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NOT THE FINAL
FRONTIER


Text and Image Porcessing By Michael Benson


I’m sitting with spacecraft engineer Mike Sierchio at the computer in his windowless office at NASA’s Jet Propulsion Laboratory in Pasadena, California. In less than three hours, a joined pair of robots called Cassini-Huygens is scheduled to shoot through a dusty gap in Saturn’s majestic rings and settle into orbit around the solar system’s second-largest planet—certainly one of the most dramatic and perilous moments of the mission jointly sponsored by the European Space Agency, the Italian Space Agency, and NASA—but Mike is entirely unruffled as he clicks open windows of live telemetry from the Cassini Orbiter’s various systems. I had asked him to give me a sense of what it’s like to pull the


Cassini captures a detail of Saturn’s rings, made up of mostly ice and dust, 2004.
strings of a school-bus-size spacecraft that’s 1.5 billion kilometers (932 million miles) away. At the time of its arrival at Saturn after almost seven years in space, Cassini is so far from Earth that it takes an hour and 24 minutes for its signal to get here—and that’s at the speed of light.
    Suddenly, Mike’s pager goes off. He removes it from his belt, squints at it for a second, then returns it without comment. A few minutes later he opens a window on his screen that immediately fills with red warning messages. “Now these are potential problems; in normal circumstances any one of these could be a real emergency,” he says. “But we know they’re all supposed to be that way for the burn”— the imminent firing of Cassini’s main engine, which will effectively slam on the spacecraft’s brakes, allowing it to stay in Saturnian orbit. “In fact, we locked the alarms down for the burn, but the spacecraft doesn’t know that. That’s
why Cassini just paged me.”
    “What?” I say, startled.
    “Well, you saw my pager go off just now, right? That was Cassini, trying to alert me that something might be wrong. But it isn’t, it’s okay.” Mike looks amused by my surprise.
    He has just been paged from Saturn.
    Far more than any other solar-system object discernable through an amateur telescope, the planet Saturn, with its weightless, perfectly symmetrical rings, reliably elicits an audible gasp of appreciation from its viewers. Many professional astronomers credit their first youthful glimpse of this eerie gemstone—a planet that seems to have been wrought, as though on some kind of vast cosmic lathe—as the catalyst for their subsequent careers.
    The sixth sphere from the Sun, Saturn is vast, with a diameter more than nine times that of Earth, and its complex
He has just been paged from Saturn. ring system is almost a million kilometers (620,000 miles) from end to end. The rings are made up of chunks of ice and dust combed by gravity and kinetic motion into many thousands of distinct concentric ringlets. They are astonishingly thin in relation to their width—and they appear to be endlessly intricate, something that Cassini should go a long way toward confirming in detail during its four-year prime mission. The “F” ring, for example, seems to be braided. Complete with the rings’ bulging, yolk-like central planet, the whole composition is one of the great bravura displays of natural beauty in the visible universe.
    Saturn’s cloud-shrouded moon Titan, meanwhile, is only slightly smaller than Mars and covered by frigid hydrocarbon gases. One of the last major pieces of unexplored real estate in the solar system, Titan has been the target of keen scientific conjecture for many years because its atmosphere,
believed to contain a wide spectrum of complex carbon-based molecules, is thought to be very similar to that of the Earth before the appearance of life here. Titan’s soupy haze, which gives the moon its orange-brown color, was almost entirely impenetrable until Cassini’s arrival, when the spacecraft plunged through and above the ring plane, with its lengthy main-engine burn continuing as it arced back down and under the rings again. Once captured by the planet’s gravity, Cassini continued swooping in an elliptical arc, switched its engine off, then swiveled to turn its cameras toward the rings. The ultra-close-up pictures, received on Earth the following morning, revealed a level of detail previously only theorized: among other things, rippling gravity waves within the ring material were visible for the first time—mathematically perfect manifestations of the gravitational attraction of distant moons wheeling by well outside the ring system.


Phoebe, one of Saturn’s icy and battered moons, 2004.
    A day later, Cassini made its first pass of Titan. Cassini’s first images of Titan were predictably murky, but they revealed linear, circular, and curvilinear features possibly indicating tectonic activity—as well as a prominent methane cloud crowning its south pole. Confounded scientists, who had predicted the existence of lakes or even oceans of liquid ethane and methane, looked in vain for the telling glint of reflected light. But these images were taken from a distance of 339,000 kilometers (210,600 miles). Cassini’s subsequent flybys of the moon taking place now are much closer, several under a thousand kilometers (620 miles), and should produce pictures of far higher resolution. During some passes the orbiter will use its radar, which will “see through” Titan’s atmosphere to create highly detailed topographical maps.
    It’s a measure of Titan’s potential importance—both in fleshing out our understanding of the deep history of the solar
system and in analyzing what amounts to a kind of refrigerated time capsule potentially containing the conditions for life—that it will also be probed physically. Attached to Cassini’s instrument-studded, foil-wrapped carapace is another robot: the European Space Agency’s Huygens atmospheric probe, which was scheduled to detach from the orbiter on December 25, 2004, and glide toward Titan, plowing into the moon’s opaque smog on January 14 and taking about two hours to spiral slowly down to the surface under a succession of parachutes. If all goes well, it will sample the atmosphere as well as send back spectacular panoramic views of the Titan landscape.
    Cassini-Huygens is by far the most capable and ambitious contemporary robotic deep-space mission to date— the cutting edge of early-21st-century space exploration. Together these two robots are redefining the very
Back when we thought the earth was flat, sea monsters lurked on the horizons of our partially charted planet. perimeter of the solar-system map. Back when we thought the earth was flat, sea monsters lurked on the horizons of our partially charted planet, a sphere now well triangulated by GPS satellites and positioned among the multiple turning worlds of a vast new frontier. We tend to forget how recently environments far closer than the outer solar system were first made accessible by the seemingly inexorable human drive to explore. Consider that it was only a little over a hundred years ago that the first prototype heavier-than-air machines left the ground.
    The Cassini mission was named after the French-Italian astronomer Jean-Dominique Cassini, who in 1676 discovered the large gap in Saturn’s rings that now bears his name. The attached Huygens atmospheric probe is named for the Dutch astronomer and scientist Christiaan Huygens, who discovered Titan in 1655. Huygens later also realized that


Saturn’s rings and atmospheric banding as seen by Cassini, 2004.
Kinetikon pictures from Source Images courtesy of NASA, JPL, and Space Telescope Science Institute.
Saturn's mysterious protrusions, which had first been observed but not understood by a baffled Galileo in 1610, were in fact a “thin flat ring, nowhere touching.” Some four centuries later, in early September 2004, a new European was added to this distinguished list of planet gazers: Cassini imaging team member Dr. Carl Murray of Queen Mary University of London, who spotted a tiny moon and a wispy new outer ringlet in observations conducted just days before Cassini achieved orbit.
    In late April 2004, I met Bob Mitchell, the rail-thin, quietly good-humored Cassini project manager. Mitchell, who has been in the space-probe business since its earliest days, meaning the fledgling interplanetary missions of the 1960s, has a subtle but unmistakable aura of competence to him.
    After a detailed rundown of Cassini’s objectives and capabilities, Mitchell took me to the spacecraft’s control
This link between massive deep-dish telecom installations on Earth and the faint whispery streams of data coming down from deep space can be extremely fragile. center, a surprisingly intimate half-circle of computers, monitors, winking closed-circuit telephones, and time-code readouts. Two project engineers sit bathed in the electronic glow of this high-tech alcove. A loudspeaker emits the occasional acronym-packed snippet of ground-control jargon. A particularly prominent pair of LCD screens hangs above the engineers. The left-hand screen features a graphic rendition of blue-white Earth, half in sunlight and half in shadow, with Continental Europe on the right and Madrid, the location of one of three massive Deep Space Network antennas, clearly marked. The right screen depicts Cassini, a small insectoid form closing in on ringed Saturn. As the Earth rotates, one hemisphere turns toward Saturn as another revolves away; communications with Cassini are thus handed off between the almost equally spaced antennas at Goldstone, California, USA; Canberra, Australia; and Madrid.
    This link between massive deep-dish telecom installations on Earth and the faint whispery streams of data coming down from deep space can be extremely fragile. With Madrid situated on the Iberian plain, something as prosaic as the rain in Spain can sometimes kill receptivity altogether— resulting in a terminal loss of data.
    “Are we over Madrid?” Bob casually asks one of his engineers.
    “Yep, for another 40 minutes,” the engineer replies—an exchange that sounds routine only in the extraordinary context of Cassini’s mission. The orbiter’s “altitude” over Madrid is, according to Bob, “about nine AU.”
    An AU, or astronomical unit, is the distance between the Sun and the Earth.   

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