Focus Optimization of a Cryogenic Collimater Using Interferometric Measurements and Optical Modeling

Space Dynamics Laboratory at Utah State University (SDL/IJSU) optimized the focus of an off-axis, cryogenically cooled infrared collimator for cryogenic operating temperatures. Historically, collimator focus was optimized at ambient temperatures where interactive focus adjustment and testing coulà be performed. The focus shift that occurred when the optics were cooled was minimized by collimator design, and the change was negligible compared to the spatial resolution of the IR sensor measuring the collimator\u27s simulated point source. However, the focus determined at ambient temperature does not meet the image quality requirements of state-of-the-art sensors. The method used by SDL to determine optimal focus at cryogenic temperatures applies classical optical techniques to the cryogenically cooled environment. System level interferometric measurements are first made to characterize the system wavefront error. These measurements are then applied to an aberration- free optical model to evaluate system focus for a wavelength of 12 tim. The method also uses a knife edge test to refer the interferometric measurements to the aperture located near the focal point of the collimator. This paper discusses the physical test setup, outlines the optical model and analysis procedure, and presents results before and after focus optimization of a multifunction infrared calibrator

SABER Instrument Design Update

This paper describes the design of a 10-channel infrared (1 .27 to 16.9 jim) radiometer instrument known as SABER (sounding of the atmosphere usingbroadband emissionradiometry) that will measure earth-limb emissions from the TiMED (thermosphere-ionospheremesosphere energetics and dynamics) satellite. The instrument telescope, designed to reject stray. light from the earth and the atmosphere, is an on-axis Cassegrain design with a clam shell reimager and a one-axis scan mirror. The telescope is cooled below 210 K by a dedicated radiator. The focal plane assembly (consisting of a filter array, a detector array, a Lyot stop and a window) is cooled to 75Kby a miniature cryogenic refrigerator. The conductive heat load on the refrigerator is minimized by a Keviar support system that thermally isolates the focal plane assembly from the telescope. Kevlar is also used to thermally isolate the telescope from the spacecraft. Instrument responsivity drifts due to changes in telescope and focal plane temperatures as well as other causes are neutralized by an in-flight calibration system. The detectOr airay consists ofdiscrete IJgCdTe, JnSb and InGaAS detectors. Two InGaAS detectors are a new long wavelength type, made by EG&G, that have a long wavelength cutoffof2.33 im at 77 K

Calibration Considerations and Scoring the Quality of Calibration

This paper gives an introduction to “Guidelines for Radiometric Calibration of Electro-Optical Instruments for Remote Sensing” and includes a typical calibration timeline, discussion on why calibration is necessary, a couple examples of calibration success, typical imaging radiometer calibration parameters, lessons learned considerations, why on-board sources are important to calibration, examples on-board calibration source types, and considerations for scoring the quality of calibration

Ground Support Equipment Calibrator Pointing Calibrations using Theodolite

Space Dynamics Laboratory performed various combinations of pointing mirror calibration of one of their vacuum and liquid nitrogen (LN2) rated ground support equipment (GSE) calibrators incorporating a pointing mirror gimbal. For this calibration approach, a theodolite was utilized to measure object space beam angles as a function of pointing mirror gimbal setting. This paper discusses the test setup, calibration uncertainty, angular coverage, measurement combinations, and explores the magnitude of dependencies

The CAESAR New Frontiers Mission: Camera Suite Calibration Planning

The Comet Astrobiology Exploration Sample Return (CAESAR) mission has been awarded Phase A study by NASA. The CAESAR mission is to acquire and return to earth a sample of the comet 67P/Churyumov-Gerasimenko. The camera suite on the spacecraft consists of 6 cameras. This suite consists of a narrow angle camera (NAC), medium angle camera (MAC), touch-and-go camera (TAGCAM), sample container camera (CANCAM), and two navigation cameras (NAVCAMs). Following optical and mechanical validation at the sensor vendor, the Camera Suite is delivered to Space Dynamics Laboratory (SDL) for calibration. Camera designs were determined from mission requirements. The formulated pre-launch calibration plan quantifies camera performance at anticipated operational environmental conditions, verifies camera requirements, is heritage-based, utilizes existing equipment to reduce cost and schedule, and enhances the science value of camera data. The development of this plan and a subsequent pre-launch calibration matrix will be discussed. In-flight calibration verifies and validates the pre-launch calibration, monitors and updates calibration, and quantifies camera performance. In-flight considerations and a preliminary calibration matrix will also be discussed

The CAESAR New Frontiers Mission: Overview and Imaging Objectives

The Comet Astrobiology Exploration Sample Return (CAESAR) mission will acquire and return to Earth for laboratory analysis a minimum of 80 g of surface material from the nucleus of comet 67P/Churyumov-Gerasimenko (67P). CAESAR will characterize the surface region sampled, return the collected solid sample in a pristine state, and return evolved volatiles by capturing them in a separate gas reservoir. A key to mission success is to select a sample site that provides high science value, and that is fully compatible with safe and successful sampling. Key supporting objectives are to characterize the sample site and its geophysical and geomorphic context, and to study the comet environment to identify spacecraft hazards including moonlets, jets and plumes. These mission objectives drive a number of key imaging requirements that in turn drive camera designs and calibration: detecting 50-cm objects from 500 km; resolving 2.5-cm particles from 650 m; obtaining 5° and 30° field of view optical navigation images; identifying 1-cm particles from 50 m; imaging at multiple colors, matching a subset of the Rosetta OSIRIS filter bandpasses; documenting the sample site before, during, and after sampling at sub-cm resolution; and documenting sample acquisition during sampling and packaging inside the return capsule. In order to accomplish these goals, CAESAR carries a high-heritage suite of six well-calibrated cameras of varying fields of view and focal ranges: narrow angle camera (NAC), medium angle camera (MAC), touch-and- go camera (TAGCAM), two navigation cameras (NAVCAMs), and a sample container camera (CANCAM)

Validation Assessment Model for Atmospheric Retrievals

A linear mathematical error model for the assessment of validation activity of atmospheric retrievals is presented. The purpose of the validation activity is to assess the actual performance of the remote sensing validated system while in orbit by comparing its measurements to some relevant—validating—data sets. The validating system samples volumes of the atmosphere at times and locations that are different from the ones when and where the validated system makes its own observations. The location of the validating system can be either stationary, e.g. a ground ARM site, or movable, e.g. an aircraft or some other satellites. The true states may be correlated or not. The sampled volumes differ from each other by their location, timing, and size. The validated and validating systems have different vertical resolution and grid, absolute accuracy, and noise level. All the above factors cause apparent differences between the data to be compared. The validation assessment model makes the comparison accurate by allowing for the differences. The model can be used for assessment and interpretation of the validation results when the above mentioned sources of discrepancies are significant, as well as for evaluation of a particular validating data source

Guidelines for Radiometric Calibration of Electro-Optical Instruments for Remote Sensing

Sensor calibration increases the probability of mission success by quantifying the sensor’s response to known radiometric input, characterizing the interactions between the sensor\u27s components, and allowing systematic errors to be discovered and resolved before launch. This poster provides guidelines for conducting a successful EO sensor calibration campaign. It is intended for use by managers, technical oversight personnel, scientists, and engineers as a useful reference in planning and carrying out a sensor calibration. This content of this poster is based on a publication titled Guidelines for Radiometric Calibration of Electro-Optical Instruments for Remote Sensing. The publication is based on the authors\u27 many years of combined experience planning, reviewing, preparing, conducting, analyzing, implementing, and reporting on a variety of calibration efforts. Authors involved with this publication include, in alphabetical order: Daniel Bancroft, Jim Butler, Changyong Cao, Raju Datla, Scott Hansen, Dennis Helder, Raghu Kacker, Harri Latvakoski, Martin Mlynczak, Tom Murdock, James Peterson, David Pollock, Ray Russell, Deron Scott, John Seamons, Tom Stone, Joe Tansock, Alan Thurgood, Richard Williams, Xiaoxiong (Jack) Xiong, and Howard Yoon