J. Galbraith, K. Austin, J. Baker, R. Bettencourt, E. Bliss, J. Celeste, T. Clancy, S. Cohen, M. Crosley, P. Datte, D. Fratanduono, G. Frieders, J. Hammer, J. Jackson, D. Johnson, M. Jones, D. Koen, J. Lusk, A. Martinez, W. Massey, T. McCarville, H. McLean, K. Raman, S. Rodriguez, D. Spencer, P. Springer, J. Wong
A joint team comprised of Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratory (SNL) personnel is designing a line-VISAR (Velocity Interferometer System for Any Reflector) for the Sandia Z Machine, Z Line-VISAR. The diagnostic utilizes interferometry to assess current delivery as a function of radius during a magnetically-driven implosion. The Z Line-VISAR system is comprised of the following: a two-leg line-VISAR interferometer, an eight-channel Gated Optical Imager (GOI), and a fifty-meter transport beampath to/from the target of interest.
The Z Machine presents unique optomechanical design challenges. The machine utilizes magnetically driven pulsed power to drive a target to elevated temperatures and pressures useful for high energy density science. Shock accelerations exceeding 30g and a strong electromagnetic pulse (EMP) are generated during the shot event as the machine discharges currents of over 25 million amps. Sensitive optical components must be protected from shock loading, and electrical equipment must be adequately shielded from the EMP. The optical design must accommodate temperature and humidity fluctuations in the facility as well as airborne hydrocarbons from the pulsed power components.
We will describe the engineering design and concept of operations of the Z Line-VISAR system. Focus will be on optomechanical design.
A large format germanium immersion grating was flycut with a single-point diamond tool on the Precision Engineering Research Lathe (PERL) at the Lawrence Livermore National Laboratory (LLNL) in November – December 2015. The grating, referred to as 002u, has an area of 59 mm x 67 mm (along-groove and cross-groove directions), line pitch of 88 line/mm, and blaze angle of 32 degree. Based on total groove length, the 002u grating is five times larger than the previous largest grating (ZnSe) cut on PERL, and forty-five times larger than the previous largest germanium grating cut on PERL. The key risks associated with cutting the 002u grating were tool wear and keeping the PERL machine running uninterrupted in a stable machining environment. This paper presents the strategies employed to mitigate these risks, introduces pre-machining of the as-etched grating substrate to produce a smooth, flat, damage-free surface into which the grooves are cut, and reports on trade-offs that drove decisions and experimental results.
The requirements for beam and target alignment for successful ignition experiments on the National Ignition Facility
(NIF) are stringent: the average of beams to the target must be within 25 μm. Beam and target alignment are achieved
with the Target Alignment Sensor (TAS). The TAS is a precision optical device that is inserted into target chamber
center to facilitate both beam and target alignment. It incorporates two camera views (upper/lower and side) mounted on
each of two stage assemblies (jaws) to view and align the target. It also incorporates a large mirror on each of the two
assemblies to reflect the alignment beams onto the upper/lower cameras for beam alignment. The TAS is located in the
chamber using reference features by viewing it with two external telescope views. The two jaws are adjusted in elevation
to match the desired beam and target alignment locations. For some shot setups, a sequence of TAS positions is required
to achieve the full setup and alignment. In this paper we describe the TAS, the characterization of the TAS coordinates
for beam and target alignment, and summarize pointing shots that demonstrate the accuracy of beam-target alignment.
Off-line conditioning of full-size optics for the National Ignition Facility required a beam delivery system to allow conditioning lasers to rapidly raster scan samples while achieving several technical goals. The main purpose of the optical system designed was to reconstruct at the sample plane the flat beam profile found at the laser aperture with significant reductions in beam wander to improve scan times. Another design goal was the ability to vary the beam size at the sample to scan at different fluences while utilizing all of the laser power and minimizing processing time.
An optical solution was developed using commercial off-the-shelf lenses. The system incorporates a six meter relay telescope and two sets of focusing optics. The spacing of the focusing optics is changed to allow the fluence on the sample to vary from 2 to 14 Joules per square centimeter in discrete steps. More importantly, these optics use the special properties of image relaying to image the aperture plane onto the sample to form a pupil relay with a beam profile corresponding almost exactly to the flat profile found at the aperture. A flat beam profile speeds scanning by providing a uniform intensity across a larger area on the sample. The relayed pupil plane is more stable with regards to jitter and beam wander. Image relaying also reduces other perturbations from diffraction, scatter, and focus conditions. Image relaying, laser conditioning, and the optical system designed to accomplish the stated goals are discussed.
The Video Guidance Sensor is a key component of NASA's Automated Rendezvous & Capture Program. The Video Guidance Sensor operates from the space shuttle cargo bay and uses laser illumination of a passive target mounted on a SPARTAN satellite. The on-board camera and signal processor determine the relative position and attitude between the target and sensor. The Video Guidance Sensor flew on space shuttle mission STS-95 in November of 1998 and was a marked success. Theoretical models of the optical performance predicted the experimental results from the mission well.
The Video Guidance Sensor was flown on STS-87 in November of 1997 and is the key element of an automatic rendezvous and docking program under development by NASA Marshall Space Flight Center. The system used laser illumination of a passive target in the field of view of an on-board camera and processed the video image to determine the relative position and attitude between the target and the sensor. Comparisons of mission results with theoretical models are discussed.
KEYWORDS: Sensors, Cameras, Space operations, Video, Global Positioning System, Digital signal processing, Signal processing, Reflectors, Target recognition, Semiconductor lasers
NASA's Marshall Space Flight Center has developed an active sensor system, the ideo guidance sensor (VGS), to provide near-range relative position and attitude data. The VGS will be part of an automatic rendezvous and docking system. The VGS determines the relative positions and attitudes between the active sensor and the passive target. It works by using laser diodes to illuminate the retro-reflectors in the target, a solid-state camera to detect the return from the target retro-reflectors, and a frame grabber and digital signal processor to convert the video information into relative positions and attitudes. The current sensor design is the result of several years of development and testing, and it is being built to fly as an experiment payload on the space shuttle. The VGS system is designed to operate with the target completely visible within a relative azimuth of +/- 10.5 degrees and a relative elevation of +/- 8 degrees. The system will acquire and track and target within that field-of-view anywhere from 1.0 meters to 110 meters range at any relative roll angle and relative pitch and yaw attitudes of up to +/- 10 degrees. The data is output from the sensor at 5 Hz, and the target and sensor software have been designed to permit two independent sensors to operate simultaneously for redundancy.
The video guidance sensor is a key element of an automatic rendezvous and docking program administered by NASA. The system sues laser illumination of passive target in the field of view of an on-board camera and processes the video image to determine the relative position and attitude between the target and the sensor. Theoretical predictions and evaluations, and laboratory measurements and test are presented for the lasers, target components, camera system, signal processor, and a solar simulator.
The Marshall Space Flight Center, Alabama, in a teaming arrangement with the University of Florida, Gainesville, and the Joint Astronomy Center, Hawaii, has completed a comprehensive investigation into the feasibility of a low-cost infrared space astronomy mission. This mission would map the emission of molecular hydrogen in our galaxy at two or three previously inaccessible mid-IR wavelengths, and provide information on the temperatures. The feasibility of the low-cost mission hinged on whether a thermal design could be found which would allow sufficient passive cooling of the telescope to elimiate the need for a large, expensive dewar. An approach has been found which can provide telescope temperatures on the order of 50 K, which makes the mission feasible at low cost in low-Earth orbit.
The BRDF of a MgF2 protected Al mirror contaminated with dust particulates due to exposure to the laboratory environment has been measured and is presented for wavelengths of 633 nm, 325 nm, 121.6 nm, and 74 nm. This experimental data is compared with theoretical predictions arising from the OPALS modeling software. This model calculates the BRDF based on the measured particlate distribution found on the surface, and the optical constants of the contaminant. The OPALS software shows promise as a useful tool in the design phase of optical instruments: for drawing up contamination budgets and for incorporation into stray light analysis predicting instrument performance.
A method has been developed which allows optical system designers to determine the effects at the focal plane from noise generated due to contamination in a sensor's near field-of-view and deposited on system mirrors. This method is embodied in the PEARLSS code, which allows an 'end to end' simulation of contamination generation, transport, deposition, and the resulting performance degradation for spaceborne optical systems. The code is constructed in such a way as to allow trade studies over parameters such as system materials, dimensions, operating temperatures and wavebands, pointing directions, orbital locations, and ground-processing cleanliness levels. PEARLSS outputs include a 2-D map of the scattered/emitted noise at the first mirror, the BRDF there due to particle deposition, and a map of the structured noise on the focal plane of the sensor system. All of these outputs are generated as functions of time. A simple test case is run through the code to demonstrate its various capabilities.
KEYWORDS: Particles, Near field optics, Imaging systems, Near field, Geometrical optics, Staring arrays, Sensors, Ray tracing, Light scattering, Optical components
A method has been derived that can image radiation scattered from particles in the near field to the focal plane of an imaging sensor, using only two system level parameters. The parameters needed are the effective focal length and back focal length of the imaging system. The inherent advantages of this method are that imaging of scattered radiation and near field objects can be modelled with very little precise knowledge of the system's design, and cumbersome ray tracing techniques are not used. The method derived uses a mathematical transfer matrix to describe the system as a whole, so individual elements don't have to be modelled. Results from a sample case are presented.
Once a particle is released into the telescope field-of-view, regardless of the phenomena responsible for dislodging it from the surface, it will move through the baffle tube volume until it either leaves the open end of the tube or strikes another surface. Upon impact with a surface the particle will either stick to it or rebound at some angle and with some associated energy loss. 4BOUNCE and VBOUNCE are codes which model contamination transport in spaceborne sensors. 4BOUNCE is a fast-running code which uses a smooth cylinder and parameterizes the effects of baffle vanes. VBOUNCE models all surfaces explicitly, including vanes. Both models are intended to track particles of various materials, mass and velocity combinations as they bounce within a sensor. Trade studies were made to identify the important parameters based on the output sensitivity to the varied parameter. The results of interest for contamination impact on sensor performance is the fraction of particles remaining within the sensor view as a function of time and mass.
A method has been developed which allows optical system designers to determine the effects at the focal plane from noise generated due to contamination in a sensor's near field-of-view and deposited on system mirrors. This method is embodied in the PEARLSS code, which allows an 'end to end' simulation of contamination generation, transport, deposition, and the resulting performance degradation for spaceborne optical systems. The code is constructed in such a way as to allow trade studies over parameters such as system materials, dimensions, operating temperatures and wavebands, pointing directions, orbital locations, and ground-processing cleanliness levels. PEARLSS outputs include a 2-D map of the scattered/emitted noise at the first mirror, the BRDF there due to particle deposition, and a map of the structured noise on the focal plane of the sensor system. All of these outputs are generated as functions of time. A simple test case is run through the code to demonstrate its various capabilities.
KEYWORDS: Particles, Near field optics, Geometrical optics, Imaging systems, Contamination, Near field, Staring arrays, Sensors, Ray tracing, Light scattering
A computer model has been developed to determine the degradation of sensor performance due to contamination. These particulates may either by suspended in the near field-of-view or deposited on optical surfaces within the system. This system response simulation, PEARLSS (Particulate Effects Analysis on Response Levels of Spaceborne Sensors), is currently able to model many of the key dynamics of the particles to determine their distribution in the field-of- view and on the mirrors. Light from various sources is scattered off of the particulates. This radiation is mapped as a noise scene at the first mirror and the focal plane. The code is intended for performing parametric studies on design parameters such as sunshade geometry, system materials, temperatures, pre-launch cleanliness levels, and pointing directions. Sources of radiation currently modeled are the Sun and Earth, as well as user-defined sources. An overview of the simulation's approach to tracking contamination and scattered radiation is given.
A PEARLSS (Particulate Effects Analysis on Response Levels of Spaceborne Sensors) approach is presented with particular attention given to the code structure and on-going code developments. PEARLSS is a system response simulation which models the degradation of sensor performance due to particulates in the near field-of-view and deposited on optical surfaces. This flexible, modular code is aimed at performing parametric studies on design parameters including sunshade geometry, system materials, temperatures, prelaunch cleanliness levels, and pointing directions.
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