1

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.com2Bohn Laser Consult, Weinberg Weg 43, Stuttgart, Germany

3Paul Scherrer Institut, CH5232 Villigen PSI, Switzerland4Department 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 2009Antalya, Turkey

September 30, 2009

2

Contents1. Benefits of laser ablation propulsion (LAP)

2. Scope of this review

3. History starting with pure photon propulsion

4. 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

Benefits of LAP1) 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 24

Long March CZ-2C 30

Athena 41

Greater than the price of gold!

But it need not be so! [Myrabo Lightcraft flight, White Sands]

Photo: Courtesy Leik Myrabo

Benefits of LAP2) 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 (, 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)

5

Benefits of LAP4) 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)

6

Scope• Propulsion by laser ablation

• Primarily, applications

• Less emphasis on:

Pure photon propulsion, except for historical context

Inertial confinement fusion except as a reference point

Fundamental plasma physics theory

» Coulomb explosions, LASNEX modeling, etc

Photo courtesy Yuri Rezunkov(time exposure of flight in lab)

History in a Nutshell

• Fridrich Tsander, 1924: : Pure photon propulsionBut Cm = thrust / laser watt = 2/c = 6.7 mN/MW

• Wolfgang Möckel 1972: Basic theory of laser driven rockets• Arthur Kantrowitz6 1972: Laser ablation propulsion (LAP)

Cm ≈ 100N/MW to 10kN/MW due to plume acceleration

• Leik Myrabo 20017: Flight to 72m altitude in New Mexico desert

• Rezunkov 20064: 2N thrust demonstrated

Tsander

6 A. 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

8

Pulsed LAP TerminologyHere 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

6) Ablation efficiency AB = WE/W = mvE2/(2W) = CmvE/2

7) Energy conservation

where = <vx2>/(<vx>2) ≥ 1 is a parameter8 that is often ≈ 1

(The CmvE product = 2.0 when AB = = 1, but can’t be larger unless AB >1)

[8Phipps & Michaelis, Laser and Particle Beams, 12(1), 23-54 (1994)]

m =P / Q *

CmvE = CmIsp*go = (2/)AB

Operating RangeFrom water cannons nearly to photon propulsion!

Cm vs I sp

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

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

I sp (seconds)

Cm (N/MW)

ms minithruster (4)Saenger (15)POM air (55) Cellulose Nitrate (9) PMMA vac (9)ns Minithruster Au vac (2)Water Cannon (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 CH vac (56)Hatchett CH vac (58)Arad Al vac (57)Horisawa Al2O3 (vac) (59)

AB

500%100%10%

1%

[References below can be found in the JPP review paper]

10

Terminology, cont’dSome ancillary relationships among LSP parameters:

8) Thrust efficiency T = eoAB

9) Fuel lifetime AB = go2MIsp

2/(2PAB)

[Severe penalty paid for Isp = 10s as in water cannons]

Lots of thrust, but 10,000 times less AB than if Isp =1000s

10) Optimum coupling fluence opt = 480 0.5 MJ/m2

11) Ionization fraction where (Saha equation):

nen i

n i – 1=

2ui

u i – 1(2π AmpkT

h2 )3 / 2

exp ( –Wi,i – 1/kT)

i = 2ne/(no + ne + ni)

Opt. Coupling Fluence vs.

Theory12) Plasma regime model9:

13) Vapor regime model10:

[In Eq. 12, A is mean atomic mass, Z is mean ionic charge state, = A/2[Z2(Z+1)]1/3.

In Eq. 13, = /o, o = thrust fluence threshold,T = transmissivity from laser to surface, = ablation

layer absorption coefficient, = target solid density and = incident fluence]

Plasma model was not meant to be valid as Z 0, , 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)

Cmv =σ/Φ =

2(ρ/α) lnξ (Tξ – 1)

Φoξ

2

I spv =Φ Cm /μgo =

2Φo(Tξ – 1)

go2(ρ/α) lnξ

I spp=442

A1/8

Ψ9/16 (I λ τ)

1/4

Solution to the problem

Vapor

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09

I λ 1/2 ( -√ / )W s m

( / )Cm N MW

1. -02E

1. -01E

1. +00E

1. +01E

1. +02E

Ionization fraction

i

Theoretical Cm

( )POM Sinko

( )POM Schall

( )POM Watanabe

( )CN Phipps

( )CH Grun

( )Al Arad

Betti CH

Plasma Threshold

Ionization Fraction

Plasma

We use Cm = [i pp +(1-i) pv]/I = i Cmp + (1-i) Cmv

Laser Plasma Thruster

(Note: macro-LPT will not need T-mode) ms thruster (10mN, 250s)

ns thruster (50N, 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).

15

Liquid-fueled Laser Engine3-kW, 6.5-N engine design driven by 18x100-W fiber lasers5

See Phipps, Luke and Helgeson, reference 5.

Engine parametersMotor Mass 10.5kgFuel Mass 69.5kgFuel Type Energetic liquid polymerNo. of Fiber Lasers 18 (100W max optical each)

High Isp mode Low Isp mode

Isp 3,660 116Thrust at 3kWe input 57 mN 6.48 NRMS thrust noise 1% 1%Electrical/optical efficiency 40% 60%Mass usage rate 1.6mg/s 5.7g/sLifetime impulse 2.5MN-s 79kN-sSystem Cm 19N/W 2.2mN/WThrust efficiency 34% 123%Pin (electrical) 3kW 3kW

v for 180kg spacecraft 17.5 k /ms 555 /ms

Fiber laser amplifiers:

Time-average optica l power 1800W 1200WPpeak (optica)l , EA 1MW 670WPulse duration 10ns 1msPulse ener ,gy E A laser 1mJ 670mJPulse repetition rate 10kHz 100Hz

Lightcraft• Myrabo Lightcraft12 would, in principle, require no ablation fuel other than

ambient air, in the atmosphere.

12Myrabo, AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, OH (1982)

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 repetitively-pulsed, 10kW CO2

laser. Cm ranged from about 250N/MW for air to 900N/MW for Delrin solid propellant.

Materials problems are challenging

• Rezunkov ASLPE engine4

Uses 6kW rep-pulse CO2 laser

Wire-guided flight in laboratory Generates 2N thrust

Photo: Courtesy Leik Myrabo

17

ORIONGround-based system causes ablation jet on near-Earth space

debris targets, eventually lowering perigee until re-entry occurs

13C. Phipps, AIP Conference Proceedings 318, 466-8 (1994)

Direct Launch to LEO

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.

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)]

19

Promise for the FutureTimeframe Technology Problems to be Solved

1-2 years • Spaceflights for Laser Plasma Thruster

• ORION system

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

Building MW-class RP lasers & launch vehicles

15-20 years

• Launch to LEO with tonne payloads

Initial investment (multi-B$)

20

21

The Parameter I would like to make this point very clear. Take a “drift Maxwellian”:

1)

2)

3)

4)

f(vx,vy,vz) = CxCyCz {exp – β[(vx – u)2 + vy2 + vz2]}

< vx > = dvx

– ∞

∞vx f(vx) = Cx π / β u = u

ψ = <vx2>(<vx>)2

= {u2 + kT

mE

u2 } ≥1

If M = u/cs = 1, and cs = (kT/mE)1/2 with = cp/cv =5/3, we have = 1.60

Comment: forward peaking of most free, high-intensity laser ablation jets1 can give M≈2 and = 1.15, and we can take ≈ 1.

[1See Kelly and Dreyfus, Nucl. Inst. Meth. B32, 341 (1988)