science and Technology (S&T) community. A truly electric laser and a fitting photon source in the context of the electric ship, it offers tunability to cope with laser propagation limitations and power throttling for a broad range of utility unavailable in any of the lasers now in use or planned for the near term.

Solid State Lasers (SSL) Of particular interest to the Navy are slab and fiber lasers. Slab lasers are an older SSL technology, yet not as technically or commercially developed as fiber lasers and certainly not the most efficient. Fiber lasers are relatively new but offer greater efficiency, easier thermal management and lighter weight than slab laser configurations. These lasers, at output power of interest, with low beam quality, are commercially available (COTS) and can be purchased from catalogs. The first “high power” lasers to be introduced into the fleet on a large-scale basis are likely to be solid state slab and/or fiber lasers.

Fiber Lasers In a proof-of-principle demonstration of a fiber laser at Sandia National Laboratory in June 2006, Raytheon destroyed mortar rounds, at ranges of interest, using a commercially purchased fiber laser, thus showing the effectiveness of this type of laser, with low beam quality, against targets of interest. Furthermore, in late summer of 2006, a series of static field tests conducted at NSWC Crane, Indiana, against a variety of missile seekers at tactically significant range, demonstrated again the reliability and utility of a commercial fiber laser. These demonstrations validated the lethality model and engagement simulation and paved the way to a deployable near-term fiber laser weapon. In the fiber laser arena, there is a focus on near-term weapon system demonstration instead of development of laser device capabilities. For these demonstrations, the development time span is 2-4 years and concentration is on the use of commercially available lasers (COTS) to augment existing weapon systems capabilities. Emerging program plans involve replacing the Gatling gun in a Phalanx mount and working to improve both laser beam quality and laser output power for a demonstrator system which is currently called Laser Weapon System (LaWS). The primary objective of the LaWS Program is near-term transition of the laser weapon to the warfighter. Its shipboard missions include addressing threats such as the asymmetric threat among several others, The LaWS Program plans development of a weapon system starting in mid FY 2008 and culminating with a demonstration of capability in FY 2009.

Technology Issues with Solid State Slab Lasers In slab SSLs, external pump energy is used to stimulate changes in the electronic energy states of atoms and/or molecules within a specially prepared (“doped”) crystal (lasing medium). For reasons of efficiency, slab SSLs of interest use laser diodes as a pump source. The lasing medium is selected to

absorb and briefly  “store” energy  in an electron population  (inversion) for small  fractions of a second and then to release the energy  in the form of a coherent  laser  light beam when appropriately stimulated.   The wavelength  of  the  laser  light  depends  on  the  atomic  or molecular  structure  of  the  lasing medium.    The potential  for  compactness  and  completely  self­contained  packages  make  SSLs  attractive  for  naval shipboard and aircraft applications. 

The most serious design concern for high power slab SSLs is managing the heat balance  in the lasing materials thereby retaining beam quality.  In these lasers, most of the pump energy goes into heating of the lasing medium causing damage to the material, degrading the quality of the laser beam and resulting in low wall­plug efficiency.  PMS 405 and Office of Naval Research (ONR) sponsor several Small Business Innovative  Research  (SBIR)  efforts  that  show  promise  toward  achieving  Navy  goals  for  thermal management, efficiency and output power for slab SSLs. 

The  Radiation  Balanced  Laser  (RBL)  Project,  ongoing  at  Naval  Research  Laboratory  (NRL),  is exploring laser materials (example, ytterbium: yttrium aluminum garnet {Yb: YAG}) in which the absorption and  fluorescence  frequency spectra overlap and both are greater  than  the  laser  frequency.   When  these conditions  exist  and when  the  fluorescence  frequency  exceeds  the  pump  frequency,  cooling  of  the  laser material  can  occur  by  virtue  of  the  fluorescence  transferring  excess  power  and  entropy  from  the  laser medium to a heat sink.   Heat generation in solid state lasers can vary dramatically with pump wavelength. By careful adjustment of pump frequency and intensity, absorbed and emitted powers can be balanced and cause a null of internal heat generation. 

The Navy and  the DOD Joint Technology Office  (JTO) are monitoring and guiding development efforts on other SSL Programs, particularly  the Joint High Power Solid State Laser (JHPSSL) Program, to ensure Navy laser needs can be met.  The JHPSSL Program is shepherding solid state laser technologies toward  the  development  and  demonstration  of  a  100kW  solid  state  slab  laser.  Successful  thermal management and eye safety are key goals in this effort.

Free Electron Lasers (FEL) The FEL is a unique, electrically­powered device that offers the potential for high average power, 

essentially  unlimited  run  time  with  good  beam  quality  and  operation  at  a  wavelength  of  the  designer’s choosing.    It  functions  by  extracting  kinetic  energy  from  a  relativistic,  free  (unbound)  electron  beam  (e­ beam) and converting it to electromagnetic (EM) radiation.  The EM radiation is achieved by passing the e­ beam  through an alternating magnetic  field  in a device called an  “undulator” or  “wiggler”.     The spatially periodic  wiggler  magnetic  field  induces  transverse  force  on  the  electrons  causing  them  to  produce  EM radiation in the forward direction of the e­beam.  FEL oscillators and amplifiers have been demonstrated to produce an electrically driven, powerful source of wavelength selectable, coherent EM radiation. 

Current  plans  for  the  FEL  include  large­scale  development  under  an ONR Code  35  Innovative Naval Prototype (INP) Program planned to begin in FY 2010.  To achieve the long­term goal with respect to a FEL for the “next navy”, the major near­term focus areas are: 

1.  Development of a 100kW, preferably upgradeable, FEL with a working wavelength that can range between 1.00 and 2.20 micrometer depending on the atmospheric conditions. 

2.  A MW­class beam control system to integrate with the FEL.  The FEL offers technically challenging control issues for both electron and photon beams in the laser systems of interest.

Other US Navy Laser Weapon System Developments Laser  beam  control  technology  is  a  very  important,  integral  part  of  laser  weapon  system 

development, since without it a laser beam could not be placed on target to perform its magic.  The Sea Lite Beam Director (SLBD), developed as a prototypical laser weapon subsystem during the 1980s, remains the state­of­the­art in laser beam fire control.   Its optical system was designed to handle megawatt­class laser beam  power  and  its  acquisition  and  track  maintenance  capability  was  engineered  and  has  been subsequently upgraded in recent years to handle targets of interest.

In the not too distant future, the High Energy Laser Precision Aimpoint Tracking (HELPAT) experiment will use the SLBD to demonstrate precision tracking of a maneuvering target in the presence of background clutter. This most recent upgrade to laser beam control is engineered to enhance eventual acquisition and tracking capability in the maritime environment. It adapts existing air-to-air, combat-proven, tracking algorithms for use in the SLBD to perform precision tracking.

In another effort, the ongoing On-Axis vs. Off-Axis Concept Study will review optical technology developments over recent years and help to resolve long-standing issues regarding use of on-axis and off-axis optical systems within the beam director. In an on-axis optical system everything is symmetrical but there is a hole in the central part of the beam that can be used to advantage for some lasers. An off-axis optical system, if it can be applied, lends itself well to the inherent Gaussian laser beam, produced by the FEL, in which most of the beam power is in the central part of the beam.

Two large technical issues loom in applying the off-axis optical system to the high energy FEL are: auto-alignment of the optical system and inherent mechanical imbalance attributes in the optical system. Auto alignment can be accomplished, but it is difficult by virtue of the shapes of the off axis mirrors. The mechanical imbalance attributes arise from massive outlying components in the telescope that present complex inertial moments during high angular acceleration. Both issues must be resolved before off-axis optical systems can be useful to high energy FEL applications.

US Navy Electromagnetic Rail Gun (EMRG) Program Overview The US Navy Office of Naval Research is currently funding a Science and Technology (S&T) Innovative Naval Prototype (INP) with a goal of increasing the EMRG muzzle energy from the current “state-of-the-art” level of 8 mega joules (MJ) to tactical energy levels of 64 MJ. At these energy levels, an EMRG can provide a much needed low-cost, high-volume, all-weather Naval Surface Fire Support (NSFS) indirect fires weapon system on a ship at sea to support US military forces ashore at a range of > 200NM. The EMRG is the first ONR INP, an initiative to develop mission critical technologies and aid in the critical transition from Science and Technology (S&T) to Program of Record. An INP supports the development of technologies considered “disruptive”, or in other words, technologies that, for reasons of high risk, or departure from established requirement, or having unique Concepts of Operations (CONOPS), are unlikely to survive without top leadership endorsement. INP candidates are reviewed and approved by the Navy S&T Corporate Board, which includes some of the highest leadership within the US Navy. Focus is on Applied Research (6.2 level) and Advanced Technology Development (6.3 level) which should be planned to achieve a level of maturity suitable for insertion to acquisition. The primary goal of the INP is to move risk from acquisition, where a budget would normally be in billions of dollars for an ACAT 1 program, back to the S&T where costs are much lower. As shown in figure 3, the EMRG INP will be executed in two phases, which will culminate with a transition to an ACAT 1 program of record in the 2016 time frame. INP Phase 1 is currently focused on technology risk mitigation of key EMRG components and the development of a 32 MJ guided projectile. INP Phase 2 will focus on the development of an integrated, prototypical system, an integrated at-sea or shore-based 32 MJ demonstration, and continued technology development for the projectile to achieve a 64 MJ tactical energy level. Initial Operational Capability of the EMRG, at full 64 MJ tactical energy level, is planned for the 2020-2025 timeframe.

Figure 3 Electromagnetic Rail Gun – Technology Development Roadmap

EMRG Capabilities and Advantages Figure 4 shows the planned capabilities of the EMRG at the 64 MJ tactical energy level, with an indirect fires range of between 50 and 250 NM which will be varied mainly by varying the firing angle, with a peak altitude of approximately 800,000 feet at 50 NM and approximately 500,000 feet at 250 NM. Muzzle velocity will be approximately 2.5km/sec (or about Mach 7.5) with an impact velocity of about Mach 5.0. During its flight trajectory, the projectile spends approximately 5 minutes of its 6 minute flight above the sensible atmosphere (greater than 100,000 feet) thus simplifying airspace de-confliction. The anticipated range of the EMRG at 64 MJ (250 NM) exceeds the anticipated range of all current or near term projectiles including ERGM (about 63 NM) and LRLAP (about 95 NM) and is equal to the future assault range of the US Marine Corps (USMC) MV-22. This capability will allow the EMRG to complement USMC MV-22 tactical air assets in high operational tempo engagements and may be used to provide support for forces ashore from an off-shore at-sea platform in the event that particular operational circumstances do not support placing tactical air or ground-based fire support assets in harms way. Even at half the full tactical energy level of 32 MJ, the EMRG will have an anticipated range of approximately 110 NM which is equal to the current USMC “ship to objective maneuver” (STOM) distance of 200 km (about 110 NM).

Figure 4 Electromagnetic Rail Gun - 64 MJ Capabilities

The EMRG will accomplish these capabilities as a pure kinetic energy round without the use of any propellants or explosives. By eliminating explosive elements from the logistics train, the EMRG will provide the future warship with the ability to carry nearly 10 times the current number of on-board rounds within the same space as current magazines, extending time on station and improving the total volume of fires that be provided from the sea. Other benefits of EMRG kinetic energy projectiles include precision strike with minimal collateral damage, a simplified logistics tail, reduction in weight (typically required for magazine armor), fire fighting systems, thermal insulation, reduced life cycle cost and a significant level of flexibility provided to the US Navy warship designer not possible with conventional explosive munitions.

Conclusion The projected 7 ships of the DDG-1000 class with its innovative and flexible IPS system will be introduced to the fleet beginning in 2013. Lessons learned from this new ship class will usher in a new area of innovation that will potentially be applied to the development of the next generation IPS for implementation on the CG(X) class in the 2018 timeframe and will be further developed for ships such as the DDG(X) class in the 2020-2025 timeframe. Ships with IPS and the myriad of electric and directed energy weapons that this system enables will provide the US Military with unparalleled flexibility, increased shipboard safety, and a significant increase in volume of fires that can be brought to bear in support of our forces afloat and ashore.