ABL mission creep: alternative engagement scenarios for high energy laser weapons NIRCM - Netherlands Infrared Consulting and Modelling W. Caplan, MSE Israel Multinational BMD Conference, May 2010

IMDA May 2010 © NIRCM 2010 p. 2 OVERVIEW Description of ABL (Airborne Laser) weapon system Adaptive optics (AO) Operating environment ABL engagement zone Alternative targets and functions Summary

IMDA May 2010 © NIRCM 2010 p. 3 Baseline for discussion Emitted beam power one million watts (1,000,000 W) Effective range 200 km Optic aperture 150 cm Wavelength υm - Short Wave Infrared (SWIR) Atmospheric absorption negligible ( τ > 0.99 )

IMDA May 2010 © NIRCM 2010 p. 4 Terminology: What’s a Watt ? One watt of power is one joule of energy per second Energy to lift 1 kilogram up by 1 meter = 10 joules Chemical explosive yield of 1 gram = 4000 joules (4 kJ) Explosive yield of 1/2 lb. (250 grams) TNT ~~ 1 MegaJoule Highest power DE laser beam = 1+ Megawatt (MW) Other DE lasers emit kilowatt (kW) 100 kW roughly equivalent to a welder’s cutting torch

IMDA May 2010 © NIRCM 2010 p. 5 ABL Airborne Laser Mission:Boost phase intercept Power:1.0 ~ + Megawatts Aperture:150 cm Range: km Size:747 platform Operations: kft, above all clouds / weather Adaptive Optics beam control

IMDA May 2010 © NIRCM 2010 p. 6 ABL main features COIL laser with adaptive optics beam control –chemical laser occupies nearly entire payload of Boeing 747 aircraft Three other major sensor systems integrated –Target acquisition sensor (infrared search track IRST + range) –Target track laser (fine track with range) –Beam control laser (measures atmosphere for compensation) Adaptive Optics beam control system –required for compensating atmospheric turbulence in the beam path –the key technology (along with high energy laser) for system effectiveness Designed to destroy ballistic missile in boost phase –delivers enough energy (heat) to melt or burn booster while under high mechanical load during launch ABL operating altitude ~ 40kft (12 km) above almost all weather

IMDA May 2010 © NIRCM 2010 p. 7 ABL Engagement Sequence ACQUISITION & RANGE FINE TRACK ADAPTIVE OPTICS BEAM COMPENSATION WEAPON BEAM

IMDA May 2010 © NIRCM 2010 p. 8 Adaptive optics enables the ABL High energy laser beam propagation (range) is limited by four main factors –beam quality –diffraction –propagation through turbulent atmosphere –thermal blooming Beam quality & diffraction can be improved by design; thermal blooming is not a major factor in ABL engagements Effects of turbulence can be reduced with adaptive optics –measures (with a laser) in real time the turbulence along the path –controls microscopic shape of a flexible mirror to compensate (pre-distort) the high energy beam with distortions 180° out of phase

IMDA May 2010 © NIRCM 2010 p. 9 ENERGY SOURCE FINE TRACK COARSE TRACK CONDITIONING OPTICS INPUT ENERGY RESONANT CAVITY ADAPTIVE OPTICS MIRROR ADAPTIVE OPTICS CONTROL

IMDA May 2010 © NIRCM 2010 p. 10 Blur of Optical System Point Spread Function Before and After adaptive correction

IMDA May 2010 © NIRCM 2010 p. 11 Images from ground telescope using Adaptive Optics

IMDA May 2010 © NIRCM 2010 p. 12 Operating environment ABL operates at 12,000 m altitude Attack on the ballistic missile begins as the target enters this altitude also Aside from the weather of the troposphere, above this altitude atmospheric turbulence decreases significantly Beam propagation improves rapidly with beam elevation angle

IMDA May 2010 © NIRCM 2010 p. 13 Slant path to top of atmosphere Taking top of atmosphere at 100 km, path length through atmosphere decreases with increased elevation angle Altitude (km) <=== Elevation angle Atmosphere boundary

IMDA May 2010 © NIRCM 2010 p. 14 Turbulence structure of the atmosphere C n 2 structure constant Altitude (km) ABL altitude

IMDA May 2010 © NIRCM 2010 p. 15 Turbulence loss vs. range Range (km) Rytov variance loss decreases with altitude low altitude high altitude

IMDA May 2010 © NIRCM 2010 p. 16 Laser energy incident vs. range Lower bound of effectiveness Range (km) Beam energy on target laser energy on target (irradiance) due to ideal diffraction limited beam spread define lower bound of effectiveness as 10% of emitted energy theoretical maximum without turbulence is shown here

IMDA May 2010 © NIRCM 2010 p. 17 Typical target trajectory 240 s 90 s 120 s 150 s 180 s 210 s Down range (km) Altitude (km)

IMDA May 2010 © NIRCM 2010 p. 18 Typical engagement zone 240 s 90 s 120 s 150 s 180 s 210 s Down range (km) Altitude (km)

IMDA May 2010 © NIRCM 2010 p. 19 Trajectory, laser range, low turbulence define engagement zone Given an estimate for effective range of boost-phase kill Given that turbulence effects decrease rapidly with increased elevation angle Given that beam divergence exo-atmosphere allows much longer effective range Results in favorable conditions for post-boost target engagement

IMDA May 2010 © NIRCM 2010 p Show laser range on same scale as trajectory s 90 s 120 s 150 s 180 s 210 s

IMDA May 2010 © NIRCM 2010 p. 21 Post-boost is within effective range Down range (km) Target altitude (km) Beam energy on target Beam energy with perfect AO correction Allow 50% margin for realistic compensation

IMDA May 2010 © NIRCM 2010 p. 22 What is "effective" range ? Primary mission is against boosting missile –attack on booster / stage post-burnout is ineffective ABL can deliver at least 50% energy in post-boost engagement zone –engagement for approaching targets –other engagement geometries not considered Effective range depends on the susceptibility of the target to heat damage Possible targets –RV –post-boost vehicle "bus" –decoys or other penetration aids Other functions –decoy discrimination –real-time imaging of events –precision track

IMDA May 2010 © NIRCM 2010 p. 23 ABL against post-boost objects Possible targets –RV reentry vehicle very hardened against heat damage not a good candidate target for high energy laser attack –post-boost vehicle "bus" mechanical parts, fuel tanks, etc. susceptible to high energy attack usually a very small engagement time opportunity –decoys or other penetration aids light weight objects, thin-skinned balloons, etc. very susceptible to laser attack damage of objects other than RVs only effective in coordination with the entire missile defense battlespace Other functions –decoy discrimination response of low mass objects to laser beam can discriminate between targets and decoys if tracked with suitable sensors (MWIR or LWIR) –real-time imaging of events imaging post-boost may assist battle management for other defense systems –precision track likewise, precision track may assist battle management for other defense systems

IMDA May 2010 © NIRCM 2010 p. 24 Discrimination of objects Discrimination by temperature response to heat load –depends on object material thermal conductance/insulation object mass object internal construction time Temperature High energy laser

IMDA May 2010 © NIRCM 2010 p. 25 Further comments on post-boost Target discrimination functions –decoy discrimination response of low mass objects to laser beam requires some significant energy but probably not 1 MW damage or destruction of some objects may only complicate the battlespace –real-time imaging of events ABL beam control sensors have high resolution focal planes discrimination by imaging post-boost may not be useful without modification to system optics –precision track precision track may be time-shared between multiple objects caveat: some post-boost objects may not return enough signal from the beacon illumination beam control laser Considering all of the above... –a powerful laser for thermal discrimination may be useful, but not as powerful as the COIL –If discrimination from altitude of 40,000 ft is a useful function, may not require capability of the ABL –A suitable HALE (High Altitude Long Endurance) platform with a kilowatt-class laser and 80 cm optical aperture may meet the same functional requirements

IMDA May 2010 © NIRCM 2010 p. 26 Consider look-down: lower elevation targets Beam propagation severely limited looking down into lower atmosphere Possible targets are hostile aircraft, attacking SAMs Self-defense against hostile aircraft –can expect effective range well over 100 km, probably greater than range against ballistic missiles –target acquisition and IFF at long ranges may be difficult –can also defend upper airspace for other HVAA in vicinity Self-defense against large high-altitude SAMs –expect SAMs to be less susceptible than aircraft, but still possible –engagement time for SAM flyout is limited - may not be enough –target acquisition would be challenging (MAWs and RWR not suitable) –engagement geometry may not be possible

IMDA May 2010 © NIRCM 2010 p. 27 Summary ABL beam propagation geometry is favorable for post-boost engagement / tracking Primary target is a "hardened" target for HE laser Secondary targets and / or discrimination may be useful function Precision image & track may be useful function Should be considered in the battle management context

IMDA May 2010 © NIRCM 2010 p. 28 Questions...

IMDA May 2010 © NIRCM 2010 p. 29 Reference...