The Lunar Volatile and Mineralogy Mapping Orbiter (VMMO) comprises a low-cost 12U Cubesat with deployable solar arrays, X-Band/UHF communications, option of electric or chemical propulsion, the Lunar Volatiles and Mineralogy Mapper (LVMM) payload, and an optional GPS receiver technology demonstrator. LVMM facilitates three operational modes: Active mode using illumination of the lunar surface at 532nm, 1064nm, and 1560nm to enable volatiles mapping during the lunar night and within Permanently-Shadowed Regions (PSRs); Passive mode during the lunar day with spectral channels at 300nm, 532nm, 690nm, 1064nm, and 1560nm for mapping lunar surficial ilmenite (FeTiO3); and a Communications mode for an optical data downlink demonstration at 1560nm. Previous lunar missions have detected the presence of water-ice in the lunar South Pole region. However, there is considerable uncertainty with regards to its distribution within and across the lunar surface. A number of planned future missions will further map water ice deposits, but the spatial resolution of these observations is expected to be on the order of kilometres. The LVMM using single-mode fiber lasers can improve the special resolution of the mapping to 10s of metres. VMMO has completed the Phase A study with ESA. This paper discusses the baseline LVMM payload design and its dual-use applications for both the stand-off mapping of lunar volatiles and a high-speed optical data link demonstration. In particular, the supporting fiber-laser technology readiness was advanced through ground qualification.
GHGSat is world’s first nanosatellite dedicated for monitoring greenhouse gas (GHG) and air quality gas (AQG) emissions from any industrial site in the world. The satellite was designed and constructed by MPB Communications to monitor carbon dioxide (CO2) and methane (CH4) from a low earth orbit (about 500 km). To reach the designated resolution of less than 50 meters and high precision of greenhouse gases monitoring, the nanosatellite has large aperture in order to collect enough optical signal. The aperture of about 10cm causes significant stray light issues with limited solution options without adding too much weight to the light weight satellite. As the stray light was the main concern in this project, many precautions was taken. As a solution for blocking unwanted light, baffle with many vanes was used. However, having the vanes is not optimal solution without high absorbing coating applied on it. The coating requirements was low reflectance, no outgassing in space environment and long life stability, being a satellite inaccessible for maintenance. The chosen coating for stray light elimination was Acktar Vacuum BlackTM. Hemispherical reflectance and BRDF data was examined before making the choice. The satellite was launched in June 2016 and the images was analyzed to ensure the aimed resolution and precision of the optical system. After almost two years of activity, no visible changes was discovered in image quality nor stray light issues detected.
The MEOS Miniature Earth Observing Satellite is a low-cost mission being developed for the Canadian Space Agency with international collaborations that will innovatively combine remote correlated atmospheric/land-cover measurements with the corresponding atmospheric and ecosystem modelling in near real-time to obtain simultaneous variations in lower tropospheric GHG mixing ratios and the resulting responses of the surface ecosystems. MEOS will provide lower tropospheric CO2, CH4, CO, N2O, H2O and aerosol mixing ratios over natural sources and sinks using two kinds of synergistic observations; a forward limb measurement and a follow-on nadir measurement over the same geographical tangent point. The measurements will be accomplished using separate limb and nadir suites of innovative miniature line-imaging spectrometers and will be spatially coordinated such that the same air mass is observed in both views within a few minutes. The limb data will consist of 16-pixel vertical spectral line imaging to provide 1-km vertical resolution, while the corresponding nadir measurements will view sixteen 5 by 10 km2 ground pixels with a 160-km East-West swath width.
To facilitate the mission accommodation on a low-cost microsat with a net payload mass under 22 kg, groundbreaking miniature guided-wave spectrometers with advanced optical filtering and coding technologies will be employed based on MPBC’s patented IOSPEC technologies. The data synergy requirements for each view will be innovatively met using two complementary miniature line-imaging spectrometers to provide broad-band measurements from 1200 to 2450 nm at about 1.2 nm/pixel bandwidth using a multislit binary-coded MEMS-IOSPEC and simultaneous high-resolution multiple microchannels at 0.03 nm FWHM using the revolutionary FP-IOSPEC Fabry-Perot guided-wave spectrometer concept. The guided-wave spectrometer integration provides an order of magnitude reduction in the mass and volume relative to traditional bulk-optic spectrometers while also providing significant performance advantages; including an optically immersed master grating for minimal optical aberrations, robust optical alignment using a low-loss dielectric IR waveguide, and simultaneous broad-band spectral acquisition using advanced infrared linear arrays and multiplexing electronics.
This paper describes the trial bread-boarding of the groundbreaking new spectrometer concepts and associated technologies towards the MEOS mission requirements.
MPB Communications (MPBC) is developing solutions to the monitoring requirements of spacecraft based on its fiber-laser and Fiber Bragg Grating expertise. This is cumulating in the Fiber Sensor Demonstrator for ESA’s Proba-2 that is scheduled for launch in 2007. The advantages of the MPBC approach include a central interrogation system that can be used to control a variety of different fiber-optic sensors including temperature, pressure, actuator status, and propellant leakage. This paper reviews the design and ground qualification of the FSD system in preparation for integration with Proba-2. The FSD will provide monitoring for various Proba-2 subsystems, including a hybrid propulsion system. Some of the challenges associated with using fiber-optics in space are discussed.
Infrared spectroscopy probes the characteristic vibrational and rotational modes of chemical bonds in molecules to provide information about both the chemical composition and the bonding configuration of a sample. The significant advantage of the Infrared spectral technique is that it can be used with minimal consumables to simultaneously detect a large variety of chemical and biochemical species with high chemical specificity. To date, relatively large Fourier Transform (FT-IR) spectrometers employing variations of the Michelson interferometer have been successfully employed in space for various IR spectroscopy applications. However, FT-IR systems are mechanically complex, bulky (> 15 kg), and require considerable processing. This paper discusses the use of advanced integrated optics and smart optical coding techniques to significantly extend the performance of miniature IR spectrometers by several orders of magnitude in sensitivity. This can provide the next generation of compact, high-performance IR spectrometers with monolithically integrated optical systems for robust optical alignment. The entire module can weigh under 3 kg to minimize the mass penalty for space applications. Miniaturized IR spectrometers are versatile and very convenient for small and micro satellite based missions. They can be dedicated to the monitoring of the CO2 in an Earth Observation mission, to Mars exobiology exploration, as well as to vital life support in manned space system; such as the cabin air quality and the quality of the recycled water supply.
16x1 programmable microshutter arrays allowing control of the light transmitted through a transparent substrate supporting the array were successfully fabricated using surface micromachining technology. Each microshutter is basically an electrostatic zipping actuator having a curved shape induced by a stress gradient through the actuator thickness. When a sufficient voltage is applied between the microshutter and the actuation electrode surrounding the associated microslit area, the generated electrostatic force pulls the actuator down to the substrate which closes the microslit. Opening the slit relies on the restoring force. High light transmission through the slit area is obtained with the actuator in the open position and excellent light blocking is observed when the shutter is closed. Static and dynamic responses of the device were determined. The pull-in voltage to close the microslit was about 110 V and the response times to close and open the microslit were about 2 ms and 7 ms, respectively.
Fiber Sensor Demonstrator (FSD) developed by MPB Communications (MPBC) is the first demonstration of a full fiber-optic sensor network in the space environment on a satellite. FSD has been launched on ESA’s Proba-2 satellite in November 2009. FSD contains twelve temperature sensors to measure the temperature at different locations in the satellite, and one High-Temperature sensor to measure the transient high temperature in the thruster, as well as one pressure sensor to measure the xenon tank pressure. First set of on-orbit test data were obtained in January 2010. The FSD unit successfully established the communication with Proba-2. The temperature of FSD unit was also acquired through a AD590 sensor inside the unit. The measurements of all the optical fiber sensor lines will be evaluated after the testing results obtained. The FSD contains twelve specially-packaged FBG temperature sensors to measure the temperature at different locations in the propulsion system and the spacecraft over the range of −60°C to +120°C. A high-temperature sensor is provided to measure the transient temperature response of the thruster to beyond 350°C. There is also an innovative P/T sensor that provides both temperature and pressure measurements of the Xe propellant tank. The preliminary data of on-orbit functional testing and temperature measurements are provided mainly in Section 6.
Atmospheric reentry transition is produced at hypersonic velocity and is accompanied by a sharp excessive heat load for a few minutes, on the exposed materials, leading to a temperature increase of more than 1000°C. MPBC developed optical fiber sensors for such temperatures with special packaging optimizing between protective capability and fast thermal conductivity. The fiber sensors were calibrated with thermocouples first using standard oven, then with stationary plasma at Von Karman Institute (Belgium) followed by a test within a wind tunnel (1000°C, 8 Mach number) at DLR-Cologne.
The Fiber Sensor Demonstrator (FSD), for ESA’s Proba-2 satellite is the first demonstration of a full fiber-optic sensor network in the space environment on a satellite.
KEYWORDS: Actuators, Spectroscopy, Camera shutters, Transmittance, Infrared spectroscopy, Signal to noise ratio, Sapphire, Electrodes, Reactive ion etching, Infrared radiation
Programmable microshutter arrays were designed to improve the attainable signal to noise ratio (SNR) of a miniature
dispersive spectrometer developed for space applications. Integration of a microshutter array to this instrument provides
advantages such as the addition of a binary coded optical input operation mode for the miniature spectrometer which
results in SNR benefits without spectral resolution loss. These arrays were successfully fabricated using surface
micromachining technology. Each microshutter is basically an electrostatic zipping actuator having a curved shape.
Applying critical voltage to one microshutter pulls the actuator down to the substrate and closes the associated slit.
Opening of the microslits relies on the restoring force generated within the actuated zippers. High light transmission is
obtained with the actuator in the open position and excellent light blocking is observed when the shutter is closed. The
pull-in voltage to close the microslits was about 110 V and the response times to close and open the microslits were
about 2 ms and 7 ms, respectively. Selected array dies were mounted in modified off-the-shelf ceramic packages and
electrically connected to package pins. The packages were hermetically sealed with AR coated sapphire windows. This
last packaging step was performed in a dry nitrogen controlled atmosphere.
Design, fabrication and characterization of a 16x1 programmable microshutter array are described. Each shutter controls
the light transmitted through a microslit defined on the transparent substrate supporting the array. Two approaches were
considered for the shutter array implementation: sweeping blades and zipping actuators. Simulation results and
fabrication constraints led to the selection of the zipping actuators. The device was fabricated using a surface
micromachining process. Each microshutter is basically an electrostatic zipping actuator having a curved shape induced
by a stress gradient throughout the actuator thickness. When a sufficient voltage is applied between the microshutter and
an actuation electrode surrounding the microslit area, the generated electrostatic force pulls the actuator down to the
substrate which closes the microslit. Opening the slit relies on the restoring force due to the actuator deformation.
Microshutter arrays were fabricated successfully. High light transmission through the slit area is obtained with the
actuator in the open position and excellent light blocking is observed when the shutter is closed. Static and dynamic
responses of the device were determined. A pull-in voltage of about 110 V closes the microslit and the response times to
close and open the microslit are about 2 and 7 ms, respectively.
Based on the principle of the Integrated Optical Spectrometer (IOSPEC), a waveguide-based, longwave infrared (LWIR) dispersive spectrometer with multiple input slits for Hadamard spectroscopy was designed and built intended for passive standoff chemical agent detection in 8 to 12μm spectral range. This prototype unit equips with a three-inch input telescope providing a field-of-view of 1.2 degrees, a 16-microslit array (each slit 60 μm by 1.8 mm) module for Hadamard binary coding, a 2-mm core ZnS/ZnSe/ZnS slab waveguide with a 2 by 2 mm2 optical input and micro-machined integrated optical output condensor, a Si micro-machined blazing grating, a customized 128-pixel LWIR mercury-cadmium-telluride (MCT) LN2 cooled detector array, proprietary signal processing technique, software and electronics. According to the current configuration, it was estimated that the total system weight to be ~4 kg, spectral resolution <4cm-1 and Noise Equivalent Spectral Radiance (NESR) <10-8 Wcm-2 sr-1cm-1 in 8 to 12 μm. System design and preliminary test results of some components will be presented. Upon the arrival of the MCT detector array, the prototype unit will be further tested and its performance validated in fall of 2007.
Among all trace gases, the carbon dioxide and methane provide the largest contribution to the climate radiative
forcing and together with carbon monoxide also to the global atmospheric carbon budget. New Micro Earth
Observation Satellite (MEOS) mission is proposed to obtain information about these gases along with some
other mission's objectives related to studying cloud and aerosol interactions. The miniature suit of instruments is
proposed to make measurements with reduced spectral resolution (1.2nm) over wide NIR range 0.9μm to
2.45μm and with high spectral resolution (0.03nm) for three selected regions: oxygen A-band, 1.5μm-1.7μm
band and 2.2μm-2.4μm band. It is also planned to supplement the spectrometer measurements with high spatial
resolution imager for detailed characterization of cloud and surface albedo distribution within spectrometer field
of view. The approaches for cloud/clear-sky identification and column retrievals of above trace gases are based
on differential absorption technique and employ the combination of coarse and high-resolution spectral data. The
combination of high and coarse resolution spectral data is beneficial for better characterization of surface
spectral albedo and aerosol effects. An additional capability for retrieval of the vertical distribution amounts is
obtained from the combination of nadir and limb measurements. Oxygen A-band path length will be used for
normalization of trace gas retrievals.
We have successfully fabricated two types of optical switch devices, namely, all-optical switch (VO2/quartz) and electro-optical switch (VO2/TiO2/ITO/glass) based on semiconductor-to-metallic phase transition characteristic of vanadium dioxide (VO2) smart coatings. The VO2 active layer, the TiO2 buffer layer, and the ITO transparent conductive electrode used in these devices, were achieved by reactive pulsed laser deposition. The optical switching of the fabricated devices was investigated at λ = 1.55 μm. The semiconductor (on) to metallic (off) phase transition was controlled by photoexcitation of VO2 in the case of the all-optical switch, and by an external electric-field between the ITO and the VO2 layer in the case of the electro-optical switch. The extinction ratio (on/off) is found to be much higher for the all-optical switch than for the electro-optical switch. For the all-optical switch, extinction ratio of about 22 dB and 12 dB are obtained in the transmission and reflection modes respectively. In the case of the electro-optical switch, the extinction ratio is about 12 dB in the transmission mode and 5 dB in the reflection mode.
High-resolution, miniature integrated spectrometers have been constructed for the NIR and MIR spectral ranges, based on MPBT's proprietary IOSPEC technology. Advanced slab-waveguide integrated optics have been employed to extend the performance of the miniature IR spectrometers to rival that of much larger FT-JR spectrometers. Monolithic integration of the miniature spectrometer, input optics and detector array provides a very compact and robust package that is suitable for industrial and field environments. Despite the compact size of the spectrometers, resolutions of 4 to 8 cm-1 are achievable over dedicated spectral ranges (2000 to 4000 nm, respectively). These spectrometers are coupled to 256channel linear detector arrays controlled by software based on Visual C++ to provide rapid spectral acquisition and analysis. This technology facilitates on-line infrared spectral analysis of an industrial or biochemical process at scan rates exceeding 200 spectra/sec. Since the spectral data is measured directly, significantly less data processing is required than for FT-JR techniques, allowing more CPU time for spectral identification and analysis. Multi-channel, time-resolved spectral measurements permit the study of the intermediate steps in a process or reaction. This paper discusses recent advances in the performance of the miniature integrated spectrometers. New detector geometries and data processing techniques have facilitated a substantial improvement in the overall system SNR over that feasible with typical sequentially-scanned detector arrays. Preliminary experimental transmittance spectra of optical filters and plastics are presented.
The availability of a relatively low-cost miniature integrate dIR spectrometer facilitates the application of IR spectroscopy to numerous spectral analysis and identification tasks. Recent advances in semiconductor material processing now provide the technology for the development of planar optical waveguides that exhibit good transmission characteristics in the mid-IR spectral range. Chalcogenide and fluoride glass fibers are commercially available which allows their use for coupling light to the integrated spectrometer. Integration of the slab waveguide structure with an input IR fiber and an output IR detector array thus results in a very compact device that can be used in numerous field and industrial applications such as gas detection, water analysis, chemical process monitoring, geological and agricultural surveys, and pollution monitoring. In the present work, these new materials and technologies have been exploited for the implementation of a miniature integrated optic SPECtrometer (IOSPEC) for the 2 to 6 micrometers spectral range. In the developed miniature spectrometer, broadband light is coupled into the spectrometer through an IR fiber, then subsequently dispersed into its spectral components by a diffraction grating made by anisotropic etching of silicon and finally focused on an IR detector array. This paper discusses some of the performance and design aspects of the current third generation IOSPEC technology; namely the use of IR fiber arrays in order to improve the device throughput and resolution, and the coupling of IOSPEC to advanced linear IR detector array technology.
A non-contact nine channel fiber optic laser vibrometer has been developed to measure the vibrations of low mass flexible space structures. The Multi-Channel Fiber optic VIBrometer (MCFVIB) system is based on a commercial single channel laser vibrometer and a fiber-optic distribution system. This entailed the development of appropriate systems architecture for the optical signals, active 1 X 9 optical switch, and optical sensor heads suitable for coupling the reflected test signal back into the fiber optic system. MCFVIB employs single-mode, polarization maintaining fibers to maintain the signal coherence. The performance of the MCFVIB was tested at various vibrational frequencies using a shaker. Correlation of the measurements against those measured by an accelerometer indicate excellent linearity and accuracy for the fiber optic vibrometer system.
A multi-channel laser measurement system based on a commercially available single-channel laser vibrometer has been developed to measure the vibrations of low mass flexible space structures. The first generation of the multi-channel laser vibrometer is bulk-optic based system with laser being switched by an acousto-optical modulator. To overcome some of its drawbacks, for instance, being physically large and cumbersome, requiring tedious alignment, the second generation of the system was developed which employs fiber-optic technique to distribute the laser signal to the desired fiber-optic laser head. The design of the fiber-optic switch minimizes the power loss of laser beam in such a way that the vibrometer can work in its optimal range. Both bulk-optic and fiber-optic multi-channel vibrometers were verified using accelerometers on a light weight communication satellite antenna reflector. The modal parameters of the reflector were identified using measured frequency response functions both from laser vibrometer and from accelerometers. The result show that the laser system gives virtually the same result as the accelerometers.
A miniaturized, planar-grating optical spectrometer for the 2 to 6 micrometer range has been designed and fabricated. This has entailed development of a slab waveguide structure suitable for the infrared, a broad-band optical grating structure and fiber-based, IR input/output optics. Broad- band light is coupled into the spectrometer through a pig- tailed IR fiber and is subsequently dispersed into its spectral components and can be focused either onto a thermo- electrically (TE) cooled HgCdZnTe detector array or an IR fiber array. Integration of the optics and detector provides exceptional optical alignment and a very compact package that is suitable for various airborne and terrestrial applications.
The excitation processes in a DC glow discharge ignited using a saddle-field electrode configuration have been examined using optical emission spectroscopy (OES) for discharges established in SiH4, and in Ar/SiH4 and N2/SiH4 gas mixtures. The emission intensities of excited gas-phase species are correlated with plasma probe mass and energy spectral analysis of the resulting reactive radicals impinging onto the substrate holder. Discharges ignited in SiH4 exhibit strong Si optical emission lines relative to the SiH lines, reflecting extensive gas-phase decomposition of the starting SiH4. The corresponding mass spectra of positively charged radicals exhibit a dominant peak at 28 amu that is associated with Si+. The resulting deposition rate of a-Si:H scales linearly with the flow rate of SiH4. The addition of argon to the glow discharge in SiH4 assists the gas-phase dissociation of the SiH4 as indicated by higher partial pressures at 28 and 29 amu, corresponding to the enhanced formation of Si and SiH. Moreover, gas-phase interactions with excited argon result in greater excitation of the background H2, leading to a higher concentration of atomic hydrogen in the discharge. Ionized atomic hydrogen dominates the discharge current at higher Ar to SiH4 gas flow ratios. OES spectra of DC saddle-field discharges in N2/SiH4 gas mixtures indicate strong activation of N2+ and good dissociation of the SiH4 over a wide range in flow ratios, facilitating the preparation of Si:N:H films with stoichiometries ranging from N/Si = 0 to 1.8.
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