|RISKS VS. RETURNS|
Is the Cassini Mission safe?
October 21, 1997
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Questions answered in this forum:
What is the Cassini mission all about? What could cause an accident when Cassini swings by Earth? What damage would an accident cause? Why was plutonium selected to power Cassini? What other energy sources could have been used to speed up the mission? How can NASA risk public safety for planetary exploration?
Mitchell Miglis of Melbourne, FL asks:
I have always been an avid supporter of space exploration. Recently, however, I have become quite concerned about the direction NASA is taking in using relatively large quantities of plutonium in spacecraft.
I live about forty miles from Cape Kennedy. My question is very straightforward: what gives NASA the right to risk public health and safety (to any extent) in the interest of pure science research (planetary exploration)? The argument that the chances of a catastrophic event are minimal ring hollow after the Challenger disaster and a recent Atlas-Centaur detonation several months ago. Why not probe Saturn in several smaller missions which would have much smaller power requirements? Does not the possibility of nuclear contamination in this and other future nuclear missions cancel out the possible rewards offered by this type of research?
Steven Aftergood of the Federation of American Scientists responds:
What gives NASA the right? The "textbook" answer is that we live in a representative democracy, and our representatives in Congress have repeatedly authorized and approved funding for Cassini.
But this is not quite a satisfactory answer, since we know that Congress often makes errors of judgments and fails to represent broad public interests.
Still, the fact is that we live a world of risks. In this case, NASA has subjected the Cassini mission to layers of independent and public review. Several panels of reviewers who have no financial or institutional stake in the mission examined all aspects of it in depth, and reached a relative consensus that the risks involved in proceeding were small.
Is it conceivable that they could all be wrong? Yes. But we have no better way of making decisions in our society.
In the absence of some compelling new information or analysis, it was not realistic to expect a radical restructuring of the Cassini mission in the months prior to launch, even if that were technically possible.
On the other hand, it does make sense to have a debate now about future space missions that have not yet been funded or firmly committed to. Exactly what are the realistic technical options for space power in the near- to mid-term? Is adequate emphasis being given to the development of alternate power supplies? Do we really want to place new demands on our aging and decrepit plutonium production facilities? What should the objectives of our space program be?
Dr. John Gofman of the University of California at Berkeley responds:That is the 64 trillion dollar question and I am delighted that you have brought it to the fore, while most everyone else dances around avoiding this serious question .
The answer is that large government agencies and some industries simply take that right into their hands. There is no basis for their doing so other than that our society has been asleep this past 50 years and all new developments simply arrogate this right to themselves. Either we change that now while we are discussing Cassini or we go on, and one day that will lead to an irreversible situation in which we won't fare much better than the dinosaurs did with the meteor crash.
Twenty-five years ago and today my colleagues and I advocated a plan which would eliminate this nonsense we go through for every new technological adventure. The promoter now does his engineering and advocacy, and then he also decides not only what is "good for us to do" but he then also decides on the health and safety issues in which he may not be at all competent.
Our plan is that five to 10 percent of the funds for a new adventure like NASA be transferred to several independent non-governmental institutes whose sole function is to study all the adverse features of the venture, what we call Adversary Science Centers. Make the positions secure and attractive so some of our best talent wants to work there. Then at intervals the promoters and adversary scientist will meet to see what they both believe and find.
Many projects will disappear in this process, and they will rarely be missed. Sometimes, the two sides will reach a true consensus based on facts and logic. Instead of the artificial consensus we generally have now where the promoter and his agents tell us all the wonders of his project and how marvelously safe it is. Anyone who does not agree is soon jobless. We are lucky to escape as well as we have, but some things will be irreversible.
And with respect to Michell's question, I think the adversary groups should include people who are capable of discussing the ethical ground rules and what they ought to be, and demand that the promoter respond to the ethical question. If we had the adversary groups in operation,and they had access fully to all the data and all the calculations, we would soon enough come to reasonable decisions whereas now the public does not even know what has been found and is being hidden from their view.
It won't be easy-- promoters are hard hitters for their pet projects-- but today poor citizens concerned with their daily bread for their families are asked to find out what is wrong with certain massive projects, while the promoters have lovely offices , laboratories and salaries and all the media devices to trumpet their point of view. Not a level playing field. And either millions of us decide we want and insist on a level playing field with adversary science or we will one day be in far bigger trouble than surrounds a Cassini.
Dr. Gary Bennett, former NASA scientist, responds:NASA is responsible for conducting its missions safely in a way that does not present undue risks to the public. NASA and the Department of Energy conducted extensive environmental and safety testing and analyses to ensure the safety of the Cassini mission in the unlikely event of an accident. This work has shown that an accident would not result in a "catastrophic event." Proof of this can be found in two real-life accidents: the explosion of the Nimbus B-l's launch vehicle in 1968 and the explosion of the oxygen tank on Apollo 13 in 1970. In both cases, the radioisotope heat sources survived the return to Earth as they were designed to do.
The choice of radioisotope thermoelectric generators was not made lightly. Other options (including solar power) were considered but it turns out that in the cold, dark, radiation-rich environment of Saturn, radioisotope thermoelectric, generators were the only available option. Some critics, who have never had to design a spacecraft or its electrical power system, have charged that NASA could have used solar power. In fact, NASA looked at a solar array design, but the solar option was too heavy to launch. Saturn is so far from the Sun that it receives only about one percent of the sunlight Earth gets. This means that if a spacecraft needs one kilowatt of power at Saturn, it must have an array that will produce at least 100 kilowatts at Earth. Moreover, the intense cold and the radiation belts around Saturn would seriously damage, if not totally disable, a solar array.
Splitting Cassini into "smaller missions" would cancel many of the scientific benefits of a global observer like Cassini-- analogous to watching a concert without being able to hear the music. If each of these "smaller missions" were flown, they would still require the large amount of propellant to slow them down at Saturn (making them relatively large spacecraft). They would still require enough power from RTGs to take care, of the scientific instruments, the basic "housekeeping" activities of the spacecraft, and send the data back from distant Saturn. (In general, it takes more power and larger antennas the farther the craft goes from Earth.) So a series of "smaller missions" would probably end up involving at least as much plutonium-238 as Cassini -- and certainly more launches!
Th Cassini RTGs have been designed to survive a wide range of postulated accidents. (If automobile engineers used the same design philosophy they would have to assume the occurrence of a crash, and then design a protective cocoon for the occupants of the car.) The goal has been to make the risk as low as practical. Careful attention is paid to such missions so that there is no undue risk. In assessing the risks, which were publicly presented through the environmental impact statement process and through a public meeting in Florida, the historical failure probability of the Titan launch vehicle was considered so that the analyses would be as realistic as possible (and not make them "ring hollow").
The rewards from missions like Cassini include giving us a better understanding of how the Solar System formed and how we came to be. How one assesses the rewards of any activity is a personal judgment. The American philosopher Morris Cohen once asked whether we would accept a magical chariot that would take us anywhere if the price would be 30,000 lives lost every year. Of course, we would all say "No!" But we have accepted that chariot -- the automobile - and the price. My own assessment is that the rewards of exploring Saturn are, worth the incredibly small risk associated with Cassini. As a member of the Sierra Club and a contributor to a number of environmental and humanitarian organizations, I am more concerned about the dangers of international terrorism, ethnic cleansing, proliferation of nuclear weapons, and environmental degradation. During the month-long blitzkrieg by the Cassini critics, hundreds of people were brutally murdered in Algeria, hundreds more died in a ferry accident in Haiti, and thousands of people were facing death in Africa. In the final analysis, we need to be knowledgeable and active in dealing with the risks facing us while keeping a sense of proportion in these matters.
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