Known to many as "Dr. Comet" because of his extensive research on the icy objects, Whipple serves as a professor with the Harvard-Smithsonian Center for Astrophysics (CfA) and has practiced astronomy research for nearly 75 years. CONTOUR launched at 2:47:41 a.m. EDT (0647.41 GMT) aboard a Delta 2 rocket from a pad at the Cape Canaveral Air Force Station in Florida.

Although Whipple was unavailable for an interview, his longtime colleagues said his impact on the field of astronomy has been profound, both in the United States and around the world.

"He is the dean of the whole subject of comets," said Brian Marsden, director of the Minor Planet Center and a researcher at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, during a telephone interview. Marsden is a 43-year colleague of Whipple. "He has much to offer for the success of this mission."

Originally from Iowa, Whipple now lives in Belmont, near Harvard University. He graduated first from the University of California Los Angeles, then later from UC Berkeley. In 1930, while still a student in Berkeley, he also calculated one of the first orbits for the then-newly discovered planet Pluto.

Whipple published his seminal work in 1950, when he theorized that comets were put together like "dirty snowballs," a mixture of ice, dust and rocky particles all clumped together. The model was confirmed by the European Space Agency's (ESA) Giotto mission in 1986, when it passed by Halley's Comet, though most scientists now believe comets contain less water than previously thought. Over the last couple of years, astronomers have begun referring to comets as "icy dirtballs" instead of "dirty snowballs."

"It might seem obvious to people now that comets are made up of ice and dust, frozen together, but it wasn't back then," said Marsden of the time of Whipple's 1950 research. "Then, most people thought comets were made of grains of sand, not held together at all."

Between 1955 and 1973, Whipple served as director of the Smithsonian Astrophysical Observatory (CfA), and was instrumental in moving it from Washington D.C. to Cambridge. In addition to studying comets, Marsden added, Whipple is a talented administrator, and saw the future need to track satellites from the earth even before Sputnik, the first such craft, was launched by the Russians in 1957.

For his efforts to develop a worldwide network of satellite tracking stations, Whipple was awarded the President's Award for Distinguished Public Service in 1963 by President John F. Kennedy. The achievement, Whipple has said in the past, remains his life's greatest honor.

Prior to a fall in January, Whipple was very active with the CfA, and enjoyed riding to work on a bicycle from his nearby home. Marsden said that although Whipple is not always right, he's the first to admit it and is friends with most of those around him.

"It's amazing how he's been writing papers and working five and a half days a weeks these last few years," Marsden said, adding that Whipple often came in on Saturday morning to work. "If the rest of us do well at his age, it would be remarkable."