I promise this is the last Voyager post for the time being. But while I was researching the history of the program for Saturday’s post, I came across all of these cool factoids that either didn’t fit into the narrative, or did fit, but would have made the post gargantuan. And I couldn’t bear to not use them somewhere.
Ever give any thought to how strong the radio signal would be from a superannuated space probe, low on power, and currently almost 19 billion kilometers away? Not strong. In fact, when the signal reaches Earth, it’s gasping along not at one watt, nor half a watt, nor even a tenth of a watt — but 10 to the -16th power of a watt. Let’s write that out:
A standard digital watch uses 20 billion times more power. And Earth’s deep-space tracking antennas can actually pick that up!
Remember when I wrote that Jupiter has a nasty radiation field, so the electronics had to be hardened? If an unshielded human were sitting inside either of the Voyagers when they sailed past Jupiter, that human would have been bathed in a radiation dose equal to 1,000 times the lethal level.
When we humans take a picture in low light, we have to use a long exposure and then hold the camera very steady to avoid blurring. The Voyagers had to take very long exposures and hold the camera very, VERY steady, considering how little light they were working with (and the fact that image stabilization software hadn’t been invented yet). Of course, holding a camera steady on a spacecraft really means holding the spacecraft itself steady. Voyager’s engineers managed to keep the angular rates of the craft (i.e., the change of angle in its position relative to the object being photographed — as the craft was rocketing through space at Ludicrous Speed) to a rate 15 times steadier than the movement of a clock’s hour hand. If that doesn’t boggle your mind, how about this: at Neptune, even that wasn’t enough because so little light from our Sun makes it out that far. So the engineers devised methods to keep the angular rates 30 times steadier than a clock’s hour hand.
Related to that, Voyager’s gyroscopes can detect spacecraft angular motion of one ten-thousandth of one degree. To put this in perspective, the apparent angular motion of the Sun in our sky, during a time period of a single second, is 40 times that.
When the Voyagers used Jupiter’s gravity to slingshot themselves toward Saturn, they picked up sun-relative speed to the tune of an additional 37,500 mph (60,350 kph).
Here’s the cool part: since energy is always conserved, the energy transfer to the Voyagers meant energy taken away from Jupiter. Those slingshot maneuvers actually slowed Jupiter in its solar orbit — by about one foot (30 cm) per trillion years.
When Voyager 2 used additional slingshot maneuvers at Saturn and Uranus, it reduced its total trip time by 20 years compared to an unassisted Earth-to-Neptune route.
Voyager 2 arrived at Neptune within 100 km (62 miles) of its target coordinates. Given its trip distance to that point of 7,128,603,456 km (4,429,508,700 miles), this was the equivalent of sinking a golf putt on a green where the golfer is standing in Portland, Oregon, and the hole is nearly all the way across North America in Ottowa, Ontario (Canada). Of course, this assumes that the putter gets to make a few tiny course corrections to the ball along the way. But only a few! (Voyager’s thrusters are minuscule, so the only real places to make course adjustments were during the planetary slingshot maneuvers.)
After Voyager 1 completed its mission at Saturn and Titan, Carl Sagan and a young scientist named Carolyn Porco floated a new idea: to turn Voyager around and take a photograph of Earth. They conceded that the photograph would have zero scientific value, since at that distance Earth would be too tiny to make out any detail, but thought it would provide a useful perspective.
While the idea was generally supported, there were concerns about possible damage to Voyager’s cameras from being pointed back toward the Sun. And there were delays. In fact there were several years worth of delays, until the NASA Administrator stepped in and made it a priority.
Carolyn Porco sat down with Candy Hansen of JPL, and together the two scientists calculated exposure times and wrote the command sequence for an entire “Family Portrait” series of photographs. The instructions were sent, and on 14 February 1990, Voyager turned around and began its new mission. The outer planets were photographed first, just in case there was sun damage to the camera, and then the visible inner planets were snapped. The series lasted until 6 June 1990, at which point a mosaic of 60 images had been recorded. One of them showed Earth as a pale blue dot, less than a single pixel in diameter. It became one of the most famous photographs of all time.
Carolyn Porco went on from her Voyager work to head up the imaging team for Cassini, which has been responsible for some of the most astounding and beautiful imagery to land on our planet, not to mention huge advances in our understanding of the Saturn system. Carl Sagan, inspired by the photograph he’d suggested almost ten years earlier, wrote the famous “Pale Blue Dot” essay in his book of the same name.
Sagan died only two years after the publication of Pale Blue Dot: A Vision of the Human Future in Space. Thankfully, his reading of that essay was recorded, and today you can find any number of videos mixing his words and voice with visual interpretation. Some are quite fancy, but I believe the best is one of the simplest, from Sagan’s own website, with Vangelis’ unmistakeable music from Cosmos.
The text is below.
From this distant vantage point, the Earth might not seem of any particular interest. But for us, it’s different. Consider again that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.
The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves.
The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand. It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another and to preserve and cherish the pale blue dot, the only home we’ve ever known.