Barbara Howard: The mission of the Cassini spacecraft launched almost 20 years ago to study Saturn and its moons is complete. Cassini ran out of fuel at long last today and plunged into the planet's atmosphere. One of the many scientists who worked on Cassini over its run has Massachusetts ties. Dr. Richard French is a professor of astrophysics and astronomy at Wellesley College. He was at NASA's Jet Propulsion Laboratory in Pasadena California today monitoring Cassini. He's with us on the line to discuss the spacecraft's mission. Thanks for joining us, Dick.

Richard French: I'm grateful for the opportunity.

Barbara Howard: So, first of all, give us some background on what Cassini was all about.

Richard French: Cassini was an international mission that was conceived in the mid and late 1980s to go back to Saturn after the very successful Voyager spacecraft that explored Saturn, Uranus, Neptune, the outer solar system. Those earlier spacecraft had seen Saturn just flying by. And the Cassini mission was to go back and study Saturn in detail by orbiting the spacecraft for years.

Barbara Howard: Well, how did you get involved in the mission? What was your role?

Richard French: My ultimate role was to be the team leader for one of the 12 instruments on the spacecraft, the so-called radio science instrument. We use the radio signal as a scientific tool to study Saturn and Titan's atmosphere and rings and to do other scientific experiments.

Barbara Howard: What kind of research has come out of Cassini? What's to be learned?

Richard French: The most marvelous part about the Cassini mission is the great variety of things that were there to be explored. Saturn is an amazingly diverse environment. First, there is the moon Titan appropriately named Titanic. It would be its own planet if it were orbiting the sun, and it has an atmosphere denser than the one we're breathing. It has rivers and oceans of methane and liquid ocean interior. There are a host of other moons. The rings, the interior storms on Saturn that we study from the earth. So it's a very rich and diverse world with many, many things to learn.

Barbara Howard: Are you more involved in doing research in the transmissions from Cassini or were you actually hands on with the machine itself?

Richard French: Well, a little bit in between. Everybody who's on the science team participated in the design of the mission itself and all of the detailed planning of the observations and in the execution of getting the spacecraft to a point where we wanted to [sic] a particular time. And then, in analyzing the data. And I think one of the lessons that was most gratifying and interesting to learn is that scientists aren't necessarily trained to be cooperative, but on a mission like this, you learn very quickly the social skills not to be arguing that your science is better than everybody else because after 20 years, that argument gets a little stale.

Barbara Howard: Well, you guys worked together to put this thing together. I understand you started back in 1990 on the project. Is that right?

Richard French: That's right.

Barbara Howard: And you had to have some affection, I would think, for this little space ship being launched way out there. I mean, what was it like today to watch it come to an end?

Richard French: It was … it was overwhelmingly emotional in a way I hadn't anticipated. There have been two metaphors I think that have been used: One of them is to think of Cassini as almost a family member that's valiantly fighting against the fatal disease and eventually it will lose the battle against tumbling into the atmosphere and that's … I can't help but be a little bit of a morose attitude and a sense of loss. But another metaphor is that Cassini ran a long race and we’re cheering it across the finish line. I tried very hard to accept the latter cheerful metaphor, but I found myself very sad at the loss of what really felt like a family member.

Barbara Howard: Take me there. While you were watching these final moments, what was it like for you?

Richard French: It was remarkable. So, we could see a little radio signal displayed in a complex pattern on the screen and to those of us who've been looking at these patterns over the years, it was like watching a heartbeat on CSI as a patient is about to be given electroshock therapy, where we're waiting for the signal to dip to indicate that the spacecraft had finally tumbled into the atmosphere and we could hear audible gasps in the audience. And then, when the final signal was gone, and we knew that Cassini really was no more, I made use of the Kleenex that had been appropriately provided in my chair and just found myself weeping.

Barbara Howard: So it was a pretty emotional moment?

Richard French: I think most of us recovered quickly and felt an enormous pride at the opportunity to have worked in an international team of thousands on arguably the most successful space mission ever. I'm, you know, honored to have had a chance to do that and to share my love of space with others. And I think at a time when facts have a malleability, that those of us would wish that when you actually can show something to be true, it would be believed. Participating in something that is really science based and excites the entire public beyond political boundaries, feels like a precious opportunity.

Barbara Howard: Well thanks for joining us, Dr. French.

Richard French: You're welcome.

Barbara Howard: That’s Dr. Richard French. He is a professor of astronomy and astrophysics at Wellesley College, and he's one of the scientists who worked on Cassini, the spacecraft that for nearly 20 years has been surveying Saturn and its moons. Cassini spent the final day of its fuel today sent out a final transmission as it entered Saturn's atmosphere. Dr. Richard French was there to monitor that.