Above:
Helix Of Nebula Venus crosses the line of sight between the sun and Earth four times every 243 years in pairs separated by eight years. Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.
Orbital
High Efficiency Far and Near Ultraviolet Detectors with Tailored Response for SPARCS
In the search for extraterrestrial signs of life, many researchers are focusing on exoplanets —or planets that exist beyond our solar system— so far away that they cannot be directly imaged using currently deployed missions. Flagship mission concepts, such as the Habitable Exoplanet Imaging Mission (HabEx) andthe Wide-Field Infrared Survey Telescope (WFIRST), will use large telescopes to directly image and characterize exoplanets by masking starlight. Interpretation of data for assessing the habitability of the exoplanet from these large telescopes requires a complete view of nearby star’s ultraviolet (UV) activity. A new small mission called the Star-Planet Activity Research CubeSat, or SPARCS, will do just that in 2021.
The goal of SPARCS is to take a step back and examine the flares and other stellar activities of red dwarf stars, which are less than half the size of our sun and with 1 percent of its brightness. There are about 40 billion red dwarf stars in the Milky Way galaxy, and the mission—with the help of unique ultraviolet sensors developed by the Microdevices Laboratory (MDL)—will provide insight into habitable star systems and give researchers clues about how to interpret exoplanet data from bigger space telescopes.
In 2018, the SPARCS mission was one of only two CubeSat missions selected for funding by the Astrophysics Research and Analysis program, which manages the Astrophysics CubeSats and suborbital missions for NASA. SPARCS would be the first mission to provide dedicated, long duration UV observations of red dwarf stars. SPARCS achieves this in a six-unit CubeSat— the size of a cereal box— by using a small telescope and high-performance UV camera. Astrophysics missions typically depend on large aperture telescopes, and thus have been more challenging to fit the form factor of small CubeSats. With innovations in high-efficiency silicon UV detectors, where the need for high voltage and bulky detectors is eliminated, astrophysics UV CubeSat missions like SPARCS are becoming a reality. The data gathered by SPARCS would help scientists better understand exoplanet habitability potential by revealing their UV environment. These data are crucial to interpreting observations of planetary atmospheres in the context of their host star, whose ultraviolet activity may affect the nearby planets’ atmospheric signatures and our assessment of their habitability.
SPARCS is a collaborative effort between Arizona State University and JPL. JPL is responsible for delivery of the SPARCam, an ultraviolet camera with two channels in the far ultraviolet (FUV) and near ultraviolet (NUV). At the heart of the SPARCam arethe detectors, each with a response tailored at MDL to optimize the SPARCS science return by maximizing the sensitivity to each spectral band while rejecting the out-of-band light—a breakthrough for silicon detectors. Silicon detectors are used universally on NASA missions, creating images that are crucial for the entry, descent, and landing process, as well as providing images for necessary context in science measurements. Image-tube based detectors have been used extensively in the ultraviolet spectral range in the past; however, they are bulky, have low sensitivity, and require high voltage. With advancements made at MDL, silicon detectors now have a UV response five to tentimes higher than an flight instrument image-tube detectors. Through nanoengineering, researchers have made it possible to produce silicon arrays with unprecedented capabilities. They have achieved tailorable response such that these silicon detectors have high sensitivity in the ultraviolet while rejecting background from visible and infrared sources. In collaboration with the industry, MDL is leveraging investments in silicon imaging technology to develop and deliver unique ultraviolet sensors based on the latest silicon detector designs.
Principal investigator for SPARCS is Professor Evgenya Shkolnik at Arizona State University’s School of Earth and Space Exploration. Principal investigator for the SPARCam is Shouleh Nikzad at MDL, April Jewell at MDL is the lead for the detector.
Left:UV Flux The stellar UV flux has a dramatic effect on a planet’s detected atmospheric content. The plot shows an Earth-like planet spectrum in the habitable zone of an active (red) and inactive (gold) M4 dwarf. The spectrum of Earth around the Sun is shown black for comparison. Adapted from Rugheimer et al., The Astrophysical Journal, vol. 809, issue 1, pp. 57, 2015.
Right:Uninterrupted observations The CubeSat platform of SPARCS allows for dedicated, uninterrupted observations of its targets for days or even weeks. Data from such prolonged observations are essential to the development of stellar models but are not available from larger missions such as Hubble Space Telescope (HST) and Galaxy Evolution Explorer (GALEX), which must share observation resources.
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April Jewell at the MDL 8-inch MBE used for 2D doping of the detectors for SPARCS.
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Left:The SPARCam detectors are 2D-doped CCDs that are individually optimized for the SPARCS FUV and NUV bands.
Right:The SPARCS payload includes a small telescope and SPARCam, which together to occupy <3 U of the CubeSat volume (1 U=10 cm3) Image courtesy Nathaniel Struebel of AZ Space Technologies LLC, working in partnership with the Arizona State University SPARCS mission team.
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