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Ultraviolet Solar Blind Sensors for Microsatellites and Small Satellites


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Space Technology OBJECTIVE: Develop innovative manufacturing methods to produce high quality ultraviolet (UV) and Vacuum UV (VUV) photodetectors for use in space on microsatellites (microsats) and small satellites (SmallSats) with strong visible wavelengths rejection. DESCRIPTION: Improvements in the manufacturing of UV and VUV sensors are needed by the Navy to meet sensitivity and stray light rejection demands of compact optical systems designed for operation in space on the next generation of microsats being designed to study the ionosphere,1,2,3 and thermosphere4, and for use in other Navy applications. Availability of high-quality photodetectors will allow for future mission growth. The Navy is seeking to foster the development of affordable optical components and systems with broad application to space-based remote sensing systems. Current detector technology involves either fragile glass phototubes or photodiodes, both of which have unwanted visible light sensitivity. Typical CubeSat UV sensors used in SmallSats have been commercial off-the-shelf (COTS) or custom photomultipliers with fragile components and require high voltages for operation. Innovative detectors are sought with the ruggedness, mass, and material properties necessary to produce high-quality spaceflight optical elements. Innovative techniques are sought to develop solar blind detectors needed for the new class of remote sensing instruments. UV and VUV detectors used for remote sensing of the ionosphere, including PMTs and solid-state sensors, typically feature an unwanted sensitivity to visible light. These sensitivities are normally attributed to impurities in the sensor materials. Goals are a ratio of 10^5 improvement in the UV/visible sensitivity. Solidstate devices are preferred since they do not require high voltages and require less power. High purity, wide bandgap materials can be considered as well as innovative light filtering schemes. Devices should be composed of compatible spacecraft materials, be low outgassing, survive at temperatures of -50ºC to +60ºC, and have the ability to survive a NASA GEVS5 vibration specification and thermal test environment, all typical of the requirements imposed for flight on small spacecraft. Technologies proposed should not contain hazardous or high outgassing materials and should be capable of being integrated into typical optical systems. It is desired that their containers be moderately electrically and thermally conductive to avoid developing static charge and thermal gradients in space. They should be durable and able to withstand normal optical component handling procedures. They should be delivered in an optically clean state and be robust enough to withstand precision cleaning and vacuum baking as part of normal spacecraft processing. PHASE I: Develop and demonstrate concept feasibility for an innovative UV and VUV sensor technology meeting Navy needs for microsat optical systems. Demonstrate performance advantages over current technology by producing sample devices that can be tested to Navy requirements. GSE circuits will be provided that allow the Navy to test the devices in Navy facilities. While exact sensor responsivities are not specified for Phase I, the awardee will establish that the device can be used in the UVC range with windows and that it is capable of operating windowless or with MfF2 windows for the VUV region. Focus research on visible light rejection and materials. The path to using this technology to produce VUV detectors should be defined. Proposed sensor concepts should meet the following thresholds: Deliverable Design Characteristics: Maximum sensor mass = 35g Sensor area: = 1mm^2 UVC sensitivity: 100 mA/W UVC/Vis: > 10^5 Dark current < 10 nA Survival Temp range: -50 - +60°C Full sensitivity (windowless): for UV and VUV Vibration, Shock, and Thermal: NASA GEVS5 PHASE II: Develop a Phase II prototype sensor of the > 1mm^2 size class for evaluation in the VUV. The prototype will be evaluated to determine its capability in meeting the performance goals defined in Phase II Statement of Work (SoW) and the Navy need for solar blind UV and VUV sensors. The prototype design should provide collecting areas no less than 1mm^2 (objective), and should show applicability to be utilized with various electronics and spacecraft architectures. Deliver a minimum of five of these prototypes to the Navy for evaluation. Perform detailed analysis to ensure materials are rugged and appropriate for Navy application. Environmental, shock, and vibration analysis will be performed. Optical checks will include UV & VUV sensitivity, dark current, signal to noise (S/N), and UV/Vis rejection ratio. Prototype windowless VUV sensors will be produced and tested. PHASE III DUAL USE APPLICATIONS: Apply the knowledge gained in Phase II to build an advanced sensor, suitably configured for a smallsat application, including flight spares and interface electronics, and characterize its performance in the UV & VUV as defined by Navy requirements. Working with the Navy and applicable Industry partners, demonstrate application to a DoD Space Test Program (STP) flight test. Support the Navy for test and validation to certify and qualify the system for Navy use. Explore the potential to transfer the UV/VUV sensor system to other military and commercial systems (NASA, University, Optics Industry). Market research and analysis shall identify the most promising technology areas and the company shall develop manufacturing plans to facilitate a smooth transition to the Navy. REFERENCES: 1. Budzien, Scott et al. “Comparison of second and third generation 135.6 nm ionospheric photometers using on-orbit and laboratory results.” SPIE Proceedings, Volume 11131, CubeSats and SmallSats for Remote Sensing III; 1113102 (2019) 2. Attrill, G.D.R.; Nicholas, A.C., Routledge, Graham et al., “Coordinated Ionospheric Reconstruction CubeSat Experiment (CIRCE), In situ and Remote Ionospheric Sensing (IRIS) suite,” Journal of Space Weather and Space Climate, (2020) in press. 3. Nicholas, Andrew C., et al. "Triple magnesium ionospheric photometer (Tri-MIP) instrument overview." CubeSats and SmallSats for Remote Sensing V. Vol. 11832. SPIE, 2021. 4. Fritz, Bruce. Tiny Remote-sensing Instrument for Thermospheric Oxygen and Nitrogen: A Concept Study. NAVAL RESEARCH LAB WASHINGTON DC, 2022. 5. NASA General Environmental Verification Standards (GEVS), Rev. A, GSFC-STD-7000 (2013). KEYWORDS: Ultraviolet; UV; UV sensors; vacuum ultraviolet; VUV sensors, detector technology, detector fabrication, spaceflight optics, spaceflight structures
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