CAPE CANAVERAL -- Despite the fears and objections of many who thought the mission far too risky, NASA's plutonium-powered Cassini spacecraft launched without incident early Wednesday morning, October 15, 1997, beginning a seven-year, 2 billion-mile journey to the ringed planet Saturn.
Cassini is the most expensive and the biggest unmanned exploratory spacecraft ever sent into space. NASA says it represents the last of its kind: missions requiring monster budgets and years of preparation. However, if Cassini functions as planned, it will return a bonanza of scientific information.
Because Cassini must operate far from the sun for many years, NASA determined that the only suitable on-board power source would be plutonium. Similarly, the Galileo probe, currently orbiting Jupiter, is powered by 48 pounds of plutonium, and the Ulysses solar probe carries 24 pounds. Even the Sojourner rover on Mars has a small amount of plutonium -- less than one-third of an ounce.
But Cassini's 72 pounds of plutonium fuel is the most plutonium ever launched into space and became the focus of major public concern.
Opponents of the mission argued that no amount of safeguards could prevent a terrible disaster if the rocket blew up during or shortly after launch. They noted that plutonium is probably the most deadly substance known on earth, and that the huge Titan 4B rocket carrying Cassini is notoriously prone to blow up on the launch pad.
NASA officials said that the odds of any problem at all were below 1000 to 1, and the chances of releasing plutonium into the atmosphere were far less. Opponents said those odds were not nearly good enough and were overly optimistic in any case. But in the end, the White House and a federal judge turned down all the objections and gave the OK for the launch.
John H. Gibbons, chief of the White House Office of Science and Technology Policy, said on October 3 that he approved the launch of Cassini after concluding that "the important benefits of this scientific mission outweigh the potential risks."
On Saturday, October 4, police arrested 27 protesters at Cape Canaveral during a peaceful demonstration that drew an estimated 1,200 Cassini opponents to the launch site. Among those arrested was 87-year-old Peggy McIntire of St. Augustine, Florida. She and the others deliberately forced their own arrest by attempting to scale the fence surrounding the launch facility. They were charged with trespass.
Federal judge David Ezra on October 11 refused to delay Cassini's launch, overturning the objections of Green Party activists and the Florida Coalition for Peace and Justice. Judge Ezra said the economic and scientific harm that NASA and other defendants in the case would suffer if the launch were delayed outweighed the potential harm asserted by the two groups.
On October 15, those who believed the mission would launch safely were proven correct.
Scientists and engineers cheered and embraced when Cassini shot out of Earth orbit 40 minutes after liftoff and streaked at nearly 25,000 mph toward Venus and, ultimately, Saturn.
"It's beautiful. It's beautiful," murmured Charles Kohlhase, Cassini's science and mission design manager. "We've been waiting a long time for this."
"We're all very excited. We knew there wouldn't be a problem," said the Energy Department's Beverly Cook, who is in charge of Cassini's nuclear load. "But we were prepared. It's designed [to withstand] accidents. I'd hate to have lost this mission, but there wasn't going to be a safety problem."
Cassini's $3.4 billion mission won't really begin until the spacecraft reaches Saturn in July, 2004. The seven-year route to get there requires two gravity-assisted "sling-shot" fly-bys of Venus.
The spacecraft also will sweep within 500 miles of Earth in 1999, which scares some Cassini opponents even more than the launch itself. Cook said there is less than one chance in a million that the probe would re-enter Earth's atmosphere in 1999 and spread plutonium.
If all goes well, the huge Cassini spacecraft -- as big as a small bus and weighing 12,500 pounds -- will be the first earth visitor to orbit Saturn. During its four year mission, it will orbit the ringed planet 74 times. Previously, three spacecraft -- Pioneer 11 and Voyagers 1 and 2 -- flew past Saturn in the late 1970s and early 1980s.
Cassini also will sweep 45 times past Titan, Saturn's largest moon and the second-largest moon in the solar system. A major highlight of Cassini's mission will be the release of a European-built probe to land on the frigid but intriguing Titan, which has a dense atmosphere and conditions that scientists hope might reveal important clues about how life evolved on earth.
"The scale of this project kind of matches the majesty of the place where it's going," said Wesley Huntress Jr., NASA's space science chief.
Highlights in Cassini's "Grand Tour" -- the 2.2 billion-mile journey to Saturn -- include Venus fly-bys in April 1998 and June 1999, Earth fly-by in August 1999, Jupiter fly-by in December 2000, arrival at Saturn in July 2004, Titan moon probe landing in November 2004, and scheduled mission completion in July 2008.
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