Edward Carroll Stone Jr. (January 23, 1936 – June 9, 2024) was an American space physicist, professor of physics at the California Institute of Technology, and director of the NASA Jet Propulsion Laboratory (JPL) from 1991 to 2001. He was the project scientist of the Voyager program, which sent two spacecraft to the outer Solar System's giant planets and became the first spacecraft to enter interstellar space.
Stone led the Voyager mission for 50 years, from 1972 until his retirement in 2022, overseeing the spacecraft's encounters with Jupiter (1979), Saturn (1980–1981), Uranus (1986) and Neptune (1989). Under his leadership, the mission discovered active volcanism on Jupiter's moon Io, new moons and ring systems. The Voyagers continued beyond the planets to cross the heliopause and enter the interstellar medium, with Voyager 1 becoming the first spacecraft to leave the Solar System in 2012, followed by Voyager 2 in 2018. The Voyager mission became the longest-running NASA mission, with Stone being its face and advocate.
As JPL director, Stone oversaw the successful launches of Mars Pathfinder with the first Mars rover Sojourner, Mars Global Surveyor, Cassini–Huygens and other missions during NASA's "faster, better, cheaper" era. Throughout his career, he served as principal investigator on nine NASA spacecraft missions, including SAMPEX, the Advanced Composition Explorer and scientific instruments on the Galileo and STEREO missions.
Stone's contributions to space science earned him the National Medal of Science (1991), the NASA Distinguished Public Service Medal (2013), and the Shaw Prize in Astronomy (2019). He was elected to the National Academy of Sciences in 1984 and played key roles in establishing major astronomical facilities, including overseeing the creation of the Laser Interferometer Gravitational-Wave Observatory (LIGO) during his tenure as chair of Caltech's Division of Physics, Mathematics and Astronomy, and supervising the construction of the W. M. Keck Observatory.
Early life and education Edward Carroll Stone Jr. was born in Knoxville, Iowa, on January 23, 1936, to Edward Carroll Stone Sr., a construction superintendent, and later a garage-door-installation company owner, and Ferne Elizabeth Stone ( Baber), a bookkeeper. He was the elder of two sons. Stone grew up in Burlington. While at school he worked at a J.C. Penney department store and was a member of the Burlington Municipal Band playing French horn.
Stone studied at Burlington Junior College in Iowa, and continued his education at the University of Chicago, where he earned his M.S. (1959) and Ph.D. (1964) degrees in physics. Initially, he planned to study nuclear physics, but became interested in space physics after the launch of the Soviet Sputnik in 1957. Stone began astrophysics research in 1961, working on a cosmic-ray telescope carried by the Discoverer 36 spy satellite. He worked on it under the cosmic-ray researcher John A. Simpson's supervision. The experiment became his PhD thesis, titled Low energy cosmic-ray protons. While in Chicago, Stone also worked with Eugene Parker; he said later that "Parker taught me how to reduce a problem to its nuts and bolts, to a picture."
Caltech Stone moved to Caltech to work on space physics with Rochus Eugen Vogt in 1964, and helped him establish the Space Radiation Laboratory. He became a full faculty member in 1967. In 1976, Stone was named professor of physics, later the David Morrisroe Professor of Physics, and was chair of the Division of Physics, Mathematics, and Astronomy from 1983 to 1988; during his tenure he oversaw the establishment of the Laser Interferometer Gravitational-Wave Observatory (LIGO). He also served as director of the Caltech Space Radiation Laboratory, and as vice president for Astronomical Facilities. He was the vice-chair of the Thirty Meter Telescope Board of Directors. He also served on the board of the California Association for Research in Astronomy (CARA) for nearly 25 years, and oversaw the construction of the W. M. Keck Observatory. He was also a W. M. Keck Foundation director, and chaired the Keck Foundation's Science and Engineering Committee for 24 years.
Voyager program In 1964, Gary Flandro, a summer student at JPL, found out that a rare planetary alignment of the giant planets would allow a mission he called "the Grand Tour". Such an alignment occurs every 175 years; Flandro calculated that the best option was to launch spacecraft in 1977. Gravity assist maneuvers were already known, but according to Flandro he was the first to notice the opportunity to visit the giant planets. NASA was reluctant to finance the proposed mission of four spacecraft, but the proposal eventually transformed into the Voyager program.
In 1972, Stone became the project scientist for the Voyager program that sent two space probes to the giant planets in the outer Solar System. He was invited for the position by Harris "Bud" Schurmeier, the mission's first project manager; according to Schurmeier, Stone was proposed as the project scientist by Rochus Vogt, who was involved in the Grand Tour mission planning from the start. Stone himself was reluctant at first: as a scientist, he didn't want to sacrifice a lot of time for administrative work. Stone was also the principal investigator for the Cosmic Ray Subsystem experiment on both Voyager spacecraft.
Stone supervised the work of 11 teams of about 200 scientists; he organized "the clique-like teams" and work groups for key points of interest, "moons, rings, atmosphere and magnetosphere". Stone had the final word on observation target selection, instrument usage, and the spacecraft trajectories. A NASA official who was present at the first Voyager meeting, observed that "Stone knew more about every one of their instruments than the P.I.s themselves knew."
Stone also became a spokesman for Voyager, and became well known to the public in the 1980s, after he held dozens of press conferences announcing Voyagers' discoveries. According to the Voyager project manager Norman Haynes, Stone "revolutionized the world of project science".
Stone said that planetary encounters and the discovery of volcanism on Io were the most memorable events of the Voyager mission for him. He recounted the team's regular work process:
Stephen P. Synnott recounted how Stone let him name a moon of Jupiter that he discovered on Voyager photos in 1980, saying "it looks like you've found yourself a moon" after checking the calculations. Synnott chose Thebe from a list of names suggested by the IAU.
Stone was the main advocate and salesman of the Voyagers. After the last planetary encounter he was able to receive funding for an extended mission, the Voyager Interstellar Mission. The Voyagers became the only spacecraft that left Solar System into interstellar space.
Jamie Sue Rankin became Stone's last PhD student. Her thesis was on the Voyagers' interstellar space data; she graduated in 2018 and became the Voyagers' deputy project scientist in 2022. Before Rankin, Stone refused to advise graduate students for about 25 years. Later, Rankin became the Voyager's deputy project scientist.
The Voyager mission visited all four giant planets and is the only spacecraft that visited Uranus and Neptune. It is NASA's longest-running spacecraft mission. In 2022, Stone retired after holding the role of the Voyager project scientist for 50 years.
Simultaneously with being the Voyager's project scientist, Stone taught first-year physics at Caltech, using examples from it: "The wonderful thing about planetary fly-bys is there’s a lot of freshman physics that you can talk about: the encounters, the trajectories."
JPL
Though Stone is better known as the Voyager's project scientist, he served as a principal investigator for multiple other missions. He was the PI of the Cosmic Ray Experiment on Orbiting Geophysical Observatory-6 (OGO-6, 1969), the PI of the Electrons and Hydrogen and Helium Isotopes experiments on Interplanetary Monitoring Platform 7 (IMP-7, 1972) and IMP-8 (1973), was involved into the cancelled ASTROMAG (1980s), was the PI of two instruments of the cancelled International Solar Polar Mission (1981), the PI of a heavy-ion counter on the Galileo mission to Jupiter (1989), the PI of SAMPEX (1992), the PI for the Advanced Composition Explorer (1997), and co-investigator of STEREO mission's High Energy Telescope (HET) and Low Energy Telescope (LET) (both part of the In-situ Measurements of Particles and CME Transients (IMPACT) instrument package) (2006). Stone also "oversaw the redesign of the cooling system" on the Spitzer Space Telescope (2003), and was an investigator on the Integrated Science Investigation of the Sun instrument on the Parker Solar Probe (2018).
In 1991, Ed Stone–a well-known, enthusiastic and respectable scientist–was made the JPL director. His directorship was during the difficult period of the 90s: with the Cold War and the Space Race between the US and the USSR finished, NASA saw dwindling budgets and introduced the so-called "faster, better, cheaper" approach, that encouraged smaller, cheaper missions built with the help of third-party contractors, efficiently "commercializing" the research lab and forcing it to work with industry. Cost-cutting had to be done by Stone, who tried to adapt a new management culture at JPL, while at the same time trying not to hurt science. The plans were to downsize the lab and fire around 30% of JPL personnel by the end of the decade; Stone and Caltech leadership even feared that JPL could be closed.
The "faster, better, cheaper" (FBC) approach was described as:
JPL had little experience in small missions at the time: its "flagship" missions, like Voyager, Cassini, and Galileo, employed hundreds of people for decades. Cassini, for example, "directly supported maybe 500 work-years, about 10 percent of total lab staff [and] provided close to 20 percent of the lab budget". In order to comply with budget restrictions and save the mission, Cassini was downsized; to save $250 million, the scan platform had to be removed from the plans. Stone himself saw the "faster-better-cheaper" as a cultural change of the lab's engineering practices.
Stone also became a proponent of a management culture change at JPL, and installed Richard Laeser (former Voyager project manager) to apply total quality management (TQM) at all levels. Reorganization was required to meet NASA needs, and TQM "emphasized customer service", even though few people at JPL saw NASA as their customer. Many employees were against the new management practices.
The most successful, "model" example of an FBC mission was the Mars Pathfinder lander and the first Mars rover, the Sojourner. The mission cost around 200 million dollars and was widely reported in the press, appearing on the covers of Time and Newsweek. Other missions were less fortunate: in 1998–1999, six missions were launched; four of them failed, including two Mars orbiters. Both JPL (Stone) and the NASA administration (Daniel Goldin) acknowledged that they pushed too far with the FBC; no project manager of the failed missions was fired.
According to Peter J. Westwick, as the director of JPL, Stone was a "cautious revolutionary". He retired in 2001; his successor, Charles Elachi, "felt no need to change JPL's culture".
Retirement and death Stone retired from Voyager in 2022, after holding the role for 50 years, but remained professor emeritus at Caltech. He died in Pasadena, California, on June 9, 2024, at the age of 88.
Personal life Stone was a shy man, and worked 100-hour weeks at times. Alan C. Cummings, the Cosmic Ray Subsystem co-investigator, who worked with Stone for fifty years, described him as "very calm ... the smartest guy I ever met. He was a multiplexer supreme." Stone was profiled in 1990 for The New York Times by Michael Norman: