Von R. Eshleman
Von R. Eshleman died peacefully on September 22, 2017, five days after his
93rd birthday. Although he began his career in radar astronomy, he is best known
as a pioneer in the use of spacecraft radio signals for precise measurements in
planetary exploration — specifically, the radio occultation method for profiling
planetary atmospheres and ionospheres, which has now been "brought home"
for monitoring Earth's atmosphere using GPS satellites.
Von was the youngest of four boys born in Covington, Ohio, a farming community
with a large population of Old German Baptist Brethren, from which his grandfather
had broken away in the late 1800s. He progressed rapidly through his early school
years, then served as an electronics technician in the U.S. Navy during World War II
(1943-46). While stationed in Italy at the end of the war, he became intrigued by the
possibility of bouncing radio signals from the lunar surface. Although his own
ship-based experiments were unsuccessful, this curiosity guided his professional
life for the next 60 years.
He attended the General Motors Institute of Technology and Ohio State University
before graduating with a bachelor's degree in electrical engineering from George
Washington University in 1949. While at GWU, he met and married Patricia
Middleton and they had the first of four children. Recruited to graduate school
at Stanford University by Fred Terman, he obtained an MS in 1950 and a Ph.D.
in 1952. His doctoral research, supervised by Mike Villard and Larry Manning,
was on radio reflections from ionized meteor trails in the upper Earth's atmosphere.
After serving five years as a member of Stanford's Electrical Engineering research
staff, Von was promoted to Assistant Professor in 1957, then Associate Professor,
and finally full Professor in 1962. With colleagues Allen Peterson and Ray
Leadabrand, he founded the Stanford Center for Radar Astronomy in 1962, which
oversaw two-way dual-frequency radio propagation experiments between Stanford's
150-foot antenna ('The Dish') and Pioneers 6-9 in orbit around the Sun, measuring
the density, velocity, and structure of the solar wind.
By the mid-1960s Eshleman's team had refocused on planets and on the
telecommunications signals normally used to transmit spacecraft images and
other remotely acquired data. The radio signals themselves are perturbed when
a spacecraft flies behind a planet; by measuring the small changes in frequency,
it is possible to determine the temperature and pressure profile of an occulting
atmosphere (very similar to the results returned by a weather balloon) and the
electron density of an ionosphere. The experiments were originally proposed
for an 'uplink' geometry (transmission from Earth to the spacecraft), but only
'downlink' implementations were approved. Nonetheless, graduate students
Gunnar Fjeldbo and Len Tyler (among others) perfected the technique and were
rewarded with the first profiles from Mars (cold and thin) and Venus (hot and
dense) in 1965 and 1967, respectively. Eshleman and his associates also
demonstrated that properties of planetary surfaces could be derived from radio
echoes reflected from the Moon and Mars.
Eshleman was not involved in Pioneer 10 and 11 radio occultation experiments
at Jupiter until it became apparent that the radio results differed radically from
results obtained by other instruments. Over several years, Von and others
worked out the corrections needed for analysis when planets are oblate (as the
gas giants are because of their rapid rotation). The effects of turbulence and
magnetic fields were incorporated by Bjarne Haugstad and Dave Hinson. Von
led the Radio Science Team through the very successful Voyager 1 and 2
planning, implementation, and Jupiter encounters, then handed off day-to-day
operations to Tyler.
After Voyager, Eshleman focused on topics such as evolute flashes during deep
radio occultations, stellar gravitational lenses and their effects on propagating
radio waves, ring particle dynamics, absorption in planetary atmospheres (with
students Paul Steffes and Tom Spilker), and retro-reflection from icy planetary
surfaces. Although not a member of the science team, he got to see the ultimate
radio occultation experiment (an uplink implementation) when New Horizons
passed Pluto and signals transmitted from Earth were perturbed by its barely
Dozens of graduate students benefited from Von's direct mentoring; but he was
also an innovative classroom teacher. He converted a mezzanine-level class on
electromagnetics to a generalized "waves" class for a broader audience of
Stanford graduate students — such as those interested in acoustics, seismology
and oceanography. For advanced undergraduates, he developed a new class
called "Planetary Exploration", which was attractive to students with science,
engineering, and mathematics skills but who were not majoring in astronomy.
Von maintained contacts with industry, serving as a consultant for North American
Rockwell and Watkins-Johnson. He advised the McGraw-Hill Book Company,
the National Bureau of Standards, and (of course) the National Aeronautics and
Space Administration. He also served briefly as Deputy Director of the Office
of Technology Policy and Space Affairs in the U.S. Department of State. But
he always returned to the skilled and productive use of electromagnetics to
explore the universe — a task that his associates recall that he not only wanted
to do, but to do well.
Richard Simpson and other colleagues