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| RISKS VS. RETURNS Is the Cassini Mission safe? October 21, 1997 |
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Return to this forum's introduction.
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 used 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?
The Online NewsHour asks: To begin, could we hear a bit about the mission itself? What information will be gathered? How will this information be useful to scientists?
Steven Aftergood from the Federation of American Scientists responds:
Cassini is the largest and most ambitious (and most expensive) planetary mission ever undertaken. It is carrying some 800 pounds of scientific instruments to Saturn where it will conduct experiments including photographic and radar imaging, atmospheric sampling, and various studies of Saturn's system of planetary rings and satellites.
Ultimately, the data gathered by Cassini could provide new insights into the development of the solar system and even the origin of life on Earth.
Cassini will be useful first of all to the scientists who will try to interpret its findings. But it has a greater significance for the public and, in fact, for all of humanity.
This is the first time in the history of our species that we have had the ability to send human tools of such sophistication to the planet Saturn and to extend human awareness there. Earlier generations might have been wiser or better than we are, but they could not have created or launched a space craft like Cassini. This mission is one of our society's historic contributions to human evolution.
Dr. Gary Bennett, retired NASA scientist, responds:
The Cassini spacecraft will conduct a four-year exploration of Saturn, its rings, and its moons. Cassini will add to our knowledge of the outer gas giant planets (Jupiter, Saturn Uranus, and Neptune), which are composed mostly of hydrogen and helium. Scientists have theorized that these planets formed by different processes from those which led to Earth, Mars, Venus, and Mercury. Understanding these giant planets, in particular the Saturnian ring system will aid in understanding how solar systems form and why the planets are so different. All of this helps us to understand our home world. (If we had no information on other planets, our models would always be suspect for having been force-fitted to Earth and with no predicative powers.)Evidence suggests that the Saturnian system suffered some kind of major disruption about one billion years ago- Was this a larger version of the Shoemaker-Levy impact on Jupiter or the dinosaur-killing impact on Earth? Why does Saturn radiate about 80 percent more heat than it receives from the Sun? Saturn has more moons of greater variety than does any other known planet—it's like a miniature solar system. The moon Enceladus may be spewing ice from water volcanoes. Titan, the largest moon of Saturn, is larger than the planets Mercury and Pluto and it is the only satellite with an appreciable atmosphere. In fact, the orangish, nitrogen rich atmosphere is so thick we can 't see to the surface. Titan may be like a frozen, organically rich early Earth that could tell us much about how the chemistry of life developed.
The Voyager and Pioneer spacecraft tantalized us with scientific information gathered in quick flybys; now, we are filling in the gaps by spending enough time at Saturn to understand its environment in greater detail (as the Galileo spacecraft is doing at Jupiter). There are 27 scientific investigations on Cassini's agenda. For example, Cassini will perform dozens of radio occultation measurements of Saturn's atmospheric structure. Cassini's imaging system will provide scientists with detailed pictures of Saturn's outer here atmosphere and help understand why Saturn has such high winds when it is so far from the Sun. Cassini will also sample the magneto sphere of Saturn, that complex structure of magnetic fields and ionizing particles that surround the planet. All told, the Cassini Orbiter carries twelve sophisticated scientific instruments which have much better sensing abilities than the instruments carried on the earlier Voyager and Pioneers.
One of the exciting aspects of the mission is the Huygens Probe which will penetrate the obscuring atmosphere of Titan to give us our first images of the surface of this planet with its organic compounds (and possibly organic oceans). Built by the European Space Agency, the Huygens Probe carries six scientific instruments to study the atmosphere and surface of Titan. While no one expects to find life in such a cold environment where temperatures may be around -180 degrees Celsius (-290 degrees Fahrenheit) causing any water to be frozen into ice as hard as rocks, still the precursor chemistry in terms of organic (carbon-bearing) compounds is there. With Huygens actually sampling the atmosphere and, we hope, the surface of Titan, Cassini will use radar to penetrate the atmosphere and map the surface.
Next: What could cause an accident when Cassini swings by Earth?
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