At the first press conference after the Stardust
spacecraft flew past comet Wild 2 in January 2004,
a reporter asked, "What is a whipple?" Like Edwin
Hubble, another great astronomer had become synonymous
with a piece of space hardware. The first part of
the answer was that a whipple is a Whipple bumper,
a clever, lightweight structure invented by Fred Lawrence
Whipple and designed to protect the spacecraft from
the 6-kilometer-per-second impact of comet rocks as
large as a centimeter across. The second part was
that Fred Whipple was the originator of our modern
understanding of comets and a key reason why there
was a mission to a comet. Whipple's icy-conglomerate
model outlined why comets were made of ice and dust
and not the tenuous particle swarms called flying
sandbanks that they were previously imagined to be.
Fred was a remarkable person whose long career spanned
three-quarters of a century. He died in Cambridge,
Massachusetts, on 30 August 2004 following a prolonged
illness.
Fred was born on 5 November 1906 in Red Oak, Iowa.
He studied at Occidental College in Los Angeles and
received his AB in mathematics at UCLA in 1927 and
completed his PhD in astronomy at the University of
California, Berkeley, in 1931. He was an instructor
at Stanford University in 1929, and, in 1931, became
a staff member of the Harvard College Observatory
in Cambridge, where he worked for more than 70 years.
From the beginning of his career, Fred had developed
a strong and long-lasting interest in meteors. In
the 1930s, he started the Harvard Meteor Project,
which ultimately included measurements with both optical
and radio methods. He was motivated early on by his
belief that some meteors had hyperbolic orbits and
came from other planetary systems. Fred calculated
the radiant, an apparent source direction, of meteors
coming from the star Sirius, but measurements of thousands
of meteors did not yield unambiguous detection of
extrasolar meteors. (More recent work using spacecraft-
and ground-based radar on smaller particles finally
found the elusive extrasolar component that intrigued
Whipple back in the 1930s.) In 1936, he made the first
measurements of the atmospheric density at 60 km by
determining the drag-induced deceleration of meteors.
Eleven years later-a decade before the first satellite
launch-Fred first described his Whipple bumper in
a paper published in the Astronomical Journal.
In that short article, he calculated the meteoroid
impact risk that future spacecraft would face. In
two classic papers published in the Astrophysical
Journal in 1950 and 1951, he described what comets
are, how they evolve, and how they relate to meteor
streams. His vision of comets as conglomerates made
of dust and volatile ices, often called dirty snowballs,
quantitatively explained the more than 1000-year lifetimes
of periodic comets. The model also explained the odd
behavior of comets that deviate slightly from purely
gravitational orbits as being the result of the rocket
effect of anisotropic sublimation and jetting of volatiles
into space. Previous suggestions for the devious motions
of comets had included the presence of an unknown
resistive medium. Fred's two papers have been the
most-cited works in the Astrophysical Journal
during the past half century.
Fred became the director of the Smithsonian Astrophysical
Observatory when it moved in 1955 to begin an association
with the Harvard College Observatory. As director
for the next 18 years, he helped to form the Harvard-Smithsonian
Center for Astrophysics (CfA). He was a superbly innovative
and imaginative scientist, an instigator, and a skilled
administrator who also was involved with remarkable
engineering feats. In addition to the invention of
the meteor bumper, he is internationally famous for
his work in World War II on aluminum foil chaff (code-named
"window" by the British), shreds of aluminum foil
that were dropped from aircraft as a countermeasure
to Germany's radar. That work earned him the nickname
"Chief of Chaff." Early in the war, he co- invented
a cutter that would turn 3 ounces of aluminum foil
into 3000 half-wave dipoles, and he also found optimum
aspect ratios for the foil strips that would work
over a range of radar frequencies. President Harry
S Truman awarded Fred a Certificate of Merit in 1948
for that work.
Fred's earlier work on meteors and other natural
space objects led him to artificial satellites and
the birth of the US space program. That program officially
began in 1954 when the Office of Naval Research asked
Fred, Fred Singer, and Wernher von Braun to make specific
proposals for the American satellite program, an effort
that was part of the International Geophysical Year
(1957-58).
Fred built a worldwide network of cameras to precisely
track satellites with the intention of improving the
global geodetic uncertainty from hundreds of meters
to 10 meters. When the Soviet Union launched Sputnik
in October 1957, one of the cameras was already set
up and took precise data. Fred also set up Moonwatch,
a global network of amateur astronomers using special
Moonwatch telescopes, small refractors that looked
downward at the image of the sky that was bounced
off an upward-facing flat mirror. The Moonwatch program
provided the first publicly available US information
on Earth's first artificial satellite. The satellite
effort evolved into a tracking network of elegant
Baker-Nunn cameras that were optical marvels of the
space age. In 1963, President John F. Kennedy gave
Fred the Distinguished Federal Civilian Service award
for his work contributing to the birth of the space
age.
Fred remained quite active and influential until
his death at age 97. He lectured to teachers and other
attendees at the 1999 launch of the Stardust comet
mission, and he was an official co-investigator of
the Contour comet mission launched in 2002. He participated
in the development of large multimirror telescopes;
the Fred Lawrence Whipple Observatory on the summit
of Arizona's Mt. Hopkins includes the 6.5-m Multiple
Mirror Telescope, the Whipple 10-m Gamma Ray Telescope,
and others.
In addition to his remarkable scientific, technical,
and organizational contributions, Fred was also revered
by colleagues for his ever-handy telescoping pointer,
his car's "COMETS" license plate, and his outstanding
collection of astronomical neckties. A small but spectacular
collection of those ties is on permanent display at
the visitor center at the base of the impressively
winding road that leads to Whipple Observatory. For
those who love comets, meteors, or any of the other
many things on which Fred Whipple worked his magic,
a pilgrimage to see his ties is highly recommended.
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