Download Altitude (km)

ABL mission creep:
alternative engagement scenarios for
high energy laser weapons
NIRCM - Netherlands Infrared Consulting and Modelling
W. Caplan, MSE
www.nircm.com
Israel Multinational BMD Conference, May 2010
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. 2
Baseline 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. 3
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 100 - 300 kilowatt (kW)
 100 kW roughly equivalent to a welder’s cutting torch
IMDA May 2010 © NIRCM 2010 p. 4
ABL 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. 5
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. 6
ABL Engagement Sequence
ACQUISITION & RANGE
FINE TRACK
ADAPTIVE OPTICS BEAM
COMPENSATION
WEAPON BEAM
IMDA May 2010 © NIRCM 2010 p. 7
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. 8
FINE TRACK
COARSE TRACK
CONDITIONING OPTICS
ADAPTIVE OPTICS MIRROR
INPUT ENERGY
ENERGY SOURCE
ADAPTIVE OPTICS CONTROL
RESONANT CAVITY
IMDA May 2010 © NIRCM 2010 p. 9
Blur of Optical System
Point Spread Function Before and After adaptive correction
IMDA May 2010 © NIRCM 2010 p. 10
Images from ground telescope using Adaptive
Optics
IMDA May 2010 © NIRCM 2010 p. 11
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. 12
Slant path to top of atmosphere
Altitude (km)
Taking top of atmosphere at 100 km, path length
through atmosphere decreases with increased
elevation angle
Atmosphere
boundary
200
100
0
75
60
45
30
15
0
<=== Elevation angle
IMDA May 2010 © NIRCM 2010 p. 13
Turbulence structure of the atmosphere
Altitude (km)
1000
100
ABL altitude
12
10
1
 19
110
 18
110
110
 17
 16
110
110
 15
Cn2 structure constant
IMDA May 2010 © NIRCM 2010 p. 14
Turbulence loss vs. range
 7
 11 
 
 
2
6
2  6 

R  0.124 k
 Cn  R
Rytov variance
1
low altitude
0.1
loss decreases with altitude
0.01
110
110
high altitude
3
4
50
100
150
200
250
Range (km)
IMDA May 2010 © NIRCM 2010 p. 15
Laser energy incident vs. range
 laser energy on target (irradiance) due to ideal diffraction limited beam
spread
 define lower bound of effectiveness as 10% of emitted energy
Beam energy on target
 theoretical maximum without turbulence is shown here
0.8
0.6
0.4
Lower bound of
effectiveness
0.2
LB
0
0
500
1000
1500
2000
2500
3000
Range (km)
IMDA May 2010 © NIRCM 2010 p. 16
Typical target trajectory
200
Altitude (km)
240 s
150
210 s
180 s
100
150 s
120 s
50
90 s
0
0
100
200
300
400
500
600
Down range (km)
IMDA May 2010 © NIRCM 2010 p. 17
Typical engagement zone
200
Altitude (km)
240 s
150
210 s
180 s
100
150 s
120 s
50
90 s
0
0
100
200
300
400
500
600
Down range (km)
IMDA May 2010 © NIRCM 2010 p. 18
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. 19
... Show laser range on same scale as trajectory ...
200
240 s
150
210 s
180 s
100
150 s
120 s
50
90 s
0
0
100
200
300
400
500
600
IMDA May 2010 © NIRCM 2010 p. 20
200
Target altitude (km)
Beam energy with perfect AO correction
0.8
150
0.6
100
0.4
Beam energy on target
Post-boost is within effective range
50
0.2
Allow 50% margin for realistic compensation
LB
0
0
100
200
300
400
500
0
600
Down range (km)
IMDA May 2010 © NIRCM 2010 p. 21
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. 22
ABL against post-boost objects
 Possible targets
–
RV
•
•
–
post-boost vehicle "bus"
•
•
–
reentry vehicle very hardened against heat damage
not a good candidate target for high energy laser attack
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
•
–
real-time imaging of events
•
–
response of low mass objects to laser beam can discriminate between targets and decoys if
tracked with suitable sensors (MWIR or LWIR)
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. 23
Discrimination of objects
 Discrimination by temperature response to heat load
– depends on
• object material thermal conductance/insulation
• object mass
• object internal construction
Temperature
High energy laser
time
IMDA May 2010 © NIRCM 2010 p. 24
Further comments on post-boost
 Target discrimination functions
–
decoy discrimination
•
•
–
real-time imaging of events
•
•
–
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
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. 25
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. 26
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. 27
Questions ...
IMDA May 2010 © NIRCM 2010 p. 28
Reference ...
IMDA May 2010 © NIRCM 2010 p. 29