I got totally sidetracked by Voyager stuff yesterday, and today I’m still immersed. We’ll have to return to the Alcobaça Monastery next week. In the meantime…did you know that the Voyager program came very close to never happening? And I mean never happening, as in, not in our lifetimes or the next several generations.
THE GRAND TOUR — how it all began
The original plan for the two Voyagers was to send them on a “Grand Tour” of the outer planets, i.e. Jupiter, Saturn, Uranus and Neptune. But the nearly incomprehensible distances between these planets would normally preclude a little bitty probe from hitting all four of them within its mechanically feasible lifespan. Not only that, but those planets have GINORMOUS orbits, and they’re all whirling around on their own schedules, so the occasions when all four of them just happen to line up in a neat row are extremely rare.
Once every 175 years.
Guess when it last happened?
In the late 1970s.
Thus the opportunity astronomers were gifted with in the 1970s was not going to happen again until the 2150s. It was truly now or never. It was almost never.
In 1965, a CalTech grad student working at JPL figured out trajectories for various paths intersecting various combinations of the four outer planets and, in some cases, even Pluto. (It was still a planet back then, poor thing.) All of the launches for these trajectories would have to take place between 1975 and 1981. The clock was ticking.
Scientists got enthused. Even President Nixon joined the party, and said preparations would begin in 1972.
But then the cost estimates started coming in. And NASA, with its Congress-controlled budget, was also having to pay for the final Apollo missions, Skylab, the Viking program, and the beginning of the Space Shuttle program. The Grand Tour program, with its lofty goals, high costs, and lack of “sexy” visuals, couldn’t compete. It was axed in late 1971. Too bad, so sorry, try again in another 175 years, m’kay? Maybe Congress will have given NASA a bigger budget by then.
WHEN LIFE HANDS YOU LEMONS — reconfigure them and call them something else
The folks at JPL were smart, though. They said, “What if we just go to Jupiter and Saturn? Less money!” NASA said that would be all right, especially since the new probes would be modeled on the already-proven Mariner program, which had seen successful trips to Venus, Mars and Mercury. Accordingly, the program was renamed Mariner-Jupiter-Saturn ’77, or MJS’77. (Those folks were great at tech, but terrible at catchy names.) The “77″ referred to the expected launch year.
Ten Mariner probes had already been made, so the new ones were called Mariner 11 and Mariner 12. Construction and preparations began, but it soon became obvious that flying to Jupiter and Saturn was a whole different ballgame than trips to the inner planets. Besides the vast distances involved, Jupiter has a vicious radiation field that would fry the probes’ electronics unless they were drastically hardened. Because the outer planets are so far from the sun, photovoltaic panels could not be used for power. It had to be nuclear, which necessitated other changes. The onboard computer program needed to be far more robust — practically on the level of HAL from 2001: A Space Odyssey — so that the probes could operate all of their own systems and make their own decisions in real time, rather than waiting tens of hours for communications from Earth. And that all-important communication necessitated redundant systems, to guard against costly mission failure.
By the time these and other modifications were made, Mariner 11 and 12 had changed so much from earlier Mariner models that the project manager lobbied to give the project a new name. Instead of MJS, it should be called Voyager.
There were three Voyager models built: a non-flying proof of concept for testing, and two functioning models. The test model was called Voyager 1 — officially, VGR77-1. The others were VGR77-2 and VGR77-3. By the time of launch, though, the working models were renamed. Voyager 2 became 1, and Voyager 3 became 2.
In the six prior years of development, there was one giant taboo at JPL: NEVER DISCUSS THE POSSIBILITY OF SENDING THE VOYAGERS PAST SATURN. That program was axed, remember? We weren’t going there. We were only going to Jupiter and Saturn. Wink wink, nod nod. But by 1977, with all the modifications and incredibly advanced technology now installed in the Voyagers, higher-ups at NASA began thinking differently. Maybe those new probes would survive past Saturn. Maybe one of them could make it as far as…Uranus!
THE VOYAGE BEGINS
Voyager 2 launched on 20 August 1977, with Voyager 1 following on 5 September. Voyager 1 quickly established itself as the rabbit of the two, outpacing its sibling right off the bat and reaching Jupiter on 5 March 1979. Voyager 2 didn’t get there until four months later. After their Jupiter flybys, both probes sailed on toward Saturn, where they diverged.
Voyager 1 was sent to take a close look at Titan, Saturn’s largest moon. Titan is huge, 50% larger than our own Moon and 80% more massive, which means it’s got a big gravity well. When Voyager 1 swung around it in November 1980, the gravity boost accelerated the probe off the ecliptic plane and thus off the path of any further planetary flybys. Voyager 1 had officially accomplished its mission. It was three years old, had survived the traverse of unthinkable distances, and was done. It was given a mission extension — to search for the heliopause boundary — but that was just a pipe dream. Nobody really thought it would survive long enough, and NASA/JPL turned their attention toward its sibling.
Voyager 2 approached Saturn in August 1981 and executed a perfect flyby. Since it was still in great working order, it was sent course corrections for a slingshot past Saturn and a new heading toward Uranus. At this point, Voyager 2 was going above and beyond its original mission. (And the nerds at JPL were probably all elbowing each other and grinning.)
On 24 January 1986, Voyager 2 made its closest pass by Uranus and was able to send back photographs. It became the first — and only — spacecraft to explore a planetary body outside the orbit of Saturn, and still it wasn’t done. Now five years past its expected operating lifespan, Voyager 2 was ready for more. So JPL used the flyby of Uranus to change its trajectory and give it a boost in speed, and Voyager 2 went sailing toward Neptune. It probably wouldn’t get there, but it sure didn’t hurt to try.
Three and a half years later, it got there. Voyager 2 flew past Neptune on 25 August 1989. It was now twelve years old, eight of which were considered icing on the cake, and yet it still had life in it. So it was swung around Neptune and sent on a very close flyby of Triton. This encounter sent it zinging off the ecliptic, ending its original mission and marking its entry into the extended mission of finding the heliopause boundary. It headed “south” of the ecliptic, while Voyager 1 was going “north.”
The Voyager mission is truly a rags-to-riches story. First it was cancelled, then rescued from the dustbin but given a truncated mission, then the mission was extended…and extended again…and extended again. By the time Voyager 2 beamed back its magnificent photos of Neptune and Triton, both probes were scientific rock stars. Many public television stations in the US even carried live broadcasts to show the images as soon as they reached Earth.
It has been twenty-four years since that Triton flyby, and Voyager 2 is still going. Voyager 1, of course, just made history by breaking through the heliopause and entering interstellar space. Voyager 2 is on its way to doing the same thing. These probes were designed to last four years; they are now 36 years old and counting. They’ve lost function in many of their instruments and their power is down to a whisper, but they are still accomplishing the very definition of cutting-edge science. They are survivors, but more than that, they’re a testament to human ingenuity — and pure, devious stubbornness.
(All images from Wikipedia.)