Space Topics: Voyager
The Stories Behind the Mission: Bruce Murray
As Told to A. J. S. Rayl in 2002
on the occasion of Voyager's 25th anniversary
Bruce C. Murray served as the only geologist on the team planning the Grand
Tour, which was cancelled by NASA in 1972, but which led to Voyager the same
year. He later became the Director of the Jet Propulsion Laboratory (JPL),
a position he held from 1976 to 1982, the early glory years of the mission.
While leading JPL, he co-founded The Planetary Society with Carl Sagan, and
currently serves as Chairman of the Board of Directors. He is now an emeritus
professor of geology and planetary sciences at the California Institute of
Technology.
"The Voyager mission was an extraordinary, epochal voyage of discovery
that I liken to Captain Cook's explorations of the then-hidden parts of the
world. It will be remembered in much the same way as we remember Cook.
Voyager was the culmination of many things, much as was Cook's voyage. Cook
dealt with scurvy, proved he was an extraordinarily good navigator, and used
the technology that had developed to the point where sailing to new lands
was feasible. Voyager represented the coming together of rocket technology,
computer and information technology, politics, the priorities of nations,
and the right timing. It would be 176 years before the next planetary alignment
would allow for a trip like this. As Tom Paine {former NASA Administrator
and Planetary Society director} used to say -'The last time that {alignment}
happened was when Thomas Jefferson was President, and he blew it.'
Overcoming technical challenges
Just as Cook and his crew had to deal with the adversities that come with
exploration, so did the Voyager team. A number of equipment failures took
place early on, long before Jupiter and the team was forced to handle them
on the spot. The improvisations in response to failures aboard the spacecraft
were outstanding.
First, Voyager 2's electronic brain suffered a kind of robotic 'vertigo'
right after launch. In its confusion, it switched to backup sensors, presuming
its 'senses' to be defective. Still, there was no relief from its disorientation
Fortunately, the upper-stage Centaur attitude-control system stayed in charge
and corrected the disequilibrium of Voyager's brain just before separating
from it. Unlike Cook's ships, the Voyagers were semi-autonomous robots.
At a later point, the spacecraft's robotic 'alter ego' {executive program}
frantically tried to correct an orientation failure it sensed and shut down
all communications with Earth. The new super-sophisticated fault protection
in Voyager's brain had been programmed to shut off communication to Earth
during such emergencies and fix itself. For some reason, the spacecraft's
computer logic was running rampant. This was extremely scary-the second spacecraft,
Voyager 1, was to launch in less than three weeks. We had to figure out quickly
what could be done.
As it turned out, Voyager 2 had reacted to vibrations from the unlatching
of its instrument boom. As it was trying to reorient itself, it had a complex,
sensitive reaction to small dust particles from the rocket propulsion. These
particles sometimes drift near a spacecraft. When lit by the Sun, they are
much brighter than the stars that the spacecraft's optical detector normally
tracks; it had been trying to follow the dust particles and the tracker was
reorienting the spacecraft accordingly. Corrections were patched onto computer
programs on Voyager 2, and a new mechanism to reduce vibrations from the instrument
boom was installed on Voyager 1 before it launched.
The team improvised again when a key communications element failed. The radio
signal that is transmitted by the spacecraft back to the Earth suffers a Doppler
shift, that is, it is like the train whistle going by an observer at the station,
which sounds higher as it approaches the station and lower as it goes away.
In the case of Voyager, the sound is always going away, so there's a steady
downward shift in tone. The exact amount depends precisely on how fast it's
going.
So the commands, instead of being at the steady tone - high C, if you will,
using a musical analogy - are shifted off to, say, C-sharp. The amount they
shift is critical to the ability to hear them. The special device that automatically
makes that adjustment failed. The danger was it could have happened on the
other one too.
We had duplicate systems on board, but this failure was unexpected - all
failures are I suppose - and the coordinates for switching receivers were
such that they inhibited us from switching between receiving and sending on
the duplicate equipment. We did not dare switch again because we were afraid
we would lose it. So we had a tone-deaf system on one spacecraft with the
risk of the same thing happening on the other one.
This was such a delicate system that, to communicate over these long distances,
the frequency had to be absolutely precise. That meant for every command that
we sent, the engineers had to calculate very precisely the tone shifts so
this tone-deaf receiver could hear it. It worked.
The communication system is also temperature-sensitive, so as the temperatures
in the spacecraft changed, the frequency setting on the receiver shifted a
bit. A fraction of a degree of temperature was enough to throw it off. The
team also had to coordinate that data with how fast the spacecraft was moving.
The communications people, the mechanical engineers, and the people who do
the thermal modeling figured it all out. If we had not had a first-rate engineering
team, we might not have achieved all our goals.
The spirit of adventure
An example of the adventuresome spirit of the engineering team is the fact
that Voyager 1, which was going to Saturn and Titan, was targeted to go in
close to the rings of the planet and get the best possible view of Titan.
The best way to do that was to fly behind Titan as seen from the Earth. That
meant that you would break communication with Earth. If the spacecraft failed
when it was behind Titan, you would lose the Titan information and the information
on the rings of Saturn.
This was another tough decision and Ray Heacock, who was managing the spacecraft
at that point, made the call - yes, we're going to fly behind Titan - even
though there were problems with the spacecraft.
The self-confidence of the team made a big difference. They knew these robots
so intimately that they knew how to take chances. Unlike Captain Cook, Voyager
couldn't moor in a port for repairs. We really had to do it right the first
around. That's quite different than exploring Mars with orbiters, as we're
doing now.
In the old days of fly-bys, the missions were short and those who built the
spacecraft, operated it, and saw it through to the end. With Voyager, with
a long, long flight time, we had to gradually replace and train new people.
The designers and the operators of the systems developed a real symbiotic
relationship with these robotic beasts that went on for years. It had been
a special challenge and so far it remains unparalleled.
More than a dot on a plate
A moment that was particularly special for me was when the pictures of Miranda
were returned by Voyager 2. When I first worked on the Grand Tour, a the only
geologist on the team, my task was to convince the astronomically oriented
group that those little dots on the plates that represented the satellites
were important, that they had a story to tell. While the scientists were interested
in the rings of Saturn and of the banding of Jupiter, they were less interested
in those little dots.
Then when the pictures of Uranus' Miranda, came back, they were absolutely
astounding. Here was this little moon, less than 500 kilometers across- and
yet it was far from being just a dead, cratered body. It had, instead, a completely
weird surface.
Trapped inside a soap bubble
In the grandest moments of Voyager, however, I felt claustrophobic - wondering
where this mission was leading us. I had grown up interested in the outdoors.
I went into geology and worked in the oil business before I went into the
Air Force and discovered space. Psychologically and professionally, I am anchored
to Earth and yet in my own lifetime I have been able to participate in the
exploration of Mercury, Mars and the outer solar system. In my mind I have
really been there. That's all happened in my professional lifetime. Now, if
all this could be experienced in one person's lifetime, as one of Captain
Cook's crew, if you want to look at it that way - what next?
I came to the somber conclusion that the stars are so distant, and given
that no one has yet conceived of a feasible way to get there, I felt confined.
Even with the most powerful telescopes, we are limited in how far we can see.
I felt like I was trapped inside a soap bubble, our solar system, within the
giant balloon of the universe. We had suddenly shot out to the edge of where
we can go.
Of course, we still have Pluto and the Kuiper Belt to explore, but the next
step after that is a huge one -- something like one of Captain Cook's crew
looking at the Moon and saying, 'I wonder when we're going to be able to go
there.' Cook's crew would have been disappointed. It would take another 200
years. Now there are people like myself living through this period of time
and wondering -- how do we break out of here? It may be 200 years. It may
be 2,000.
A highpoint in human exploratory trajectory
Voyager has not diminished what Captain Cook did. It just suggests, in my
view, that we've hit another high point on the human exploratory trajectory.
I'm proud and delighted to have been around this time when something as significant
as this could have been done. If it takes 200 years or 2,000 years to achieve
the breakthrough that will take us to the stars, Voyager will still be viewed
as an enormous breakout from the constraints that then existed.
This may sound strange, and I could be wrong, but suppose a mission to Alpha
Centauri is developed with some magic new propulsion system. I'm not sure
it would be as rewarding scientifically in its time as the Voyager mission
was in its time. Voyager explored so many planets, so many satellites, so
many rings, things that we didn't know were there. Going to another star,
probably a fly-by at a fraction of the speed of light. It will be terribly
important and we will certainly discover a lot of things. But from this foreshortened
point of view, looking ahead another century or two, the first trip to a star
will have a fantastic effect on human concepts of their own potential. Whether
or not it will have as transforming an effect as Voyager did, I'm not so sure.
The transforming effect of Voyager
While Voyager had some similarities to Apollo, it is also something different.
The Moon landings were all about the astronauts. That's what manned flight
is all about - human life and death, risk and adventure. Apollo established
a high watermark of what humans can do - 300,000 people working together for
10 years can produce an extraordinary outcome. Nobody has ever done anything
on the scale of Apollo.
With robotic exploration, it's about us because our brains, our eyes and
our feelings are connected out there. We were the first to Venus, the first
to Mars, and those were very difficult missions at the time. We had a team
at JPL that had the self-confidence to work together to accomplish something
that was once thought to have been impossible.
The exploration of space, however, exists only because it influences people
beyond the small group who actually do it. If Cook or the polar explorers
never wrote about their discoveries, they wouldn't have made any difference,
because people wouldn't know about it. It's the same thing with Voyager. Voyager
became an adventure of the mind and spirit. The true significance of this
mission is the fact that the public could witness it as it was happening
Voyager was connected to the world through radio signals, first to the Deep
Space Network (DSN), then through television. That meant that our brains were
connected to the spacecraft. It was as if we were there with Voyager. We took
the adventure. That's what was transforming in terms of the relationship people
feel toward their own Solar System.
The Voyager mission touched millions and millions of human beings, enlarging
their perspective of the Solar System and what we as a human species can do.
The next step - which we are just beginning to do in the case of Mars - is
to provide a public connection with things like rovers, to create an interactive
relationship. This is going to elicit a broad public participation in exploration.
We'll show this with Red Rover Goes to Mars. That's going beyond having our
brains connected passively as when Voyager went by planet after planet, and
stepping into the future where our brains are connected interactively.
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