A.J.S. RaylSep 05, 2002

The Stories Behind the Voyager Mission: Charles Kohlhase

Charles Kohlhase served as Mission Design Manager for Voyager from 1974 to 1989. He brought more than a decade's worth of experience working on the Mariner and Viking missions to the position. Following Voyager, he was science and mission design manager for the Cassini/Huygens mission to Saturn and Titan. Subsequently, he has worked as a consultant on the Genesis, Kepler, and Mars Exploration Program missions.

Today, Kohlhase serves on The Planetary Society Advisory Council and works as an artist, specializing in combining the mediums of computer graphics and photography.

"I had come to JPL in 1959 and worked on a number of early projects - mostly Mariner missions, but the dream I'd always had was to be a mission analysis and engineering (MA&E) manager. I wanted to be on the firing line, rather than being in the technical divisions, doing studies and writing technical reports. In 1974, I was chosen to be the MA&E manager (later referred to as mission design manager) for Voyager. Actually, the project was called Mariner Jupiter Saturn 1977 or just MJS77. A more ambitious mission - the Grand Tour - had been cancelled and MJS77 took its place. The initial plans were to launch two spacecraft, using use Mariner technology, just to Jupiter and Saturn and no further.

Bud Schurmeier was the first project manager, and when he left to become the associate director of JPL, John Casani stepped into that position. John and others of us thought: 'Mariner Jupiter Saturn 1977 - what a mouthful.' We decided to have a contest to give the mission a better name before it departed. We put a lot of possible names on the blackboard one day -- Nomad, Pilgrim, Antares and others, then we voted on them. We liked Voyager the best.

There was a little bit of superstition about using that name, because there had been a huge effort to design a mission to Mars that would launch on the Saturn C5, the same vehicle that took the Apollo astronauts to the Moon. And we were going to launch two orbiter-lander combinations piggy-backed, stacked on top of this. It was a huge investment - a Saturn and all of your payload sitting on a single launch. It had been named Voyager. From those ashes arose Viking, but many of us remembered the Voyager story and wondered: 'Are we going to put some kind of curse on it and jinx it if we give it that name? Then we said -- 'We're not weirdoes. We're scientists and we don't believe in things like that.' Obviously, the name did anything but jinx it. Voyager has been the most successful mission of exploration probably ever.

A master plan

It was my job to come up with the master plan. It was the job, essentially, of mission architect, sort of like a glorified tour planner. Basically, I had to take the scientific objectives and then build a mission around them, considering everything and taking in all aspects, from the launch vehicle to scientific instruments, the scientists' goals, how we would use gravity assist, and so on -- and then determine what requirements every element places on the others.

What does the scientific payload on the spacecraft, for example, need in terms of power? How accurately does it have to point? How much data does it have to collect? How steady does it need to hold the cameras? What are the light levels out there? How will we use the radio telescopes - can we use the 34-meter or do we need the 64-meter antennas?

My job was to make sure that the mission could be done reliably and that the requirements each element placed on one another were balanced - that they were all reasonable and would all support the scientific desires.

One of the first jobs was to pick the trajectories. We had thousands of possibilities. We spent six to eight months winnowing them down based on the scientists' priorities, the intensity of the radiation fields, the navigation sensitivities, the locations of the moons - looking for those trajectories that had as many of the natural satellites as close to the flight paths as possible. We searched and searched, changing dates constantly back and forth, and rating the values of the different flybys.

We finally settled on Voyager 1 emphasizing Io at Jupiter and Titan at Saturn and, if it succeeded, then Voyager 2 would be directed to continue on to Uranus and Neptune. It was an incredible choice. You might imagine the huge amount of scientific debate. Which is worth more - Titan … or Uranus, Neptune and their rings and moons? Was Voyager 2 up to making the longer journey, or should we play it safe and just optimize another Saturn flyby? Fortunately, we didn't have to make that choice. Both missions were entirely successful!

An alignment that occurs every 176 years - which some people call a Grand Tour (although it doesn't include Pluto) - was about to happen and 1977 was the best-matched year for Jupiter, Saturn, Uranus and Neptune to be in just the right positions. An alignment that includes Jupiter through Pluto only happens once every 600 years. But we had all but Pluto and it was a wonderful opportunity. The next earlier opportunity would have been 1801, about the time the first train ran in England. The next opportunity would be 2153, when the technology will be totally different and everything will have changed, when Earth's environment will have either been totally trashed or, if we take the critical precautions, hopefully spared. The thing that was so neat was that our technology was ready just in time to seize this sort of optimal 1977 launch opportunity. And we seized it.

I lived Voyager. I breathed it. Over the years, I had slowly developed the tools of the trade and they became second nature to me. They had become a part of my technical intuition. I could walk into a room and hear someone state a problem for the first time and, in seconds, I knew the answer. That's an unusual feeling. I also processed nagging problems while sleeping, almost always awaking with the correct answer.

One of the skills was not to get dragged down by details. All of the trajectory design pretty much works using something called conic sections, for example, such as using hyperbolas and ellipses. I knew the basic equations so I could always step back and stop from being dragged into too much detail. I could get an answer that was within 2-3% of the right answer and do that quickly. That's cocky, and I should be modest. But I got so that I was really, really fast in arriving at the right solution.

Voyager launches past problems

When it came time for launch, I was down at the Cape in the blockhouse sitting next to John Casani watching them both go. The Voyager 2 launch went fine, but there were a couple of glitches. We had gyro swaps during the high initial roll rate of the launch vehicle, and one of the booms didn't seem to have fully locked into place, so we scurried around trying to figure out what went wrong and our engineers made another set of strong springs that they installed on the Voyager 1 spacecraft to make sure it popped out. But Voyager 2 eventually was up there and I remember we all celebrated after the launch at a local seafood place with wine and shrimp in Cocoa Beach.

Another technical problem involved what turned out to be some miscalculations on the effect of plume impingement on some blanket-wrapped support struts. That was fairly serious and it was one that, through the flight, I and my mission planning people had to deal with. At one point, it looked like we might not have enough propellant to make it to Neptune, but we did some clever workarounds. We figured out ways to reduce the delta-V for trajectory corrections, and hence the propellant. It worked and we got past Neptune, and the propellant on board is probably good through 2025, although the electrical power might limit us sooner.

At another point, the scan platform stuck and we had to figure that out. We lost one of the receivers on Voyager 2 and the other one was tone-deaf, and there were a number of little things like that that happened. But when those things did happen, a dozen of us would get together in a room and figure something out, test it and send it up to the spacecraft. It always worked and the Voyagers kept going.

The art of space

Voyager returned so many images, that it's impossible to consistently pick one as a favorite. But there is one image that has particular meaning to me. It's taken at Jupiter several days out, through the narrow angle camera, showing Io and Europa over the disk. It was at this point in the mission that these Galilean satellites were beginning to look like their own fascinating worlds. We were just beginning to start seeing detail - a gold and reddish-orange Io, and little sharp marks on pale vanilla Europa. We knew that we were seeing new worlds up close for the first time in all of history.

A personally exciting time for me was when Jim Blinn, one of the great pioneers in computer graphics, and I worked on the flyby animations. We'd been doing just simple wire-frame animations before. Jim was hired at JPL to work with me - my budget paid his salary - and he developed software to simulate the flybys, and then I would use them to make each little movie script. We worked as a pair. We did Voyager 1 and 2 -- in sequence -- Voyager 1 at Jupiter; Voyager 2 at Jupiter, Voyager 1 at Saturn, and so on.

It was great to see the finished product. Since we released these before the flybys, one of the challenges we had in making the movies was that before we got to these planets we didn't know what the moons actually looked like up close, so we had {renowned space artists} Don Davis, and later Rick Sternbach, work with us. Don helped us render surfaces of things for best guesses when we didn't know what they actually looked like. We would imagine what the surfaces would look like and Don would paint them. But once Voyager 1 arrived and took the real pictures, we would quickly patch the photographs of the real moons on the animation before we made the Voyager 2 animations. So the second in the series was always better.

Exploratory Experience

All the missions before Voyager had only one destination. Mars is an exciting place. But when you fly by Mars, you see Mars and you may see Phobos or Demos. Voyager saw almost 60 different worlds in the course of 12 years. It was fascinating, sort of like visiting some prehistoric island somewhere, like in a movie. Jupiter had 15 or so worlds, including four Galilean satellites, and we discovered more in the process. But having them become faces with features and mountains and everything was something I will never forget.

The fear had been that every satellite out there would just be some ancient heavily cratered uninteresting world, that every one would look like our Moon, a kind of barren place. People romantically enjoy the Moon, but let's face it, if you look at the surface, it's not the most exciting place you've ever seen. But the moons of Jupiter, Saturn, Uranus and Neptune were all different. Io had nine active volcanoes at the time. Europa had a frozen ice crust with cracks in it and some of the hairlines of the cracks were white, which seemed to indicate that water had oozed up and refrozen fresh on the surface. Ganymede looked like it had been plowed up by plate shifting and countless impacts. Callisto was also interesting in its own way, with the residual rings from an enormous impact in its remote past.

When we got to Saturn, we found the rings were thousands of ringlets and gaplets with these spoked features on them. Titan was totally socked in - this orange ball of dense gas. The first images of Mimas came back with that huge impact crater - so big that if it had been any bigger it would have broken the Moon apart. When the image was put up at Von Karman {Auditorium at JPL} somebody in the back of the room said: 'My-god, it's the Death Star.' There was serious science, but there was also fun here. The real thrills though were seeing all the new worlds.

Heart-warming Fame

There were some unexpected perks that came along with being part of the Voyager team. Somehow I had wound up being Angie Dickinson's escort once and, after that, I always wound up taking her and her daughter around. I also got to meet all the science fiction writers - from Ray Bradbury, Arthur Clarke, Robert Heinlein, Larry Niven, Jerry Pournelle and others -- and the original Star Trek crew.

One time I gave a talk in Beckman Auditorium to about 700 science teachers from around the United States. It was one of the good-feeling highpoints in my life. We had just had a successful Saturn encounter with Voyager 1 and I had been scheduled to talk with them about the mission. I walked in the back of Beckman Auditorium and, as soon as I walked in, all 700 people stood up and started applauding. They respected what the Voyager team had done. You never forget that. I had tears in my eyes by the time I reached the podium.

A year or two later I was at the lab and this big box comes in the mail. Inside, there's this beautiful quilt. It's from a fifth grade class in Libby, Montana, whose teacher had been one of the science teachers in the audience. She had been inspired enough by what I had to share with them that she had raised the money in the community to buy a sewing machine. Then she had every student in her class, over a period of nine months in the school year, each sew one patch for this quilt and they put it altogether with silver thread. So experiences range from the adrenalin-pumping excitement of discovery to heart-warming, personal, human experiences.

On the funny side, I stood in for Gentry Lee one time at a Star Trek convention at the L.A. Convention Center. I walked into the auditorium and there were 4500 people waiting for this talk. I had been sandwiched between DeForest Kelley and William Shatner, which is why there were so many people there. Giving a live talk to that many people is an experience. The podium is up on this stage and you have to ascend seven or eight steps to get there. Rather than having stage fright, I suddenly felt this enormous sense of power like an evangelist must feel, and the oddest thing happened. I felt I could just seize the audience. I gave this incredibly confidant and powerful talk. I don't know whether that happens to other people, like congressmen who get in front of 30 mikes, whether they develop a sense of power or what. But I did feel it that one time and it is a real experience. You feel like nobody can touch you.

Above and beyond everything though, the greatest experience was working with a special team of people, none of whom let any of the other down, and having led the design of the Voyager mission, the planning, deciding which sequences we'd put together and how we'd do the observations - and having it either work perfectly or finding a workaround the few times it didn't. Then having the opportunity to go along with these wonderful robots during each encounter.

No other mission has ever seen so many worlds, all of which are part of our Solar System. It was a chance that came around once in every 176 years and we prepared for it, we designed the right things to do and we did it - and it will likely prevent me from ever being a bum drinking cheap wine in an alley somewhere. Seriously, the upshot of it all was that it was a unique opportunity, captured by the dreams and sweat of a dedicated team. Out of that emerged an enormous success story, the greatest mission of planetary exploration to this day. That's the story of Voyager."

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