An optics system that mimics the structure of a lobster’s eyes could be employed on the International Space Station to enable NASA to precisely locate, characterize and alert other observatories about the source of gravitational waves. The Transient Astrophysics Observatory on the International Space Station, or ISS-TAO, is being considered by NASA as a potential Explorer Mission of Opportunity. An international team is currently refining its two instruments: a NASA-provided soft x-ray wide-field imager (WFI), which is equipped with the lobster-eye optics, and the Israel Space Agency-provided gamma ray transient monitor. Lobster eyes are made up of long, narrow cells that each reflect a tiny amount of light from a given direction. This allows the light from a wide viewing area to be focused into a single image. WFI’s optic works the same way as the crustacean’s. Its eyes are microchannel plates — thin, curved slabs of material dotted with tiny tubes across the surface. X-ray light can enter these tubes from multiple angles and is focused through grazing-incidence reflection, giving the technology the wide field of view that is necessary for finding and imaging transient events that cannot be predicted in advance. Lobster-eye optics have yet to be used in a space application, investigator Jordan Camp said. The Goddard-provided soft x-ray wide-field imager proposed for a mission called ISS-TAO borrows heavily from nature. The images on the left and center show close-up views of a crustacean's eyes; the image on the right shows a manmade microchannel plate. Both operate the same way. Both gather light from multiple angles, focusing it into a single image to provide a wide field of view. Courtesy of J. Camp. From its berth on the International Space Station, the ISS-TAO would monitor the sky in search of transient x-rays and gamma rays unleashed during black-hole and neutron-star mergers and supernovae. These powerful upheavals generate gravitational waves. In 2016, scientists revealed that LIGO had detected gravitational waves from two separate events involving the collision of black holes in other galaxies; others have been reported since. In October 2017, LIGO announced the first-ever detection of gravitational waves from the merger of two neutron stars. NASA's Fermi Gamma-ray Space Telescope detected a weak burst of high-energy light, the first ever to be unambiguously connected to a gravitational-wave source. Half a day later, observatories around the world had found the location in visible light, pinpointing a gravitational wave source for the first time. The ISS-TAO would serve as a sentinel, said investigator Scott Barthelmy. In addition to conducting all-sky surveys of transient x-ray sources, the ISS-TAO would locate the x-ray counterparts to sources of gravitational-wave events, gather data and communicate the events' position to other observatories so that those researchers could begin their own observations. Goddard Principal Investigator Jordan Camp (center) and Co-Investigator Judy Racusin are leading an international team advancing a proposed mission to characterize the sources of gravitational waves. Deputy Principal Investigator Scott Barthelmy (left) holds an important mission technology -- the micro-channel optic. Courtesy of NASA/W. Hrybyk. “LIGO and Virgo [a recently upgraded interferometer facility in Pisa, Italy] form the advanced network of gravitational-wave observatories,” Camp said. “They will alert us to the most exciting candidates . . . Although these facilities can detect the ripples in space-time, they can’t focus gravitational waves and instead achieve their source localization by timing of noisy signals. Thus, they can’t precisely locate their sources.” In contrast, the ISS-TAO would point its lobster optics to the large portion of the sky identified by LIGO and Virgo and then focus X-rays to localize and characterize these sources, he said. Should ISS-TAO be selected as an Explorer Mission of Opportunity, Camp believes he could complete the mission and launch by 2022, just a few years after the scheduled launch of the James Webb Space Telescope. The Webb observatory also could be enlisted to observe the explosive events that generate gravitational waves, he said. For more information, visit the NASA web site.