DRACO is the only instrument on the Double Asteroid Redirection Test (DART) spacecraft. DRACO is a narrow angle camera designed to provide final images of the Didymos system at less than 0.50 m/px ground scale as well as provide images to be used for the Small-body Maneuvering Autonomous Real Time Navigation (SMARTNav) targeting system on board the DART spacecraft. DRACO includes an F/12.6, 2625mm focal length Ritchey-Chrétien telescope with a field-flattening lens. Images are taken with a 6.5um CMOS image sensor, the BAE CIS2521F, by the DRACO Focal Plane Electronics (FPE) and transferred to the spacecraft. Images are then processed for blobs and centroids for use in SMARTNav and either downlinked in real-time or recorded on the spacecraft for later playback. DRACO is thermally isolated and operated at -80°C to -20°C. Alignment was completed at room temperature, with additional checks after vibration testing and a focus shim was added for operation at cold temperature. Performance is near-diffraction limited and in-flight performance matches well with ground measurements. The BAE CIS2521 is measured to have very low read noise (< 2 e-) and negligible dark current. DRACO was integrated on the DART spacecraft in June 2021 after a successful instrument development and test campaign. DRACO is currently in use on the DART spacecraft after a successful commissioning. It will be used as the primary guidance sensor for the DART impact in September 2022 and provide high-resolution images of the Didymos system.
We report on the calibration of the Compact Midwave Imaging Sensor (CMIS) which has been developed by The Johns Hopkins University - Applied Physics Lab (JHU/APL) under a grant from the NASA Earth Science Technology Office (ESTO). At the heart of the CMIS instrument is a newly-developed high operating temperature (HOT) detector made from III-V compounds in a Type II Superlattice design. The instrument is sensitive to 3 particular bands in the IR spectrum which have been noted for their usefulness in determining cloud coverage and temperatures. The bands used were centered at 2.25 μm, 3.75 μm and 4.05 μm. The focal plane array (FPA) was based on the FLIR ISC0405 640×512 pixel readout integrated circuit with 15 μm square pixels. The CMIS design included a 5 zone “butcher block” filter placed in close proximity to the FPA and refractive optical elements contained inside the barrel of the cold shield such that the optics were cooled to approximately the same temperature as the FPA. A small-size, low-power closed-cycle cooler was used to maintain the FPA and the optics at a temperature of 150 K, at which the dark current was low enough to allow integration times longer than 50 ms for cold background scenes. JHU/APL developed the camera control electronics (CCE) and data processing unit (DPU) for running the FPA, performing image processing functions on the data and storing it in memory. The CCE and DPU were designed for possible use on an orbital payload but for the airborne flight the commercial versions of some of the parts specified for spaceflight were used. This paper will describe the laboratory calibration procedures and results.
Plastics are often used in mine and IEDs. Difficult to detect with traditional approaches, plastics are spectrally active in the shortwave and mid-infrared due to vibrational absorptions from the C-H bonds of which they are composed; bonds and vibrations that are diagnostic of and spectrally vary with composition. Hyperspectral infrared imaging has proven exceedingly capable of detecting and categorizing plastics. Here we pursue a dual-band imaging approach that leverages the ubiquitous presence of the ~1.7-micron harmonic of the ~3.4-micron fundamental absorption feature for a low SWaP (Size, Weight, and Power) instrument concept. The 1.7-micron band is also in a spectral region free of telluric and almost all geologic absorption features, making its presence in a reflectance spectrum almost a unique marker for plastics. We have developed and tested a two-camera, dual-band sensor, emphasizing imaging over spectroscopy and implementing on-camera processing to achieve near real-time, partially autonomous detection and imaging of plastic objects. The sensor has proven successful in discriminating and imaging plastics such as fiberglass, styrene, and acrylics from background materials such as grass, dirt, rocks, and brush. The sensor is challenged by certain plastics, especially thin, transparent plastics (less relevant to mines and IEDs) even if they are spectrally active near 1.7 microns. Also, photometric variations in the observing conditions can mask weak plastic signatures. We will discuss our current measurement and technical approach, the results and the challenges that remain to implementing an effective low SWaP sensor for the detection and imaging of plastic objects.
NASA's Europa Clipper will carry two cameras as part of the Europa Imaging System (EIS). Both the wide angle camera and narrow angle camera have identical focal plane modules, each containing a CMOS image sensor and patterned optical filter array. The filter array enables multispectral pushbroom imaging in six bands, spanning 380nm to 1000 nm, adding additional science capability for surface characterization and searching for evidence of recent activity. The EIS filter array is monolithic in construction, with all bands coated on a single substrate. Each stripe measures only 320 μm wide-equivalent to 32 pixels on the image sensor-leaving most of the field of view clear for full frame panchromatic imaging. Using photolithography, a mask is applied to the filter substrate and developed, leaving only the desired pattern exposed. The filter is then deposited onto the substrate and the mask removed. This process is repeated for each additional band on the array until all filters have been applied. The filters are then aligned with the image sensor rows using a machined metal housing, placing it as close as possible to the focal plane. As part of a technology development program to qualify them for space flight, several filters have been performance tested for resistance to radiation exposure, thermal cycling, vibration, and dry heat microbial reduction for planetary protection.
The Double Asteroid Redirection Test (DART) is a spacecraft that will impact the smaller body of the binary asteroid Didymos. As a technology demonstration, this will be the first time a kinetic impactor is used to perturb the motion of a near earth object. This technique could someday be used to deflect a dangerous asteroid on a future collision course with Earth. As the only instrument aboard DART, the Didymos Reconnaissance and Asteroid Camera for OpNav (DRACO) serves two purposes. First, DRACO provides images to the Small-body Maneuvering Autonomous Real-Time Navigation (SMARTNav) algorithm, allowing the spacecraft to precisely locate and impact the target. In its final moments, DRACO will also characterize the impact site by providing high resolution, scientific imagery of the surface. Derived from the Long Range Reconnaissance Imager (LORRI) on New Horizons, the telescope is a 208 mm aperture, f/12.6, catadioptric Ritchey-Chrétien, with a 0.29 degree field of view. A lightweight opto-mechanical structure, with low CTE mirror substrates and a composite baffle tube, maintains telescope focus in the low temperature environment of deep space. At the focal plane is a 2560 by 2160 pixel, panchromatic, front-side illuminated complementary metal oxide semiconductor (CMOS) image sensor, with digital output, global shutter, and low read noise. A highly integrated focal plane electronics (FPE) module controls the sensor and relays data to the spacecraft.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has created a unique design for a compact, lightweight, and low-power instrument called the Compact Midwave Imaging Sensor (CMIS). Funded by the NASA ESTO Instrument Incubator Program (IIP), the goal of this CMIS development project is to increase the technical readiness of CMIS for retrieval of cloud heights and atmospheric motion vectors using stereo-photometric methods. The low-cost, low size, weight and power (SWaP) CMIS solution will include high operating temperature (HOT) MWIR detectors and a very low power cooler to enable spaceflight in a 6U CubeSat. This paper will provide an overview of the CMIS project to include the high-level sensor design.
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