Identification CMOS Imager Applications Space Werner Ogiers IMEC,
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GSTP/ASCMSA/Integrated Radiation-tolerant Imaging System P60280-MS-RP-001
Identification CMOS Imager Applications Space
Werner Ogiers IMEC, division Kapeldreef B-3001 Leuven tel:+32.(0)16.281.376 fax:+32.(0)16.281.501 ogiers@imec.be
Identification CMOS Imager Applications Space
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name Werner Ogiers Bart Dierickx date signature
Document history record
issue date March 1997 description change evaluation version
Identification CMOS Imager Applications Space
Author: Werner Ogiers
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Table contents
Table contents Purpose Scope Related documents Abbreviations acronyms_ 1.Introduction 2.Characteristics CMOS imagers 3.Spaceborne camera system design_ 4.Applications overview_
4.1.Scientific earth observing instruments 4.2.Astrophysics instruments_10 4.3.Planetary instruments: remote imaging 4.4.Planetary instruments: near imaging, landers rovers_13 4.5.Spacecraft optical guidance navigation
4.5.1.Star trackers 4.5.2.Earth sensors 4.5.3.Short distance guidance 4.5.4.Rendezvous sensors
4.6.Spacecraft optical communication_23 4.7.Spacecraft robotics_23 4.8.Spacecraft visual telemetry 4.9.Spaceborne microgravity physics experiments 4.10.Miscellaneous
5.Conclusions
5.1.Applications requirements overview_27 5.2.Discussion recommendations 5.3.Noise 5.4.IRIS requirements preliminary specifications_34
5.4.1.Target applications 5.4.2.IRIS imager optical specifications 5.4.3.IRIS imager functional specifications 5.4.4.IRIS demonstration system outline_36
6.References_
Identification CMOS Imager Applications Space
Author: Werner Ogiers
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Purpose
This document identifies potential space applications CMOS image sensors.
Scope
This document deliverable Work Package 4100 GSTP activity Analog Silicon Compiler Mixed Signal ASICs, contract number 11970/96/NL/FM.
Related documents
P60280-MS-RP-002, Survey CMOS Imagers P60280-MS-RP-003, IRIS: CMOS Imager Camera Requirements Analysis, Preliminary Specifications Development Path
Identification CMOS Imager Applications Space
Author: Werner Ogiers
Doc. ref.: Date: Issue: Page
P60280MS-RP-01 5/3/97
Abbreviations acronyms
MFOV NFOV SFPNR WFOV active pixel sensor charged coupled device fill factor field view focal plane array medium field view modulation transfer function narrow field view near infra-red passive pixel sensor signal fixed pattern noise ratio signal noise ratio star tracker wide field view visible light spectrum
Identification CMOS Imager Applications Space
Author: Werner Ogiers
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P60280MS-RP-01 5/3/97
1.Introduction
This survey covers possible applications spaceborne CMOS cameras. applications limited conventional imaging visible light. Deep infra-red ultra-violet imagers, well spectrometers, included. areas where integrated CMOS imaging sensors seems feasible discussed somewhat more depth. From applications list desirable features specifications versatile microcamera compiled. This list will serve background against which define IRIS integrated camera system demonstrator. study then concluded with noise analysis calculating imager sensitivity relating imaging stars given visual magnitude.
2.Characteristics CMOS imagers
Image sensors based commodity digital CMOS processes have been emerging past years, mostly industrial applications. While still rivalling performance best CCDs, CMOS active pixel sensors have their properties that make them suitable plethora applications. Compared CCDs, CMOS imagers bring benefits size weight: control driving requirements CMOS focal plane arrays lower than CCD. Moreover, CMOS imagers integrated with analogue digital functions same die. This makes CMOS vision systems attractive spacecraft general miniature spacecraft distributed systems particular. power: CCDs highly capacitive devices, addition needing control voltages 15V, whereas CMOS imagers standard 3.3V power supplies. radiation hardness: CMOS imagers implemented using radiation-tolerant technologies, which protects them from proton-induced bulk defects. Further, inherent radiation hardness CMOS devices leads directly weight size savings system less radiation shielding needed. simple analogue signal conditioning: active pixel sensors typically deliver relatively high-level output signals from low-impedance nodes. versatile access image plane possible, enabling functions like windowing, subsampling, analogue pixel binning,
Identification CMOS Imager Applications Space
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windowing, direct readout scene-of-interest, yields several opportunities: higher frame rates given system bandwidth, shorter minimal integration times, simpler control: driving processor discard superfluous data, power savings, localised tracking illumination gain control present). with complex digital analogue electronics integrated, CMOS imagers made into versatile, powerful easy instruments. system integration leads higher reliability. Integration analogue electronics analogue-to-digital converters yields systems chip that highly insensitive externally induced noise interference.
Pronounced CMOS disadvantages are: lower fill factor (10-25%) when compared (50-80%). This problem leads lower photo-sensitivity. Possible solutions involve on-die microlenses advanced pixel architectures with higher effective photon collecting capabilities. standard CMOS imagers have seemingly lower quantum efficiency: typically 30-40% against best CCDs. However, CMOS process relatively simply modified allow deposition interference layer onto imager die. This layer couples incoming light better silicon, yields higher quantum efficiency, 80%, specific wavelength. disadvantageous centroiding function resulting from less than 100% fill factor complex photo-sensitive area shape. image plane non-uniformity resulting from extra circuitry active pixels. worse noise performance: commercial CCDs realise noise electrons, scientific imagers even down noise electron equivalent noise CMOS imagers ranges from 1000 electrons. electrons become possible future. higher dark current generation: dark current originates among others from impurities silicon substrate, causing non-uniformity temporal noise. processes optimised dark current, standard CMOS processes not. Dark current decreases with temperature, that cooling used when required. CMOS's currently limited performance sensitivity, noise dark current reduces global optical sensitivity compared CCDs. This turn typically requires longer exposure times same scene, limiting vision system's throughput. most integrating CMOS sensors feature line-wise integration simultaneous with line-wise readout, i.e. lines exposed scene interest mutually different times, analogous moving-blade mechanical shutter when operated high speeds.
Identification CMOS Imager Applications Space
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Frame transfer CCDs first collect scene over entire array, only after this transfer captured image readout circuits, like mechanical shutter operated slow speeds. This difference behaviour kept mind limiting some applications. CMOS developments: [11] predicts future demise favour science-grade CMOS imagers. However, feel that careful with such predictions: high-end applications, will keep lead years come because evolution CCDs stopped yet. also noted that predictions [11] based CMOS imagers obtained with carefully selected modified CMOS-processes, thereby obliterating cost portability factors that should come with CMOS imaging technology. other hand, safely expected that near future CMOS shall evolve quality level where performance-wise compete with CCDs critical applications, while adding unique benefits. sketch such imager might comprise 1024x1024 resolution, 70dB signal noise ratio, video readout rate onchip integrated control data processing.
3.Spaceborne camera system design
When assessing imagers imager applications space use, worthwhile keep following issues dependencies mind: With sensors given maximum size there trade-off between high resolution small pixel size hand, noise high sensitivity other hand. More generally said: smaller imaging pixels less sensitive, which leads higher noise floor longer exposure times. space-borne imager systems desirable have small dimensions, weight, power consumption heat generation. first means attain this have high degree integration system electronics. Moreover, highly integrated systems offer additional potential local intelligence, means digital and/or analogue processing power, which converts sensor into real sensing instrument further into versatile, possibly re-usable configurable, easy-to-interface smart sensor system. addition, compact system easier make compliant with ever-present radiation hardness demands flight standard equipment. same reason great benefit migrate hard camera system specifications towards image sensor, which tends relatively cheap silicon, rather than rely inherently costly optical and/or electromechanical means achieve given performance. Examples sensor with high Quantum Efficiency avoid complex optics, with noise dark current comply with
Identification CMOS Imager Applications Space
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specifications ambient temperatures, thus without reverting imager cooling system. However, trade-off always easy. example, problem focusing imager solved with active even automatic focusing low-f optics, with high-f, large depth view optics. latter option simpler smaller, goes expense optics transmittance, calling more sensitive imager leading lower SNR. [43] offers intriguing solution: pushbroom scanning performed with linear arrays. Each array offset from others mounted different focal distance from optics. means external control array that momentarily focus selected read. Generally, high sensitivity implies highly transmittant optics. Such system then susceptible damage from high light intensities, e.g. originating from direct light. solution mechanical electrical (LCD) shutter hood, associated control system, protect imager when necessary. This violate general requirements mass, complexity high reliability space use. called electronic shutters present some imager chips control amount electrons generated incoming photons pixel. However, they offer protection against thermal damage extraneous exposure. With increasing integration systems onto silicon, other system parts gain dimensional importance, sometimes quite proportion their task. Examples passive components, seemingly auxiliary functions (voltage regulators, clock generators, line drivers, optical interfaces,.), component packages interconnection structures. clear that further research into methods full system integration into high density packaging techniques will necessary towards future ([6],[33],[41]) With scientific instruments proliferating, ever producing more data, spacecraftearth communications bandwidth bound become major bottleneck. Intelligent instruments, sensors subsystems (navigation) that their data pre-processing, needing only communication evaluated, interpreted data, will become necessity. Likewise, spacecraft subsystems should evolve towards larger degree autonomy. Where possible, science instruments should combined into single multifunctional instruments, into custom modules that make shared resources control, processing, communication, Combined scientific imagers optical navigation systems fine example here. these cases, highly integrated systems comprising CMOS sensors processors useful. reliability camera systems mostly dominated actual sensor, driving electronics their interfaces. redundancy scheme where multiple sensor/electronics pairs share optics does seem feasible miniature system optics electronics tend closely highly integrated. Alternatively, cameras being dimensionally compact lightweight, full redundancy obtained only small cost. Partial redundancy higher versatility with almost-identical
Identification CMOS Imager Applications Space
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imaging systems. differences between camera systems chosen that they global system's functionality, without jeopardising initial backup function second camera. Examples such differences field view, viewing direction: [33] proposes having sensors, each with slightly different orientation, that least both always free from blinding. savings dimensions, weight power consumption inherent integrated CMOS imaging systems make them extremely well suited board micro spacecraft. such spacecraft cheaper, they will tend used larger numbers than conventional craft. This again calls more autonomous flights, ground stations proving considerable burden. Again, integrated multi-functional CMOS systems with local intelligence will provide necessary building blocks such craft.
4.Applications overview
4.1.Scientific earth observing instruments Imagers earth observing purposes require high optical qualities such very large array sizes, noise, high dynamic range colour multi-spectral banded vision (either with external filters with on-chip filters). addition normal image capturing visible spectrum, photonic spectrometer systems also used. latter case, very expected illumination levels (due either dispersion optical input signal over multiple pixels passage through narrow band filter) spectral contents sensor require imagers with extremely noise wide response bandwidth, typically from near infrared near Propulsion reports mass spectrometers charge detectors based existing CMOS imager architectures. envisage that short term CMOS sensors will meet requirements high-quality earth imaging, thus compete with conventionally used CCDs. Moreover, need highly-integrated imaging systems felt less severely large earth monitoring satellites than microsatellites deep-space craft. CMOS cameras suited lower-end earth imaging, where almost same conditions planetary imaging hold. 4.2.Astrophysics instruments Astrophysical optical sensors such space telescopes spectroscopic instruments demand high-end performance from their imaging parts. Dynamic range must large, with associated minimal noise. Imager sizes resolution must huge megapixels, with pitches small 5µm). example 9kx7k scientific recently reported ([35]). Imagers limited visible spectrum only used spaceborne
Identification CMOS Imager Applications Space
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telescopes. ground based systems requires wider bandwidth well into UVzone, relative opacity earth atmosphere. CMOS imagers compete here time come. Typically, scientific CCDs most certainly have lower noise floors (down noise electron versus electrons with CMOS) till have larger formats (9kx7k versus 2kx2k). Scientific CCDs highly specialised niche technology that will likely addressed CMOS developments, latter essentially driven telecommunications industrial consumer markets. 4.3.Planetary instruments: remote imaging Planetary imaging atmospheric surface studies required exploratory missions, fly-by missions lander ground exploration missions (see later). Both spectrometer instruments (see Earth Observing Instruments) conventional imagers used. normal imaging, trade-off needed between image resolution available communication bandwidth. hand this calls medium size imagers pixels), other hand this clear case where local image compression windowing capacities wished for. high effective dynamic range sensor desired, implemented pixel architecture itself with logarithmic response pixels) electronic shuttering (integrating pixels), eliminate needs mechanical shutter resulting impact mass, system complexity reliability). Colour multispectral imagers useful certain applications. fly-by missions high speed spacecraft relative target (asteroids, requires high readout rates short exposure times avoid visible blurring image taken. This then calls lownoise, highly sensitive imagers cases where high illumination levels present. [32] states that attitude stability limiting factor with imaging micro satellites. Without sub-degree attitude control, swath scanning pushbroom image systems preserve scene geometry. this reason, electronic cameras that capture whole scene once, i.e. sufficiently small exposure time, must used overcome this ownmotion problem. However, reducing exposure time reduces imager's sensitivity. Table lists specifications implementation issues some recent future planet imaging systems.
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Mission
Mars Surveyor Orbiter Colour Imagers
Clementine Multi-Spectral Scientific Camera
Clementine High Resolution UV/VIS/NIR Camera
Near Earth Asteroid Rendezvous Flyby MultiSpectral Camera
Galileo High Resolution Multi-Spectral Scientific Camera
Dimensions (cm) Mass (kg) Power Optics (degrees) Format (pixels) Digitisation (bits) Frame (Hz) Imager rate
6x6x12
90x30x25
6x6, 140x140 1000x1000
0.41 4.65 4.2x5.6 384x288
0.4x0.3 384x288
f/3.4 2.9x2.25 574x244
0.5x0.5 800x800
(non-linear)
(non-linear)
interline CCD, 30-30000
frame transfer
frame transfer
(dB) Dynamic range (e-) Spectrum (nm) Comments
250-1000
400-1100
300-1100
400-1100
400-1100
offset gain control, DSP+ASIC, image correction, windowing
offset gain control
variable integration time 25µs-1s
embedded 1802 processor, mechanical shutter
table overview planetary imagers
Identification CMOS Imager Applications Space
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cross-section these specifications suggests these requirements usable small CMOS APS-based planet imaging camera: format: 512x512 1024x1024 dynamic range: high possible, either linear, analoguely compressed gain/offset converted with least bits effective signal noise dynamic window with bits effective dynamic range spectral response: visible area, preferably near-IR near-UV well. On-die colour filters useful, multi-spectral bands required mission enables (using pushbroom scanning) electronic shutter local control, windowing, interfaces serial lines local processors data processing and/or compression.
4.4.Planetary instruments: near imaging, landers rovers addition requirements flown planetary imagers, limited mass budget available rovers landers stresses importance miniaturisation integration imager systems. Lander cameras used assistance with landing, i.e. landing site selection navigation during descent. They also serve scientific purposes such panoramic views, close range views, macro/microscopy (the latter perhaps with lightweight camera head mounted deployment device). this would require several cameras, each with dedicated optics task hand, this stresses even more need drastic miniaturisation. example, Marsnet programme, three cameras specified Mars lander: panoramic camera: degrees FOV, colour, optional stereo vision, high-resolution, 1.6kg descent imager: taking nested images, 0.2kg close-up imager: mounted instrument-deployment device, 0.3kg
give more detailed idea lander imager requirements, specifications Mars Surveyor Lander Descent Imager given: Mission: Mars Surveyor Lander Descent Imager Dimensions (cm): 5x5x10
Identification CMOS Imager Applications Space
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Mass (kg): 0.42 Power (W): (degrees): 73x73 Format (pixels): 1024x1024 Frame rate (Hz): 0.5, limited 1Mb/s data link Imager: interline CCD, (dB): 60dB Dynamic range (e-): 30-30000 Spectrum (nm): 500-800 Comments: exposure time 250µs, limited lander's motion-induced smear, acquisition nested images during descent, offset gain control: dynamic range effectively, 56166 control moderate data compression
Next scientific planet surface exploration imagers good rovers automatic vehicle guidance, such tasks navigation, crash prediction, ranging. Various techniques developed robotics industry used, possibly combined with custom camera topologies (stereo vision obstacle detection, addition, many spacecraft applications imagers apply another lander systems too. [12] Describes novel optical radar terrain scanner comprising moving parts, rather based modulated flood illumination scene, synchronised with intensified imager. NASA acknowledges that potential applications this device plenty, including terrain observation during landing, obstacle collision detection rover robots, craft manoeuvring docking, robot manipulator control. Future improvements device will concentrate resolutions beyond pixels square, multi-spectral scanning CMOS imager arrays. [17] recognises stereovision based vision systems during tasks identification orientation position determination man-made objects surroundings, including surface mapping during remote sensing planets landing site selection along scientific safety-related criteria surface-relative navigation, hazard avoidance, during landing
Identification CMOS Imager Applications Space
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in-situ operations lander (drilling, sample acquisition, rover path planning, navigation, hazard avoidance
4.5.Spacecraft optical guidance navigation optical navigation, position attitude determination well trajectory guidance spacecraft based optical information stellar objects, gathered through imagers. states that purely optical navigation, while perhaps having less accuracy than other methods, sufficient number cases, most certainly closer concept autonomous guidance necessary processing data output optical system less intensive than that conventional systems that make Doppler ranging radio data types. Moreover, optical instruments tend less complex more reliable than inertial sensors such gyroscopes ([33]). With tendency towards rigidly mounted science instruments enhanced reliability dimensional savings pointing instruments tracking scientific subjects will become application field where craft's attitude control system use. Even with non-rigidly mounted instruments, conventional optical trackers used find track instrument's subject, thereby freeing instrument system itself from doing conventional classification stellar objects would distinguish star trackers proper, extended body trackers, feature trackers earth/sun sensors. these have their properties, although there motion towards combining their functionalities into versatile compact instruments, informally named celestial trackers. Current research into future celestial trackers concentrated Propulsion ([1], [2], [4]) ("Attitude Sensor Concepts Small Satellites", consortium headed Sira, [33]). 4.5.1.Star trackers 4.5.1.1.Applications generally, star trackers acquire star field patterns determine spacecraft position attitude. Viewed hardware level, star trackers comprise optics, imager data processing subsystem. Their functionality, star sensing position/attitude determination, almost wholly defined system's software. With different processing, functions become possible, making celestial tracker into versatile sensor following applications ([10],[11],[13],[19]):
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detection tracking stellar objects (stars, earth, sun, moon, planets, asteroids, navigation, including fully autonomous spacecraft guidance. detection tracking non-stellar objects rendezvous docking. object surface tracking feature extraction docking landing. tracking science instrument pointing guidance. topographical analysis extended stellar bodies autonomous determination scientifically relevant areas. communication link pointing. double scientific camera. tracking spacecraft-ejected pellets gravitational field mass estimation objects.
According [13], navigational task during typical deep space mission broken down into phases, each having their requirements with regards celestial imager, that ideal tracker accomodates these phases: post-launch attitude determination, with tracking extended objects such earth sun, well bright stars. navigational phase, tracking stars local (faint) objects, such asteroids. encounter phase, using normal star fields well target itself approach.
[19] pictures autonomous spacecraft relying versatile system named AFAST (Autonomous Feature Star Tracker). AFAST uses knowledge solar system bodies capabilities navigate spaceship through departure, cruise, encounter actual scientific mission, without intervention from ground station. part AFAST should general purpose celestial scene interpretation system, useful applications mentioned above. article states that eventually optical AFAST systems will replace other means navigation. 4.5.1.2.Application-specific requirements
System integration
spacecraft dimensions tend grow smaller, traditional attitude sensors star trackers unwieldy expensive. Therefore radically high degree integration called
Identification CMOS Imager Applications Space
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future trackers, bearing mind that reduction size, weight power beneficial conventional space ship well. [33] states requirements generation celestial trackers: lower volume mass, smaller satellites higher level intelligence, autonomy greater survivability (radiation, thermal) greater producibility, lower cost greater versatility, multifunctionality faster update rates. When these requirements complied with, resulting optical tracker will performant enough replace conventional navigation sensor.
Optical constraints
requirements posed sensors such generation trackers driven from demands involved with imaging objects ranging from faint asteroids stars itself. These images then subject operations such sub-pixel centroiding, parallax measurement feature extraction. Sensitivity: When imaging star fields, expected differences between intensity stars interest amount orders magnitude visual magnitudes), centered around stars faint magnitude Moreover, when closer celestial bodies have tracked too, sensor's dynamic range, saturation level noise limit have cope with direct illumination from simultaneous with dimly asteroids others. practice, this requires high performance imager field temporal noise (which determines sensitivity) well static noise (non-uniformity dark current). Optics: Imaging faint point sources requires fast narrow field view optics, while imaging feature tracking extended objects, well quick finding smaller ones, asks medium- wide-sized field view.[11] states that modern star trackers have evolved towards using WFOV optics, enabling them used feature trackers extended objects well. other hand, WFOV tracker algorithms then limited stars brighter than while wide field view makes impossible tracker feature imaging very nearby objects. found that combination WFOV star tracker with co-aligned NFOV scientific camera, with shared control, ideal. tracker imager used conventional attitude position determination, well rough identification feature extraction
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subjects case subject hasn't been studied great detail before, thus contributing autonomy craft) pointing NFOV scientific camera. latter then completely free major job: gathering scientific data. [13] then concludes that such coupled NFOV/wide-aperture scientific camera alternatively double dedicated tracker faint objects such asteroids 6-13 stars. Likewise, [19] proposes two-camera system with faint star tracker having degree, using imagers 512x512 1024x1024 pixels, system sensitivity down imaging tracking extended objects, widened degrees, with same type imager sensitivity objects down When double imager system wanted possible, both sets requirements reconciled degrees tracker with sensitivity. Fill Factor: Precise centroiding parallax measurement star fields requires good modulation transfer function sensor potentially well-known controlled intra-pixel behaviour too, when sub-pixel centroiding attempted: while frame-transfer CCDs feature optical fill factor 100%, photosensitive area CMOS imagers smaller than nominal area pixel. Even more, with outline that sensitive area often being quite irregular, pixel's behaviour highly geometrydependent probably even isotropic. compensate pixel geometry interfering with successful centroiding very high imager resolution used. high relative resolution always beneficial these precision measurements; implemented with very high imager array size and/or narrow field view. Postprocessing compensation based known pixel geometry might feasible too, adds system complexity. lower accuracy centroiding with CMOS imager sufficient simply de-focus optics, that each star generates smeared image over several pixels ([13]). Readout Speed: During attitude sensing based close objects opposed remote star fields) during target edge detection feature extraction, high relative speeds between spacecraft bodies encountered. prevent blurring images, short capture times mandatory. photovoltaic sensitivity most imagers proportional effective exposure time, this will eventually limit faintest objects that distinguished. (Note, however, that star tracking algorithms have been reported that take blurring into account that even make it.) This limit gains even more importance light current move towards greater purely optical navigational sensors, with eventual purpose fully replace conventional inertial sensors such gyroscopes. This drives need fast recovery star sensors that outclass inertial sensors. Normally this would require image position update rates 30Hz, figure that attainable this moment. compromise, combination 10Hz optical navigation sensor with low-cost inertial sensor high-speed slewing deemed useful temporal solution ([33]).
Identification CMOS Imager Applications Space
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Applicability CMOS imagers
following properties CMOS imagers relevant celestial tracking systems. integration imager application-specific programmable data processors low-power technology necessity obtain compact versatile star trackers. result, global reliability particularly radiation hardness will improved too. Most CMOS imagers have fill factor that inferior that frame transfer (1030% versus 80%). obtain higher photonic sensitivities facilitate centroiding this fill-factor should improved upon. Strategies this exist, namely integrated microlenses development advanced pixel architectures with higher effective fill factor. imaging objects with wide range brightness against essentially dark background, variable exposure times (integration times) needed. short exposure required properly image bright objects, else they would saturate imager even make bloom. long integration required image faint stars. CMOS imagers easily made blooming-tolerant, while implementation variable integration times (also known electronic shuttering) straightforward. Imaging scene with vastly different subject brightnesses made possible. This would require more exposures with different settings, followed post processing correlate images. describes CMOS imager with so-called regional exposure control non-destructive readout: each area image periodically read under processor control until locally attained signal noise ratio sufficient hand. This scheme even enhances system's data collection autonomy, a-priori knowledge object brightness needed. CMOS regional electronic shuttering optimal exposures from first time around. opposed CCDs, CMOS imagers made with support windowing (areaof-interest readout) subsampling. Some architectures even allow random access space time. These properties largely speed image acquisition once applicationrelevant areas total field view known. possible found fastrecovering star trackers, where once necessary stars have been tracked down, they followed attitudes quickly updated simply fast readout small windows around these stars. main problem with using CMOS active pixel sensors celestial tracking purposes lower sensitivity, resulting from noise, fixed pattern offset dark current. These problems should addressed carefully design CMOS star tracker. Temporal noise should minimised, while remaining non-uniformity pixel level should below that noise floor.
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Specifications existing future celestial trackers
Mission/ Type [14] HD-1003 ([15]) NEAR ([16]) NASA FY94 Pluto Flyby ([18]) sole attitude control system NASA Deep Space ([9]) Oersted Satellite Tracker ([10]) WFOV science camera Cherenkov detector 22x16 0.29 30x40 Clementine ([22])
Application
antenna pointing
commercial
attitude control, instrument pointing
Mass (kg) Power (degrees) Imager
interline
Format (pixels) Cooling Sensitivity Quantisation (bits) Update rate (Hz) Noise (e-) Comments
1000x510
512x512
1025x512
1024x1024
576x384
-25°C
10°C
trackers, mechanical windowing, integration time 0.0625-2s, self-test
tracks stars
tracks stars
local filtering, frame buffer, windowing buffer
motion compensation software, integration time 100s
recalibrates radiation degradation
90+60
table specifications modern star trackers
Identification CMOS Imager Applications Space
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listed systems CCDs, many with cooling. Most them have sensitivities around with relatively high update rates: 5-10Hz. Note very long integration time high-sensitivity (M=13) tracker. After survey more than current systems under development, many them aimed small satellite applications, company Sira comes following `average' requirements generation tracker ([33]): FOV: 15x20 degrees format: 576x770 pixels pitch: lens: 51mm update rate: 10Hz sensitivity: accuracy: arcsec arcminute
preliminary requirements specifications celestial tracker developed under ASCoSS/CETS programme ([33]) then: format (pixels): 256x256 pixel pitch (µm): 25x25 smaller) architecture: integrating transistor CMOS scanning: sequential only, optional windowing frame rate: 5-10 imager power dissipation: 50mW signal saturation level: 100000e-, noise level: <400e-, <4mV ADC: bits imager non-uniformity: 50mV saturation
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offset correction: off-chip subtraction dark current induced offsets, dark current reduction cooling, in-flight monitoring substrate radiation damage recalibration effective fill factor: >15% spectral range: 400-900nm electronic shutter: (frame time frame time/256) antiblooming: optics: 20x20 degrees FOV, f/1.2 system interface: RS-422 system functionality: completely integrated miniature celestial tracker, with remote cooledimager head system implementation: Multi Chip Module system dimensions: specified, presumably around 6x6x6cm, excluding baffle
4.5.2.Earth sensors Visible-light earth sensors seen particular cases extended object celestial trackers. Deep infra-red earth sensors require their PtSi-technology which compatible with standard CMOS imagers. 4.5.3.Short distance guidance scannerless terrain mapper described [12] used during spacecraft docking manoeuvring single-ended ranging position/attitude determination instrument. double-ended instrument described [24], comprising target with retroreflectors sensing device with lasers actively illuminating target. conventional video camera plus frame grabber used image capture. system operates range, rendering whole insensitive visible-light background illumination levels, rate frames second. proved useful docking operations from 0.5m distances.
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4.5.4.Rendezvous sensors Visual navigation during approach rendezvous between spacecraft between spacecraft celestial object boils down tracking extended objects. Therefore rendezvous problem solved with sensors that essentially identical WFOV celestial trackers. important note here that WFOV trackers enable navigation system simultaneously image subject rendezvous, approach planning, number attitude reference stars, thereby avoiding periodical re-orientation craft attitude verification([36]). 4.6.Spacecraft optical communication future high-speed optical communication systems between spacecraft, communications terminal tasks optical sensors. first obviously capturing incoming data stream. second task comprises detection remote craft, using wide field view optical sensor, evaluation position smaller FOV, pointing actual communication instruments, and, during communication, tracking incoming beam remote station.[37] describes prototype such system, based 256x256 imager. worth note here that article prescribes refresh rate 500Hz during positional tracking. Other proposals such systems have full frame rate 40Hz, subwindow rate going 4kHz. CMOS imager with high-speed windowed readout extremely suited this task, although should noted that this reduces available exposure time range 2000 tracking based actual communications beam laser beacons, then inherent bloomingtolerant architectures some CMOS imagers advantage. laser wavelengths currently situated near infra red, usable response down 900-1000nm necessary. on-chip integration high-speed optical receiver tracking imager possible, from electronics point view using splitting optics. [42] describes 180MHz CMOS-compatible optical receiver based binary active pixel with 15µx15µ sensitive area. 4.7.Spacecraft robotics Applications vision systems space robotics numerous. First, camera-based systems could used position motion determination robotic members, such space shuttle's large robotic service arm. Such measurement system then used part motion feedback arm's control loop. Second, multiple videocameras mounted robot arm, hand head used visual feedback reality control systems. Specific requirements camera used such control loops high frame rate latency.
Identification CMOS Imager Applications Space
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more complex vision system based this approach could attribute robot autonomy, being position motion sensing objects manipulate. this then local robotics well e.g. approach satellites satellite subsystems geostationary servicing vehicle. Above applications vision systems solving general problem identification, position attitude sensing objects reference frame final end-effector guidance robotic arms robots themselves. While there some similarities with rendezvous sensors, active and/or passive targets, well stereovision, used here. [29] describes NASA's plans autonomous free flying camera platform monitoring extra-vehicular robotic activities space, rationale being want more flexible views such operations than provided fixed, baseline cameras. helps cutting down crew EVA, requirements posed baseline cameras expansion robotic operations. mass: 45-90kg teleoperated autonomous flight close proximity shuttle station transmission life video images.[43] describes similar system miniature implementation. imager format 2kx2k pixels proposed order high quality full coverage craft under scrutiny little possible exposures, this minimising amount necessary manoeuvring fuel consumption autonomous camera.
Additional tasks dedicated vision systems found safety automatic collision avoidance, researched European Esprit project VISTA. CMOS imagers robotic tasks, image resolution noise levels sufficient computer vision. small distributed cameras entire vision systems facilitated CMOS's small dimensions, system integration power. Crash detection sensors other custom optical systems readily made CMOS imager technology. control robotic arms requires high frame processing rate 30Hz), windowing subsampling CMOS imagers, potentially with integrated preprocessing logic focal plane intelligence called smart-sensors), obvious choices. noted that industrial vision robotics among most important driving forces behind development terrestrial CMOS imagers. 4.8.Spacecraft visual telemetry Visual inspection spacecraft conditions that otherwise only indirectly, often ambiguously, inferred (e.g. switches) useful application. Examples are:
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orientation verification attitude sensing subassemblies, e.g. deployment antennae solar panels, verification positional state covers, resonance analysis susceptible structures during deployment motions spacecraft, surface degradation monitoring temperature monitoring characterisation thruster plumes engine exhausts (IR) measurement alignment and/or thermally-induced distortions craft parts.
Visual verification assembly states visual measurements distortion only require static images, while analysis motion vibrations calls either high image rates, lower image rates with interleaving static images with long exposure times provoke blurring effect). Surface monitoring alignment measurement require higher resolutions close views subject hand. Pixel response visible band sufficient, except temperature measurement plume characterisation, where bandwidth extending near-IR needed. describes system measuring distortion alignment large antennas. uses cameras with 2048 2048 pixels optically active target obtain accuracies range from distance from 4.5m object. ESA's Visual Telemetry System ([39],[40],[41]) uses continuous time CMOS imager obtain 512x512 images rate frame second. purpose deployment monitoring solar panels antennas. system distributed, with centralised DSP-based unit control remote cameras, interfacing spacecraft JPEG image compression. camera units have on-chip ADCs well local logic static noise suppression, windowing interleaving. Further specifications camera modules are: imager: IMEC Fuga random access format: 512x512 lens: WFOV, quantisation: greyscale optical range: decades, log-compressed, bloom-free SNR: 43dB spectral response: 550-750nm size: 51x58x68mm
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weight: 180g power: 130mA interface: 3.125Mb/s duplex serial line, electrical RS-422
telemetry imagers used distributed fashion spacecraft, these further specifications arise: high degree miniaturisation power consumption resistant very harsh environments (mechanically, thermally radiation) immune direct sunlight simple standardised interface protocol easy connection host computer spacecraft, e.g. using electrical optical serial lines high degree local intelligence, possibly even including local data compression when high image rates used.
With telemetry imager evolving into small intelligent system with high autonomy, inclusion extra analogue inputs local ADC, local health monitoring such temperature, extra digital analogue outputs, control local devices such tilt motors, light sources other, non-camera related components, into telemetry architecture seem worthwhile. intelligent imager already rather high complexity deals with high data rates, these options imply much extra burden cost. Taking camera flexibility autonomy even further, versatile monitoring camera systems become feasible. [30] describes automated system performing visual surface inspection remote space platforms. system scans across object's surface detect report flaws. Flaws caused collisions with micro-meteorites debris, degradation environmental harshness, assembly mismatches, .Differencing finding flaws requires that sensor noise performance good well-known. Tele-operation wished, while artificial illumination background illumination compensation necessary. Electronic shuttering synchronisation with strobing illuminator needed here. system mentioned here bears some resemblance free flying camera platform described earlier. CMOS imagers very well suited general purpose visual telemetry their inherent ruggedness, small size weight local control options.
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4.9.Spaceborne microgravity physics experiments Imagers used photogrammetric fluid physics experiments, replacing standard film-based cameras, thus enabling real telemetry such experiments. High resolution needed, together with image rates frames second [32].Likewise, cameras useful motion analysis human beings zero-gravity conditions, well possibly other life sciences disciplines. 4.10.Miscellaneous [31] describes versatile camera that performs pan, tilt, zoom rotation images without moving parts. system comprises hemispherical fish-eye lens, imager powerful on-board processing compensate lens distortion perform mentioned camera functions, rendering output from `virtual camera'. Such system useful where moving camera used, e.g. because possible obstruction. CMOS-technology suited such system because promised integration processors.
5.Conclusions
5.1.Applications requirements overview Table gives overview discussed applications their particular requirements with regards cameras.
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applications list
legend
scientific earth observing
non-critical
astrophysics
desirable, useful
planetary imaging
critical, required
landers rovers
optical navigation
optical communications
robotics
telemetry
physics experiments
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application format fill factor spectral response sensitivity/noise frame rate windowing subsampling focal plane intelligence electronic shutter local control/DP dimensions power
2048
1024
table applications' requirements overview
During specification IRIS imager, requirements common most applications (namely 1,3,4,5,7,8) will taken into account. Useful camera functionality will added, long does increase total imager complexity much jeopardise success imager development. 5.2.Discussion recommendations following paragraphs shall discuss several specifications features with regards listed applications. requirements that common great number applications will outlined, with specific purpose attaining baseline specification demonstration general purpose microcamera space use.
format
imager format between 1024 pixels square desirable. maximum imager size limited lithographic process desired pixel sensitivity.
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fill factor
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CMOS imagers attain fill factors range, depending amount in-pixel electronics. applications where precise knowledge inter-pixel optical behaviour required, such centroiding, this extracted from layout geometry from modulation transfer function (MTF) measurements.
spectral response
imager's spectral reference essentially constant standard CMOS silicon process, i.e. 400-1000nm. Outside NIR-VIS-NUV bands, special, non-standard processes used extend CMOS imager's bandwidth.
sensitivity, noise, static non-uniformity dark current
With applications such star trackers scientific imaging imager's absolute sensitivity noise behaviour paramount importance. star tracker, acceptable minimum sensitivity would capability imaging star visual magnitude with small-size optics within reasonable exposure time second shorter. This will used yardstick when further specifying microcamera demonstrator. Sensitivity function imager's base noise total light-capturing area pixel. Generally, large pixel area (fill factor) with underlying storage capacitance advantageous eventual photovoltaic sensitivity. importance fill factor clear, once more, active pixels have limited fill factor their very nature, high sensitivity implying large pixel and/or little in-pixel processing. temporal noise attained careful design correlated double sampling. latter, however, only possible with integrating imagers requires storage either reset signal level individual pixels. This done imager itself, using single-CCD-like pixel architecture [4], expense carefully selected modified CMOS process. Alternatively, off-chip possible, using external processor frame memory, solution (yet) suited highly integrated two-chip system. Note that stochastic nature dark current also contributes temporal noise, possibly requiring cooling certain applications. Imager non-uniformity dark current-induced fixed pattern noise have compensated with most applications. With continuous time random access imagers, only feasible off-chip storage subtraction reference background image. With integrating imagers, correlated double sampling double sampling able suppress normal non-uniformities. Non-uniformities caused dark current generation removed these processes. this case, post processing background image subtraction needed.
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on-chip requires complex pixel architecture, suggest only on-chip applications where system dimensions integration important. other hand, applications where limited amount remaining fixed pattern offset allowed, i.e. where total compensation non-uniformities dark current nonuniformities demanded, propose combination both off-chip reference background pattern subtraction. Thus microcamera demonstrator, preferred solution single chip integrating imager with on-chip lacking external compensation components. With regards imager dynamic range saturation levels, noted that continuous time imagers made with in-built logarithmic compression, effectively coding decades light intensity differences into logarithmic voltage output scale. While such behaviour crude scientific purposes, useful non-critical applications such telemetry, benefit that exposure control needed all. other hand, (more limited) dynamic window integrating imagers controlled electronic shuttering (a.k.a. variable integration time).
frame rate
imager frame pixel rate essentially design parameter, limited speed on-chip amplifiers and/or analogue digital convertor. requirements speed star trackers robotics: order cope with high update speeds trackers control systems, well with video images telepresence, frame rates 30Hz desirable. using windowing, even higher (sub)frame rates attained. However, high frame rates always expense exposure time thus sensitivity.
windowing subsampling
Windowing subsampling useful many applications, they allow faster interaction with data processing unit lower amounts data transferred. Both features straightforward continuous time imagers. reverse true with integrating imagers: windowing subsampling possible, with some limitations. This situation somewhat unlucky, especially star trackers, imager technology featuring pure random access suffers from lower noise performance, vice versa. Analogue-domain subsampling (pixel binning) preferred, serious impact pixel architecture. microcamera demonstrator, propose limited windowing digital subsampling capabilities.
focal plane intelligence
Inclusion (analogue) signal processing circuitry, either in-pixel, on-chip implicitly imager's geometry possible with CMOS. However, such solution would very application-specific, like time-to-crash detection robotics, tile centroiding star trackers. generic demonstrator, such intelligence will built into FPA.
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electronic shutter
Electronic shuttering adapts integrating imager's exposure time illumination conditions scene hand. Such variable integration time design option that built into imager's architecture. Integration times smaller than inverse frame rate (but equal multiple line scan time) require specific control structures signals. Integration times longer than standard frame rate require lowering system's pixel clock frequency, leading smaller frame rate. microcamera demonstrator will feature both types integration time control. imaging scenes with wide dynamic contrast with unknown illumination suggest take exposures, with long time, other with short time, correlate resulting images.
local control processing
Local control easy interfacing with signal processors spacecraft required applications, more since this prime advantages CMOS imagers. Other useful camera functionality comprises extra analogue digital input-output facilities, used local (distributed) telemetry control peripherals. More specific data processing such data compression feature extraction useful applications like lander rover cameras, star trackers machine vision. Their integration imager-die feasible, will pursued demonstrator, whose local intelligence will limited versatile interfacing high-level control windowing subsampling.
dimensions power
System dimensions power important spaceborne applications. demonstrator minimum-size system will chosen, essentially leading one-chip vision system. power attained operating imager frame rates, this compatible with some applications. 5.3.Noise application fields chosen micro camera demonstrator, celestial trackers pose most stringent requirements with regards imager sensitivity noise.
Imager noise levels
prescribes minimal signal noise ratio successful centroiding star field images. This will baseline calculation imager sensitivity requirements star trackers visual magnitudes brighter. number photons emitted point source object visual magnitude
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10-(Mx2/5) 5x1010
number signal electrons induced imaging device's pixel are: Ne,s (spread) quantum efficiency. fill factor, pixel's light sensitive fraction area. spread: number pixels incoming light focused Taking, example 1cm2, 30%, 80%, spread reasonably realistic situation compact CMOS imager, amount signal electrons generated star would Ne,s,5 3000 e-/s total amount noise electrons permissible successful further processing would then based SNR=10: Ne,n,5 Ne,s,5 eSo, camera having total noise contribution electrons capable imaging star with integration time second. different integration times, same system's sensitivity would (always keeping mind that generation dark current electrons puts practical limit integration time, case uncooled CMOS imagers this amounts seconds maximum): electrons/second
10.0
table sensitivity function integration time 300e- noise imager
Imager requirements
noted that photon counting instruments have uncertainty their photoconversion process equal square root number generated electrons (so-called photon shot noise). linear encoding imager's full dynamic range therefore wasteful. Non-linear compression, carried analogue domain, automatic externally controlled gain-riding analogue gain stages preceding enables more efficient cheap convertors.
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5.4.IRIS requirements preliminary specifications following paragraphs preliminary requirements expected specifications I(ntegrated) R(adiation tolerant) I(maging) S(ystem) under development GSTPASCMSA framework given. 5.4.1.Target applications purpose IRIS project develop integrated CMOS imager chip with enough versatility used several spaceborne applications, notably planetary imaging, landers rovers, navigational sensors, robotics, visual telemetry. During specification development phases, main emphasis will implementation minimally-sized integrated (one-chip) image system. actual sensor performance must meet certain criteria, some aspects here sacrificed favour miniaturisation. More concrete, clear that resulting noise behaviour preclude sensor from being used high performance attitude sensor. This major deficiency, miniature attitude sensors already covered more detail another research project ([33]). 5.4.2.IRIS imager optical specifications
process characteristics
0.7µm Mietec digital CMOS radiation hardness: will assessed under GSTP/ASCMSA/WP1200 1400.
electro-optical characteristics
integrating active pixel sensor format: pitch: 12-15µ fill factor: ~80%, using proprietary technique noise: 2mV, 400e- worst case internal saturation level: 100000eanalogue domain SNR: 54dB worst case
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dark current generation (25°C): ~40000e-/s maximum exposure time: ~2-3s peak quantum efficiency: fixed pattern noise: limited on-chip Double Sampling correction, resulting nonuniformity saturation level optical bandwidth: 400-1000nm pixel rate: 10Hz, 2.6Mps power: 17mA ADC, 13mA 1MHz
5.4.3.IRIS imager functional specifications readout mechanism: frame scan, non-destructive readout possible windowing, with restrictions subsampling, with restrictions variable integration time with electronic shutter on-chip ADC, effectively user-controllable gain digital interfaces: serial command serial data out, parallel data out, formats discussed with ESTEC analogue output with sample hold external analogue inputs local
5.4.4.IRIS demonstration system outline During first phase project, IRIS imager without on-chip timing control logic will made. controller will implemented externally, using Xilinx XC4000series FPGA. second phase, controller will migrated onto imager chip, evaluation first imager been successful.
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both phases demonstrator microcameras will built, allowing testing evaluation IRIS features. These microcameras will small possible, while still using off-the-shelf commercial components processes.
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6.References
E.R.Fossum, "Assessment Image Sensor Technology Future NASA Missions", SPIE vol.2172, 1994 E.R.Fossum, R.K.Bartman, A.R.Eisenman, "Application Active Pixel Sensor Concept Guidance Navigation", SPIE vol.1949, 1993 C.C.Clark, A.Eisenman, S.Udomkesmalee, E.F.Tubbs, "Application Technology Future Celestial Trackers", SPIE vol.2466, 1995 O.Yadid-Precht, C.Clark, B.Pain, C.Staller, E.Fossum, "Wide Dynamic Range Star Tracker", SPIE vol.2654, 1996 R.J.Durrant, R.J.Flower, R.K.Child, "Feasibility Assessment Spacecraft Monitoring Camera", British Aerospace Space Systems report TR0093, 1994 A.Martinez Aragon, "Future Applications Micro/Nano-Technologies Space Systems", ESTEC/TD/SPD/SSD J.Becker, L.Gatti, H.G.Maas M.Virant, "Three-Dimensional Photogrammetric Particle-Tracking Velocimetry", ESTEC/Instrumentation Division R.Garcia Pietro, G.A.E.Crone, D.Scheulen, K.Priesett, S.Manhart, D.Brian, "Active Compensation Techniques Spacecraft Antennas. Part Measurement Correction Distortion", ESTEC/Structure Mechanics Division S.Bhaskaran, J.E.Riedel, S.P.Synnot, "Autonomous Interplanetary Missions", SPIE vol.2810, 1996 Optical Navigation
[10] J.L.Joergensen, A.R.Eisenman, C.C.Liebe, "Autonomous Vision Space, Advanced Stellar Compass Platform", SPIE vol.2810, 1996 [11] C.Clark, O.Yadid-Pecht, E.R.Fossum, P.Salomon, E.Dennison, "Application Arrays Star Feature Tracking Systems", SPIE vol.2810, 1996 [12] J.Sackos, B.Bradley, C.Diegert, "Scannerless Terrain Mapper", SPIE vol.2810, 1996 [13] P.Salomon, E.R.Fossum, C.Clark, E.Dennison, "Active Pixel Sensors Autonomous Spacecraft Applications", SPIE vol.2810, 1996 [14] K.Noguchi, K.Sato, R.Kasikawa, N.Ogura, K.Ninomiya, T.Hasimoto, E.Hirokawa, "CCD Star Tracker Attitude Determination Control Satellite Space VLBI Mission", SPIE vol.2810, 1996
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[15] L.W.Cassidy, "Space Qualification HDOS' HD-1003 Star Tracker", proceedings SPIE vol.2810, 1996 [16] T.E.Strikwerda, H.Landis Fisher, "Analysis NEAR Star Tracker Flight Data", SPIE vol.2810, 1996 [17] L.W.Cassidy, "The HDOS HD-1003 Star Tracker", SPIE vol.2466, 1995 [18] A.Eisenman, Technology Tracker Pluto Mission Spacecraft", proceedings SPIE vol.2466, 1995 [19] S.Udomkesmalee, G.K.Man, B.A.Wilson, "Creating Autonomous Spacecraft with AFAST", SPIE vol.2466, 1995 [20] J.E.Kalshoven, D.Tom, "Evaluation Multi-Spectral Linear Array Detectors Spaceborne Applications", SPIE vol.589, 1985 [21] A.K.Jakubowski, P.Mohan, R.K.Kapania, P.Crisafulli, D.Hammerand, "Eight-Meter UV/Visible/IR Space Telescope", SPIE vol.2478, 1995 [22] J.F.Kordas, I.T.Lewis, B.A.Wilson, D.P.Nielsen, H.Park, R.E.Priest, R.F.Hills, M.J.Shannon, A.G.Ledebuhr, L.D.Pleasance, "Star Tracker Stellar Compass Clementine Mission", SPIE vol.2466, 1995 [23] J.F.Kordas, I.T.Lewis, B.A.Wilson, D.P.Nielsen, H.Park, R.E.Priest, W.Travis White, M.J.Shannon, A.G.Ledebuhr, L.D.Pleasance, "UV/Visible Camera Clementine Mission", SPIE vol.2478, 1995 [24] R.T.Howard, M.L.Book, "Improved Video Guidance Sensor Automated Docking", proceedings SPIE vol.2466, 1995 [25] Malin Space Science Systems, "Mars Surveyor Orbiter Color Imager MARCI", 1996 [26] NASA, "The Clementine Mission",
[27] P.Plancke, "Application Computer Vision Space", ESA: Preparing Future, Vol.2, September 1992 [28] Malin Space Science Systems, "Near Earth Asteroid Rendezvous: MultiSpectral Imager", [29] D.L.Wells, "Autonomous ExtraVehicular Activities Robotic Camera",
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[30] J.Balaram, "NASA Space Telerobotics Program: Machine-Vision Surface Inspection", [31] L.Martin, "NASA Space Telerobotics Program:Omni-View, Electronic Zoom Camera", [32] M.Fouquet, "Earth Imaging With Microsatellites", Ph.D.Thesis, Centre Satellite Engineering Research, University Surrey, 1996 [33] Sira Electro-Optics, "Attitude Sensor Concepts Small Satellites", project proposal ESA, 8/8720/34, 1996 [34] M.Trishberger, R.Aceti, P.Underwood, A.Pomilia, M.Cosi, F.Boldrini, "The Attitude Sensor Package Experiment: From Concept Operation", Journal 1993, vol.17 [35] M.Halloran, "7000x9000 Imaging Integrated Wafer", Advanced Imaging, Januari 1996 [36] R.Bonsignori, L.Maresi, "Sensor System Comet Approach Landing", proceedings SPIE, vol.1478, 1991 [37] K.Pribil, J.Flemming, "SOLACOS High Datarate Satellite Communication System Verification Program", SPIE vol.2210, 1994 [38] M.Stieber, M.McKay, G.Vukovich, E.Petriu, "Vision-Based Sensing Control Space Robotics Applications", Proceedings 1996 IEEE Instrumentation Measurements Technology Conference, 1996 [39] R.Durrant, M.Evans, "Visual Telemetry System: Demonstrator System Specification", MMS, 1995 [40] D.Uwaerts, W.Ogiers, "Visual Telemetry System Camera Module: Engineering Model Functional Description", P43302-IMRP24, IMEC, 1996 [41] D.Uwaerts, W.Ogiers, "Visual Telemetry System Camera Module: Engineering Model Technical Documentation", P43302-IMRP23, IMEC, 1996 [42] K.Ayadi, M.Kuijk, P.Heremans, G.Bickel, G.Borghs, R.Vounckx, Monolithic Optoelectronic Receiver Standard 0.7µm CMOS Operating 180MHz Light Input Energy", IEEE Photonics Technology Letters Vol.9, January 1997 [43] S.Amimoto (chair), "Workshop Sensors Transducers", Proceedings International Conference Integrated Micro/Nanotechnology Space Applications, November 1995
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Identification CMOS Imager Applications Space
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