Roger J. Thomas (1942–2015)

It is with great sadness that we inform you that our friend and colleague Dr. Roger J. Thomas passed away on May 19, 2015. He is survived by his wife Jan, daughter Elaine, and two grandchildren.

Roger was a scientist of immense integrity, focus, and commitment. Born in Detroit, Michigan on July 3, 1942, he graduated from Cass Technical High School and attended the University of Michigan, receiving a B.S. in Physics in 1964, an M.S. in astronomy in 1966, and a Ph.D. in Astronomy in 1970. He came to NASA Goddard Space Flight Center (GSFC) as a National Research Council Resident Research Associate in 1970 and soon joined the Solar Physics Branch as a civil servant scientist. For his decades of distinguished service, he was awarded the prestigious NASA Exceptional Service Medal in 2009. He received many other NASA and external awards for his key contributions to space missions and sounding rocket investigations.

Dr. Thomas was an internationally recognized expert on the design and scientific use of imaging extreme ultraviolet spectrographs. He provided the optical design or advised on numerous solar EUV spectrographs flown by NASA or ESA and was widely recognized for his vital role in their record of success. He created optical designs for the CDS/NIS instrument on SOHO and the EIS instrument on Hinode, as well as for many sounding rocket instruments, including MOSES, SUMI, RAISE, VERIS, and UVSC. Above all, Roger was a linchpin of the GSFC SERTS and EUNIS sounding rocket investigations over a span of 30 years and 13 flights.

Roger Thomas made lasting contributions to the technology of solar EUV optics. In 1986, he developed the first computer-controlled system for fabricating grazing incidence EUV telescopes to feed high-resolution spectrographs. This system found application in four successful sounding rockets and is incorporated in the EUV light source used to provide absolute radiometric calibration for instruments on SOHO and Hinode. In 1992, he conceived the idea of using a toroidal grating system to produce EUV spectral images with only a single reflection, and he developed new software to ray-trace and optimize such designs. His concepts were proven on the SERTS sounding rocket and culminated in the SOHO/CDS and Hinode/EIS instruments. Roger led the first effort to apply multilayer interference coatings onto gratings of high groove density; at the time, a noted specialist in multilayer coatings assured him his idea would never work. The result was a new generation of EUV spectrographs with unprecedented efficiency. In recent years, he led the way in introducing toroidal variable line space gratings as an essential design feature of the current generation of solar EUV spectrographs.

Dr. Thomas served as the Study Scientist for the Solar Cycle and Dynamics project (1978–1981), the Deputy Chief of NASA’s Solar and Heliospheric Physics Office (1983–1984), Deputy Project Scientist for the Orbiting Solar Laboratory (1990–1992), and Project Scientist for the Orbiting Solar Observatory missions from 1976–1983.

Dr. Thomas conducted a wide range of pioneering studies of spatially imaged, high-resolution EUV spectra of coronal structures. Among his interests were the determination of elemental abundances and their possible variations, investigations of coronal heating mechanisms, and quantitative characterizations of physical plasma conditions in different solar features. Analyzing spectroscopic data from the Orbiting Solar Observatories, he co-discovered the “precursor phase” that often provides a vital early warning of a building solar flare. The method he devised in the 1980’s for deriving the effective temperature and differential emission measure of a solar plasma from broad-band sensor measurements, developed originally for GOES X-ray measurements, was also adapted to imaging instruments on the Yohkoh, SOHO, TRACE, and STEREO missions. He compiled one of the first extensive catalogs of the solar EUV spectrum, which was for years a touchstone in the field and stimulated dozens of papers on the underlying atomic physics. He led the effort to obtain an absolute radiometric calibration for the EUNIS sounding rocket experiment, a key aspect of its scientific value. He authored or coauthored more than 80 scientific publications in refereed journals, and at least 180 other scientific or technical papers. He retired in January 2010 after nearly 40 years of federal civil service.

Beyond his technical excellence, a major reason that Roger Thomas was so often sought as a Co-Investigator on satellite and sounding rocket instruments was his unselfish willingness to conceive and share his most advanced designs with any group that had the potential to do important science by incorporating them. That was just one aspect of the core integrity and idealism that made him an esteemed colleague and friend.