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ISS

ISS

Nature's Canvas
Nature's Canvas

Location, location, location. It's true for real estate and for taking the best pictures.

The cameras with the best location in the solar system are more than 800 million miles from Earth, orbiting the ringed planet onboard the Cassini spacecraft.

"We are the eyes of Cassini," says Dr. Carolyn Porco, Cassini Imaging Team leader and director of the Cassini Imaging Central Laboratory for OPerationS (CICLOPS), Space Science Institute, in Boulder, Colo. "Our cameras capture all the dramatic sights and vistas there are to see around Saturn. And through their imagery, they convey a sense of adventure, a sense of 'being there,' that we could otherwise only imagine."

Officially named Imaging Science Subsystem (or ISS) the instrument consists of a wide-angle camera and a narrow-angle camera. The narrow-angle camera provides high-resolution images of targets of interest, while the wide-angle camera allows more extended spatial coverage at lower resolution.

"What our cameras do is miraculous really. They convert the fleeting and indifferent fluctuations of electric and magnetic fields into powerful emotion," Porco says. "Who can fail to be moved when seeing some of our beautiful images? Certainly not I."

At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 microns on a side. The data system allows many options for data collection, including choices for on-chip summing and data compression. The narrow-angle camera packs plenty of power too, and could see a quarter -- 2.4 centimeters (0.9 inches) across -- from a distance of nearly 4 kilometers (2.5 miles).

Team members do it in the road with a little help from their friends.
Team members do it in the road with a little help from their friends.


"We record invaluable high resolution, two-dimensional information from the near-ultraviolet to the near-infrared on Saturn and its rings and moons in an immediately recognizable form," Porco explains. "In order to understand the architecture of Saturn's rings, the geology of the Saturnian moons or the character of Saturn's atmosphere, we need to take detailed images. That's our job."

Another part of the job for Porco's team, of course, is to make movies. Using time-lapse imagery, the team provides scientists with an ideal tool to study time-variable phenomena and celestial motions.

"We've caught spectacular footage: from complex motions in Saturn's atmosphere to the dances of icy moons to the rippling motions in Saturn's F ring," Porco says. "Not only are these scientifically informative, they are mesmerizing. Makes me feel a bit like Steven Spielberg!"

To increase the images' scientific value, each camera on Cassini has two filter wheels designed to take images at specific wavelengths of light. The narrow-angle camera has 12 filters in each wheel for a total of 24 filters; the wide-angle has 9 in each wheel for a total of 18. Some filters only allow light of a certain color to reach the sensor. Combining three such images can produce a color image. The most scientifically interesting images are calibrated in order to turn the electrical signals that emerge from the CCDs into an absolute measure of brightness.

The two cameras on Cassini have already returned a visual feast of images.

Fantasy made real
Fantasy made real


"Some of my favorite images are those in black and white, showing the shadow-draped Saturn atmosphere, the paper thin rings, and one or two lonely little moons," Porco says. "The multiple-world compositions are also stunning."

Scientifically speaking, Porco says she was most surprised by the moon Enceladus.

"I'm particularly excited about our results on Enceladus," Porco says. "It has been a remarkable discovery to find the south pole of Enceladus so warm, young, fractured, organic-rich in places and venting icy particles and water vapor into space."

The instrument sends to Earth an average of 2,700 raw images a month. The cameras can also obtain optical navigation frames -- images of Saturn's moons against a star background -- that are used to keep the spacecraft on the correct trajectory.

For more information, read the engineering technical write-up or visit the science team's Web site http://ciclops.org.

At a Glance

  • Wide Angle Camera [WAC](20 cm f/3.5 refractor; 380-1100 nm; 18 filters; 3.5ox3.5o)
  • Narrow Angle Camera [NAC](2 m f/10.5 reflector; 200-1100 nm; 24 filters; 0.35ox0.35o)
  • Mass (current best estimate) = 57.83 kg
  • Peak Operating Power (current best estimate) = 55.90 W
  • Peak Data Rate (current best estimate) = 365.568 kilobits/sec
  • Dimensions (approximate) = 95x40x33 cm (NAC); 55x35x33 cm (WAC)
  • Mass (current best estimate) = 57.83 kg
  • Peak Operating Power (current best estimate) = 55.90 W
  • Peak Data Rate (current best estimate) = 365.568 kilobits/sec
  • Dimensions (approximate) = 95x40x33 cm (NAC); 55x35x33 cm (WAC)