Space Topics: Voyager
The Stories Behind the Mission:
Linda Morabito Kelly
As Told to A. J. S. Rayl in 2002
on the occasion of Voyager's 25th anniversary
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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