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