Denis Laurin

Eye-safe digital 3-D sensing for space applications

This paper focuses on the characteristics and performance of an eye-safe laser range scanner (LARS) with short- and medium-range 3-D sensing capabilities for space applications. This versatile LARS is a precision measurement tool that will complement the current Canadian Space Vision System. The major advantages of the LARS over conventional video-based imaging are its ability to operate with sunlight shining directly into the scanner and its immunity to spurious reflections and shadows, which occur frequently in space. Because the LARS is equipped with two high-speed galvanometers to steer the laser beam, any spatial location within the field of view of the camera can be addressed. This versatility enables the LARS to operate in two basic scan pattern modes: (1) variable-scan-resolution mode and (2) raster-scan mode. In the variable-resolution mode, the LARS can search and track targets and geometrical features on objects located within a field of view of 30 by 30 deg and with corresponding range from about 0.5 to 2000 m. The tracking mode can reach a refresh rate of up to 130 Hz. The raster mode is used primarily for the measurement of registered range and intensity information on large stationary objects. It allows, among other things, target-based measurements, feature-based measurements, and surface-reflectance monitoring. The digitizing and modeling of human subjects, cargo payloads, and environments are also possible with the LARS. Examples illustrating its capabilities are presented.

Characterization results of EMCCDs for extreme low-light imaging

EMCCDs are capable of extreme low light imaging thanks to sub-electron read-out noise, enabling single-photon counting. The characterization of e2vs CCD60 (128 x 128), CCD97 (512 x 512) and CCD201-20 (1024 x 1024) using a controller optimized for the driving of EMCCDs at a high (≥10 MHz) pixel rate per output with < 0.002 e- total background signal. Using the CCD Controller for Counting Photons (CCCP), the horizontal and vertical CIC, dark current and EM gain stability are characterized.

NEOSSat: a Canadian small space telescope for near Earth asteroid detection

Although there is some success in finding Near Earth asteroids from ground-based telescopes, there is a marked advantage in performing the search from space. The ability to search at closer elongations from the sun and being able to observe continuously, allowing quick revisits of new asteroids, are some of the unique benefits of a space platform. The Canadian Space Agency (CSA) together with Defense Research and Development Canada (DRDC) are planning a micro-satellite platform with a 15 cm telescope dedicated for near space surveillance. The NEOSSat (Near Earth Object Surveillance) spacecraft is expected to be able to detect 20 v magnitude objects with a 100 sec exposure, with a 0.85 deg FOV, on a 1024x1024 CCD, and sub arcsec pointing stability. For detection of NEO small bodies, it will be able to search an area from 45 degrees solar elongation and approximately 40 degrees north to south degrees in elevation. The observation strategy will be optimized to find as many asteroids as possible, based on recent models of asteroid population. Ground based telescopes will also be used to complement follow-ups for orbit determination when possible. The microsatellite is based on the CSA very successful MOST micro-satellite, operating since 2003. Baselined for launch in 2010, the NEOSSat is a shared project with DRDC to demonstrate the technology of an inexpensive space platform to detect High Earth Orbit (HEOSS) earth-orbiting satellites and debris.

Three-dimensional tracking and imaging laser scanner for space operations

This paper presents the development of a laser range scanner (LARS) as a three-dimensional sensor for space applications. The scanner is a versatile system capable of doing surface imaging, target ranging and tracking. It is capable of short range (0.5 m to 20 m) and long range (20 m to 10 km) sensing using triangulation and time-of-flight (TOF) methods respectively. At short range (1 m), the resolution is sub-millimeter and drops gradually with distance (2 cm at 10 m). For long range, the TOF provides a constant resolution of plus or minus 3 cm, independent of range. The LARS could complement the existing Canadian Space Vision System (CSVS) for robotic manipulation. As an active vision system, the LARS is immune to sunlight and adverse lighting; this is a major advantage over the CSVS, as outlined in this paper. The LARS could also replace existing radar systems used for rendezvous and docking. There are clear advantages of an optical system over a microwave radar in terms of size, mass, power and precision. Equipped with two high-speed galvanometers, the laser can be steered to address any point in a 30 degree X 30 degree field of view. The scanning can be continuous (raster scan, Lissajous) or direct (random). This gives the scanner the ability to register high-resolution 3D images of range and intensity (up to 4000 X 4000 pixels) and to perform point target tracking as well as object recognition and geometrical tracking. The imaging capability of the scanner using an eye-safe laser is demonstrated. An efficient fiber laser delivers 60 mW of CW or 3 (mu) J pulses at 20 kHz for TOF operation. Implementation of search and track of multiple targets is also demonstrated. For a single target, refresh rates up to 137 Hz is possible. Considerations for space qualification of the scanner are discussed. Typical space operations, such as docking, object attitude tracking, and inspections are described.

Short- and medium-range 3D sensing for space applications

This paper focuses on the characteristics and performance of a laser range scanner (LARS) with short and medium range 3D sensing capabilities for space applications. This versatile laser range scanner is a precision measurement tool intended to complement the current Canadian Space Vision System (CSVS). Together, these vision systems are intended to be used during the construction of the International Space Station (ISS). Integration of the LARS to the CSVS will allow 3D surveying of a robotic work-site, identification of known objects from registered range and intensity images, and object detection and tracking relative to the orbiter and ISS. The data supplied by the improved CSVS will be invaluable in Orbiter rendez-vous and in assisting the Orbiter/ISS Remote Manipulator System operators. The major advantages of the LARS over conventional video-based imaging are its ability to operate with sunlight shining directly into the scanner and its immunity to spurious reflections and shadows which occur frequently in space. Because the LARS is equipped with two high-speed galvanometers to steer the laser beam, any spatial location within the field of view of the camera can be addressed. This level of versatility enables the LARS to operate in two basic scan pattern modes: (1) variable scan resolution mode and (2) raster scan mode. In the variable resolution mode, the LARS can search and track targets and geometrical features on objects located within a field of view of 30 degrees X 30 degrees and with corresponding range from about 0.5 m to 2000 m. This flexibility allows implementations of practical search and track strategies based on the use of Lissajous patterns for multiple targets. The tracking mode can reach a refresh rate of up to 137 Hz. The raster mode is used primarily for the measurement of registered range and intensity information of large stationary objects. It allows among other things: target-based measurements, feature-based measurements, and, image-based measurements like differential inspection in 3D space and surface reflectance monitoring. The digitizing and modeling of human subjects, cargo payloads, and environments are also possible with the LARS. A number of examples illustrating the many capabilities of the LARS are presented in this paper.

Electron-multiplying CCDs for future space instruments

The rapid proliferation of Electron Multiplying Charge Coupled Devices (EMCCDs) in recent years has revolutionized low light imaging applications. EMCCDs in particular show promise to enable the construction of versatile space astronomy instruments while space-based observations enable unique capabilities such as high-speed accurate photometry due to reduced sky background and the absence of atmospheric scintillation. The Canadian Space Agency is supporting innovation in EMCCD technology by increasing its Technology Readiness Level (TRL) aimed at reducing risk, cost, size and development time of instruments for future space missions. This paper will describe the advantages of EMCCDs compared to alternative low light imaging technologies. We will discuss the specific issues associated with using EMCCDs for high-speed photon counting applications in astronomy. We will show that a careful design provided by the CCD Controller for Counting Photons (CCCP) makes it possible to operate the EMCCD devices at rates in excess of 10 MHz, and that levels of clock induced charge and dark current are dramatically lower than those experienced with commercial cameras. The results of laboratory characterization and examples of astronomical images obtained with EMCCD cameras will be presented. Issues of radiation tolerance, charge transfer efficiency at low signal levels and life time effects on the electron-multiplication gain will be discussed in the context of potential space applications.

Eye-safe imaging and tracking laser scanner system for space applications

This paper discuses the development of a short wavelength infrared laser ranging scanner system at the Canadian Space Agency in cooperation with the National Research Council Canada. A laser source at 1.54 micrometers wavelength is chosen for its relatively eye-safe property. The scanner system is to be considered for use as a space vision system for applications such as robot vision, satellite acquisition and tracking and high resolution 3D imaging for inspection. As an active system, this laser scanner offers an important advantage over conventional vision systems by providing its own illumination and having no dependence on ambient lighting. While providing relatively eye-safe operation, the choice of IR wavelength also improves the background rejection of solar radiation, the latter being about 5.8 times lower than in the visible. The system possesses two modes of operation for making range measurements: triangulation for short distances (0.5 m to 20 m) and time- of-flight for greater range (10 m to beyond 1 km). A short pulse high repetition rate laser is required for time-of- flight measurements. For space applications, the laser must be compact, rugged and efficient while operating in the eye- safe spectrum (1.5 to 1.8 micrometers ). Currently, a YAG laser with an OPO is used to demonstrate the systems operation at 1.54 micrometers , but is too bulky for a space environment. Eventually it will be replaced with a more compact and efficient fiber laser currently being developed. This paper presents the results of the capabilities and performance of the scanner.

EMCCDs: 10 MHz and beyond

EMCCDs are capable of MHz pixel rate whilst maintaining sub-electron readout noise. Tens of frames per second are common place for large and medium EMCCD formats (1k×1k, 512×512), while smaller formats can reach hundreds and even thousand of frames per second. For applications where speed is a key factor, overclocked EMCCD were used at or beyond the manufacturer’s specifications. Very few data were published on the impacts of high speed clocking of EMCCDs, either vertically or horizontally. This paper presents characterization results of EMCCDs clocked at high speed.

Design and fabrication of a lightweight laser scanning mirror from metal-matrix composites

This paper discusses the design and fabrication of ultra lightweight laser scanning mirrors from two types of metal-matrix composites for the next generation Space Vision System (SVS). The materials selected for this study were SiC particulate reinforced aluminum composite and beryllium-aluminum (AlBeMet) composite. Three mirror designs were made and compared in terms of mass, rotating inertia and first mode natural frequency. Mirror surface layer selection and processing were discussed. Problems encountered during the mirror fabrication and the ways to solve it were presented.

Canadian contributions studies for the WFIRST instruments

WFIRST-AFTA is the NASA’s highest ranked astrophysics mission for the next decade that was identified in the New World, New Horizon survey. The mission scientific drivers correspond to some of the deep questions identified in the Canadian LRP2010, and are also of great interest for the Canadian scientists. Given that there is also a great interest in having an international collaboration in this mission, the Canadian Space Agency awarded two contracts to study a Canadian participation in the mission, one related to each instrument. This paper presents a summary of the technical contributions that were considered for a Canadian contribution to the coronagraph and wide field instruments.