A.J.S. RaylSep 05, 2002

The Stories Behind the Voyager Mission: Linda Morabito Kelly

Linda Morabito Kelly began working at Jet Propulsion Laboratories while still a student at the University of Southern California. In 1974, she accepted a fulltime position as an engineer in the Satellite Ephemeris Development and Orbit Determination section JPL. There, she worked on a number of projects, including the Viking mission to Mars until 1978, when she was brought onto the Voyager mission and became Cognizant Engineer of the Optical Navigation Imaging Processing System (ONIPS). Today, she serves as Program Development Manager at The Planetary Society.

"I started working at JPL as an engineer right after earning my degree in astronomy from the University of Southern California and had worked on a variety of projects, including Viking. In late 1977, I was asked to participate in the process of creating a star catalogue for the Voyager mission, which was already on its way to Jupiter and Saturn.

To navigate a spacecraft like Voyager, two data types are needed -- Earth-based radio data and spacecraft-based data, specifically pictures taken by the spacecraft of the moons of Jupiter against a star background. We needed to extract the positions of the stars and the Galilean moons -- Io, Europa, Ganymede, and Callisto - in the pictures to a very high accuracy so that we could determine the spacecraft's position relative to those moons. No star catalogue existed anywhere in the world that had the stars' celestial coordinates to the accuracy that the Voyager mission needed. So Voyager commissioned production of its own star catalogue.

The opportunity of a lifetime

In the summer of 1978, the opportunity of a lifetime presented itself. The cognizant engineer of the Optical Navigation Imaging Processing System (ONIPS) - the mini-computer dedicated to finding the centers of the star and satellite images used to help precisely navigate Voyager - unexpectedly left. The position was offered, I accepted it and launched into the work.

The Voyager navigation area was this huge bullpen area and ONIPS had its own corner, partitioned off with glass walls. Remember, this was in the era when a mini-computer like this could fill an entire room and had to be cooled. So when I would walk into the ONIPS area there would be this blast of these air conditioners from below the floor. It was cold, noisy, and an interesting environment in which to work.

ONIPS was a MODCOMP IV mini-computer with many peripheral devices and my responsibility was to continue the work of developing the software used to perform the necessary image extraction function, determining with high accuracy the centers of these objects so that the spacecraft could be navigated. I had to be completely aware of how this computer behaved and how it would function.

The Voyager cameras were vidicon cameras, which have a lot of optical distortion associated with them. The vidicon electron beam, for example, would bend toward the very bright, overexposed images of the moons of Jupiter, thereby producing distortions from what is actually being photographed. The images of the moons had to be overexposed, so that we could detect the faint stars in the background. All the distortions had to be accounted for and then removed from the processing to find the centers of the images of the moons and stars.

The a priori location of the stars and satellites would be received by ONIPS from the large Univac 1108 computer, and then our high accuracy data of where they actually appeared would be sent back to the Univac 1108, where the entire navigation process and reduction of the data would take place.

As Voyager got closer and closer to encounter with Jupiter, there were some 20 of us on the Navigation Team working very, very hard and around the clock. The importance of the work that we were doing was very evident to all of us. What the Voyager Navigation Team accomplished in getting the spacecraft to Jupiter has been compared to threading a needle miles and miles away from the location. I could not imagine working with a finer group of people - their competence and enthusiasm. It was an outstanding team and I was genuinely honored to have been a part of it.

Data pouring down like rainfall

During February 1979, as Voyager was nearing encounter at Jupiter, the optical navigation data processing began for mission operations. I was working a minimum of 14 hours a day. The images taken by the spacecraft would come to JPL through the Deep Space Network (DSN) and then appear on the JPL monitors as they were received. I would get up with the Sun and would cross the laboratory to Building 264, feeling the excitement building as I got to watch Jupiter itself as the spacecraft was approaching it.

As the cloud patterns of Jupiter became more clearly discernable, I knew this was a mission that was going to show us things we could have never possibly even dreamed of. With the sheer beauty and the amount of information coming through, I sensed that the many wonders that would be revealed by these two spacecraft was something beyond anyone's imagination.

By February 1979, the data was falling down on us like rainfall and the images were coming in at all hours of the day and night. The digitized images for navigation were hand-carried on large data tapes to our area. All of the pictures used for navigation were gray-scale images of the moons of Jupiter against star backgrounds, while the images that went to the Science Imaging Team were color. I would process our images to find the high accuracy centers of and then transmit them to Jim Campbell, who was overseeing the radio data, and Steve Synnott, who was in charge of the optical data. Then, they would work very hard to determine the location of the spacecraft for trajectory correction maneuvers.

Directly above us on the 3rd floor was the Science Imaging Team headquarters. At one point, we were interrupted by some very excited members of the science team, who brought down the first image of what they believed was a ring around Jupiter. While there was an entire image processing facility across the street from the building we were in where the scientists could send their images to be enhanced, I had some of that capability at my fingertips right downstairs. Therefore, ONIPS was probably the logical first place for these scientists to bring their image. I remember everybody in the navigation area crowding around the monitors as I performed something called a linear stretch on the image to increase the contrast. This barely visible object that appeared to possibly be a ring came into full view. There before us was the ring of Jupiter and we were seeing it for the very first time. Someone there had a video camera and in the tape - which I happened to see weeks later -- you can see all of these hands pointing at this newly discovered ring around Jupiter. It seemed as if all these hands were almost dancing in front of my monitor.

The joy of discovery

During one of the brief times I was able to return home, I remember turning on the television and seeing the Science Imaging Team present the first close-up images of Io at a press conference. What I was seeing in those images was so unlike anything we had ever seen in the Solar System before. I remember gazing at some of the images and weeping from the sense of what was being discovered. As navigators, we were not often able to see these press conferences because of the time constraints and the demands of our jobs. But on this particular day, I happened to catch one color image of Io that showed this unusual heart-shaped feature on the surface. It was so remarkable it was almost shocking. I had expected yet another dead, crated moon, and yet this seemed alive. It moved me deeply and it's something I remember vividly.

After the Jupiter encounter - which took place on March 5, 1979 - I was continuing to routinely process images for navigation. By this point, however, these particular images would not be used for the post-encounter trajectory correction maneuver, but for something we called post-encounter satellite ephemeris reconstruction where we improve our knowledge of the orbits. While it was still important data, it didn't have the urgency of the work that was done before.

On the morning of March 9, I arrived at my station and began processing several images taken by the Voyager 1 spacecraft as it was looking back over its shoulder for one last view of the Jovian system. This one image, which had been taken by the spacecraft the day before, had been put up like all the other images on the monitors at JPL for everyone to see. But when I performed a linear stretch to look for a dim star - the same capability that enabled my computer to see that first image of the ring of Jupiter, I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent-shaped. It seemed unbelievable that something that big had not been visible before, but my linear stretch popped it into view. It was a moment that every astronomer, every planetary scientist lives for. When you see something like that it evoke the deepest questions of your scientific interest. I have absolutely no recollection even to this day of the star that I was looking for at the time.

After some initial inquiries and checking with the head of the Optical Navigation Team, I was alone with that image of Io and had a few quiet moments to reflect. I had the sense that I was seeing something that no one else had seen before. Without verification, it was only a sense, but I knew what I was seeing was that it was extremely important. Those moments were the stuff of dreams. They passed quickly as I dug in to determine what this anomaly was.

My instincts as a scientist took over and even though I was working in the field of engineering at the time, I was an astronomer by training and very, very well prepared to move this forward. I wanted to know what this was. I immediately began considering each and every possibility. Was it real or not? I systematically consulted the camera experts to determine whether it could be an artifact, blemish, or whether any quality of the camera might be able to induce the appearance of this anomaly. We considered all possibilities, including that of a newly discovered satellite.

Over the next six hours, every single possibility of what this anomaly might be was eliminated, until only one possible explanation remained - the anomaly was correlated with the surface of Io. This hypothesis emerged when I, Andy Collins, Peter Kupferman, Steve Synnott, and Tom Duxbury reviewed all the other options and finally agreed that the anomaly must have something to do with Io.

Still, since the anomaly was so large, it was extremely difficult to accept that it could have anything to do with the surface. In this saturated and overexposed image of Io, there were no surface details at all. Stanton Peale {University of California, Santa Barbara} and his colleagues had recently published a paper in which they predicted volcanic activity on Io. The appearance of this anomaly was consistent with that, specifically with the way sunlight might illuminate a gas shell or volcanic plume. But at this point, was a more work needed to be done.

Ed Stone, the Project Scientist, came down to look at the image and I remember the absolute wonder on his face. He took in the image and anomaly. Then, very quietly, said 'This has been an incredible mission,' and he repeated that several times. When Ed left, the work began to correlate the anomaly with the surface of Io.

The fulfillment of every astronomer's dream

Using the sub-spacecraft approximate latitude and longitude, Steve Synnott and I determined that the point of origin of the anomaly correlated very nearly with the large heart-shaped feature on Io. It was late on Friday and people were heading home for the weekend. Peter and I continued on working into the night. As Peter said: 'The more you work with it, the more you think it's real.' It's very hard to describe what it's like to be working with something that no one has ever seen before. In the absence of any other information, however, the information you have in front of you does begin to suggest certain things.

When that correlation took place, I recalled the moment of seeing that large heart-shaped feature on Io in the color image presented during the Science Imaging Team's press conference. It suddenly came back to me that it had moved me to tears - and it made me wonder if I hadn't been gazing into some kind of destiny. Later that evening, I went over to my parents' home for dinner. When I told my father what had happened, he looked at me and said: 'Do you realize you may have discovered the first volcanic activity outside the Earth?' It was wonderful to hear him say that. That night, I dreamed about the things I wanted to do the next morning.

Saturday morning I came in and was proceeding with the next steps. Ed Stone came down again with Bob Parks, the Project Manager, and asked to see the image again. I don't even think I introduced myself. I was just so excited to share with them this incredible image. Ed Stone said: 'If it's verified, it will be a wonderful discovery.' It was amazing because I was so engrossed in what I was doing that it wasn't until much later that day that I remembered he said that to me.

The discovery was verified Monday morning. Needless to say, the Nav team was very excited. Personally, I felt the sheer joy of being involved in the accumulation of new knowledge. It was the greatest, greatest experience that any scientist could ever hope for. Going back over the science data, the scientists realized that the volcanic plumes had been everywhere but had not been recognized.

Now, more than a generation of students has grown up with the discoveries of Voyager and has been influenced by the knowledge reaped by these images and scientific data. I love sharing the discovery story with students, because it says that the field of science is anything but boring. It is a process of increasing our knowledge of the Universe around us. It also serves as encouragement for students to consider science as their career and that with hard work and diligence they could make a valuable contribution.

Voyager re-defined our view of the outer planets and the worlds that orbit them. I was privileged to be a part of the unveiling and to have discovered volcanic activity on Io. Apart from the science, I think the happiness it gave my parents and, without question, the influence it had on the many young people who told me that they entered the field of planetary science because of having heard of the discovery definitely have been the greatest rewards for me. My experiences on the Voyager mission and the discovery is the fulfillment of any astronomer's dream."

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