KEYWORDS: LIDAR, Mars, Pulsed laser operation, Sensors, Staring arrays, Receivers, Distance measurement, Monte Carlo methods, 3D acquisition, Laser energy
Future planetary and lunar landers can benefit from a hazard detection (HD) system that employs a lidar to create a highresolution
3D terrain map in the vicinity of the landing site and an onboard computer to process the lidar data and
identify the safest landing site within the surveyed area. A divert maneuver would then be executed to land in this safe
site. An HD system enables landing in regions with a relatively high hazard abundance that would otherwise be
considered unacceptably risky, but are of high interest to the scientific community. A key component of a HD system is
a lidar with the ability to generate a 3D terrain image with the required range precision in the prescribed time and fits
within the project resource constraints. In this paper, we present the results obtained during performance testing of a
prototype "GoldenEye" 3D flash lidar developed by ASC, Inc. The testing was performed at JPL with the lidar and the
targets separated by 200 m. The analysis of the lidar performance obtained for different target types and albedos, pulse
energies, and fields of view is presented and compared to key HD lidar requirements identified for the Mars 2018 lander.
Optical metrology system reliability during a prolonged space mission is often limited by the reliability of pump laser diodes. We developed a metrology laser pump module architecture that meets NASA SIM Lite instrument optical power and reliability requirements by combining the outputs of multiple single-mode pump diodes in a low-loss, high port count fiber coupler. We describe Monte-Carlo simulations used to calculate the reliability of the laser pump module and introduce a combined laser farm aging parameter that serves as a load-sharing optimization metric. Employing these tools, we select pump module architecture, operating conditions, biasing approach and perform parameter sensitivity studies to investigate the robustness of the obtained solution.
We have designed and built a hollow-core fiber frequency reference cell, filled it with CO2, and used it to demonstrate
frequency stabilization of a 2.05 μm Tm:Ho:YLF laser using frequency modulation (FM) spectroscopy technique. The
frequency reference cell is housed in a compact and robust hermetic package that contains a several meter long hollow-core
photonic crystal fiber optically coupled to index-guiding fibers with a fusion splice on one end and a mechanical
splice on the other end. The package has connectorized fiber pigtails and a valve used to evacuate, refill it, or adjust the
gas pressure. We have demonstrated laser frequency standard deviation decreasing from >450MHz (free-running) to
<2.4MHz (stabilized).
The 2.05 μm laser wavelength is of particular interest for spectroscopic instruments due to the presence of many CO2
and H20 absorption lines in its vicinity. To our knowledge, this is the first reported demonstration of laser frequency
stabilization at this wavelength using a hollow-core fiber reference cell. This approach enables all-fiber implementation
of the optical portion of laser frequency stabilization system, thus making it dramatically more lightweight, compact, and
robust than the traditional free-space version that utilizes glass or metal gas cells. It can also provide much longer
interaction length of light with gas and does not require any alignment. The demonstrated frequency reference cell is
particularly attractive for use in aircraft and space coherent lidar instruments for measuring atmospheric CO2 profile.
The Frequency Doubler (FDR) is a component of the External Metrology subsystem on NASA's Space Interferometry
Mission, performing second harmonic generation using quasi-phasematched PPLN waveguides pigtailed
with polarization maintaining fiber. The need for harmonic generation on SIM is explained. Packaging and
results of performance and space-qualification testing of the FDR are described.
Photonic time-stretch has been proposed as a signal preprocessor to perform A/D conversion in otherwise inaccessible high frequency regimes. We have demonstrated time-stretching of MM-wave signals at frequencies up to 102 GHz down to 11 GHz , using an electrooptic modulator fabricated with the new polymer material PC-CLD. This application takes advantage of the inherent wideband capabilities of the PC-CLD material system, which has also demonstrated good optical insertion loss and high non- linearity at 1.55 micrometers . The dispersion penalty inherent to time-stretching imposes an additional bandwidth limit to that imposed by the modulator. A single-sideband modulator configuration is proposed to reduced the effect of this penalty.
The Cassini spacecraft uses a CCD-based star tracker, the Stellar Reference Unit (SRU), for attitude identification in the Attitude and Articulation Control Subsystem (AACS). SOftware to process SRU data resides in the Flight Computer (AFC) and is integrated with all other AACS functions. The Cassini mission will use autonomous star identification for initial attitude determination,and a star tracking function for maintaining attitude, both performed by processing pixel data produced by the SRU and sent to the AFC via a dma interface. Because of the complexity of the StarID software, special software simulation tools were created to simulate the SRU output as a function of commands, spacecraft attitude, and star screen, and allow the introduction of fault conditions.
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