Post on 20-Dec-2015
ABL mission creep: ABL mission creep: alternative engagement scenarios for alternative engagement scenarios for high energy laser weaponshigh energy laser weapons
NIRCM - Netherlands Infrared Consulting and Modelling W. Caplan, MSEwww.nircm.com Israel Multinational BMD Conference, May 2010
IMDA May 2010 © NIRCM 2010 p. 2
OVERVIEWOVERVIEW
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 discussionBaseline for discussion
Emitted beam power one million watts (1,000,000 W)
Effective range 200 km
Optic aperture 150 cm
Wavelength 1.315 υm - Short Wave Infrared (SWIR)
Atmospheric absorption negligible ( τ > 0.99 )
IMDA May 2010 © NIRCM 2010 p. 4
Terminology: What’s a Terminology: What’s a Watt ?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 100 - 300 kilowatt (kW)
100 kW roughly equivalent to a welder’s cutting torch
IMDA May 2010 © NIRCM 2010 p. 5
ABL Airborne LaserABL Airborne Laser Mission: Boost phase intercept
Power: 1.0 ~ + Megawatts
Aperture: 150 cm
Range: 100 - 300 km
Size: 747 platform
Operations: 35 - 40 kft, above all clouds / weather
Adaptive Optics beam control
IMDA May 2010 © NIRCM 2010 p. 6
ABL main featuresABL 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 ABL Engagement SequenceSequence
ACQUISITION & RANGE
FINE TRACK
ADAPTIVE OPTICS BEAM COMPENSATION
WEAPON BEAM
IMDA May 2010 © NIRCM 2010 p. 8
Adaptive optics enables the Adaptive optics enables the ABLABL
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 SystemBlur of Optical System
Point Spread Function Before and After adaptive correction
IMDA May 2010 © NIRCM 2010 p. 11
Images from ground telescope using Images from ground telescope using Adaptive OpticsAdaptive Optics
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Operating environmentOperating 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 Slant path to top of atmosphereatmosphere
075 60 45 30 15 00
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Taking top of atmosphere at 100 km, path length through atmosphere decreases with increased elevation angle
Alt
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<=== Elevation angle
Atmosphere
boundary
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Turbulence structure of the Turbulence structure of the atmosphereatmosphere
1 1019 1 10
18 1 1017 1 10
16 1 1015
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Cn2 structure constant
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ABL altitude
IMDA May 2010 © NIRCM 2010 p. 15
Turbulence loss vs. rangeTurbulence loss vs. range
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loss decreases with altitude
low altitude
high altitude
IMDA May 2010 © NIRCM 2010 p. 16
Laser energy incident vs. Laser energy incident vs. rangerange
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Lower bound of effectiveness
Range (km)
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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 trajectoryTypical target trajectory
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IMDA May 2010 © NIRCM 2010 p. 18
Typical engagement zoneTypical engagement zone
0 100 200 300 400 500 6000
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Down range (km)
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IMDA May 2010 © NIRCM 2010 p. 19
Trajectory, laser range, low turbulence Trajectory, laser range, low turbulence define engagement zonedefine 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. 20
... Show laser range on same scale as ... Show laser range on same scale as trajectory ...trajectory ...
0 100 200 300 400 500 6000
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IMDA May 2010 © NIRCM 2010 p. 21
Post-boost is within effective Post-boost is within effective rangerange
0 100 200 300 400 500 6000
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Beam energy with perfect AO correction
Allow 50% margin for realistic compensation
IMDA May 2010 © NIRCM 2010 p. 22
What is "effective" range ?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 ABL against post-boost objectsobjects
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 objectsDiscrimination 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-Further comments on post-boost 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 Consider look-down: lower elevation targetstargets
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
SummarySummary
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 ...Questions ...
IMDA May 2010 © NIRCM 2010 p. 29
Reference ...Reference ...