Tuesday, July 14, 2015

The End of the Beginning

Fifty-six years, six months, and fourteen days.

That sounds like a long time, and in terms of a single human life, it is. But in terms of humanity's lifetime, it's barely a blink of an eye. And I think that's the proper context, because it's the length of an era that ended today. By the time I finish writing this, I expect that we will have heard, one way or another, about whether or not the New Horizons spacecraft survived its encounter with Pluto. That encounter brings to a close the first era of humanity's exploration of the Solar System.

I place the beginning of this era on the first of January 1959, with Luna 1's flyby of the Moon. Luna 1 had been intended to hit the Moon, not fly by. But since these were early days yet, barely more than a year after the very first Earth satellite, rockets and guidance systems weren't all that reliable. Nevertheless, it became the first man-made object to enter heliocentric orbit. It's still out there, somewhere.

Venus, being the closest planet to Earth, was an obvious choice for our first planetary mission. Mariner 1 was intended to be the first, but again, guidance systems were still fairly new and not entirely reliable. The range safety officer had to hit the big red button when the Atlas-Agena booster decided it wanted to go for an unplanned excursion. They'd learned a thing or two, though, and in those early days they tended to plan these missions in pairs. If one of them didn't work, the other one probably would. And so it was that Mariner 2 became the first to fly by Venus on the fourteenth of December in 1962.

Staying with the pattern, the next target became the next farthest planet from Earth: Mars. And the script looks remarkably similar -- Mariner 3 was intended to be the first, but ... No, it wasn't the guidance system this time. This time, the payload shroud failed to open properly, and the spacecraft couldn't get any sunlight on its solar cells. The spacecraft limped along on battery power for a bit, then died, and drifts in eternal Solar orbit. Again, though, this is exactly why they planned these things in pairs. Mariner 4 came off without a hitch, and flew by Mars exactly fifty years ago today, returning the first-ever close-up pictures of another planet.

From 1965 to 1973, there was a bit of a drought of "firsts", partly because Project Apollo soaked up a bunch of time, money, and talent... But also because the next steps were going to be really difficult. And besides which, they had something pretty clever in mind, and had to wait for the right opportunity.

The next pair of probes to launch were Pioneer 10 and Pioneer 11, bound for Jupiter. "Wait," you may ask, "isn't Mercury closer?" Well, sure. But Mercury is also really, astoundingly fast. And that makes it a fairly tricky target. They had an idea, but they weren't 100% sure it would work. Anyway, the Jupiter launch window opened up first in any case. In December of 1973, Pioneer 10 gave us our first close-up look at the biggest of the planets, its system of moons, and its terrifyingly powerful radiation belts.

But we hadn't given up on Mercury. No, even though we'd have to do some pretty fancy work with a pool cue to get us there. Mariner 10, the last of its series, launched in November of 1973, and pioneered a technique we'd use again and again in the future: the gravity assist. We couldn't build a rocket powerful enough to fling a probe by Mercury -- well, we could, but no one was willing to allocate a Saturn V to the mission -- so we'd hitch a ride by Venus and steal a small bit of its momentum to get us the rest of the way. This gives us a twofer: two planetary visits for the price of one. Four, actually; Mariner 10 flew by Mercury three times. First in March 1974, then again in September 1974, and again in March 1975.

This proved good practice for the main event. Remember Pioneer 11? Pioneer 11 followed up its Jupiter encounter with an encore at Saturn in September of 1979. But even that was merely a warm-up. Another pair of probes were coming through, and in scientific terms they were armed for bear.

Bar none, the single spacecraft that broke more trail than any before or since just about has to be Voyager 2. Both Voyagers flew by both Jupiter and Saturn. And both were launched at a very fortuitous moment ... a moment when the four giant planets line up in such a way that one trajectory can link them all. Voyager 1's Grand Tour was cut short, though, to give it more time to give Saturn's moon Titan a close-up look. It would be left to Voyager 2 to take it all the way home. In addition to Jupiter and Saturn, Voyager 2 flew by Uranus in January 1986, and Neptune in August 1989. No one has been to either one since.

After this, there was another period of drought ... for much the same reason. The outer planets are hard to get to. It would be almost a quarter-century before we finally got around to finishing out the initial reconnaissance of the Solar System. Dawn has been cruising around the Asteroid Belt for quite some time, first orbiting Vesta before flying over to take up station around Ceres. I won't dwell on that, though, especially since I've so recently written about it.

Which brings us to what we've been watching this last month or so.

Pluto has been, at most, a vague blob. What we didn't know about it was ... well, about everything. Once we'd found its moon Charon we could get some idea about its mass, but we were never entirely sure how big it was. Or precisely what it was made of. Or what it looked like. But even if we never hear from New Horizons again, what it's already found has utterly revolutionized our knowledge of the outskirts of our system. Even if we can't call it a planet anymore, there can be no doubt that these are worlds. Even if we never get another byte of data, what's already been gathered will keep scientists busy for years.

I don't have to write any more about that hypothetical though. Because we have a hard lock on a healthy ship. And over the next sixteen months, at an agonizing 4K bits per second, New Horizons will empty its tape recorders into our data banks.

I can scarcely imagine what it's seen these last twenty-four hours.

Soon, I won't have to.

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