Table Of ContentActaAstronautica105(2014)192–200
ContentslistsavailableatScienceDirect
Acta Astronautica
journal homepage: www.elsevier.com/locate/actaastro
ICAN: A novel laser architecture for space debris removal
Rémi Soularda,b, Mark N. Quinna,b, Toshiki Tajimaa,c, Gérard Mouroua,n
aIZEST,ÉcolePolytechnique,91128Palaiseau,France
bIZEST,CEA-Saclay,DSM-IRAMIS-SPAMbât.522p.148,91191Gif-sur-Yvette,France
cDept.ofPhysicsandAstronomy,UniversityofCaliforniaatIrvine,Irvine,CA92697,USA
a r t i c l e i n f o a b s t r a c t
Articlehistory: The development of a fiber based laser architecture will enable novel applications in
Received15May2014 environmentswhichhavehithertobeenimpossibleduetosize,efficiencyandpowerof
Receivedinrevisedform traditional systems. Such a new architecture has been developed by the International
1September2014 CoherentAmplificationNetwork(ICAN)project.Herewepresentananalysisofutilizing
Accepted3September2014
an ICAN laser for the purpose of tracking and de-orbiting hyper-velocity space debris.
Availableonline16September2014
With an increasing number of new debris from collisions of active, derelict and new
Keywords: payloads in orbit, there is a growing danger of runaway debris impacts. Due to its
Orbitingsolar-poweredlaser compactnessandefficiency,itisshownthatspace-basedoperationwouldbepossible.For
Spacedebrisremoval
differentdesignparameterssuchasfiberarraysize,itisshownthatthekHzrepetition
Laserablation rateandkWaveragepowerofICANwouldbesufficienttode-orbitsmall1–10cmdebris
Fiber-basedlaser
withinasingleinstancevialaserablation.
Beamcombining
&2014IAA.PublishedbyElsevierLtd.Allrightsreserved.
1. Introduction burn-up. With increasing collisions and more frequent
deployments it is of course impossible to alleviate such a
The heralding of the space age over 50 years ago problemvianaturaldecayespeciallyforhigherorbits.With
inadvertently began increasing the risk of subsequent ratesofdebriscreationexceedingtheirnaturaldecaythere
low-earth-orbit(LEO)spacemissionsthroughtheintroduc- is growing danger of chain reactions as described by the
tionoforbitaldebris.Whatexistsasaninnocuousflakeof Kessler syndrome [1–3]. Fragmentation debris (1–10cm)
materialonEarthcaninLEObecomeabullet-likeprojectile arenowconsideredasthemainthreattobreakingupthe
with a relative velocity of over 30,000km/h with the farlessnumerouslargeobjectssuchasderelictrockets[4].
potentialtoimpactgreatdamageonspacebasedhardware, Withincreasingcostsanddangerstospacemissionsthere
optics and even astronauts. There are millions of such is a significant motivation to develop new tools for active
unintended satellites orbiting between 100 and 2000km removalandcatalogingofspacedebris.
abovetheearth,afractionofwhicharetrackedandknown. Coincidentalwiththefirstsatellites,thedemonstration
Thisspacedebrisextendstolargerchunksofmaterialfrom of the first lasersbeginning in 1957 with microwaves and
fullyintactinstrumentstofrozencoolantdropletsandhas then optical amplification in 1960 have enabled an abun-
seenincreasinggrowthinitspopulationsincethearrivalof dance of new disciplines inpure science and applications.
Sputnik in 1957. With an ever increasing number of With rapidly evolving technology, laser science has found
hypervelocity debris there remains little achieved in application in a host of terrestrial environments. Together
removal other than natural orbital decayand atmospheric withprecisefocusabilityanddirectionality,lasershavealso
beenappraisedasameansforremovalofspacedebris[5,6].
Ratherthanvaporization,itisonlynecessarytoreduce
nCorrespondingauthor.Tel.:þ33169334174. the orbital velocity by a few percent and thus push the
E-mailaddress:[email protected](G.Mourou). debristoalowerorbitafterwhichthedragoftheearth's
http://dx.doi.org/10.1016/j.actaastro.2014.09.004
0094-5765/&2014IAA.PublishedbyElsevierLtd.Allrightsreserved.
R.Soulardetal./ActaAstronautica105(2014)192–200 193
Δ
atmosphere completes the process of re-entry and burn- is for sufficient v in order to reduce the orbital angular
up. Approaches using ground-based laser systems have momentumofthedebristherebyloweringitsperigeeand
been studied using large optics to deliver the energy accelerating its re-entry to the Earth's atmosphere. This
through the atmosphere onto the debris some hundreds momentum transfer is a function of the laser energy on
ofkmoverhead[5,7].Alternatively,giventheinadequate the debris, E, and the efficiency of the coupling denoted
L
size, average power and efficiency of traditional lasers, bythecoefficientC :
m
designsforlocalizeddebrisremovalbyanorbitingsystem Δp¼mΔv¼(cid:2)C E ð1Þ
m L
hasuptonownotbeenpermissible[6].
Recent development of the novel fiber-based laser Considering an initial orbit altitude, Ai, the required
architecture ICAN [8] shows that a new paradigm of change in velocity can be estimated using the Hohmann
diode-pumped laser technology is within grasp, enabling transferapproach[10,11].Thisinvolvesshiftingthedebris
high average power operation with kHz repetition and particle from an initial circular orbit to an elliptical one
energy efficiency near 40%. Here in this article we show with a perigee near A0¼100km altitude where re-entry
thatsuchasystemopensanewfrontierondebrisremoval to the atmosphere occurs. For an ipniffitffiffiiffiaffiffiffilffiffiffiffioffiffiffiffirbit altitude
with the realization of an orbital solar-powered ICAN Ai¼800km the velocity is vi¼ GME=r¼7452m=s
debrissweeper. where the radius r¼ReþAi. Here, G, ME and RE are the
gravitationalconstant,Earthmassandradiusrespectively.
Totransferintoanellipticalorbitwithperigeer ¼R þA ,
2. Requirementsofdebrisremoval p e 0
therequiredchangeinvelocityiscalculatedusing
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Monitoring and trackingofspace debris is an ongoing Δ
v 2r
challengeandthereissomedegreeofuncertaintyonthe v ¼ ðrþrp Þ(cid:2)1 ð2Þ
i p
populations for different sizes and orbits. For known
objects 410cmthereisthepossibilityofusingcollisional resulting in Δv=v ¼2:5% which translates into Δv¼
i
avoidance for manned or sensitive spacecraft. For sizes 193m=s.
o1cm there exists shielding materials such as with Depending on the laser pulse duration, τ, there exists
Kevlar which can be utilized. The size range 1–10cm is anoptimallaserfluenceF incidentonthedebrissurface
opt
especiallyproblematicasitisdifficulttoshieldorindeed forefficientcouplingofrecoilthrust.AsshowninFig.2(a),
avoid such debris. Their size also prohibits continuous a threshold occurs at (cid:3)100ps for which the optimal
tracking and as shown in Fig. 1(a), the peak in debris fluencpeffifficffihanges from a constant (cid:3)1J=cm2 to increasing
distribution for 1–10cm sizes in low-Earth-orbit occurs with τ such that at 10 ns pulses a 5J=cm2 fluence is
near 800km. In this section we will show the laser required.Thisfluencecorrespondstotheoptimalvalueof
requirementsforremovalofsuchdebrisatthisorbit. the coupling efficiency C . Values of C typically span
opt opt
The laser provides the means to deliver a brief recoil 10–100μN=W fordifferent laserconditions and common
impulse by ablating a thin surface layer on the debris. debris materials including multi-layer insulation and alu-
As shown in Fig. 1(b), the ablated material forms a jet minum alloys. For the following calculations we take the
normal to the surface which induces a recoil in the exampleofaluminumandforshortlaserpulses o100ps
oppositedirectionslowingthedebrisbyΔv.Thegoalhere anvalueofC ¼20 μN=Wisappropriate[12].
opt
Fig.1. (a)Thepredicteddistributionofdebrisinlow-Earthorbitfor1–10cmdebrisaccordingtoMASTER-2009[9].Thepeaknear800kmisinlargepart
thedebrisremainingfromtheIridium,CosmosandFenhyun-1csatellites.(b)Aschematicoftheorbitaladjustmentrequiredtore-entrydebris.Herealaser
pulseinducesarecoilbysurfaceablation.Thismodifiesthedebrisvelocityfromacirculartoellipticalorbitwithaperigeenear100kmaltitudewhere
rapidre-entryoccurs.
194 R.Soulardetal./ActaAstronautica105(2014)192–200
Fig.2. (a)Theoptimumfluenceformomentum-couplingisshownusingpdffiffiffiataforavarietyofmaterialsfromPhippsetal.[12],illustratingthethresholdto
thermalabsorptionatpulsedurationτ4100pswhichincreaseswith τthereafter.(b)Thetotallaserenergyrequiredfordebrisremovalfordifferent
orbits.Inthiscase,calculationsareshownforaluminumwithsizesof3,5and10cmwithacouplingefficiencyof20 μN=W[12]andassuminganarea/
massratioof0:1m2=kg[13,14].
Table1 In the case of the 10cm aluminium debris at 800km,
Comparisonoftypicalgroundandspace-basedoptionssummarizingthe the required Δv¼194m=s, for negligible thickness the
energyrequirementsfordifferentlaserpulsedurationsand10cmdebris massm(cid:3)70gsowehaveE (cid:3)mΔv=C ¼690kJ.Con-
locatedatorbitof800km.ForsmallL,asinspaceoperation,theoptimal total opt
sidering respective repetition rates as shown in Table 1,
pulseenergyandaperture(Eopt; D)requirementsforlaserarerelaxed
comparedtogroundbasedoperation. thisenergycouldbedeliveredinsecondsforaspacebased
ICAN system. Further examples for different orbits and
Laser (Hz) τ(s) Fopt(J/cm2) L(km) M2 D(m) Eopt(J) debrissizesarecalculatedandshowninFig.2(b)inclusive
of mass loss from ablation at a rate of 8(cid:4)10(cid:2)9kg/J for
Space 103 10(cid:2)12 1 100 (cid:3)1 1.3 77
Ground 10 10(cid:2)9 5 800 2 20.4 393 aluminum[6].
3. Space-basedICANLaserSystem
For an optimal fluence F the corresponding pulse Regarding a laser system for debris de-orbiting there
opt
energyE andfocusedspotsized onthedebrissurface areanumberofdesignfactorswhichshouldbeconsidered
opt L
canbeestimated.Theseparameterscanbecalculatedfora for space based operation. For a solar-powered system a
given distance to the debris L and laser aperture D as high electrical efficiency is required. Likewise with high
E ¼πðd =2Þ2F andforspotradiusd =2¼M2λL=D.This relative velocity 410km=s, interaction times are short
opt L opt L
spotsizeislimitedbythebeamqualityM2andwavelength o10s,andhencegoodaveragepowerandhighrepetition
λ
ofthelaserandforgoodenergyefficiencyshouldbeless rates are demanded. Heat dissipation, compactness and
thanorequaltothedebrissize. robustnessarealsokeyfactorsforoperationinspace.Allof
Anillustrativeexamplewouldbetocomparetherequire- these factors are absent with traditional gas or crystal-
ments to ablate the debris created by the Fengyun-1C and based laser technology which are limited by poor wall-
Iridium-CosmossatelliteswhichcontributetotheLEOpeak plug efficiency ⪡0:1% and poor heat dissipation limiting
distributionlocatednear800kmorbit.Asaconsequenceof the repetition to a few Hz and hence providing very low
relative position, ground based and space-based laser solu- average power ≲10W. However with the rapid develop-
tions will entail distinct regimes of size, energy and pulse ment of fiber-based diode-pumped laser science, embo-
duration. It is apparent that nanosecond durations are died by the ICAN concept, these design factors can be
appropriate for atmospheric transmission, while in space realized.
shorter picoseconds pulses can be utilized. The distance to Bytheirintrinsicgeometry,theratioofsurfaceareato
thedebrisisofcourseakeyfactorindeterminingthefocus active volume of optical fibers enable more effective
requirementsforthesystem.Forthespaceoptionweusea dissipationofheatthantraditionalmediaprovidingaccess
distance L ¼ 100km and a perfect beam quality both of to kHz repetition rates in pulsed-mode. Similarly, the
whicharepossibleconsideringICANasdescribedinSection orders of magnitude improvement in electrical efficiency
3. While from a ground based perspective, at L ¼ 800km, of diode pumping over traditional lasing-media is well
even with adaptive optics the beam quality together with known(430%)asistheirhighaveragepower(410kW).
losses will distract so M241. For this comparison, using a Transport within single mode fibers provides increased
laserspotsizeequivalenttoa10cmsizedebris,weseewith robustness of the system which is critical for stability of
theoptimalfluencesasperFig.2(a)thattherequiredlaser optical systems in orbit. The ICAN concept comprises an
aperture and energy can be considerably relaxed with array of thousands of phase-combined fibers enabling a
designingaspace-basedoption. very high degree of beam control providing diffraction
R.Soulardetal./ActaAstronautica105(2014)192–200 195
limitedfocusingandbeamshapingwiththepotentialfor A conceptual design of an orbiting ICAN system is
adapting to target surface interaction conditions shown in Fig. 3. Here, an array of solar panels provide
heuristically. thekW'spowerrequiredforthemulti-channelfiberlaser.
For the principle ICAN design [8] each channel in the Inordertodeliverpulsesover100kmthebeamwouldbe
array provides E ¼1mJ of laser energy with λ¼1μm expanded to meter scales via multiple optics such as a
fiber
wavelength.Theoutputofallthefibersafteramplification simple telescope design. Here primary and secondary
arethenphased-combined[15]producinganarraywhere mirrors provide mechanical motion to steer and focus
the phase of each laser pixel can be precisely controlled. the beam with course precision. Such a system will also
Thisresultsinabeamofexcellentspatialqualityandtotal function in reverse by collecting the reflected laser light
energy of 1–100J per pulse. The more fibers that are from the high velocity space debris enabling its tracking
phased, the moreenergy is extracted.To be accurate,the and characterization via diagnostics related to debris
pulse compressor efficiency (E 80%) and the percentage velocity and orientation. With complete control of the
oftheenergyinthemainlobeofthebeam(E70%)inthe wavefront,intrinsictotheICANconcept,fineprecisionof
far-field should be taken into account. Operating in a thefocaldistance,spotsizeandsteeringofthebeamcan
pulsed mode and controlled via chirped-pulse- beachieved.Also,sincethewavefrontofthephasearrayis
amplification [16], such a system would provide short tunableatratesof (cid:3)103Hz,anICANsystemcanevaluate
pulses (10(cid:2)9(cid:2)10(cid:2)15s) at kHz repetition rates with the debris surface conditions with kHz pulses and respond
abilitytorapidlyfocusandadaptitswavefrontforvarying quicklywithparametersforanoptimalinteraction.Sucha
target conditions. Reducing pulse duration to (cid:3)100ps heuristic approach could rapidly scan and optimize the
results in a minimum F as discussed in Section 2. The couplingintermsofrecoiltrustorreflectivitywithdebris
opt
resulting interaction distance and the time between the ofdistinctorientation,rotationandsurfacetype.
laser and debris for optimal ablation is increased thus A simple operational schematic of an ICAN satellite is
decreasing the average shooting power required for the shown in Fig. 4(a) assuming that debris trajectories are
system.ConversionfromIRtoUVwavelengthsisanoption roughly co-linear with respect to the satellite trajectory.
in that it improves coupling efficiency and increases Illustratedherearethe3modesofoperation:
interaction range further which even with conversion
lossesimpliesareductionintheshootingpowerrequired. 1. Scanningmode:thebeamisexpandedusingthemode
However,suchaschemewouldincreasetheoverallcom- lens and with mechanical mirror motion sweeps a
plexityofthesystemandisnotimplementedhere. volume of space for debris in a sequence of pulses.
Fig.3. TheICANconceptfororbitaldebrisremoval.Poweredbythesolararray,theamplifiedbeamfromthecombinedarrayoffibersisexpandedviathe
telescopetoapertureDwhichenablesfocusingtolargedistances,L≳100km,whilethephasearraycontrolswavefrontandhencethefocaldistanceofthe
beam.Reflectedlightfromthedebrisisalsocollectedbythetelescopeandenablesprecisediagnosticsforitssizeandvelocity.
196 R.Soulardetal./ActaAstronautica105(2014)192–200
Fig.4. (a)AnoperationalschematicfortheICANdebrissweeper.Thefieldofviewhalf-angle,θandthelimitingdistancesareshownindicatingthezones
fortracking,scanningandshooting.(b)Thebeam-expandingmirrordiameterrequiredasafunctionofdistanceL.Theupperandlowerlimitforshooting
distances,Lmax,Lmin,areshownfordifferentfiberarraysizes.Amirrordiameterof3misusedincalculationsinthetext.
ThemaximumdistanceforscanningL islimitedby μ
scan and with a precision of 150 m to steer more finely the
the minimum detectable signal and is c100km as
beam angularly. Course focusing is possible using axial
discussedbelow.Atthisdistancethebeamisexpanded translation over millimeters at a speed of 500μm=s for
toπr2scancmindiameterandscansatotalareaofπr2min. scanning and over 100μm at a speed of 20μm=s for
2. Tracking mode: as the detected debris object travels
tracking. Fine precision of the beam is achieved with
towardsthesystem,betweenL toL ,thelaserspot
scan max individual phase control of each fiber pixel. We expect that
isreducedtomatchthedebrissizebytranslationofthe phasecontrolenablesasteeringprecisionof0:01μradovera
2nd mirror. Sufficient time within the tracking zone
range of 0.05mrad. Also, this phase control enables fine
shouldenablecompletediagnosisoftheobjectinterms
adjustment of the laser focus tending to transform the
of its velocity vector, etc. The mode lens is removed
defocused beam in the scanning volume to a diffraction
beforeenteringtheshootingzone.
limited spot on the target at the end of the tracking
3. Shooting mode: focusing to diffraction limited spot
operation.Theresponsetimeofthebeamfocusingdevice
sizes by the phase array is restricted to distances L
max isabout1mswhichiswelladaptedtotargetthemoving
andL .Herethefluenceisthensufficienttoablatethe
min debris.Forcoherentbeamcombiningweexpectverygood
debrissurfaceanddecreaseitsvelocity.Thegoalhereis beamqualitywithM2(cid:3)1forthecentrallobe.
tode-orbitcmdebrisinasinglepass.
3.1. Scanningandtrackingmodes
In order to limit the mechanical requirements (telescope
angularspeed,laserpower)onthesystemwerestrictthe Active scanning for debris and subsequent tracking is
acceptance angle for debris resulting in a cylindrical achieved using the telescope and diagnostic systems as
interaction volume while retaining a manageable debris shown in Fig. 4(a). After reflection from the debris, the
flux.Inthefollowingcalculationoftheserangesweusea laser light is directed to the diagnostic systems via a
primary mirror/aperture diameter of D¼3m and a focal faraday isolator. To follow the debris trajectory a CCD
length of 5m. We assume that the primary mirror has a cameraimagesthezoneilluminatedbythelaser.Measur-
maximum scanning speed of α(cid:3)11=s and this enables ing time delayof the scattered light enables the distance
steeringofthebeamuptoθ¼51fromtheopticalaxisof fromthedebristothelaser-satellitetobeestimatedtomm
the telescope with a precision of 0.11. The secondary precision. Speed can be evaluated using Doppler-based
mirror has a diameter of 40cm, a focal length of 0.5m diagnosticsorsimplybymeasuringthedistancebetween
andcanmovetransversallyover5cmataspeedof5mm/s pulses.
R.Soulardetal./ActaAstronautica105(2014)192–200 197
Toscanfordebristheexpandedlaserbeamsweepsthe Solvingbothexpressionswithf ¼L2 α=Awearriveat
scan scan
areaπr2 atadistanceuptoL .Thisareaisscannedina themaximumscanningdistance:
min scan
dseeqfiuneendceboyfπpru2slcsaen.saTthearvaatleueofofsfcanLsecaanchiscolivmeritinedgabnyatrheea Lscan¼Lmaxþvreαl(cid:4)(cid:4)rA2min ð7Þ
rotationalspeedofthemirrorsystem:
which results in values of 100–340km depending on the
α¼rscanfrep ð3Þ number of fibers as shown in Table 2 when α¼11=s and
Lscan Nlim¼50 photo-electrons. Calculating the size of the
scanning area r and pulse rep-rate f enables the
andtheminimumsignaltotriggeradetection: scan scan
operatingpowerforthesystemtobeestimatedas (cid:3)kW.
Nlim¼ηehlνSΩdebris ð4Þ 3.2. Shootingmode
whichisthenumberofphoton-electronsproducedatthe
detector by the reflected laser light assuming a quantum Debris detected near Lscan is tracked until it arrives
efficiencyηe¼50%.Thelaserlightscatteredbythedebris, within the focusing range of the phase array Lmax-Lmin.
withsizeS,isassumedtobelambertianandtheluminance Here a burst of pulses must be delivered to the debris
is:l¼ρF =π withρthealbedoestimatedtobe0.5and surfacetoprovideablationandhencearecoilimpulsefor
F ¼Es=cπanr2 is the fluence at L . The solid angle sufficient Δv for re-entry. Let us estimate what can be
scan L scan scan
defined by debris to the telescope at distance L is achieved with1000,10000and100000 fibersforaCAN
scan
Ω ¼πðD=2Þ2=L2 andr iscalculatedby laser in the case of aluminum debris of 3cm and 10cm
debris scan scan
insize.
r
rscan¼pffiffiffiffiffimffiffiffiiffinffiffiffiffiffiffiffiffiffi ð5Þ As shown in Fig. 2(b), the total laser energy Etotal
f t
scan scan required to move such material from an orbit of 800km
wherethetimerequiredtoscanis:t (cid:3)ðL (cid:2)L Þ=v . to re-entry at 100km is 60kJ and 690kJ respectively.
scan scan max rel
Substituting l and Ω into Eq. (4) we derive another Using the orientation as shown in Fig. 4(a) we assume a
debris
expressionforrscan: relative speed of laser and debris of vrel(cid:3)15km=s in
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi opposite directions at this altitude. For the optimal cou-
D=2 η ρSE A plingcoefficientavalueof20 μN=Wisusedwhichisone
rscan¼L hνeπN L ¼L ð6Þ ofthelowestintheliterature.Resultsofthesecalculations
scan lim scan
arepresentedinTable3.
Table2 The fiber number and the diameter of the telescope
Scanning parameters of 3cm and 10cm debris for 1000,10000 and define the focal range where the energy is optimally
100000fibers. distributed on the target. As discussed previously, to
optimize the coupling efficiency between the laser and
Fibernumber 1000 10000 100000
thedebrisanoptimalfluenceF hastobereached.This,
opt
Debrissize 3 3 10 cm thediameterof thetelescopeDandtheenergydelivered
Nlim 50 50 50 p-e by the laser EL define a maximum focusing distance for
α 1 1 1 1/s suchaninteraction:
Lscan 110 180 300 km sffiffiffiffiffiffiffiffiffiffiffi
rrEmsLcainn 3010.88 61010.8 4100060.1 mkJm Lmax¼ πFEoLptMD2λ ð8Þ
tscan 6 8 9 s At this distance the fiber array makes its maximum
Frepscanning 120 100 30 Hz
Averageoperatingpower 0.1 1.0 4.0 kW divergent wavefront. The laser could begin to operate at
a larger distance but the interaction efficiency decreases
Table3
CharacteristicsofaspacebasedICANlasersystemforremovalofdebrisfromaltitudeof800kmwithrelativevelocity15km/sinasingleinstance.The
calculationsreferto1cm,3cm,and10cmspacedebrisat800kmorbitwith1000,10000and100000fibersrespectively.
Fibernumber 1000 10000 100000 1mJ/fiber
Debrissizeremoved 3 3 10 cm
SpotsizeatLmax 1 3 10 cm
Lmin 10 20 70 km
Lmax 20 60 170 km
Δt 0.7 2.7 6.7 s
Averageshootingpower 90 25 100 kW
Repetitionrate 90 2.5 1 kHz
rmin 0.88 1.8 6.1 km
αmax 3.7 1.9 0.5 1/s
Debrisflux 0:36(cid:4)10(cid:2)4 1:4(cid:4)10(cid:2)4 18(cid:4)10(cid:2)4 /s
Debrisremoved 1:1(cid:4)103 4:5(cid:4)103 56(cid:4)103 /yr
198 R.Soulardetal./ActaAstronautica105(2014)192–200
quickly.TheequivalentminimumfocusingdistanceLminis Table4
limited by the focal length of the telescope and the Estimatesforthepayloadweightinthe
maximum convergent wavefront produced by the phase case of a 1kW ICAN system with 104
fibers operating with 3.33kW input
array. The interaction time is then calculated using the
powerat30%efficiency.
relativevelocityv ofthedebris:
rel
Δt¼Lmax(cid:2)Lmin ð9Þ Item (kg)
vrel Fiberlaser 900
Solararray 222
The maximum and minimum ablating distances are
Heatsink 101
showninFig.4(b)asafunctionofthebeamdiameterfor
Telescope 350
1000, 10000 and 100000 fibers. The average power for Otheroptics 50
thesysteminshootingmode,requiredtodeliversufficient Propellant 250
Δvforre-entryinasingleencounterisP¼E =Δt with Other 500
total
the equivalent repetition rate f¼P=E . As shown in Total 2373
L
Table 3, for small debris, o3cm, an array of 104 fibers
delivering 25kW within 2.7s would be sufficient while
larger 10cm debris require 105 fibers and 100kW for telescopeprimary.Forthemaximumapertureconsidered
removalinasinglepass.Inthecaseofdebristravelingat here,3m,thiswouldequateto (cid:3)7m2or140kg.Inclusive
alateraldistanceofrminandvelocityvrel¼15km=swecan ofotheropticswewillconsideravalueof350kgequiva-
estimate the peak angularvelocityrequiredfor thebeam lenttothe3.5mtelescopeoftheHerschelSpaceObserva-
during shooting as αmax which for the 104 fiber system tory. In the case of gas propellant for maneuvering and
resultsinavalueof (cid:3)21=s. orientating the system in orbit we estimate 130kg. For
In order to estimate the flux of debris within the comparison,thepropellantpayloadofthe1tonneSpitzer
shooting range of the telescope we limit the interaction telescope mission was 65kg envisaged for 5 years of
areaatLminwhichisπr2min.Accordingtosimulationsfrom operation. Also, we estimate an additional propellant of
MASTER 2009 [9], the mean density for 1–10cm debris 120kginordertofullyde-orbitthesystemattheendofits
ρd(cid:3)10(cid:2)6km(cid:2)3 near 800km orbit and the flux can be mission. Energy storage will be required to facilitate the
approximatedas higher average powers required for shooting mode and
f (cid:3)v ρ πr2 ð10Þ alsotocompensateforeclipsesduringwhichthegenera-
d rel d min tion of solar power is impossible. To account for this and
andforvrel¼15km=sthisresultsinarelativelylowfluxof all other components such as shielding we estimate an
1debrisevery2husingthevaluesshowninTable3.Over additionalweightof500kg.AssummarizedinTable4,the
ayearthisyields 4103debrisde-orbitedforthedifferent combinedweightresultsin E2.4metrictonnes.
systemdesigns.
5. Discussion
4. Missionpayload
The revolution in laser technology enabled by ICAN
As an estimate of the total weight of the payload for would inprinciple provide a means for de-orbiting small
such an orbiting system we can begin by using known fragmentation debris fromtheirlocality in space. Herein
laser systems and scalings for solar panel components in thisapplicationveryhighpeakpowerisnotnecessary.The
the case of a 1kW ICAN laser with 104 fibers. The relatively low pulse fluences needed and high repetition
compactness of diode pumped laser systems is signifi- rate implya high average power as the key requirement.
cantlygreaterthantraditionallasermediaandthesatellite Together with its excellent power efficiency and stability
solar cells are indeed more efficient per weight than an ICAN architecture can be considered as a practical
terrestrialversions. solution to cataloging and reducing the hazard of space
An industrial 100kW fiber laser produced by IPG, for debris in low-earth orbit. This is certainly the case with
example, weights 3600kg [17]. Operating ICAN at 25kW smallcmscaledebrisandthuscomplementstheexisting
during shooting mode, we can scale this weight and projects designed for removing larger payload objects
estimate900kg.Forspace-basedsolarpanelsweassume involvingnets,tethersandgrapples.
10–20kg/kW [18]. Considering an efficiency of 30% for Our comparison of space and ground-based debris
bothlaserandsolarsystems,theirrequiredinputpowers removal systems has shown that indeed such systems
are3.3kWand11.1kWrespectively.Inthecaseofa1kW arealsocomplimentary.Withdistinctlasermedia,ranges
ICANsystemtheresultsinasolarpanelweightof222kg. andenergywehaveameanstodivideoperationbetween
Assumingasolarfluxof1.347kW/m2,therequiredsurface different debris populations in terms of size and orbit.
areawouldbe11m2.Nextweaddtheweightoftheheat Without the need to carry significant fuel or coolant
sink and beam expander optics. In order to remove liquids, the lifetime of our proposed space systemwould
E8kWof waste heat, using modern radiative heat pipes be limited primarily by degradation to optics, which is
with 10kg/kW [19] results in an additional E100kg. expectedfor periods greater than 5 years, largefor space
Regarding the primary mirror mass, the areal density for missions.
large aperture space optics is presently within 20kg=m2, A most salient consideration is that actual removal of
whichisalmostafactorof10lesscomparedtotheHubble debrisisbutonecomponentofthemission.Detectingand
R.Soulardetal./ActaAstronautica105(2014)192–200 199
catalogingthe106þ populationofsmall1–10cmdebrisis willorbitat400kmdirectingaUVlaserbeamtowardsthe
equallyimportant.Nocompletepositionaldataexistsdue atmosphere.Thisbeamiscreatedviadiode-pumpedglass
to the limits of ground based radar. Hence, it is of media producing nanosecond pulses with 100mJ energy
equivalent significance that a proposed orbital debris at a rate of 100Hz. The payload also comprises a large
removercanoperateasaprecisescanneroftheseincreas- aperturetelescopeandsophisticatedinterferometrydiag-
inglyuncheckedprojectiles.Withsuchanupdatedcatalog, nostics of the reflected signals. With such increasingly
aworkflowcanbeinitiatedtoprovideprecisevalidation powerful and complex laser systems in orbit, the prece-
ofdebrisbeforeclearanceisgivenforremoval. dent is shifting towards preparing the scientific and
Security and safety are of course a major topic with political grounds for solutions to the increasing dangers
developingspacebasedlasermissions.Obviously,thelaser posedbyspacedebris.
mustbeeye-safeatgroundlevel.Atadistanceof800km, In conclusion, we have developed the concept for a
themaximumfluenceafteratmosphericabsorptionwould novel laser-based orbital system for the removal of frag-
be essentially zero. The low fluence in space is reduced mentationdebrisbasedontheICANlaserarchitecture.We
further when in scanning mode where the beam is have shown via analytical calculations that its high effi-
expanded for reflection of debris. Since identification of ciency, precise phase array and fast pulse repetition
objects as debris would occur over multiple transits, enables rapid scanning and removal of hyper velocity
complete data for a given orbit would enable stringent debris. Our future work will include applying detailed
controls, avoiding the much less numerous non-debris orbital simulations involving more realistic debris distri-
objects. butions and modeling the mission performance of the
Thereareindeedanumberofpossibilitiesfordesigning debris-sweeperforspecificorbits.
an initial test mission. For example, the system could be
implemented within a graveyard orbit oras a module on
theInternationalSpaceStation(ISS)[6].Inthelattercase,
Acknowledgments
the complexity would be reduced and routine mainte-
nance could be performed in-house by astronauts. Inter-
The authors would like tothankthe École Polytechni-
esting,thereisthepossibilityofusingthesuperwidefield
que, the ‘Commissariat à l'Energie Atomique et aux Ener-
telescope of the Japanese EUSO module on-board the ISS
in tandemwith an ICAN debris remover [20]. With a 601 giesAlternative’andThalesfortheirinvaluablesupportin
thiswork.
field of view EUSO is designed for detecting Cerenkov
flashes from cosmic-ray events in the atmosphere [21].
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