A Review of
Laser Ablation Propulsion
Claude Phipps1, Willy Bohn2, Thomas Lippert3, Akihiro
Sasoh4, Wolfgang Schall5 and John Sinko6
1Photonic
Associates LLC, 200A Ojo de la Vaca Road, Santa Fe, New Mexico USA 87508
Phone/Fax: 1-505-466-3877, email: crphipps@aol.com
2Bohn Laser Consult, Weinberg Weg 43, Stuttgart, Germany
3Paul Scherrer Institut, CH5232 Villigen PSI, Switzerland
4Department of Aerospace Engineering, Nagoya University, Chikusa-ku, Nagoya, Japan
5DLR Institute of Technical Physics, Stuttgart, Germany (retired)
6Micro-Nano GCOE, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya, Japan
Advanced Laser Technologies 2009
Antalya, Turkey
September 30, 2009
1
Contents
1.
2.
3.
4.
Benefits of laser ablation propulsion (LAP)
Scope of this review
History starting with pure photon propulsion
Pulsed laser ablation propulsion
•
•
Operating range
Vapor and plasma regime theory
5. Applications
•
•
•
•
•
•
Laser plasma thruster (LPT)
Laser-driven in-tube accelerator (LITA)
Liquid-fueled laser-plasma engine
Lightcraft
Laser space debris mitigation (ORION)
Direct launch to low earth orbit
6. Promise for the future
2
Benefits of LAP
1) Lower costs with laser launching. Today’s cost of launching one kg into
low Earth orbit (LEO) is equivalent to the cost of gold.
Today’s LEO launch costs
Launch System
Minimum
Cost (k$/kg)
Rockot
10
Shuttle
12
Athena 2
12
Taurus
20
ISS, commercial
22
Pegasus XL
Long March CZ-2C
Athena
24
30
41
Greater than the price of gold!
But it need not be so!
[Myrabo Lightcraft flight, White Sands]
Photo: Courtesy Leik Myrabo
Benefits of LAP
2) Lower Dead Mass
Do not have to fly turbines, pumps, tanks, exhaust nozzles, etc., along
with the payload
3) Variable Exhaust Velocity (crucial!)
• From chemical rockets up to and surpassing that of ion engines
• Accomplished by varying intensity on target (t, As)
• Permits maximum efficiency flights1,2 in which exhaust and flight
velocity are matched, leaving exhaust particles with zero momentum
1C.
W. Larson, F. B. Mead, Jr. And S. D. Knecht, “Benefit of constant momentum propulsion for large
v Missions – applications in laser propulsion,” paper AIAA 2004-0649, 42d Aerospace Sciences
Meeting, Reno, 5-8 January 2004
2Uchida,
1st International Symposium on Beamed Energy Propulsion, Huntsville, AL, 5-7 November
2002, AIP Conference Proceedings 664 214-222 (2002)
Benefits of LAP
4) High thrust density
• 30kN/m2 demonstrated in the PALLC minithruster3
5) High thrust to mass ratio
• 15kN/kg demonstrated in Russian ASLPE engine4
6) High thrust efficiency
• 125% expected for kW laser thruster5
• This is possible due to exothermic fuels
• Not a trivial distinction for spacecraft
3 C.
R. Phipps, J. R. Luke, W. Helgeson and R. Johnson, AIP Conference Proceedings 830, 224-234
(2006)
4 Yu.
Rezunkov, A. Safronov, A. Ageichik, M. Egorov, V. Stepanov, V. Rachuk, V. Guterman, A. Ivanov,
S. Rebrov and A. Golikov, AIP Conference Proceedings 830, 3-13 (2006)
5 C.
R. Phipps, J. R. Luke and W. Helgeson, AIP Conference Proceedings 997, 222-231 (2008)
5
Scope
• Propulsion by laser ablation
• Primarily, applications
• Less emphasis on:
Photo courtesy Yuri Rezunkov
(time exposure of flight in lab)
 Pure photon propulsion, except for historical context
 Inertial confinement fusion except as a reference point
 Fundamental plasma physics theory
»
6
Coulomb explosions, LASNEX modeling, etc
History in a Nutshell
• Fridrich Tsander, 1924: :
Pure photon propulsion
But Cm = thrust / laser watt = 2/c = 6.7 mN/MW
• Wolfgang Möckel 1972:
Basic theory of laser
driven rockets
Tsander
• Arthur Kantrowitz6 1972: Laser ablation propulsion (LAP)
 Cm ≈ 100N/MW to 10kN/MW due to plume acceleration
• Leik Myrabo 20017:
• Rezunkov 20064:
6 A.
Flight to 72m altitude in
New Mexico desert
2N thrust demonstrated
Kantrowitz, Astronautics and Aeronautics 10 (5), 74-76 (1972)
7 L. N. Myrabo, paper AIAA 2001-3798, 37th AIAA/ASME/ SAE/ASEE Joint Propulsion
Conference, 8-11 July 2001, Salt Lake City, UT (2001)
Rezunkov
ASLPE
Pulsed LAP Terminology
Here are the most important parameters:
1) Momentum coupling coefficient Cm=I / W=mvE/W = F/P
2) Specific ablation energy
Q* = W/m
3) Exhaust velocity
vE = CmQ*
4) Specific impulse
Isp = I /(mgo) = vE/go
5) Mass usage rate
m = P/ Q *
6) Ablation efficiency
hAB = WE/W = myvE2/(2W) = yCmvE/2
7) Energy conservation
C v = C I *g = (2/y)h
m E
m sp
o
AB
where y = <vx2>/(<vx>2) ≥ 1 is a parameter8 that is often ≈ 1
(The CmvE product = 2.0 when hAB = y = 1, but can’t be larger unless hAB >1)
[8Phipps & Michaelis, Laser and Particle Beams, 12(1), 23-54 (1994)]
8
Operating Range
[References below can be
found in the JPP review paper]
From water cannons nearly to photon propulsion!
Cm vs I sp
1.E+05
10%
1.E+04
1%
100%
500%
hAB
Cm (N/MW)
1.E+03
1.E+02
1.E+01
1.E+00
ms minithruster (4)
Saenger (15)
POM air (55)
C ellulose Nitrate (9)
PMMA vac (9)
ns Minithruster Au vac (2)
Water C annon (49,50)
USAF layered targets vac (44)
Liquid fuels (ns, vac) (47)
Liquid fuels (ms, vac) (47)
Liquid fuels (52)
LPE engine (54)
GAP:C (53)
PVN (48)
PTFE (40)
LEO launch optimum (60)
Grun C H vac (56)
Hatchett C H vac (58)
Arad Al vac (57)
Horisawa Al2O3 (vac) (59)
1.E-01
1.E-02
1.E-03
1.E-01
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Isp (seconds)
Terminology, cont’d
Some ancillary relationships among LSP parameters:
8) Thrust efficiency
hT = heohAB
9) Fuel lifetime
tAB = go2MIsp2/(2PhAB)
Opt. Coupling Fluence vs. t
[Severe penalty paid for Isp = 10s as in water cannons]
 Lots of thrust, but 10,000 times less tAB than if Isp =1000s
Fopt = 480 t0.5 MJ/m2
10) Optimum coupling fluence
hi = 2ne/(no + ne + ni)
where (Saha equation):
11) Ionization fraction
n en i
2ui
=
ni – 1 ui – 1
10
(
2 Am pkT
h
2
)
3/ 2
exp ( –Wi,i – 1/kT)
Theory
12) Plasma regime model9:

I spp = 442
A1/8
Y
(I 
9/16

Cmv =  / F =
t)
1/4
2(r / a) ln x (T x – 1)
Fo x
13) Vapor regime model10:

I spv = F C m / go =
2
2F (Tx – 1)
o
2
g o (r / a) ln x
[In Eq. 12, A is mean atomic mass, Z is mean ionic charge state, Y = A/2[Z2(Z+1)]1/3.
In Eq. 13, x = F/Fo, Fo = thrust fluence threshold,T = transmissivity from laser to surface,
a = ablation layer absorption coefficient, r = target solid density and F = incident fluence]
 Plasma model was not meant to be valid as Z  0, Y ,
Vapor model was not meant to treat the plasma state.
Problem: how do we make the transition between the two models?
9
Isp is just a matter of intensity! See: Phipps et al. J. Appl. Phys., 64, 1083 (1988)
10 New
results: J. Sinko and C. Phipps, Appl. Phys. Lett., accepted for publication (2009)
Solution to the problem
We use Cm = [hi pp +(1-hi) pv]/I = hi Cmp + (1-hi) Cmv
1.E+03
 Vapor Plasma
1.E+02
Theoretical Cm
POM (Sinko)
POM (Schall)
POM (Watanabe)
CN (Phipps)
CH (Grun)
1.E+01
Al (Arad)
Betti CH
Plasma Threshold
Cm (N/MW)
Ionization Fraction
1.E+01
1.E+00
1.E+00
1.E-01
1.E-01
1.E+01
1.E-02
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
I t1/2 (W-¦s/m)
1.E+07
1.E+08
1.E+09
Ionization fraction hi
1.E+02
Laser Plasma Thruster
(Note: macro-LPT will not need T-mode)
ms thruster (10mN, 250s)
ns thruster (50N, 3660s)
See Phipps & Luke,
reference 3.
LITA
• Laser in-tube Accelerator concepts of Sasoh11
11 A.
Sasoh, S. Suzuki and A. Matsuda, Journal of Propulsion and Power, accepted for publication (2009).
Liquid-fueled Laser Engine
3-kW, 6.5-N engine design driven by 18x100-W fiber lasers5
Engi ne param ete rs
Motor Mass
Fuel Mass
Fuel Type
No. of Fiber Lasers
10.5kg
69.5kg
Energetic liquid polymer
18 (100W max opt ical each)
High Isp mode
Low I sp mode
Pin (elect rical)
3,660
57 mN
1%
40%
1.6mg/s
2.5MN-s
19N/W
34%
3kW
116
6.48 N
1%
60%
5.7g/s
79kN-s
2.2mN/W
123%
3kW
v for 180kg spacecraft
17.5 km/s
555m/s
1800W
1MW
10ns
1mJ
10kHz
1200W
670W
1ms
670mJ
100Hz
Isp
Thrust at 3kWe input
RMS thrust noise
Electrical/opt ical efficiency
Mass usage rate
Lifet ime impulse
System Cm
Thrust efficiency
Fiber laser am plifiers:
Time-average opt ical power
Ppeak (opt ical), EA
Pulse duration
Pulse energy, EA laser
Pulse repet ition rate
15
See Phipps, Luke and
Helgeson, reference 5.
Lightcraft
•
Myrabo Lightcraft12 would, in principle, require no ablation fuel other than
ambient air, in the atmosphere.
 Biparabolic design: laser light coming from below forms a ring
focus under rim, propels craft via successive detonations in air.
 Outside atmosphere, the device would use solid ablatants
located in rim.
 Flown to 72m in spin-stabilized flight, driven by a repetitivelypulsed, 10kW CO2 laser.
 Cm ranged from about 250N/MW for air to 900N/MW for Delrin
solid propellant.
 Materials problems are challenging
•
Photo: Courtesy Leik Myrabo
Rezunkov ASLPE engine4
 Uses 6kW rep-pulse CO2 laser
 Wire-guided flight in laboratory
 Generates 2N thrust
AIAA/SAE/ASME 18th Joint Propulsion
Conference, Cleveland, OH (1982)
12Myrabo,
ORION
Ground-based system causes ablation jet on near-Earth space
debris targets, eventually lowering perigee until re-entry occurs
13C.
Phipps, AIP
Conference
Proceedings 318, 4668 (1994)
17
Direct Launch to LEO
Connection between the charts: 3.3USD/MJ of laser light delivered at 5 flights per day.
Is that reasonable14? Compare cost of wallplug energy on the ground (0.03USD/MJ).
[14See Phipps & Michaelis, Laser and Particle Beams, 12(1), 23-54 (1994)]
Above: theoretical predictions for flight in
vacuum. Laser launching facilitates frequent
launches, diluting recurrent and sunk costs.
Above: (•) flight simulation results for 1-m
diameter craft laser-launched from ho = 30km
in air compared to vacuum predictions at left.
Promise for the Future
Timeframe
1-2 years
Technology
• Spaceflights for Laser Plasma
Thruster
• ORION system
Problems to be Solved
100k$ funding
100M$ funding
2-10 years • Lightcraft flights through
atmosphere to LEO
Ablation of Lightcraft
material
5-10 years • 5kg payloads to LEO
• LEO to GEO transfer vehicles
• kW, N-thrust liquid-fuel engines
• Launch to LEO with tonne
15-20
payloads
years
Building MW-class RP
lasers & launch
vehicles
19
Initial investment
(multi-B$)
20
The Parameter y
I would like to make this point very clear. Take a “drift Maxwellian”:
1)
f(vx,vy,vz) = CxCyCz {exp –[(vx – u)2 + vy2 + vz2]}


2)
< vx > =
–
dvxv x f(v x) = C x  /  u = u
+
3)
4)
<vx2> =
š
dvx vx2 f(vx) = Cx [
–
2
y = <vx > =
(<vx >)2
2
{
kT
u2 + m
E
u2
}
3/2
+
š
u2] = [ kT + u2 ]
mE

≥1
If M = u/cs = 1, and cs = (kT/mE)1/2 with  = cp/cv =5/3, we have y = 1.60
Comment: forward peaking of most free, high-intensity laser ablation
jets1 can give M≈2 and y = 1.15, and we can take y ≈ 1.
[1See Kelly and Dreyfus, Nucl. Inst. Meth. B32, 341 (1988)
21