Simulation-To-Flight (STF-1): A Mission to Enable CubeSat Software-Based Validation and Verification

The Simulation-to-Flight 1 (STF-1) CubeSat mission aims to demonstrate how legacy simulation technologies may be adapted for flexible and effective use on missions using the CubeSat platform. These technologies, named NASA Operational Simulator (NOS), have demonstrated significant value on several missions such as James Webb Space Telescope, Global Precipitation Measurement, Juno, and Deep Space Climate Observatory in the areas of software development, mission operations/training, verification and validation (V&V), test procedure development and software systems check-out. STF-1 will demonstrate a highly portable simulation and test platform that allows seamless transition of mission development artifacts to flight products. This environment will decrease development time of future CubeSat missions by lessening the dependency on hardware resources. In addition, through a partnership between NASA GSFC, the West Virginia Space Grant Consortium and West Virginia University, the STF-1 CubeSat will hosts payloads for three secondary objectives that aim to advance engineering and physical-science research in the areas of navigation systems of small satellites, provide useful data for understanding magnetosphere-ionosphere coupling and space weather, and verify the performance and durability of III-V Nitride-based materials

LOCC: Enabling the Characterization of On-Orbit, Minimally Shielded LEDs

Over the past decade, trends have shown a substantial growth of interest for small satellite solutions, ranging from earth-orbit imaging to cheap global communication networks. Along with space-based applications, several research missions are focused on testing novel sensors and materials, group III-V nitride semiconductors being among them. Small satellite missions provide a unique opportunity to gain an understanding of the reliability and operational characteristics of these materials when exposed to the harsh environment of space. Such insight will lead to unique space applications of these materials in larger missions. While the nature of electronic and optoelectronic devices involving III-V materials under the bombardment of ionizing radiation has been reported, these findings have mostly been established via controlled tests in terrestrial laboratories. In this work, a Low-powered Optoelectronic Characterizer for CubeSat (LOCC) has been developed to perform in- situ current-voltage measurements of III-V nitride based optoelectronic devices on-orbit. Lastly, it is important to note the use of III-V nitride materials in this experiment. Custom InGaN LEDs have been fabricated with a center emission wavelength of 465 nm The LOCC system includes a spectral confirmation module that is used for luminescence characterization of the devices. While most current-voltage measurement instruments are made for laboratory benches and consume higher amounts of power, this system is designed using low-power integrated circuits that are capable of supplying the necessary current while maintaining low-power operation. The system must also operate within the data transfer and storage limitations of the CubeSat platform. LOCC is designed to transmit the experimental results to the satellite’s controlling computer via an I2C bus. The characteristics of low- power consumption and small information storage requirements make LOCC an excellent match for this science mission. This paper details the design and control of the LOCC system. The design includes block diagrams, PCB layout, interfacing, and control. Additionally, the resulting current-voltage measurements, required wattage, and required data storage will be presented to illustrate functionality. This instrumentation will enable the study of III-V nitride based optoelectronic devices in space, as well as parallel advancements of electronics and optical sensors that can be used for short-distance range finding and shape rendering systems for satellite servicing missions

Improvement in the Light Extraction of Blue InGaN/GaN-Based LEDs Using Patterned Metal Contacts

We demonstrate a method to improve the light extraction from an LED using photonic crystal (PhC)-like structures in metal contacts. A patterned metal contact with an array of Silicon Oxide (SiO x ) pillars (440 nm in size) on an InGaN/GaN-based MQW LED has shown to increase output illumination uniformity through experimental characterization. Structural methods of improving light extraction using transparent contacts or dielectric photonic crystals typically require a tradeoff between improving light extraction and optimal electrical characteristics. The method presented here provides an alternate solution to provide a 15% directional improvement (surface normal) in the radiation profile and ~ 30% increase in the respective intensity profile without affecting the electrical characteristics of the device. Electron beam patterning of hydrogen silesquioxane (HSQ), a novel electron beam resist is used in patterning these metal contacts. After patterning, thermal curing of the patterned resist is done to form SiO x pillars. These SiO x pillars aid as a mask for transferring the pattern to the p-metal contact. Electrical and optical characterization results of LEDs fabricated with and without patterned contacts are presented. We present the radiation and intensity profiles of the planar and patterned devices extracted using Matlab-based image analysis technique from 200 μm (diameter) circular unpackaged LEDs