The Stories Behind the Voyager Mission: Bruce Murray

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.