Engineering topics
Publications and source records attributed to Aram Gragossian.
We describe development of a silicon photonic optical transceiver for integration into NASA's Navigation Doppler Lidar. We demonstrate lidar operation using the on-chip optical balanced receiver.
We analyze performance changes on a NASA-developed lidar system resulting from vibration loads expected during spacecraft landing. Vibration-induced laser linewidth broadening and reduced measurement precision are demonstrated and related to vibration level and target range.
NASA is developing an entry, descent, and landing (EDL) lidar system, the Navigation Doppler Lidar (NDL), for high-precision landing on the Moon, Mars, and beyond. The current flight NDL systems use 1550 nm fiber-optic components for frequency-modulated continuous wave (FMCW) ranging beyond 5 km, but have reduced performance under vibrational and thermal stresses during EDL. Here we describe recent efforts to develop a breadboard silicon photonic optical transceiver for integration into NDL to reduce instrument size and improve robustness to environment and demonstrate the optical balanced receiver performance during testing with the breadboard NDL unit. Initial testing shows improved suppression of common mode noise by 25 dB over the current receiver, but a 10 dB reduction in signal to noise ratio (SNR) resulting from coupling losses from fiber to the on-chip waveguides. Future work will target reduced coupling loss, hermetic packaging, and co-integration of a single sideband suppressed carrier modulator into the same chip.
NASA is developing a Navigational Doppler LiDAR (NDL) for use in missions involving robotic and human landing scenarios on solar system bodies. The NDL provides unprecedented accuracy in position and velocity measurement for the guidance, navigation and control (GNC) subsystem of a spacecraft. NDL performance has been characterized over different phases of its development through ground tests, helicopter flight tests, and onboard rocket-powered test vehicles, however, none of these tests provided measurements over its full performance envelope. For this reason, a high speed rocket sled test was recently conducted to resolve both range and velocity up to the maximum limits of the NDL. This test campaign was performed at the Supersonic Naval Ordnance Research Tracks (SNORT) facility, Naval Air Weapons Station China Lake, as part of the Safe & Precise Landing and Integrated Capabilities Evolution (SPLICE) project.
The operation of a coherent Doppler lidar, developed by NASA for missions to planetary bodies, is analyzed and its projected performance is described. The lidar transmits three laser beams at different but fixed directions and measures line-of-sight range and velocity along each beam. The three line-of-sight measurements are then combined in order to determine the three components of the vehicle velocity vector and its altitude relative to the ground. Operating from over five kilometers altitude, the NDL provides velocity and range data with a few cm/sec and a few meters precision, respectively, depending on the vehicle dynamics. This paper explains the sources of measurements error and analyzes the impacts of vehicle dynamics on the lidar performance.
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The operation of a coherent Doppler lidar, developed by NASA for missions to planetary bodies, is analyzed and its projected performance is described. The lidar transmits three laser beams at different but fixed directions and measures line-of-sight range and velocity along each beam. The three line-of-sight measurements are then combined in order to determine the three components of the vehicle velocity vector and its altitude relative to the ground. Operating from over five kilometers altitude, the NDL provides velocity and range data with a few cm/sec and a few meters precision, respectively, depending on the vehicle dynamics. This paper explains the sources of measurement error and analyzes the impact of vehicle dynamics on the lidar performance.
A coherent Doppler lidar has been developed by NASA for providing vector velocity and altitude data to landing vehicles. Future robotic and manned missions to planetary bodies demand precise ground-relative velocity and altitude data to execute complex descent maneuvers for safe, soft and pinpoint landing at a pre-designated site. Operating from over five kilometers altitude, this lidar provides velocity and range data within a few cm/sec and a few meters precision, respectively, depending on the vehicle dynamics. Two upcoming lunar landing missions will serve as the technology demonstration for robotic and manned landing missions to the Moon, Mars, and other solar system destinations. This paper describes the lidar design and its expected performance on landing vehicles.
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The new generation of Navigation Doppler Lidar has been designed, developed, and tested for lunar missions. Comprehensive environmental testing is performed to assess the performance of the instrument for upcoming lunar missions and future missions to the Moon and other planetary bodies.
Global Positioning System (GPS) is commonly used in terrestrial navigation for vehicle position and velocity knowledge. In the absence of a GPS signal, past landing missions to planetary bodies primarily relied on radar to provide the necessary data to execute descent and landing maneuvers. We have developed a coherent Doppler lidar, called Navigation Doppler Lidar (NDL), that offers several critical advantages com-pared to radar, including significantly higher precision with reduced size, mass, and power.
A coherent Doppler lidar has been developed to address the need for a high-performance, compact, and cost-effective velocity and altitude sensor onboard landing vehicles. One of the core subsystems within NDL is its signal processing architecture. The primary function of this subsystem is to digitize the analog output of the homodyned signal received from the photo-diode associated with each telescope, process this signal in the frequency domain, and then turn this information into velocity and range measurements. A secondary function of this subsystem is to setup and control the internal components within NDL and to enable the instrument to interface with external systems by receiving commands, sending telemetry, and synchronizing its measurements with external clocks and pulses. This paper will give an overview of the signal processing architecture within NDL. This will include a discussion on its fundamental processing components and the core signal processing algorithms. Command, telemetry and internal component controls will also be discussed as will how the signal processing architecture has also evolved over the years of development. We will discuss provisions for robust operation including Triple-Mode Redundancy (TMR) within NDL’s Field Programmable Gate Array (FPGA) and storage elements, a fault-tolerant boot process, and Error Detection and Correction (EDAC) on the Static Random-Access Memories (SRAMs). Finally, we conclude this paper with how this architecture could continue to evolve.
A Flash Lidar utilizing a novel Super-Resolution technique has been developed for providing Terrain Relative Navigation and Hazard Avoidance capabilities onboard landing vehicles.
The new generation of Navigation Doppler Lidar has been designed, developed, and tested for lunar missions. Comprehensive environmental testing is performed to assess the performance of the instrument for upcoming lunar missions and future missions to the Moon and other planetary bodies.
Transparent electro-optic (EO) devices can potentially be used for efficient, high speed, and low mass non-mechanical beam steering. Transmission through EO devices will affect the wavefront quality and aberration of both the transmitted and received laser light. The consequences of wavefront distortions on coherent detection are not fully understood. Therefore, we have tested the performance of coherent detection lidar using liquid crystal polarization grating (LCPG) beam steering device. We will discuss the impact of LCPG beam steering devices on the performance of NASA’s Navigation Doppler Lidar, built for providing altitude and vector velocity data to aerial and space vehicles.
Missions to solar system bodies must meet increasingly ambitious objectives requiring highly reliable “precision landing”, and “hazard avoidance” capabilities. To meet these needs, we have developed two lidar sensor systems that can be used individually or in concert depending on the mission requirements. One is Navigation Doppler Lidar (NDL) capable of providing vehicle precision vector velocity and ground-relative altitude and the other is an Imaging Flash Lidar for Terrain Relative Navigation and Hazard Detection and Avoidance. Using both lidar sensors together will enable landing anywhere and under any lighting condition. The NDL performance has been extensively characterized through numerous ground and aircraft flight tests and will be soon demonstrated on two lunar landing missions (mid-2023). The Flash Lidar performance is currently being assessed onboard a drone and will soon be tested on helicopter and fixed-wing aircraft platforms. This paper describes both lidar sensors and their expected operation on landing vehicles.
A Flash Lidar utilizing a novel Super-Resolution (SR) technique has been developed for providing Terrain Relative Navigation and Hazard Avoidance capabilities onboard landing vehicles. Processing algorithms for precision navigation and safe landing location identification take advantage of the uniform fixed pixels property of generated high resolution Digital Elevation Maps (DEMs) to achieve high reliability operation in near real-time. This paper describes the current and next generation breadboard units, report the results of recent dynamic tests, and explain the operational concept as envisioned for future landing missions.
A Flash Lidar utilizing a novel Super-Resolution (SR) technique has been developed for providing Terrain Relative Navigation and Hazard Avoidance capabilities onboard landing vehicles. Processing algorithms for precision navigation and safe landing location identification take advantage of the uniform fixed pixels property of generated high resolution Digital Elevation Maps (DEMs) to achieve high reliability operation in near real-time. This paper describes the current and next generation breadboard units, report the results of recent dynamic tests, and explain the operational concept as envisioned for future landing missions.