Jerry Nelson (1944–2017)

Jerry Nelson, an internationally known expert on large, segmented telescope technology, died on Saturday June 10, 2017. He was 73.

Jerry Nelson, the father of the segmented-mirror telescope and a towering figure in the history of telescope building, was born in an unincorporated area of northern Los Angeles County to a father who was a machinist and a mother who ran a children’s center. He would be the first member of his family to go to college. Jerry was introduced to astronomical research as a high school student in 1960 at the renowned Summer Science Program in Ojai (then in its second year), and to telescope building as an undergraduate physics major at the California Institute of Technology (class of 1965), when he assisted Gerald Neugebauer with the construction of a 1.5-meter infrared telescope. As a Caltech undergraduate he sufficiently impressed his lab instructor and future colleague Eric Becklin with his experimental skill that Becklin was still marveling about it 50 years later.

As a graduate student at the University of California, Berkeley, Jerry’s interests shifted to experimental particle physics. His thesis work, under the direction of Burton Moyer at the Lawrence Berkeley National Laboratory, was performed with such distinction that immediately after receiving his Ph.D. in 1972, he was awarded a prestigious Lab Fellowship that allowed him to define his own research program. Jerry used this freedom to return to astrophysics, applying his expertise in particle-physics electronics to a series of ingenious timing experiments at Lick Observatory, involving the Crab and other optical pulsars.

In 1977, University of California astronomers were forming a committee to investigate building a successor to the Lick 3-meter telescope, and Jerry, who had caught the attention of some committee members with his optical pulsar work, was appointed in order to provide something of an outsider’s perspective. Jerry characterized this appointment as “the opportunity of a lifetime,” and he would see to it that it would change not only the course of his life, but course of observational astronomy as well.

Jerry had an abiding love of first principles and an extraordinary ability to see both their furthest reaching implications and a path to getting there; his explanation for virtually every one of his remarkable physical insights would begin with: “It’s just freshman physics!” Preventing a mirror from distorting under gravity requires that its thickness increase as the square of the diameter, a fact that led Jerry directly to the concept of segmented mirrors; however, the idea of building a ten-meter diameter mirror out of 36 segments raised some formidable problems, which Jerry, working with Terry Mast, his close collaborator for 40-plus years, proceeded to solve. In particular, his development of stressed mirror polishing (with U.C. Berkeley’s Jacob Lubliner) solved the problem of how to fabricate large non-axisymmetric optical segments, and his and Mast’s development of active electro-mechanical control systems allowed large numbers of such segments to remain locked together and function as a single, continuous optical surface. The first Keck telescope was such a success when it went into scientific operation in 1993 that by 1996 there was a second virtually identical Keck; within a few more years Jerry was at work, again with Mast, on the development of what is now the Thirty Meter Telescope (TMT) project.

Jerry recognized that the enormous collecting area of the Keck Telescopes made each photon more, not less, precious, and he worked tirelessly to help design and develop state-of-the-art Keck instruments and to improve the performance of the telescopes. He reviewed the Keck night logs every morning and was a fixture as an outspoken member of the Keck Science Steering Committee.

Jerry was not only a truly great physicist, but a remarkable electrical engineer — he won both the 2010 Kavli Prize for Astrophysics and the 2012 Franklin Medal for electrical engineering — and he was a world-class mechanical engineer as well. Aspects of his personality were as impressive as his professional accomplishments. The courage he manifested in the face of criticism and personal adversity was remarkable and inspiring. Although he suffered a physically debilitating stroke in late 2011, he still came to work every day (including holidays) and was making essential contributions to both Keck and TMT up until his final days. His optimism was relentless (he was undeterred by people constantly telling him he was trying to do the impossible) and his intellectual curiosity was legendary. He was a mentor of uncommon patience and generosity, and it is doubtful whether anyone, with the possible exception of his colleague Mast, got more joy out of his work.

Overall, Jerry’s vision, expertise, technical knowledge, and leadership made the twin Keck Telescopes the first of the eight-to-ten meter class telescopes to go into operation, and, together with his efforts as the founding Director of the Center for Adaptive Optics at Santa Cruz, helped to usher in an unprecedented era of astronomical discovery, covering such diverse phenomena as exoplanets, the formation and evolution of galaxies, the acceleration of the expansion of the universe, and the black hole at the Galactic Center. He had a profound influence on the careers of a hundred astronomers and telescope engineers. His continuing influence can be seen in the segmented-mirror design of ongoing telescope mega-projects, including TMT, the European Southern Observatory’s Extremely Large Telescope, and the James Webb Space Telescope.