\n<\/p>\n
A recently developed ultra-black coating not only efficiently absorbs light, but is also extremely thin and durable, enabling its potential use on starshades that could someday support the imaging of exoplanets and potentially facilitate the detection of life beyond our solar system.<\/strong><\/p>\n The light emitted by a star can be billions of times brighter than the light reflected from its surrounding planets. This bright starlight makes it\u00a0very difficult\u00a0for a space telescope to image an exoplanet\u00a0\u2014\u00a0it\u2019s\u00a0like trying to find the light reflected from a gnat that is flying near a spotlight. In addition, the light from our Sun scatters off spacecraft surfaces\u00a0and\u00a0back\u00a0into the\u00a0telescope, contributing even more light \u201cpollution\u201d that\u00a0can easily\u00a0obscure\u00a0the\u00a0dim\u00a0light reflected from\u00a0an\u00a0exoplanet.\u00a0\u00a0<\/p>\n A\u00a0starshade\u00a0is a giant, flower-shaped spacecraft (roughly half\u00a0the size of a football field) that is designed to be positioned between a space telescope and a distant star so that it casts\u00a0a shadow from the distant star onto the telescope. A\u00a0starshade\u00a0can\u00a0block unwanted light from the parent star\u00a0to the extent\u00a0that less than one part per billion of the starlight is observable,\u00a0while allowing the much fainter light from\u00a0an\u00a0orbiting\u00a0exoplanet\u00a0to pass around the\u00a0starshade\u00a0and reach the telescope, thereby enabling its detection. But to enable a telescope to distinguish an exoplanet, a\u00a0starshade\u00a0must create an extremely pristine shadow\u00a0on the telescope. Not only must it block the starlight from the parent star,\u00a0it\u00a0must also suppress the stray\u00a0light from our Sun\u00a0that\u00a0scatters\u00a0from\u00a0the\u00a0starshade\u2019s\u00a0\u201cpetal\u201d\u00a0edges\u00a0into the telescope.\u00a0<\/p>\n Over the past decade, NASA-sponsored engineers\u00a0have explored\u00a0various\u00a0methods to address the issue of stray sunlight. For example, they developed a way to make\u00a0a\u00a0starshade\u2019s\u00a0edges razor sharp by crafting blades from amorphous metals. The edges of these blades were only 300 nanometers thick, but\u00a0data\u00a0showed that even such thin metal edges would still scatter too much sunlight into the telescope.\u00a0\u00a0<\/p>\n Researchers\u00a0also tried applying black coatings to the\u00a0starshade\u00a0edges to reduce the reflected\u00a0light. Unfortunately, the existing black coatings were far too thick; they made the\u00a0starshade\u00a0edges thicker (duller), which\u00a0actually\u00a0increased<\/em>\u00a0the\u00a0scatter. Carbon nanotube coatings, for instance, are several microns thick\u00a0\u2014\u00a0much thicker than the 300-nm\u00a0starshade\u00a0edge. Other existing coatings that rely on three-dimensional microstructures to trap light were also too thick.\u00a0<\/p>\n In 2004, David Sheikh, founder of the small business\u00a0ZeCoat\u00a0Corporation, was researching the concept of a \u201cblack mirror\u201d\u00a0\u2014\u00a0a mirror that absorbs\u00a0nearly all\u00a0incident light instead of reflecting it. He came across\u00a0a methodology\u00a0used decades ago to make light-absorbing, smooth surfaces.\u00a0\u00a0<\/p>\n Sheikh used\u00a0modern computing techniques and more\u00a0accurate\u00a0material property data\u00a0to improve this\u00a0methodology,\u00a0and\u00a0developed\u00a0a breakthrough method for manufacturing an ultra-black coating using a unique, motion-controlled, physical vapor deposition process also developed at\u00a0ZeCoat.\u00a0The coating design uses extremely thin, partially transparent metal layers that are separated by dielectric glass layers to form multiple light-absorbing, nanoscale\u00a0cavities. When the\u00a0thicknesses\u00a0of the layers are tuned precisely with the aid of a computer, incoming light resonates as a standing wave inside the cavities, where the metals absorb it. The principle\u00a0is\u00a0similar to\u00a0the Fabry\u2013Perot cavity used in lasers\u00a0\u2014\u00a0except instead of amplifying light, the light is trapped and absorbed.\u00a0This new coating turned out to be 100 times thinner than those previously tested\u00a0for use on\u00a0starshades.\u00a0<\/p>\n In 2020, NASA\u2019s\u00a0Exoplanet Exploration Program\u00a0at the agency\u2019s Jet Propulsion Laboratory (JPL)\u00a0in Southern California\u00a0chartered\u00a0a\u00a0Starshade\u00a0Science and Industry Partnership (SIP)\u00a0to maximize the technology readiness level of\u00a0starshades\u00a0to enable potential future exoplanet science missions.\u00a0As\u00a0part of this\u00a0initiative, the\u00a0new coating\u00a0developed by\u00a0Zecoat\u00a0was applied to\u00a0prototype\u00a0starshade\u00a0edges, and\u00a0engineers at JPL\u00a0used a custom-built laser\u00a0scatterometer\u00a0to measure scatter from coated and uncoated 50-cm\u00a0long\u00a0amorphous metal\u00a0blades.\u00a0These tests\u00a0demonstrated\u00a0that the new coating reduced the reflected light by a factor of about 20\u00a0\u2014\u00a0enough to enable a telescope to\u00a0image an exoplanet.\u00a0(The\u00a0results of this\u00a0effort\u00a0were published\u00a0here<\/a>\u00a0in the SPIE digital Library).<\/p>\n Building on the success of the edge coating demonstration and supported by a\u00a02021\u00a0NASA Small Business Innovative Research (SBIR)\u00a0contract,\u00a0ZeCoat\u00a0developed\u00a0a\u00a0novel\u00a0thin film deposition\u00a0process\u00a0to coat large sheets of polyimide film with a similar ultra-black finish.\u00a0The process uses multiple electron beam evaporators\u00a0to\u00a0apply thin, uniform films to\u00a0a\u00a0moving membrane substrate in a roll-to-roll\u00a0coating\u00a0process.\u00a0These\u00a0large\u00a0coated\u00a0membranes\u00a0(~ 1-meter wide and many meters long)\u00a0could be\u00a0patched\u00a0together\u00a0to form\u00a0a\u00a0starshade\u2019s\u00a0central\u00a0disk\u00a0section, as well as\u00a0its\u00a0petal\u00a0surfaces, which would\u00a0remove even more stray light and further improve the\u00a0quality\u00a0of images a space telescope could produce.\u00a0(For\u00a0additional\u00a0details,\u00a0see the\u00a0entry for this project on NASA\u00a0TechPort<\/a>\u00a0and\u00a0this article<\/a>\u00a0in the SPIE digital Library.)\u00a0<\/p>\n Besides\u00a0use on\u00a0starshades, durable black\u00a0coatings\u00a0have a wide variety of science, military, and commercial applications. For example,\u00a0they\u00a0could be used to darken constellations of\u00a0satellites\u00a0so they are less visible from the ground, or to darken surfaces near the camera on a cell phone.\u00a0\u00a0\u00a0<\/p>\n In addition,\u00a0ZeCoat\u00a0recently was awarded a NASA SBIR Phase I contract and is\u00a0applying the\u00a0thin-film\u00a0roll-to-roll coating process\u00a0described above\u00a0to develop thermal control coatings\u00a0that\u00a0are resilient\u00a0enough\u00a0to\u00a0mitigate damage from\u00a0micrometeorite strikes. These coatings could be\u00a0potentially\u00a0used\u00a0on\u00a0future\u00a0space vehicles\u00a0such\u00a0as\u00a0the\u00a0Habitable Worlds Observatory.<\/p>\n For\u00a0additional\u00a0details,\u00a0see the\u00a0<\/strong>entry for this project on NASA\u00a0TechPort<\/strong><\/a>.<\/strong>\u00a0<\/p>\n Project Lead:<\/strong>\u00a0David\u00a0A.\u00a0Sheikh,\u00a0ZeCoat\u00a0Corporation\u00a0\u00a0<\/p>\n Sponsoring Organization(s):<\/strong>\u00a0NASA Astrophysics Exoplanet Exploration Program,\u00a0NASA STMD, NASA JPL\u00a0<\/p>\n Some of the\u00a0work\u00a0described\u00a0above was carried\u00a0out\u00a0at the Jet Propulsion Laboratory,\u00a0which is managed by Caltech for NASA\u00a0(80NM0018D0004).\u00a0\u00a0<\/p>\n<\/div>\n