The Libera instrument is being developed as part of a NASA Earth Venture Continuity mission for extending Earth radiation budget (ERB) measurements by the currently operational Clouds and the Earth’s Radiant Energy System (CERES) instruments into the future. Libera will be launched on NOAA’s JPSS-4 satellite. Libera introduces several new technologies, including advanced VACNT detectors, a split-shortwave channel to quantify shortwave near-IR and visible radiation, and a wide field of view camera (WFC) that advance the state-of-the-art in Earth radiation budget measurements. The WFC is a monochromatic wide field of view camera operating at 555nm over a 123-degree field of view that will continuously observe the full Earth disk from low-earth orbit. The WFC provides a unique capability for scene identification and Angular Distribution Model (ADM) generation that complements similar measurements from the VIIRS instrument that will fly on JPSS-4 with Libera. By demonstrating that Libera’s WFC provides the data required for ADM development, a path forward for future free-flier ERB measurements will be explored. We focus on the development of the WFC, its science objectives, unique design features, its current state of development, and how it could help to enable a constellation of smaller, more cost-effective ERB instruments for the future.
As the next generation of Earth science programs demand more spectral bands, larger fields of view, faster speeds and reduced size, the optical designer will need to adapt to these new requirements. With the advent of manufacturable freeform optical surfaces, compact high-performance optical systems utilizing these surfaces are becoming practical. Freeform optics provide additional degrees of freedom for the optical designer which allow for more compact optical systems of equal performance, potentially operating at faster speeds or over wider fields of view. While numerous design studies on freeform systems have been published, little has been presented in the open literature on as built freeform systems. In this paper we describe the successful outcome of a hardware development program where we designed, built, aligned, and tested a compact WFOV three-mirror telescope with freeform surfaces. It is important that in addition to good optical performance, excellent stray light control is required in Earth remote sensing systems to minimum calibration errors across spectral bands. While compact size is often emphasized in the design of freeform systems, this needs to be balanced against the requirement for good stray light control. As such, the telescope presented in this paper balances the desire for small size with good stray light control. We present the results of the computer-aided alignment of the telescope along with measured stray light performance.
The NASA ESTO funded Multislit Optimized Spectrometer (MOS) Instrument Incubator Program advances a spatial multiplexing spectrometer for coastal ocean remote sensing from laboratory demonstration to flight-like environment testing. The multiple slit design reduces the required telescope aperture leading to mass and volume reductions over conventional spectrometers when applied to the GEO-CAPE oceans mission. This paper discusses the performance and characterization of the MOS instrument from laboratory and thermal vacuum testing. It also presents the current technology readiness level and possible future applications. Results of an ocean color data product simulation study using flight-like performance data from MOS are also covered. The MOS instrument implementation for GEO-CAPE provides system benefits that may lead to measurable cost savings and reductions in risks while meeting its science objectives.
The Multi-Slit Optimized Spectrometer (MOS) is a NASA funded Instrument Incubator Program (IIP) to advance an innovative dispersive spectrometer concept in support of the GEO-CAPE ocean science mission. As part of the instruments design and testing, we constructed a `behavioral model' of the instrument's optical engine which allows an end-to-end simulation from input radiances to nal product maps. Here we describe the model used for a rapid, but realistic, simulation of the MOS optical engine, and give illustrative examples of quantitatively tracking errors in the imaging chain from input radiances to bounds on nal product errors.
The NASA ESTO funded Multi-slit Optimized Spectrometer (MOS) Instrument Incubator Program will advance a spatial multiplexing spectrometer for coastal ocean remote sensing from lab demonstration to flight like environment testing. Vibration testing to meet the GEVS requirements for a geostationary orbit launch will be performed. The multiple slit design reduces the required telescope aperture leading to mass and volume reductions over conventional spectrometers when applied to the GEO-CAPE oceans mission. The MOS program is entering year 3 of the 3-year program where assembly and test activities will demonstrate the performance of the MOS concept. This paper discusses the instrument design, fabrication and assembly. It outlines the test plan to realize a technology readiness level of 6. Testing focuses on characterizing radiometric impacts of the multiple slit images multiplexed onto a common focal plane, and assesses the resulting uncertainties imparted to the ocean color data products. The MOS instrument implementation for GEO-CAPE provides system benefits that can lead to cost savings and risk reduction while meeting the science objectives of understanding the dynamic coastal ocean environment.
Kepler is NASA’s first space mission dedicated to the study of exoplanets. The primary scientific goal is statistical—to estimate the frequency of planetary systems associated with sun-like stars, especially the detection of earth-size planets in the habitable zones. Kepler was launched into an Earth-trailing heliocentric “drift-away” orbit (period=372 days ) in March 2009. The instrument detects the faint photometric signals of transits of planets across the stellar disks of those systems with orbital planes fortuitously oriented in our line of sight. Since the probability of such alignments is small, Kepler must observe a large number of stars. In fact, Kepler is monitoring approximately 150,000 stars with a 30-min cadence. The scientific goals led to the choice of a classical Schmidt telescope, and requirements on field-of-view, throughput, spectral bandpass, image quality, scattered light, thermal and opto-mechanical stability, and in-flight adjustment authority. We review the measurement requirements, telescope design, prelaunch integration, alignment, and test program, and we describe the in-flight commissioning that optimized the performance. The stability of the flight system has enabled increasing recognition of small effects and sophistication in data processing algorithms. Astrophysical noise arising from intrinsic stellar variability is now the dominant term in the photometric error budget.
The National Research Council’s recommended NASA Geostationary Coastal and Air Pollution Events (GEO-CAPE)
science mission’s purpose is to identify “human versus natural sources of aerosols and ozone precursors, track air
pollution transport, and study the dynamics of coastal ecosystems, river plumes and tidal fronts.” To achieve these goals
two imaging spectrometers are planned, one optimized for atmospheric science and the other for ocean science. The
NASA Earth Science Technology Office (ESTO) awarded the Multislit Optimized Spectrometer (MOS) Instrument
Incubator Program (IIP) to advance a unique dispersive spectrometer concept in support of the GEO-CAPE ocean
science mission. MOS is a spatial multiplexing imaging spectrometer that simultaneously generates hyperspectral data
cubes from multiple ground locations enabling a smaller sensor with faster revisit times compared to traditional
concepts. This paper outlines the science, motivation, requirements, goals, and status of the MOS program.
The desire to field space-based telescopes with apertures in excess of 10 meter diameter is forcing the development
of extreme lightweighted large optics. Sparse apertures, shell optics, and membrane optics are a few of the
approaches that have been investigated and demonstrated. Membrane optics in particular have been investigated for
many years. The majority of the effort in membrane telescopes has been devoted to using reflective membrane
optics with a fair level of success being realized for small laboratory level systems; however, extending this
approach to large aperture systems has been problematic. An alternative approach in which the membrane is used as
a diffractive transmission element has been previously proposed, offering a significant relaxation in the control
requirements on the membrane surface figure. The general imaging principle has been demonstrated in 50-cm-scale
laboratory systems using thin glass and replicated membranes at long f-number (f/50). In addition, a 5-meter
diameter f/50 transmissive diffractive optic has been demonstrated, using 50-cm scale segments arrayed in a
foldable origami pattern. In this paper we discuss Membrane Optical Imager Real-time Exploitation (MOIRE)
Phase 1 developments that culminated in the development and demonstration of an 80 cm diameter, off-axis, F/6.5
phase diffractive transmissive membrane optic. This is a precursor for an optic envisioned as one segment of a 10
meter diameter telescope. This paper presents the demonstrated imaging wavefront performance and collection
efficiency of an 80 cm membrane optic that would be used in an F/6.5 primary, discusses the anticipated areal
density in relation to existing space telescopes, and identifies how such a component would be used in previously
described optical system architectures.
Kepler is NASA's first space mission dedicated to the study of exoplanets. The primary scientific goal is statistical - to
estimate the frequency of planetary systems associated with sun-like stars, especially the detection of earth-size planets
in the Habitable Zones. Kepler was launched into an Earth-trailing heliocentric "drift-away" orbit (period = 372 days) in
March 2009. The instrument detects the faint photometric signals of transits of planets across the stellar disks of those
systems with orbital planes fortuitously oriented in our line-of-sight. Since the probability of such alignments is small
Kepler must observe a large number of stars. In fact, Kepler is monitoring approximately 150,000 stars with a 30-minute
cadence. These scientific requirements led to the choice of a classical Schmidt telescope, and requirements on field-of-view
(FOV), throughput, spectral bandpass, image quality, scattered light, thermal and opto-mechanical stability and in-flight
adjustment authority. We review the pre-launch integration, alignment and test program, and we describe the in-flight
commissioning that optimized the optical performance of the observatory. The stability of the flight system has
enabled increasing recognition of small effects and increasing sophistication in data processing algorithms. Astrophysical
noise arising from intrinsic stellar variability is now the dominant term in the photometric error budget.
Ball Aerospace & Technologies Corp. (BATC) has added a powerful capability to its existing imaging spectrometer
alignment and test facilities: Scanning Fabry-Perot source filters. These interferometers provide a means for efficient
instrument testing with full characterization from the ultra-violet (UV) to longwave infrared (LWIR). Spectral Response
Functions (SRF) and geometric distortions are accurately determined with a common approach. The techniques were
demonstrated with a two band cryogenic LWIR spectrometer and with the mid-wave infrared (MWIR) Spaceborne
InfraRed Atmospheric Sounder for Geosynchronous Earth Orbit (SIRAS-G) laboratory demonstration imaging
spectrometer. The spectrometer testing and performance is presented.
The Kepler spacecraft and telescope were designed, built and tested at Ball Aerospace & Technologies Corporation in
Boulder, Colorado. The Kepler spacecraft was successfully launched from NASA's Kennedy Space Center on March 6,
2009. In order to adequately support the Kepler mission, Ball Aerospace upgraded its optical testing capabilities. This
upgrade facilitated the development of a meter-class optical testing capability in a thermal vacuum (TVAC)
environment. This testing facility, known as the Vertical Collimator Assembly (VCA), was used to test the Kepler
telescope in 2008. Ball Aerospace designed and built the VCA as a 1.5m, f/4.5 collimator that is an un-obscured system,
incorporating an off-axis parabola (OAP) and test flat coated for operations in the VIS-IR wavelength region. The VCA
is operated in a large thermal vacuum chamber and has an operational testing range of 80 to 300K (-315 to 80°F). For
Kepler testing, the VCA produced a 112nm rms wavefront at cryogenic temperatures. Its integral autocollimation and
alignment capabilities allowed knowledge of the collimated wavefront characteristics to <5nm rms during final thermal
vacuum testing. Upcoming modifications to the VCA optics will bring the VCA wavefront to <20nm rms. The VCA
optics are designed and mounted to allow for use in either a vertical or horizontal orientation without degradation of the
collimated optical wavefront.
We have developed a test method using parametric phase retrieval to estimate the wavefront of a cryogenic infrared spectrometer. The phase retrieval algorithm accounts for optical system obscurations, apodization, noisy detector pixels, polychromatic sources, and spectrometer dispersion. This tool was used in establishing the optimal alignment and focus for a two channel infrared spectrometer operating in a cryogenic environment. This paper provides an overview of the technique and test implementation.
We have recently demonstrated the ability to measure the absolute change in optical power (focus) of a 152 mm diameter flat mirror in vacuum between room and cryogenic temperatures (133K) with a peak-to-valley measurement error of only 22nm. Such a measurement would be crucial to the verification of the focus of a cryogenic instrument during ground testing.
The testing utilized a vibration-insensitive interferometer and a reference mirror maintained at room temperature located within the thermal vacuum chamber. Special considerations were taken to ensure that the reference mirror experienced low axial thermal gradients, since structural modeling indicated that axial thermal gradients and axial variation of substrate coefficient of thermal expansion are critical in maintaining flatness under cryogenic test conditions. This paper will discuss the testing equipment and methodology and the corresponding analysis and results.
The High Resolution Imaging Science Experiment (HiRISE) camera will be launched in August 2005 onboard NASA's Mars Reconnaissance Orbiter (MRO) spacecraft. HiRISE supports the MRO Mission objectives through targeted imaging of nadir and off-nadir sites with high resolution and high signal to noise ratio [a]. The camera employs a 50 cm, f/24 all-reflective optical system and a time delay and integration (TDI) detector assembly to map the surface of Mars from an orbital altitude of ~ 300 km. The ground resolution of HiRISE will be < 1 meter with a broadband red channel that can image a 6 x 12 km region of Mars into a 20K x 40K pixel image. HiRISE will image the surface of Mars at three different color bands from 0.4 to 1.0 micrometers. In this paper the HiRISE mission and its camera optical design will be presented. Alignment and assembly techniques and test results will show that the HiRISE telescope's on-orbit wave front requirement of < 0.071 wave RMS (@633nm) will be met . The HiRISE cross track field is 1.14 degrees with IFOV 1.0 μ-radians.
Interferometric testing of large-sized optics in a thermal vacuum environment poses challenges not normally found in an optical metrology lab. Unless the test equipment is thermal-vacuum compatible, it must be installed in an ambient environment with the test item viewed through a window in the thermal-vacuum chamber. Limitations in chamber port size preclude normal-incidence viewing of the full aperture of large-sized optical elements. This necessitates the use of a mechanical translation of the test item to acquire multiple overlying interferograms. The interferograms are then concatenated in order to produce a full-aperture surface map of the test item. This is then used to confirm surface deformation of the entire test mirror. This paper will discuss the challenges, solutions, and results of a series of thermalvacuum tests performed on a large-scale (>40cm) silicon carbide mirror at ambient temperatures.
We report on a technique to measure the surface figure of mirrors under extreme vibrational conditions. Measurements are presented of the surface figure changes of Zerodur primary mirrors with both spherical and parabolic shapes, manufactured for the NASA Deep Impact program. Conditions ranged from room temperature to 130K. The interferometer was located outside the cryogenic vacuum chamber and did not require any active or passive vibration isolation. We show measurement repeatability of better than 1/500 waves RMS at 633nm.
Our Imaging Spectrometer Simulation Software known under the name Eikon should improve and speed up the design of a Computed Tomography Imaging Spectrometer (CTIS). Eikon uses existing raytracing software to simulate a virtual instrument. Eikon enables designers to virtually run through the design, calibration and data acquisition, saving significant cost and time when designing an instrument. We anticipate that Eikon simulations will improve future designs of CTIS by allowing engineers to explore more instrument options.
The advent of imaging spectroscopy has enabled optical sensors to be constructed that provide hyperspectral imagery on scales previously unattainable. Whereas multiband imagery on several spectral bands have been available for some time, the new generation of instruments is capable of providing imagery in hundreds or thousands of spectral bands. The price of increased measurement resolution is both greater system complexity, and, increased data processing burden.
One of the new instrument designs for producing hyperspectral imagery is the Computed Tomographic Imaging Spectrometer (CTIS). This instrument relies on a computer generated holographic mask as a dispersing element with relatively conventional optical elements and arrays. Design philosophy is discussed relative to systems requirements for using hyperspectral imaging in missile and fire control systems. Issues of optical throughput, dispersion, mask complexity, and, producability are discussed. Results are shown for masks manufactured to operate in the visible and infrared regions.
In concert with the design issues of the Computed Tomographic Imaging Spectrometer, the data processing and reduction is discussed both for remote sensing, and, typical missile and fire control applications. System tradeoff between algorithm complexity and mission is presented with regard to current algorithms and their implementation.
Completed systems are presented and results from both first and second-generation instruments are displayed. Deviation of actual operation from expectations is discussed relative to plans for further development.
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