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The big break came when we won the Descent Imager Spectral Radiometer experiment, which was the camera on board the Huygens probe. It was a spectrometer and a specialized camera to look at the Sun to determine the aerosol properties, and covered visible, infrared, violet and some of the ultraviolet.
Cassini was launched in ’97. I was primarily responsible for the software. It was really interesting software; it was adaptive in nature, so that if something happened in Titan’s atmosphere, the instrument would respond to it. At the same time, I wasn’t just an instrumentalist. We published papers along the way; we became experts in radiative transfer. We became one of the first groups that could really interpret photometric observations, and spectrometric observations of planets with thick atmospheres. We published a number of papers on Jupiter and Saturn based on the Pioneer results, and also on Venus, with the Pioneer-Venus results.
So we were well situated to analyze the Cassini-Huygens data when it came back, and it finally did in 2005. Things didn’t quite go the way we expected. The probe spun backwards from the way it was supposed to go. The probe oscillated a little more than we expected it to, and it went outside the tolerances. It made the data much harder to interpret than it would’ve been otherwise. But we’ve done it and actually we’re about to publish what we think is the definitive paper on Titan’s aerosols.
The highest moment is when I got up on January 14, 2005, and turned on the TV and already there were pictures from our instrument, sitting on the surface of Titan, showing these pebbles and this kind of dry riverbed. Obviously we had made it. We had landed on Titan. It was just unbelievable.
Cassini, of course, is a very large planetary mission. The goal is to explore Saturn and its rings, its moons—especially Titan, a large moon with an atmosphere—and the magnetic environment of Saturn. The mission came about in part because NASA was planning a mission to orbit Jupiter after the Voyager missions, and it was natural since both Voyager flyby spacecraft went on past Saturn that they would plan the same thing. The twist, though, was that the Voyager flyby of Titan turned out to be so interesting, and Titan turned out to be such an interesting place, that not only was the U.S. interested but Europe became interested.
It was a very straightforward collaboration, to get the United States to build a Saturn orbiter, and the Europeans to build a Titan entry probe that would be carried to Titan by the Saturn orbiter. The entry probe would go through Titan’s atmosphere and make measurements. That was Cassini-Huygens. By the mid-1980s, the general architecture of this mission was well-developed. There was a lot of fine-tuning of the political process so that both the European Space Agency and NASA would get going at the same time. That’s tough, because if NASA wasn’t interested, ESA couldn’t be interested, and if ESA wasn’t interested, NASA wasn’t so interested, so they had to move together.
The metaphor that vividly I remember was a balloon launching from the U of A mall, where there were like 15 or 20 manned balloons, and they were all launched. I think they don’t do that anymore at the U of A, probably for insurance purposes. You know, when a balloon takes off, it takes off. But there were these two balloons that they decided to tether together and have them take off at the same time, which was quite a stunt. Of course you can’t have one balloon get too much above the other balloon, because they’re tied together. So one balloon has to go up, then the other, and these go up in a stair-step fashion and it takes a lot longer to get to altitude before they finally cut the rope from each other and let each other go.
It was that kind of really delicate process that was required to get Cassini going in 1989-1990. A lot of us here at LPL applied for different roles; I applied for the role of Interdisciplinary Scientist, which was not someone who would build instruments, because I was mostly a theorist, but somebody who would have responsibility for a science area. I proposed for Titan’s surface, and would use instruments to understand in a holistic way what Titan’s surface was like, which was one of the big mysteries left over from Voyager.
That was my first really big proposal. It got me involved officially in Cassini. Prior to that, the mission was being studied, and ESA and NASA could involve scientists on an informal basis in the studies, but once the mission becomes official, scientists have to actually compete to get on the mission. Some well-known experts on Titan who I know didn’t get on that mission, and my career would have been totally different if I had not gotten selected.
But I did get selected, and I was later selected as well for the radar team, and I was also selected as part of the team for one of the probe instruments. So three different responsibilities. It involves a lot of travel, a lot of learning about mission planning. Just by going through that bottleneck, that narrowest point in the hourglass of getting selected for Cassini, it opened up a whole lot of things.
The launch was in ’97. It arrived at Saturn in 2004, in July, and that was just about 21 years after my first contact with the scientists planning Cassini. Now we’ve got just floods of data. The probe worked as it was supposed to. It was a real risky part of the mission but it worked. We’re getting lots of radar data; I don’t have time to work on all the data I’d like to. We’ve got several other people at LPL with major instrument responsibilities. In spite of all the attention that’s given to Mars, I’d often like to think that Cassini was an important, formative experience for this laboratory.
For the probe mission, as an Interdisciplinary Scientist, I could float around as instruments got their data back from the probe mission. I made sure I was in the porta-cabin where the imaging data came back. That was probably the most emotionally intense of those experiences, because the imaging data were received on the ground. There was a two hour period while those data packets were extracted from other kinds of data that came back from the probe in the same stream and then sent to the porta-cabin where Marty Tomasko’s camera team was located.
Once the data was on their computer, their software converted these to images, and the images were first displayed as a set of 300 thumbnails. That was the way Bashar Rizk, who was the guy in front of the computer consul, was displaying them—one second per image. So for about five minutes you looked at these 300 images, not in descent order. They were in random order, so you could see flashes of things on these thumbnails that looked like something you couldn’t recognize and then a river channel would pop up, and then something you couldn’t recognize and then a fracture would pop up. It was such a bizarre way to see these. Here were the first close-up images of Titan and the last close-up images that we’ll probably see for 20 years, all in that five minute period. That was very intense; there was a lot of screaming in that room and I was one of the people screaming.
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