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 counter-measure 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.
