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The Saturn Mission: Cassini Probed

October 15, 1997 at 12:00 AM EDT


JEFFREY KAYE: This morning the controversial Cassini space probe began its seven year journey to Saturn. The mission to explore the ringed planet and its moons is costing $3.4 billion, making it the most expensive NASA project in history. The European space assisted NASA on the project by contributing $600 million and by building a small research craft that is supposed to land on Saturn’s largest moon.

Cassini, named for the 17th century Italian French astronomer Jean-Dominique Cassini, is the largest spacecraft ever launched by NASA for planetary exploration. It is expected to travel more than 2.2 billion miles. Cassini is the first spacecraft to explore Saturn since 1981. It should arrive in the year 2004 and begin its use of cameras and spectrometers to send back color pictures and scientific data to Earth.

The spacecraft is expected to transmit more than 300,000 color images by the end of the 11-year mission. After four months of orbiting Saturn, Cassini is supposed to release a disk-shaped probe towards Saturn’s largest moon, Titan. The probe should plunge into the Moon’s dense atmosphere and parachute to a soft landing. It should then send data about the Moon’s climate and surface temperature back to Earth.

Scientists believe the probe will operate for only 30 minutes on the Moon’s frigid surface. The exploration of our solar system’s second largest planet has not come without controversy. Anti-nuclear activists have protested the launch. Earlier this month some tried to break into Cape Canaveral to stop the mission. The protest is focused on Cassini’s source of power–72 pounds of plutonium, the most ever carried by any NASA spacecraft.

GORDON CLARK, Peace Action Against Cassini: It takes about a millionth of a gram of plutonium to actually cause cancer in a human being. And we’re again talking about 72 pounds of plutonium. So even if one pound of plutonium were to survive a re-entry crash, that is theoretically enough to spread a cancer dose of plutonium all over the planet.

JEFFREY KAYE: Protesters fear people will be subjected to dangerous amounts of radiation if Cassini crashes or disintegrates when it passes by Earth in 1999. It must fly by the Earth to gather gravitational momentum in a slingshot maneuver towards Saturn. NASA has used plutonium as a power source in 24 previous missions, including the Voyager and Galileo expeditions. Typically, NASA uses solar cells for power, but for long trips like this one, plutonium is used to power the spacecraft.

JIM LEHRER: More now and to Elizabeth Farnsworth in San Francisco.

ELIZABETH FARNSWORTH: For a closer look at the Cassini mission we’re joined by Wes Huntress, associate administrator for space science at NASA. Thanks for being with us, Mr. Huntress.

How do you answer concerns like those of Gordon Clark, which you’ve just heard, that the plutonium is too dangerous and that something could happen as it passes back by Earth in ’99?

WES HUNTRESS, NASA: Well, there’s two answers to that. The first is the form in which we use the plutonium is in a ceramic form and it’s highly protected and insulated against any kind of accidents that might occur on launch. And this particular maneuver, this Earth fly-by is something that we have done many, many times before at other planets, as well as at Earth, the last time being with the Galileo nuclear-powered spacecraft. And we manage these thing with very high precision. And Cassini is, in fact, not coming nearly as close to the Earth as did Galileo and Galileo’s approach managed with very fine–one kilometer accuracy–with no difficulty whatsoever.

ELIZABETH FARNSWORTH: This is not a nuclear reactor like the reactors on the spacecraft, the Russian spacecraft that just crashed in Canada.

WES HUNTRESS: No. This is not a nuclear reactor. They are nuclear batteries. They’re not used for propulsion. It’s not a nuclear power plant. We don’t have any nuclear reactions going on. We simply use the isotope to generate heat, and from the heat we generate electricity for the spacecraft.

ELIZABETH FARNSWORTH: Mr. Huntress, the Cassini and its probe stand more than two stories high. What’s in there, in layman’s terms, what’s going to Saturn?

WES HUNTRESS: Well, a great deal of it is a propulsion system and fuel to slow us down when we get to Saturn and put us into orbit. And the rest of it is communications equipment, communicator with that long distance, control systems for the spacecraft and control systems and computers for the various instruments on board this spacecraft, both the orbiter and the probe that will be released. The whole reason for the mission, of course, is the scientific investigations that will be conducted by those instruments.

ELIZABETH FARNSWORTH: What are your greatest hopes for these instruments? What are you–what’s the single most important piece of information you’d like to learn?

WES HUNTRESS: This is a mission of discovery. It’s a mission that’s very, very comprehensive in scope, and so what we fully expect are new discoveries about the Saturn system. It’s a very, very wonderful system. Saturn, of course, is one of the biggest planets in the solar system, and with those rings, it would just barely fit between the Earth and Moon. It has a large number of moons. It has this planet-sized moon called Titan with a very thick atmosphere, organic material in its atmosphere. We fully expect that there will be rain or snow of petroleum-like chemicals on the surface, very odd, very bizarre world, and we’re certain we’re going to make fundamental discoveries about Saturn and its system.

ELIZABETH FARNSWORTH: I keep reading that you’re hoping to find something about the origin of the universe out there. What is it about Saturn or about Titan that makes you hope that?

WES HUNTRESS: Well, Saturn, it’s kind of like a miniature solar system with this large planet at the center and these rings, which are left over from some kind of process–we’re not quite sure what–and this retinue of moons makes it like a very early model of a solar system.

So we may learn something about how solar systems actually form. Titan is like a frozen example in time of how things may have been reacting chemically on a very early, primitive planet. And some of the chemistry that’s occurring there is what we believe may have happened on our early Earth to produce organic material that might have led to the origin of life on this planet.

ELIZABETH FARNSWORTH: And explain how the probe will work. As we just heard in Jeff’s piece it will only have 30 minutes on Titan. What will it be doing in that 30 minutes?

WES HUNTRESS: Actually, it has about three hours. We released the probe from the orbiter that enters the atmosphere of Titan. It has an air shield to slow it down and parachutes. And then it’ll drop on parachutes for two and a half hours through the atmosphere, making measurements. It’ll have cameras on board to take pictures as it descends of the surface and of the horizon. They ought to be absolutely spectacular of this world about which we know so little. And then after two and a half hours, it will actually land on the surface and perhaps survive for as much as a half an hour, and we ought to make measurements on the surface as well.

ELIZABETH FARNSWORTH: So it will actually be able to–I mean, does it have anything that’s reaching out on the surface like the Mars probe?

WES HUNTRESS: No. But what it does have is instruments that can penetrate whatever odd sort of soil Titan has in order to make measurements of what it’s like. And if, in fact, it should land on one of these potential petroleum-like lakes, it’ll actually flow, so we can make measurements of what it is that’s in those strange oceans.

ELIZABETH FARNSWORTH: When the Cassini’s orbiting Saturn for four years, what’s it doing exactly? Is it taking pictures? Is it radar? What’s happening in those four years?

WES HUNTRESS: A number of things. You mentioned two of them. We have a camera on board to take images of Saturn and of its rings. It’ll take images of many of the icy moons that it’ll pass by. Some of these moons are in exactly the same orbit and have kind of an interesting gravitational dance around one another. Some of them have two faces, one very dark face, one very light face, and then Titan, of course, and we’re carrying a radar so that every pass at Titan, and we’ll pass by Titan on every orbit, we’ll get radar passes to try to see through those clouds and get global data on what the surface of Titan is like, plus measurements to understand the dust and the plasma in this giant magneto spheric bubble that surrounds Saturn.

ELIZABETH FARNSWORTH: And this is a huge project, as we heard, very expensive. It’s the last of these kinds of projects as I understand it. Why and what sort of probe of Saturn would come next if it’s not a big one like this?

WES HUNTRESS: Well, this is, in fact, the culmination of a long series of spacecraft in what we call the Mariner series. It began back in 1962 with the first successful planetary mission, Mariner II to Venus. And so it’s a very comprehensive mission, and it’s designed to study a system very thoroughly and very comprehensively, which accounts for its size and its cost.

These days we’re planning to make missions which are more focused in their science objectives and try to accomplish our exploration on a more piecemeal basis one at a time. The next mission to the Saturn system I would expect might actually go to Titan once we learn more about it to try to explore more of its surface, perhaps even, for example, a balloon that would float around in the atmosphere, surveying the planet.

ELIZABETH FARNSWORTH: Okay. Well, Mr. Huntress, thanks very much for being with us.

WES HUNTRESS: My pleasure.