Optical system design and integration of the Lunar … system design and integration of the Lunar Orbiter Laser Altimeter Luis Ramos-Izquierdo,1,* V. Stanley Scott III,2 Joseph Connelly,1

Optical system design and integration of the LunarOrbiter Laser Altimeter

Luis Ramos-Izquierdo,1,* V. Stanley Scott III,2 Joseph Connelly,1 Stephen Schmidt,3William Mamakos,4 Jeffrey Guzek,4 Carlton Peters,5 Peter Liiva,6

Michael Rodriguez,6 John Cavanaugh,7 and Haris Riris2

1NASA/Goddard Space Flight Center, Optics Branch, Greenbelt, Maryland 20771, USA2NASA/Goddard Space Flight Center, Laser Remote Sensing Laboratory, Greenbelt,

Maryland 20771, USA3NASA/Goddard Space Flight Center, Electro-Mechanical Systems Branch, Greenbelt, Maryland 20771, USA

4Design Interface Inc., Finksburg, Maryland 21048, USA5NASA/Goddard Space Flight Center, Thermal Systems Branch, Greenbelt,

Maryland 20771, USA6Sigma Space Corporation, Lanham, Maryland 20706, USA

7NASA/Goddard Space Flight Center, Laser and Electro-Optics Branch, Greenbelt, Maryland 20771, USA

*Corresponding author: [email protected]

Received 15 January 2009; revised 16 April 2009; accepted 28 April 2009;posted 1 May 2009 (Doc. ID 106402); published 22 May 2009

The Lunar Orbiter Laser Altimeter (LOLA), developed for the 2009 Lunar Reconnaissance Orbiter (LRO)mission, is designed to measure the Moon’s topography via laser ranging. A description of the LOLAoptical system and its measured optical performance during instrument-level and spacecraft-level inte-gration and testing are presented. © 2009 Optical Society of America

OCIS codes: 280.3640, 220.4830.

1. Introduction

The Lunar Orbiter Laser Altimeter (LOLA) is one ofseven scientific instruments on board the Lunar Re-connaissance Orbiter (LRO) spacecraft [1], the firstmission in NASA’s Vision for Space Exploration, aplan to return to the Moon and then to travel to Marsand beyond. LRO is scheduled to launch in June 2009and arrive at the Moon five days later for a one-yearstudy from a nominal 50km altitude circular map-ping orbit. The goals of LRO are to select safe landingsites, identify lunar resources, and study how the lu-nar radiation environment will affect humans. LOLAwill use laser ranging to measure the Moon’s surfaceelevation, slope, and roughness and generate a three-dimensional map of the Moon; LOLA will also help

identify permanently shadowed regions of the Moonwhere water ice might be present [2].

LOLAwas designed and developed at NASA’s God-dard Space Flight Center (GSFC) over a period ofthree years and delivered to the NASA/GSFC LROteam on April 2008 for spacecraft-level integration.The optical and optomechanical designs, optical ma-terials and coatings, and many of the optical test set-ups used on LOLA are based on our previous work onthe NASA/GSFCMercury Laser Altimeter (MLA) in-strument. A description of MLA’s optical system andperformance has been previously published [3]; toavoid duplication this paper will focus on the opticalengineering aspects that are unique to LOLA.

2. Instrument Description

A comparison of the LOLA and MLA optical specifi-cations is shown in Table 1. The main difference

0003-6935/09/163035-15$15.00/0© 2009 Optical Society of America

1 June 2009 / Vol. 48, No. 16 / APPLIED OPTICS 3035

between MLA and LOLA is that MLA is a singlechannel instrument, while LOLA has multiple laserranging channels: MLA has a single transmitted la-ser beam, four receiver telescopes (for increased col-lecting aperture area), and a single detector, whileLOLA has five transmitted laser beams, a single,multiple FOV receiver telescope, and five detectors.LOLA can process the detector signals indepen-

dently to generate five range measurements per la-ser shot; this approach increases coverage of thelunar surface and provides local slope data. Due tothe difference in mapping orbits, 50km for LOLAand up to 800km for MLA, the laser transmitter out-put energy and receiver telescope collecting aperturerequirements are very different for the two instru-ments. Another difference between MLA and LOLAis that MLA operates at a single wavelength(1064nm), while LOLA operates at two wavelengths(1064nm and 532nm). LOLA will use the 1064nmwavelength to map the Moon and the 532nm wave-length for laser ranging from Earth to LRO [4] in or-der to improve the orbit determination of LRO to thelevel required to generate an accurate topographicmap of the Moon.

Like MLA, LOLA is composed of two subassem-blies connected by an electrical harness: the OpticalTransceiver Assembly (OTA) and the Main Electro-nics Box (MEB). An assembly drawing of the LOLAOTA is shown in Fig. 1. The LOLA OTA structure ismade of optical-grade beryllium for its low mass,high stiffness, and high thermal conductivity. TheOTA Main Housing serves as an optical bench forthe Laser Transmitter and the Receiver Telescope.The Receiver Telescope is fiber-optic coupled to fiveAft-Optics/Detector Assemblies mounted on the per-iphery of the Main Housing. A Reference Cube on theOTA is used to monitor laser to optical bench align-ment during LOLA integration and environmentaltesting and to transfer the pointing angle of theLOLA Laser to the LRO spacecraft coordinate

Table 1. Lunar Orbiter Laser Altimeter (LOLA) andMercury LaserAltimeter (MLA) Optical Specifications

Laser transmitter LOLA MLA

# Laser oscillators 2 1Wavelength (nm) 1064.3 1064.3Pulse energy (mJ) 2.7 20Pulse width (ns, FWHM) 6 6Repetition rate (Hz) 28 8Divergence (!rad, 1=e2 dia.) 100 80# Beams/laser 5 1Beam spacing (!rad) 500 n/a

Receiver optics LOLA MLA

# Receiver telescopes 1 4Objective lens size (mm, dia.) 150 125Collecting clear aperture (cm2) 154 417# Receiver FOV’s 5 1FOV (!rad, FWHM) 400 400FOV spacing (!rad) 500 n/aFiber-optic coupled Yes YesBandpass filter (nm, FWHM) 0.7 0.7# Detectors 5 1Detector type SiAPD SiAPDDetector size (mm, dia.) 0.7 0.7

Fig. 1. LOLA Optical Transceiver Assembly (thermal blankets not shown).

3036 APPLIED OPTICS / Vol. 48, No. 16 / 1 June 2009

system. The LOLA OTA is mounted to the LRO com-posite instrument deck via three titanium flexures,and the structure is fully enclosed by thermal blan-kets such that only the transmitter and receiver op-tical apertures and the radiator remain open to theexternal environment. Due to the Moon’s harsh ther-mal environment, the LOLA optical system is re-quired to operate over a wide temperature range,in a non steady state, and with large thermalgradients.The LOLA Laser optomechanical design is similar

to that of MLA: the laser is built on a small berylliumbench that mounts to the OTA Main Housing centercompartment and has an external beam expandertelescope that sets the final transmitted laser beamdivergence. But while the MLA laser was a 20mJoutput energy oscillator/amplifier design, the LOLAlaser has two independent oscillators to provide therequired 2:7mJ output energy with the lifetime andredundancy required by the LRO mission [5]. Thetwo oscillator output beams are polarization coupledinto a set of common optics that feed the externalLaser Transmitter Telescope. At the top of this tele-scope is a diffractive optic element (DOE) that gen-erates five far-field laser spots in a cross pattern.The four outer spots are separated by 500 !rad fromthe center spot, and the cross pattern is clocked by26° with respect to the LRO spacecraft velocity vectorto generate five equally spaced tracks on the lunarsurface. The DOE is the key technology that allowedfor the simple and elegant generation of the fiveLOLA Laser output beams.The LOLA Receiver Telescope has a clear aperture

(CA) diameter of 140mm and is a scaled-up versionof one of the 115mm CA diameter MLA ReceiverTelescopes. Both telescope designs have a 500mm ef-fective focal length (EFL) and use a 200 !m core dia-meter fiber optic to yield a receiver field-of-view(FOV) of 400 !m diameter. In the case of LOLA, five200 !m fiber optics are mounted on a common con-nector located at the focal plane of the Receiver Tele-scope to obtain five independent FOVs coalignedwith the five transmitted laser beams. The LOLAFiber-Optic Bundle (FOB) fans out into five indepen-dent fiber-optic cables that attach to five Aft-Optics/Detector Assemblies where the fiber-optic outputlight is collimated, filtered, and imaged at a 1!1mag-nification onto each of the five 0:8mm diameter Per-kin-Elmer silicon avalanche photodiode (SiAPD)detectors. UnlikeMLA, the LOLA receiver fiber-opticcables are not required to be the same length sinceany length difference (and hence range timing differ-ence between the five channels) can be calibratedout. The LOLA FOB fan-out fiber-optic lengths wereselected for optimum routing on the protective Delrinchannels mounted on the underside of the OTAMainHousing.The LOLA optomechanical design philosophy was

the same we used on MLA: minimize the number ofsubassembly and instrument level adjustmentsrequired to align the instrument in order to better

ensure alignment stability. All the LOLA opticaland mechanical components were toleranced suchthat upon initial instrument integration the bore-sight error between the center laser beam and thecenter receiver telescope FOV was less than the!2mrad Receiver Telescope line-of-site (LOS) ad-justment range. Like MLA, the LOLA boresight ad-justment is implemented by decentering the fiber-optic adapter at the focal plane of the Receiver Tele-scope; but in the case of LOLA, this adapter alsoallows for clocking adjustment to optimize the tan-gential boresight alignment of the four outer chan-nels. The radial boresight alignment of the fourouter channels was accomplished by tolerancingthe diffraction angle of the DOE, the focal lengthof the Receiver Telescope, and the position of the fourouter fibers on the FOB common-end connector; noindependent adjustment of the five Receiver Tele-scope FOV channels is possible because the fiber op-tics are closely packed and epoxied on the FOBcommon-end connector. Since LOLA’s laser diver-gence and receiver channel FOV are similar toMLA’s, we just modified MLA’s instrument-level op-tical alignment requirements to include the align-ment requirements for LOLA’s four outer channels.LOLA’s instrument-level alignment requirementsare shown in Table 2.

3. Laser Transmitter Telescope

The LOLA laser transmitter telescope has two func-tions: it reduces the divergence of the LOLA laser os-cillator input beam, and it splits the output beaminto five to generate a cross pattern in the far-field.The telescope is an 18! magnification, afocal, Gali-lean beam expander that expands and collimatesthe LOLA laser 1mm 1=e2 diameter, 1:8mrad 1=e2 di-vergence input beam to generate the required100 !rad 1=e2 diameter output beam divergence.The telescope has a single Corning 7980 fused silicanegative lens, a BK7G18 positive lens group, and aDOE exit optic (Fig. 2). The DOE is a diffractive beamsplitter that generates five output beams from a

Table 2. Lunar Orbiter Laser Altimeter Optical AlignmentRequirements

Instrument integrationLaser to receiver initial boresite error(center FOV)

<2mrad

Laser perpendicular to LOLA mountingplane (center FOV)

<5mrad

FOV pattern clocking with respect to LOLAinstrument coordinates

26°! 2°

Instrument alignmentLaser to receiver boresite error (center FOV) <20 !radLaser to receiver boresite error (edge FOV) <40 !radKnowledge of laser beam(s) pointing withrespect to S/C reference

!100 !rad

Instrument stabilityLaser pointing angle (relative to theLOLA mounting plane)

<150 !rad

Laser to receiver boresite error (all five beams) <150 !rad


single input beam; this is an elegant beam splittingapproach because it is simple, efficient, alignment in-sensitive (except for clocking), and environmentallyinsensitive [6]. The DOE optic is a 40mm diameterby 6mm thick fused silica substrate etched on oneside with a transmission phase grating and antire-flection (AR) coated on both sides to maximizetransmission at 1064nm. The LOLA DOE was man-ufactured by MEMS Optical from a master patternthat is replicated via a proprietary lithographic pro-cess onto a fused silica wafer from which multipleparts can be cored out. Before the final flight DOEwas fabricated, several calibration wafers were madeand tested to optimize the etch depth of the diffrac-tion pattern in order to maximize efficiency and far-field beam uniformity. The flight DOE had an overallefficiency of 80% (the other 20% is diffracted to high-er order modes outside the LOLA receiver FOV) withthe center beam having"50%more energy than eachof the outer four beams. Figure 3 shows a picture ofthe DOE, its transmitted far-field image, and the far-field image normalized cross section in two ortho-gonal axes.The telescope tube is beryllium with a titanium

flexure preloaded to 30 lb (13:6kg) in order to se-curely hold the positive lenses and DOE over all ex-pected mechanical and thermal loads. The DOE andthe tube mount both have semicircular notches, anda pin located in the flexure is used to provide a clock-ing lock feature between them. The negative lens ismounted on a titanium subcell whose axial locationis shimmed to collimate the telescope for operation in

vacuum at 1064nm. The exit optics have a 36mmdiameter exit clear aperture (a 2!1 aperture to beamratio) to prevent any significant vignetting of theoutput laser beam and allow for small decentercoalignment errors between the prime and thespare oscillator laser beams at the input to theLaser Transmitter Telescope. The LOLA LaserTransmitter Telescope was built using the same op-tomechanical tolerances, alignment requirements,and integration techniques that we used on theMLA 15! magnification laser transmitter telescope.The LOLA assembly, shown in Fig. 4(a), is 175mmlong, weighs 120 g, has an operational thermal rangeof 20! 20 °C, and a survival thermal range of #30Cto "70 °C. The expected solar background from theMoon into the LOLA Laser Transmitter Telescopeis small and inconsequential to the operation ofthe LOLA Laser, due to its small aperture and smalleffective FOV. Two flight model (FM) Laser Trans-mitter Telescopes were integrated, functionallytested at ambient pressure and in a vacuum, ther-mally qualified for survival, and delivered to theLOLA laser team for integration to the Laser Bench.

4. Lunar Orbiter Laser Altimeter Receiver Telescope

The LOLA Receiver Telescope is a scaled up versionof one of the MLA receiver telescopes. Both are500mm EFL telephoto designs, but the LOLA tele-scope has a larger diameter objective lens (150mmversus 125mm) and a longer unfolded path lengthto preserve the f =2 objective lens speed. MLA useda sapphire objective lens for its ability to survivein harsh thermal environments, but sapphire hasthe drawback of having a high density. To try to re-duce mass we also designed, built, and tested an en-gineering model (EM) LOLA Receiver Telescopeusing a BK7G18 objective lens. The optical layoutfor both LOLA Receiver Telescope designs is shownin Fig. 5. The BK7G18 design has fewer elements be-cause the objective lens is aspheric, and a single ne-gative lens can set the final telescope EFL withoutthe need to correct for the spherical aberration ofthe objective lens. The mass savings of this designwere significant (220 g), and its defocus versus oper-ating temperature negligible since BK7G18 has a

Fig. 2. LOLA Transmitter Telescope optical layout.

Fig. 3. (a) DOE, (b) far-field image (saturated), (c) image cross sections (normalized).


dn/dT an order of magnitude smaller than sapphire,but the LOLA thermal model predicted that theBK7G18 objective lens would operate with largethermal gradients during orbit around the Moondue to the high emissivity and poor thermal conduc-tivity of BK7G18. Figure 6 shows the predictedon-orbit temperatures for the two objective lens ma-terials for the LRO Hot and Cold thermal cases; tem-peratures at the lens edge and lens internal andexternal center points are shown over a time periodof three orbits. The sapphire objective lens operatesover a temperature range of "11 °C to "42 °C withnegligible thermal gradients, while the BK7G18 ob-jective lens operates over a wider #24 °C to "56 °Ctemperature range and with radial and axial ther-mal gradients of up to 25 °C. The large and con-stantly changing thermal gradient would bend theBK7G18 objective lens back and forth during eachLRO orbit. Although structural analysis and testingof the BK7G18 objective lens indicated that the lenswould survive the predicted on-orbit thermal envir-onment, we decided that it was safer to use the MLA-heritage telescope design for LOLA.The LOLA Receiver Telescope optomechanical de-

sign is also based on MLA: the same materials (ber-yllium structure and titanium flexures), tolerances,optic mounting techniques, and alignment compen-sators for focus and boresight were used. The onlychange was the increased 250 lb (113:4kg) flexurepreload required to hold the larger LOLA objectivelens. As in MLA, the telescope is folded with a dielec-tric mirror in order to fit within the allocated instru-ment volume and provide protection against an

accidental view of the Sun that could otherwise da-mage the FOB located at its focal plane. The dielec-tric mirror reflects a small spectral band centered at1064nm and would allow most incident solar radia-tion to safely scatter off its frosted backside onto theLRO instrument deck. A picture of the LOLA Recei-ver Telescope is shown in Fig. 4(b). The assembly is324mm long and weighs 1:24kg (driven mostly bythe 680 g sapphire objective lens), has an operatingtemperature range of 20! 20 °C, and a survival tem-perature range of #30 °C to "70 °C. Two flight model(FM) Receiver Telescopes were integrated, function-ally tested at ambient pressure and vacuum, ther-mally qualified for survival, and delivered to theLOLA mechanical team for integration to the OTAMain Bench.

The LOLA Receiver Telescope FOV is establishedby the FOB located at the telescope focal plane. Thetelescope side, or common end, of the FOB has five200 !m core diameter, 0.22 NA, multimode, step-index fiber optics spaced 250 !m apart in a cross pat-tern; these fiber optics define five 400 !rad diameterFOVs with a center-to-center spacing of 500 !rad.The telescope FOB mating adapter is clocked 26°to align the five receiver FOVs with the five trans-mitted laser beams. Behind the common-end connec-tor the FOB fans out into five independent fiber-opticcables that attach to the five Aft-Optics/Detector As-semblies. The LOLA FOB was fabricated in house atGoddard’s Advanced Photonic Interconnection Man-ufacturing Laboratory/Code 562 [7]. The FOB isterminated with Diamond AVIM connectors, aspace-qualified fiber-optic connector manufacturedby Textron-Tempo Inc. and previously flown on theGeoscience Laser Altimeter System (GLAS) andMLA instruments. The FOB fan-outs have thestandard version of this connector, while the FOBcommon-end has a customized internal ferrule cap-able of precisely locating and securing five fiber op-tics in a cross pattern. The fabrication of the modifiedcommon-end connector ferrule was a major part ofthe in-house FOB development effort. The DiamondAVIM connectors, together with the in-house fabri-cated mating adapters, allowed us to meet ourstringent alignment requirements and providedthe capability to mate and de-mate all fiber-opticinterfaces without losing boresight alignment or

Fig. 4. (a) LOLA Transmitter Telescope, (b) LOLA ReceiverTelescope.

Fig. 5. LOLA Receiver Telescope layouts: (a) sapphire objective, (b) BK7G18 objective.


focus. After completion of the FOB assemblyfabrication, all fiber-optic end faces were AR coatedat 1064nm by Denton Vacuum to increase the aver-age fiber-optic transmission from "90% to "97%.The flight and flight spare FOB assemblies then un-derwent vacuum testing, operational and survivalthermal testing, and vibration testing prior to deliv-ery to the LOLA instrument integration and test(I&T). A picture of the LOLA FOB assembly andits common end is shown in Fig. 7.Prior to installing the FOB on the LOLA OTA, the

FOB was used to focus the Receiver Telescope and tomeasure the FOV and cross talk performance of thecombined assembly. The Receiver Telescope/FOB in-terface allows for focus and boresight adjustments:focus is set by shimming the telescope FOB adapterand boresight by decentering the FOB adapter on thetelescope mounting flange. The FOV of the combinedLOLA Receiver Telescope and FOB can be measuredtwo ways: (1) by back-illuminating the FOB and ima-ging the Receiver Telescope output, and (2) by scan-ning a point source at the focal plane of a collimatorilluminating the receiver and plotting the outputpower of each FOB channel as a function of thesource angular position. We used both methodsduring LOLA I&T and found them to be equivalent.Figure 8 shows the back-illuminated image of thecombined LOLA Receiver Telescope/FOB assemblyand two normalized FOV plots obtained with the sec-ond method described above. Note that the plotsshow that the FOV channels have the correct angularsize (400 !rad FWHM) and center-to-center spacing(500 !rad). Plotting the multiple FOV cross sections

on a log scale shows the amount of cross talk betweenthe channels; our requirement is that the LOLA re-ceiver system have <1% cross talk in order to notbias the five independent range measurements.The results shown in Fig. 8 were obtained with thetelescope focus set for ambient pressure and were la-ter verified with the telescope focus set for vacuumduring the LOLA Thermal Vacuum (TVAC) test.

The LOLA receiver system nominal FOV was se-lected to provide sufficient boresight alignment mar-gin for each laser/receiver pair while having enoughangular distance between neighboring channels toprevent cross talk. Cross talk is mainly a concernwhen environmental factors affect the receiver FOVsize, the laser divergence, or the instrument bore-sight alignment; the first two can be caused by a tele-scope thermal defocus and the last one by a vibrationinduced telescope LOS shift. To prove that we metthe cross talk requirement under different OTAalignment conditions, we made a set of four custom,calibrated, black and white Spectralon diffuse reflec-tance targets to measure the relative response of allfive LOLA instrument channels. These 25mm dia-meter targets were placed at the focal plane of a testcollimator and illuminated by the LOLA laser whilethe signal from each LOLA Receiver FOV channelwas monitored. The first target was all white with99.3% reflectance at 1064nm, and the second onewas all black with 1.3% reflectance at 1064nm.The other two targets had 1mm diameter center in-serts that subtended 400 !rad at the focal plane ofour 2:5m EFL test collimator; one target was whitewith a black insert, and the other one was black witha white insert. The worst-case cross talk target wasthe white target with the black insert; in this case thereceiver center channel (CH1) collects little signalfrom its own laser and maximum cross talk fromthe four high-signal neighboring channels. We wereable to show that with this worst-case target the CH1cross talk signal met our <1% requirement even forcases where the boresight alignment error was aslarge as 150 !rad; we also showed that we met thecross talk requirement with the maximum expectedon-orbit Receiver Telescope defocus. (For the cross

Fig. 6. (Color online) LOLA receiver objective lens on-orbit temperature: (a) sapphire, (b) BK7G18.

Fig. 7. LOLA fiber-optic bundle (FOB): (a) assembly, (b) commonend.


talk test the Receiver Telescope focus was set forvacuum but operated at ambient pressure; the Recei-ver Telescope vacuum defocus just happens to beclose to the expected worst-case on-orbit telescopethermal defocus, and it was easier to use pressureas opposed to temperature to change the telescopefocal setting during the course of the cross talk test.The Laser Transmitter Telescope is also affected bypressure and temperature but not to the same extentas the Receiver Telescope due to its much slower f/#.)

5. Lunar Reconnaissance Orbiter Laser RangingTelescope

LOLA was modified to allow for the measurement ofan Earth-based laser ranging (LR) signal at 532nmto help determine LRO’s lunar orbit. A small LaserRanging Telescope (LRT) located behind the LROHigh Gain Antenna (HGA) will be illuminated bya pulsed laser source from NASA’s Next GenerationSatellite Laser Ranging (NGSLR) Station located atthe GSFC in Greenbelt, Maryland, USA, and fromInternational Laser Ranging Service (ILRS) sitesaround the globe. Laser ranging from the Earth toLRO can occur any time an Earth station is withinthe field of view of the LRT. The LRO HGA, with thecoaligned LRT, will be pointed at White Sands, NewMexico for routine spacecraft communications when-ever White Sands is in view. The signal collected bythe LRT will be guided by a fiber-optic cable to theLOLA Aft-Optics/Detector Channel 1 (CH1) Assem-bly, where it will be detected and time stamped. CH1was selected because this channel is aligned to thebrightest of the five LOLA laser beams and hasthe highest signal-to-noise ratio (SNR). As such,CH1 can better handle the additional backgroundnoise generated when the LRT views a solar illumi-nated Earth. Nominally, the LOLA and Earth laserpulses will be timed to stagger their arrival on theLOLA CH1 detector; however, LOLA will also sup-port asynchronous Earth ranging.The derived LRT FOV requirement is 30mrad dia-

meter, which is wide enough to see Greenbelt, Mary-land, when the LRO HGA is pointed at White Sands,New Mexico, and North America is normal to theEarth–Moon vector. The LRT aperture size is limitedto 19mm diameter by the etendue of the LOLA de-

tector, which is defined as the product of the detectorarea and its illuminating cone solid angle. The LOLASiAPD detector has a 0:7mm diameter active areaand can be illuminated at up to f =1 due to the sizeand location of the detector window. To conserve ra-diance, the product of the LRT aperture area andFOV solid angle cannot exceed the detector etendue.To bring the signal from the LRT to LOLA, a 10mlong fiber-optic cable is required. The cable is madeof three mated segments to facilitate routing insidethe two HGA gimbals, along the HGA boom, andacross the spacecraft structure to LOLA. The LRfiber-optic cable is a bundle of seven, 400 !m core dia-meter, 0.22 NA, multimode, step-index, fiber optics ina 1:28mmdiameter hexpack configuration and is ter-minated using modified Diamond AVIM connectors[7]. This FOB design matches the LR optical systemetendue, provides redundancy, andmeets all bend ra-dius routing requirements. The timing error intro-duced by using a 10m, 0.22 NA, multimode fiberoptic is only 0:4ns, which can be calibrated duringoperations and accommodated in the LOLA sciencedata analysis.

The LRT is a pupil imaging, afocal, 14:8! magni-fication, Keplerian telescope; the design images thetelescope pupil onto the LR FOB to avoid generatinga segmented FOV. An optical layout of the LRT isshown in Fig. 9. A sapphire objective lens imagesthe Earth onto a field stop aperture that sets theLRT FOV, and a molded glass aspheric field lens lo-cated behind the field stop images the objective lensonto the LR FOB. The telescope design is folded witha 532nm dielectric mirror to provide protection froman accidental view of the Sun and to facilitate routingof the LR FOB. A set of baffles mounted at the front ofthe telescope seals the gap to the HGA primary mir-ror 38:1mm diameter aperture through which theLRT looks; the baffles also prevent direct illumina-tion of the LRT objective lens for off-axis angles>12°. The LRT/Baffle Assembly can operate withthe Sun as close to 5° off axis without exceedingthe LOLA CH1 background noise generated whenthe LRT looks at a solar-illuminated Earth. TheLRT objective lens and baffles are oversized to allowfor !20mrad adjustment of the LRT LOS, which isaccomplished by decentering the field stop, field lens,

Fig. 8. LOLA receiver FOV: (a) Image, (b) CH1 FOV, (c) CH2-1-4 FOV (log scale).


and FOB subassembly. The structure of the LRT istitanium to match the coefficient of thermal expan-sion (CTE) of the optical components given the harshthermal environment expected on the HGA. A pic-ture of the flight and flight spare LRT (with baffles)is shown in Figs. 10(a) and 10(b), which shows theLRT objective lens pupil image (the image of theback-illuminated LR FOB on the LRT objective lens),and Fig. 10(c) shows the measured LRT/LR FOBFOV cross section. The combined LRT/Baffle assem-bly is 225mm long and weighs 348 g, and has an op-erating and survival temperature range requirementof 20! 30 °C and"90 °C to #40 °C, respectively. Priorto delivery to the HGA I&T team, the LRT was ther-mally qualified and vibration tested to 12:6Grms for1 minute on all three axes, without any significantchange in its optical performance or LOS.The LRToptical axis needs to be aligned parallel to

the HGA RF axis; it is not possible to bias the twobeams, one to look at GSFC while the other looksat White Sands, because the LRO orbit geometry

and the viewed Earth phase change over time. TheLRO HGA team used photogrammetric data fromthe antenna vendor as well as RF and optical mea-surements in the GSFC Electro-Magnetic AnechoicChamber to determine the pointing angle of theHGA RF beam with respect to the HGA optical refer-ence cube. We then used the HGA optical referencecube to align the LRT optical axis parallel to theHGA RF axis to within our allocated 0:36mrad par-allelism requirement. A picture of the HGA-LRTalignment setup is shown in Fig. 11. The pointing an-gle of the LRToptical axis relative to the HGA opticalreference cube was monitored during the HGA/BoomAssembly vibration and thermal vacuum (TVAC)tests, and the LRT alignment stayed within our allo-cated pointing angle requirement. In addition to thealignment tests, the 532nm transmission of the LRTand LR FOB system was measured before and aftereach HGA environmental test. The completed HGA/Boom Assembly was mated to LRO, and the final LRFOB segment was routed from the bottom of the

Fig. 9. LRO Laser Ranging Telescope (LRT) optical layout.

Fig. 10. (a) LRO Laser Ranging Telescopes, (b) pupil image, (c) FOV image cross sections.


HGA boom to the LOLA CH1 Aft-Optics LR FOB in-put port. After integration, the LR Flight Systemend-to-end performance was tested with simulated532nm and 1064nm pulsed and CW signals goinginto the LOLA Receiver Telescope and LTR to mimicthe expected Lunar and Earth laser ranging signalsand solar background levels.

6. Aft-Optics Assemblies

The five LOLA Aft-Optics Assemblies have two dif-ferent optical designs: the Channel 1 (CH1) assemblyoperates at 1064nm and 532nm to handle the LOLAcenter FOV and LRT input signals, while the otherfour Aft-Optics assemblies (CH2–CH5) operate at1064nm only and view the signals from the four out-er LOLA FOV channels. The function of the Aft-Optics is to collimate, filter, and reimage the LOLAand LRT receiver fiber optic onto the five LOLA0:8mm diameter SiAPD detectors. The CH2!CH5Aft-Optics design has 11mm EFL, f =2 Lightpathmolded aspheric lenses to collimate and refocusthe 200 !m diameter LOLA fiber optic at a 1!1 mag-nification; this lens EFL provides the <20mradcollimated beam divergence required for the LOLA 2

cavity, 1064:45nm center wavelength, 0:7nmFWHM bandpass filter made by Barr Associates.The CH1 Aft-Optics design has the same 1064nmcollimating lens and bandpass filter, but includes adichroic beam splitter and larger 532nm collimatingand detector refocusing lenses to handle the larger1:28mm diameter LRT FOB input. The LR filter isalso from Barr Associates; it has a center wavelengthof 532:25nm, but it is only 0:3nm FWHM to reducethe large solar background expected when the LRTviews the Earth in daylight. Both filters were pur-chased with center wavelengths longer than their re-spective laser wavelengths in order to tilt-tune thefilters to optimize their transmission. The bandpassof the filters shifts to a lower wavelength as the angleof incidence (AOI) increases; we determined the op-timum AOI for each filter by measuring their trans-mission as a function of AOI using a collimated,attenuated beam from the LOLA FM laser and theprime and spare LR ground lasers. The Aft-Opticsoptomechanical design allows for up to a 3° off-normal angle of incidence (AOI) on the bandpass fil-ters, which was twice our expected optimum filterAOI. The optical layout for both Aft-Optics designsis shown in Fig. 12.

Both Aft-Optics designs include a 1064nm testport that serves two purposes: it allows for theback-illumination of the LOLA FOB so we can viewand monitor the LOLA Receiver FOVand LOS align-ment during I&T, and it allows for the input of fivedifferent signal and background levels that can simu-late lunar returns for testing the receiver detectors,electronics, and signal processing algorithms. Theaddition of the test port complicated the optomecha-nical design and alignment of the Aft-Optics assem-blies, but proved very useful during instrument-levelfunctional and environmental testing. The test portis implemented with a 99%R/1%T 1064nm powerbeam splitter with a mirrored common surface tosplit the signal from the test port fiber optic to thereceiver fiber optic and to the detector focal plane.Shimming the power beam splitter with a wedgedspacer changed the angle of incidence of the colli-mated beam on the 1064nm bandpass filter in orderto tilt-tune the filter to its predetermined optimum

Fig. 11. LRO HGA-LRT alignment setup.

Fig. 12. LOLA Aft-Optics optical layouts: (a) CH2!CH5, (b) CH 1 (1064=532nm).


AOI. Tilt-tuning the LR channel was accomplishedby decentering the LR FOB Aft-Optics connector tochange the AOI of the collimated beam on the532nm filter. The CH1 Aft-Optics design allows fordifferent AOIs on the 1064nm and 532nm filterswith coincident 1064nm and 532nm images on thedetector focal plane since rotating the dichroic beamsplitter cube moves the 532nm focal plane imagewithout affecting the location of the 1064nm image.The only catch is that both filter tilt-tune adjust-ments have to be made in the same plane as the di-chroic beam splitter rotation provides adjustment in.A picture of two LOLA Aft-Optics Assemblies is

shown in Fig. 13. The CH1 design weighs 97 g whilethe smaller CH2!CH5 design is only 44:6 g. Both de-signs have an operational thermal range of 20 °C!20 °C and a survival thermal range of #30 °C to"50 °C. The mechanical components are titaniumtomatch the CTE of the optics and the beam splittersare bonded with Scotch-Weld 2216 Grey epoxy. Ther-mal defocus and beam decollimation over the ther-mal operating range is small and can be neglected.The Aft-Optics can also be aligned at ambient pres-sure and operated in vacuum without requiring de-focus compensation since the change in collimationand imaging with pressure is negligible. The Aft-Optics Assemblies mate to the beryllium detectorhousings via a titanium interface plate that allowsfor focus and decenter adjustment; the SiAPD detec-tors have the same thermal operating range as theAft-Optics Assemblies so the interface does not needto provide thermal isolation. The Aft-Optics Assem-blies are aligned to the LOLA detectors by lookingthrough the Aft-Optics LOLA receiver fiber-optic in-put port to focus and center the detector image on theFOB adapter aperture (we had previously verifiedthat the LOLA receiver fiber optic was well centeredon its connector, that the connector was well centeredon its adapter, that the test port fiber optic wasaligned to the receiver port fiber optic, and thatthe images from the 1064nm and 532nm input fiberoptics were coincident on the CH1 Aft-Optics focalplane). The LOLA Aft-Optics/Detector alignmentoptical setup is shown in Fig. 14; the inset images

show the alignment of the detector to the LOLA re-ceiver port and the coalignment of the 1064=532nmfiber-optics images on the CH1 Aft-Optics assemblyfocal plane. After the Aft-Optics/Detector alignmentwas completed, the Aft-Optics fiber-optic adaptersand the detector interface plate were “liquid pinned”(epoxy applied to a mounting flange pin alignedto an oversized hole on the mating flange) withScotch-Weld 2216 Grey epoxy. The mated Aft-Optics/Detector Assemblies were then installed onthe OTA Main Housing and electrically integratedto the detector power supply and signal processingelectronics.

We performed a radiometric end-to-end test of theLOLA and LR receiver optical systems using theLOLA and LR Receiver Telescopes, Fiber-Optic Bun-dles, and Aft-Optics Assemblies. The goal of the testwas to verify that the radiometric performance of thereceivers was close to theoretical given their respec-tive aperture, FOV, filter spectral bandwidth, andmeasured optical component transmissions. The testconsisted of measuring the LOLA and LR receiversystem output power as a function of distance tothe 10 in. diameter exit port of the NASA/GSFC Code614.4 calibration group’s 36 in. diameter integratingsphere (Fig. 15). Since the integrating sphere exitport is an extended white light source (akin to a solarilluminated Moon) when viewed up close, this testalso verified that the off-axis and out-of-band trans-mission of both receiver systems was adequate andmet the background noise assumptions that wentinto both laser ranging link margin calculations.Using the calibrated spectral radiance of the sphereexit port at 532nm and 1064nm, we calculated thatthe LOLA and LR receiver systems should collect1:0nW and 7:0nW, respectively. The LR receiversystem collected "10% more power than calculatedand was insensitive to distance over a 0:3m to6:1m range (the long dimension being limited bythe size of the clean room). The LOLA receiversystem collected 50–70%more power than calculated

Fig. 13. LOLA Aft-Optics assemblies: CH1 (left), CH2!CH5(right).

Fig. 14. LOLA Aft-Optics/Detector Assembly alignment setupand images (insets).


depending on sphere distance; this performance wassimilar to what we had measured on MLA and wastaken into account in the initial LOLA link margincalculation. The actual versus theoretical discre-pancy is because the theoretical calculation assumesan ideal bandpass filter with no transmission outsideits bandpass and an ideal telescope with zero trans-mission outside its FOV. We believe that the LR re-ceiver system performance was closer to theoreticaland insensitive to distance because the LRT has a setof baffles that limit the off-axis illumination of itsobjective lens. Instrument volume constraints pre-cluded the use of baffles to limit the off-axis illumi-nation of the LOLAReceiver Telescope objective lens.

7. Lunar Orbiter Laser Altimeter Optical TransceiverAssembly Optical Integration

The development of the LOLA optical system in-cluded building and testing engineering model (EM)copies of each optical assembly and integrating andtesting an EM OTA. The EM optical assemblies hadthe same optical components as the flight model(FM) assemblies, but used aluminum instead of tita-

nium or beryllium for the structural components. In-tegrating and testing EM assemblies early in theinstrument development program is critical to cor-rect any design flaws, verify all optomechanicalinterfaces, draft documentation and optical test pro-cedures, and identify all required optical GroundSupport Equipment (GSE). All the LOLA opticalflight model (FM) assemblies were space qualifiedper GSFC-STD-7000 General Environmental Verifi-cation Specification (GEVS) guidelines; functionaltests were performed before and after each environ-mental test. The environmental tests included opera-tional and survival thermal testing, operation invacuum, and vibration testing of the LRT and theLaser/Beam Expander Assembly. The FM OTA opto-mechanical integration was straightforward: the op-tical assemblies were bolted to the OTA MainHousing and the LOLA FOB was integrated to theReceiver Telescope and to the five Aft-Optics Assem-blies. Routing and securing the LOLA FOB to theDelrin channels on the underside of the Main Hous-ing was the only difficult task due to the bend radius

Fig. 15. LOLA and LR receiver systems radiometric test setup.

Fig. 16. LOLA FM OTA (thermal blankets not shown).


constraints of the FOB. The integrated LOLA FMOTA is shown in Fig. 16.Two optical alignment activities completed the

optical integration of the FM OTA: the boresightalignment of the transmitter and receiver and themeasurement of the pointing angle of the five trans-mitted laser beams with respect to the LOLA refer-ence cube. The LOLA boresight alignment procedureand test setup were the same as used on MLA. Toboresight the OTA, the Laser output beam is attenu-ated and viewed with a CCD camera located at thefocal plane of a 2:5m EFL collimator, the LOLAFOB is back-illuminated, and the Receiver TelescopeFOB adapter is decentered and rotated until theimages of the receiver five FOVs are centered on thefive transmitted laser beams. After final OTA bore-sight alignment, the Receiver Telescope FOB adap-ter was locked in place with four fasteners and“liquid pinned” and the FOB connector “torquestriped” to its adapter with a dab of epoxy. Figure 17shows the initial boresight alignment images forboth LOLA Laser oscillators. On these images thereceiver FOV image is in-focus because we back-illuminated at 1038nm to compensate for the LOLAReceiver Telescope defocus at ambient pressure. Thelaser images are"1:5! larger than what we expect invacuum due to the pressure defocus of the LaserTransmitter Telescope. Note also that the two LOLA

laser oscillators do not point in exactly the same di-rection (they are "35 !rad off in the vertical axis),which required a compromise in the OTA boresightalignment. The measurement of the LOLA Laserpointing angle relative to the LOLA Reference Cubewas accomplished with an autocollimating theodolitethat “aperture shared” the laser output beam and theLOLA Reference Cube and measured the orientationof the five transmitted laser beams relative to the re-ference cube "Z face (the theodolite reticule wasviewed with a CCD camera in order to see the LOLAIR laser beams). This measurement was later used totransfer the LOLA Laser pointing angle informationto the LRO spacecraft coordinate system.

The completed LOLA OTA underwent sine, ran-dom, and sine burst vibration testing to proto-flightlevels. The plan called for a sine burst test level of11:2Grms about all three axes, but a failure of thevibration table during the Z-axis test led to an overt-est condition of nearly a factor of 2. Although thestructural margin of safety remained positive, wedid see a significant boresight alignment shift afterthis test. The Z-axis vibration test was later com-pleted at another facility, and this time the OTAboresight alignment remained stable. Figure 18summarizes the OTA vibration test alignment re-sults; the left plot shows the pointing angle stabilityof the LOLA Laser center beam versus the LOLA Re-ference Cube, while the right plot shows the bore-sight alignment of both lasers to the receiver.Included in the plots are circles denoting the angularsize of the LOLA Receiver FOV, as well as our allo-cated budget for allowable alignment shifts duringthe LOLA and LRO spacecraft (S/C) level environ-mental test programs. Two things to note on theseplots: (1) the pointing shift of the LOLA Laser wassmall and within allocation, and (2) the OTA bore-sight alignment error was mostly due to a changein the Receiver Telescope LOS and was near the limitof our S/C-level allocated error budget. The need to

Fig. 17. LOLA OTA initial boresite alignment: (a) Laser 1,(b) Laser 2.

Fig. 18. LOLA OTA pre- and post-vibe alignment: (a) laser, (b) boresight.


replace an electronic component in the MainElectronics Box (MEB) at the beginning of the LOLAinstrument-level thermal vacuum (TVAC) test gaveus the opportunity to reboresight the OTA.The LOLA TVAC test lasted several weeks and

included eight hot and cold cycles that encompassedLOLA’s survival and operational thermal ranges. Forthe TVAC test the LOLA OTA was fully blanketed,mounted horizontally, and pointed at the TVACchamber optical window so we could monitor thealignment of the LOLA OTA with an externalcollimator/CCD camera system. During the TVACtest the LOLA Laser was attenuated by the LaserBeam Dump (LBD), an MLA heritage optical GSEdevice that attenuates the laser without changingits pointing angle or divergence, and the beam en-closed by a tube that went all the way to the TVACchamber window to prevent scatter or ghost reflec-tions from illuminating the LOLA Receiver Tele-scope and saturating or damaging the sensitiveLOLA detectors. At the same time the ReceiverTelescope fiber optics were back-illuminated at1061nm via the Aft-Optics test ports; we did notback-illuminate at 1064nm to prevent saturatingthe LOLA detectors (1061nm is close enough toget an in-focus Receiver Telescope image in vacuum,but far enough from the LOLA bandpass filter centerwavelength to provide sufficient attenuation in theAft-Optics). Finally, an external laser source wasused to illuminate the LOLA Reference Cube suchthat we could see on the external collimator CCDa far-field image of the LOLA Laser, the LOLA Recei-ver FOV, and the LOLA Reference Cube"Z face. TheLOLA Laser pointing angle and divergence and theOTA boresight alignment were very stable duringthe course of the TVAC test. Figure 19 shows threerepresentative boresight alignment images for differ-ent portions of the LOLA TVAC test profile. Note thesmaller size of the laser far-field image when the in-strument operates in vacuum; also note that, as ex-pected, the LOLA Receiver Telescope FOV getsslightly out of focus at the 36 °C HOT Qual operatingtemperature. After completion of the TVAC test,LOLA underwent a complete functional checkoutand was delivered to LRO for integration to thespacecraft.

8. Lunar Orbiter Laser Altimeter Integration to LunarReconnaissance Orbiter

LOLA was delivered to the NASA/GSFC Lunar Re-connaissance Orbiter (LRO) spacecraft I&T teamon April 2008 and integrated onto the spacecrafton May 2008. A photo of LOLA integrated to theLRO instrument deck, and with thermal blankets in-stalled, is shown in Fig. 20. The LOLA OTA was in-tegrated to the LRO instrument deck without anyneed for active alignment (i.e., without the need toshim the three flexure interfaces) to meet our coa-lignment requirement to the Lunar ReconnaissanceOrbiter Camera (LROC) instrument. The OTA wasdesigned to meet a <5mrad perpendicularity errorrequirement between the LOLA Laser center outputbeam and the LOLA mounting plane defined by the

Fig. 19. LOLA Laser 2 TVAC boresite alignment: (a) ambient, (b) hot qual., (c) cold qual.

Fig. 20. LOLA integrated to the LRO spacecraft.


three mounting flexures. The pointing angle of theLOLA Reference Cube with respect to the LRO Mas-ter Reference Cube was measured and documented,and the pointing angle of the five transmitted LOLAlaser beams with respect to the LRO Star Trackeroptical axis was established. After the LRO HGAwith the integrated LR system was installed onLRO, the LR FOB Segment 3 wasmated to the LOLAAft-Optics CH1 LRT input port and an end-to-end LRsystem test was performed. Full functional tests ofthe LOLA and LR optical systems, including measur-ing the OTA boresight alignment and the alignmentof the LRT to the HGA reference cube, were per-formed before and after each LRO environmen-tal test.The collimator system used during LOLA I&T and

TVAC test to monitor the instrument alignment wastoo large and cumbersome to use for the LOLAS/C-level alignment tests, so the MLA-heritageLTR/Risley Target Assembly was reconfigured forLOLA use. This target includes a tube that attachesto the LOLA Laser Transmitter Telescope and fullyencloses the LOLA laser beam, the Laser BeamDump (LBD) to attenuate the laser energy, a LateralTransfer Retroreflector (LTR) to send the LOLA laserbeam back into the LOLA Receiver Telescope aper-ture, and a set of motorized Risley prisms to deviatethe retroreflected laser beam in two orthogonal axesover a !650 !rad range. The LTR is a hollow cube-corner section comprised of a flat mirror and a roofmirror assembly that translates and flips the inputlaser beam by 180°; the device is alignment insensi-tive and was manufactured by PLX Inc. to an accu-racy of <2 arcseconds (<10 !rad). The function of theLTR/Risley Target Assembly is to scan the LOLALaser far-field image across the LOLA Receiver Tele-scope focal plane in order to generate cross-sectionalplots of the receiver FOV and to determine the bore-sight error of each of the five transmitted beams withrespect to their corresponding receiver channels.Figure 21 shows the results obtained after LOLA in-tegration to LRO for the LOLA Laser 1 oscillator. Theboresight error for every channel was <11 !rad andwas obtained from the cross-sectional FOV plot cen-

ter offset; the shape of the FOV cross sections werenot top-hat, and the measured FWHM was slightlylarger than the nominal 400 !rad receiver FOV be-cause the test was conducted at ambient pressurewith both the LOLA Transmitter Telescope and theLOLA Receiver Telescope out of focus. As expected,the CH1 curve was "50% higher than the rest be-cause the laser center beam has more energy. We re-peated this test after the LRO vibration test andafter the LRO TVAC test without observing any sig-nificant shift in LOLA’s boresight alignment. Thetest was repeated one final time after the fully-integrated LRO spacecraft arrived at the Astrotechprocessing facility near the Cape Canaveral AirForce Station launch site in Florida, and LOLA’sboresight alignment was still stable and within allo-cation. We also measured no change in the alignmentof the LRT with respect to the HGA reference cubeduring the course of the LRO environmental test pro-gram and one final time at Astrotech.

9. Conclusion

This paper presented the optical system design,optical integration, and optical test results for theLOLA instrument, a multichannel laser altimeterrecently developed at NASA’s GSFC. LOLA incorpo-rates novel optical technologies such as a diffractiveoptic element to generate multiple transmitted laserbeams, a fiber-optic bundle to generate multiple re-ceiver FOVs aligned to the multiple transmitted la-ser beams, a test port on the Aft-Optics/Detectorassemblies to facilitate instrument alignment andtesting, and a laser ranging (LR) system capable ofimproving the orbit determination of LRO aroundthe Moon. LOLA instrument-level integration andtesting was completed on April 2008, and LRO space-craft-level integration and environmental testingwas completed on December 2008. During both theinstrument and the spacecraft level functional andenvironmental test programs, LOLA performed welland met all of its optical design requirements. As ofthis writing, the LRO spacecraft is undergoing finalcheckouts at the Astrotech facility in Florida. LRO is

Fig. 21. (Color online) LOLA Laser 1 S/C level boresite alignment: (a) X axis, (b) Y axis.


scheduled to launch aboard an Atlas V rocket onJune 2009 for its five day ride to the Moon.

The work presented in this paper would not havebeen possible without the contributions of manyother individuals at NASA/GSFC. In particular wewould like to thank Mr. Clarence (Sid) Johnson,Dr. Danny Krebs, Dr. Anne Marie Novo-Gradac,Dr. Anthony Yu, Dr. George Shaw, Ms. MelanieOtt, Mr. Rob Switzer, Mr. Joe Thomas, Mr. AdamMatuszeski, Mr. Keith Cleveland, Dr. Xiaoli Sun,Mr. Rob Taminelli, Mr. Jay Smith, Mr. Ron Zellar,Mr. Craig Coltharp, and Mr. Glenn Jackson.

References1. G. Chin, S. Brylow, M. Foote, J. Garvin, J. Kasper, J. Keller,

M. Litvak, I. Mitrofanov, D. Paige, K. Raney, M. Robinson,A. Sanin, D. Smith, H. Spence, P. Spudis, S. A. Stern, andM. Zuber, “Lunar Reconnaissance Orbiter overview: theinstrument suite and mission,” Space Sci. Rev. 129,391–419 (2007).

2. D. E. Smith, M. T. Zuber, G. B. Jackson, J. F. Cavanaugh,G. A. Neumann, H. Riris, X. Sun, R. S. Zellar, C. Coltharp,J. Connelly, R. B. Katz, I. Kleyner, P. Liiva, A. Matuszeski,E. Mazarico, J. F. McGarry, A. M. Novo-Gradac, M. N. Ott,C. Peters, L. A. Ramos-Izquierdo, M. H. Torrence, E. Mazarico,

J. Connelly, D. D. Rowlands, T. Zagwodzki, L. Ramsey, D. D.Rowlands, S. Schmidt, V. S. Scott III, G. B. Shaw, J. C. Smith,J.-P. Swinski, M. H. Torrence, G. Unger, A. W. Yu, and T. W.Zagwodzki, “The Lunar Orbiter Laser Altimeter investigationon the LunarOrbiter Reconnaissancemission,” Space Sci. Rev.(to be published).

3. L. Ramos-Izquierdo, V. S. Scott III, S. Schmidt, J. Britt,W. Mamakos, R. Trunzo, J. Cavanaugh, and R. Miller, “Opticalsystem design and integration of the Mercury LaserAltimeter,” Appl. Opt. 44, 1748–1760 (2005).

4. H. Riris, X. Sun, J. F. Cavanaugh, G. B. Jackson,L. Ramos-Izquierdo, D. E. Smith, and M. Zuber, “The LunarOrbiter Laser Altimeter (LOLA) on NASA’s Lunar Reconnais-sance Orbiter (LRO) Mission,” Proc. SPIE 6555, 65550I(2007).

5. A. W. Yu, A. M. Novo-Gradac, G. B. Shaw, G. Unger,L. Ramos-Izquierdo, and A. Lukemire, “The Lunar Orbiter La-ser Altimeter (LOLA) Laser Transmitter,” Proc. SPIE 6871,68710D (2008).

6. J. G. Smith, L. Ramos-Izquierdo, A. Stockham, and S. Scott,“Diffractive optics for moon topography mapping,” Proc. SPIE6223, 622304 (2006).

7. M. N. Ott, R. Switzer, R. Chuska, F. LaRocca, W. J. Thomes,and S. MacMurphy, “Development, qualification andintegration of the optical fiber array assemblies for the LunarReconnaissance Orbiter,” Proc. SPIE 7095, 70750P(2008).


Documents

Optical system design and integration of the Lunar … system design and integration of the Lunar Orbiter Laser Altimeter Luis Ramos-Izquierdo,1,* V. Stanley Scott III,2 Joseph Connelly,1