ABL mission creep: alternative engagement scenarios for high energy laser weapons NIRCM -...

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


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 )


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


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


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


ABL Engagement ABL Engagement SequenceSequence

ACQUISITION & RANGE

FINE TRACK

ADAPTIVE OPTICS BEAM COMPENSATION

WEAPON BEAM


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


ENERGY SOURCE

FINE TRACK

COARSE TRACK

CONDITIONING OPTICS

INPUT ENERGY

RESONANT CAVITY

ADAPTIVE OPTICS MIRROR

ADAPTIVE OPTICS CONTROL


Blur of Optical SystemBlur of Optical System

Point Spread Function Before and After adaptive correction


Images from ground telescope using Images from ground telescope using Adaptive OpticsAdaptive Optics


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


Slant path to top of Slant path to top of atmosphereatmosphere

075 60 45 30 15 00

100

200

Taking top of atmosphere at 100 km, path length through atmosphere decreases with increased elevation angle

Alt

itu

de

(km

)

<=== Elevation angle

Atmosphere

boundary


Turbulence structure of the Turbulence structure of the atmosphereatmosphere

1 1019 1 10

18 1 1017 1 10

16 1 1015

1

10

100

1000

12

Cn2 structure constant

Alt

itu

de

(km

)

ABL altitude


Turbulence loss vs. rangeTurbulence loss vs. range

50 100 150 200 2501 10

4

1 103

0.01

0.1

1

R2

0.124k

7

6

Cn

2 R

11

6

Range (km)

Ryt

ov

vari

ance

loss decreases with altitude

low altitude

high altitude


Laser energy incident vs. Laser energy incident vs. rangerange

0 500 1000 1500 2000 2500 30000

0.2

0.4

0.6

0.8

LB

Lower bound of effectiveness

Range (km)

Be

am

en

erg

y o

n t

arg

et

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


Typical target trajectoryTypical target trajectory

0 100 200 300 400 500 6000

50

100

150

200

240 s

90 s

120 s

150 s

180 s

210 s

Down range (km)

Alt

itu

de

(km

)


Typical engagement zoneTypical engagement zone

0 100 200 300 400 500 6000

50

100

150

200

240 s

90 s

120 s

150 s

180 s

210 s

Down range (km)

Alt

itu

de

(km

)


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


... Show laser range on same scale as ... Show laser range on same scale as trajectory ...trajectory ...

0 100 200 300 400 500 6000

50

100

150

200

240 s

90 s

120 s

150 s

180 s

210 s


Post-boost is within effective Post-boost is within effective rangerange

0 100 200 300 400 500 6000

50

100

150

200

0

0.2

0.4

0.6

0.8

LB

Down range (km)

Tar

get

alt

itu

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(km

)

Be

am

en

erg

y o

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arg

et

Beam energy with perfect AO correction

Allow 50% margin for realistic compensation


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


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


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


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


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


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


Questions ...Questions ...


Reference ...Reference ...

ABL mission creep: alternative engagement scenarios for high energy laser weapons NIRCM -...

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