Image: Cassini
NASA
An artist's view shows the Cassini orbiter passing by Saturn's rings.
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updated 11/8/2006 2:52:07 PM ET 2006-11-08T19:52:07

The Cassini spacecraft is roughly halfway through its looping voyage of the Saturn system and is continuing to return a bounty of data on the ringed planet and its moons. Yet all journeys must have an end, and Cassini's eventual fate is now being discussed.

"Current planning is for a two-year mission extension that ends on July 1, 2010," said Robert Mitchell, NASA's Cassini mission program manager. "However, presuming that the spacecraft continues to function well, it's reasonable to expect that one or more further extensions will be supported."

Sometime around 2012, Cassini, like the oceangoing ships of old, will likely need to be decommissioned. However, the spacecraft cannot be towed to some nearby shore to be dismantled; she must either drop anchor, be scuttled, or cast off her gravitational moorings altogether.

"Perhaps the most likely option is to leave Cassini in a long-lived orbit that would have little to no risk of ever hitting anything," Mitchell said. "Another is to impact Saturn like Galileo did at Jupiter, although there are some complications with this one."

The complications arise from the beautiful wafer-thin rings that girdle the planet and the fact that in order to dive into Saturn, Cassini would have to pass through them — a risky maneuver that could render the spacecraft uncontrollable.

Crash landing?
"Another option is to identify one of Saturn's icy moons as an acceptable candidate and impact the spacecraft onto it," Mitchell said.

Slideshow: Month in Space: January 2014 Yet this option also holds an inherent risk arising from the three plutonium-bearing radioisotope thermoelectric generators, or RTGs, that Cassini uses as a power source.

"The issue is the heat that would be generated by the RTGs and the environment that would be created (melted ice) that could be conducive to the viability of any Earth organisms that might have survived on the spacecraft to that point," says Mitchell.

Mission planners make great effort not to contaminate alien worlds with terrestrial life.

The third option: raise anchor and escape the Saturn system altogether. Such a maneuver would require numerous flybys of Saturn's largest moon Titan to sling the spacecraft free of the ringed planet's environs.

If Cassini were to be cut adrift in this manner, her controllers have two further choices: either bring her sunward or let her escape deeper into the outer solar system.

Many options
Should Cassini be directed back toward the inner solar system, it is likely her final port of call would be Jupiter, Mitchell explained, "One possibility is to escape Saturn and then most likely put the spacecraft on an impacting trajectory with Jupiter. This appears to be feasible, but the flight times get to be rather long."

Cassini's leisurely final journey need not end at Jupiter; rather the giant planet's gravity could fling Cassini into position for an impact on Mercury. Such an impact would provide valuable data on the composition of Mercury's surface and could feasibly occur around 2021 to be observed by the BepiColombo spacecraft.

Alternatively, if Cassini were cast into the solar system's outer depths, there is a small chance she may provide further scientific reward in the form of a flyby of an outer planet or Kuiper Belt object.

"Some very preliminary analysis indicates that this might be possible. However, the flight times involved and the status of spacecraft consumables at that time make anything like this quite an unlikely option," says Mitchell.

NASA is to make the final decision on Cassini's eventual fate later in the mission.

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Photos: Best of Cassini

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  1. Starring Saturn

    This backlit view of Saturn was voted the favorite image to come from the Cassini orbiter - and it has been described as "perhaps the most stunning photograph ever taken." The image, captured on Sept. 15, 2006, shows two faint rings that were discovered by the Cassini team. And at the highest resolution, Earth itself appears as a pale blue dot just to the left of the brightest rings, at about the 10 o'clock position. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  2. Dark rings

    An infrared image from the Cassini orbiter, acquired May 24, 2007, reveals clouds beneath the hazes in Saturn's atmosphere, as well as the unilluminated side of the giant planet's rings. The shadows of the rings fall upon the planet's cloud layer. This image shares the honors as the favorite black-and-white picture from Cassini. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  3. Abstract art

    A Cassini image from May 10, 2006, shows the shaded edge of Saturn's disk, rounded by dark rings seen nearly edge-on. The crescent disk of Titan, Saturn's largest moon, can be seen in the background beyond the rings. This image shares the honors as the favorite black-and-white image from Cassini. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  4. Pearly moons

    Two of Saturn's moons - Tethys and Enceladus - look like pearls backdropped by the planet's disk in this image, captured on July 24, 2007. The thin "string" connecting the pearls is actually the plane of the planet's rings, seen edge-on. The rings cast a dark shadow on Saturn's disk. Two other moons appear in this image, although they can barely be made out at the highest resolution: Hyperion is near the lower left corner of the image, and Epimetheus is the slightest of specks between Tethys and Enceladus. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  5. Saturn from on high

    The Cassini spacecraft provides a high-contrast view of Saturn and its rings, as seen from above. This portrait is actually a mosaic of 36 images taken on Jan. 19, 2007, from about 40 degrees above the plane of the rings. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  6. Shadows on clouds

    Saturn's darkened rings cast shadows on the planet's blue and gold cloud tops, while the moon Dione hangs like a dot in the black sky beyond. This image was taken by the Cassini spacecraft on Feb. 4, 2007, from a distance of about 800,000 miles. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  7. View from below

    Cassini coasts beneath giant Saturn, staring upward at its gleaming crescent and icy rings. A great bull's-eye pattern is centered on the south pole, where a vast, hurricane-like storm spins. This view, obtained on Jan. 30, 2007, looks toward the lit side of the rings from about 26 degrees below the ring plane. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  8. Pastel planet

    Dark and sharply defined ring shadows appear to constrict the flow of color from Saturn's warmly hued south to the bluish northern latitudes. Scientists studying Saturn are not yet sure about the precise cause of the color change from north to south. The different colors may be due to seasonal effects on the atmosphere. The images that went into this mosaic were obtained by the Cassini spacecraft on Feb. 4, 2007. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  9. Ringing success

    This ultraviolet image from the Cassini spacecraft shows the detailed composition of Saturn's outer C and inner B rings from left to right, with the inner B ring beginning a little more than halfway across the image. The general pattern is from "dirty" red particles to the denser ice shown in turquoise as the ringlets spread outward. (University Of Colorado, LASP / AP) Back to slideshow navigation
  10. A is for amazing

    This ultraviolet image shows the A ring, beginning with a 'dirty' interior of red followed by a general pattern of more turquoise as it spreads away from the planet, indicating a denser material made up of ice. The red band roughly three-fourths of the way outward in the A ring is known as the Encke gap. (University Of Colorado, LASP - NASA / Reuters) Back to slideshow navigation
  11. Casting a shadow

    This image taken by Cassini shows the planet Saturn casting a shadow over its rings. (NASA - JPL - Caltech / Reuters) Back to slideshow navigation
  12. Titan revealed

    This is an infrared image of Titan, one of Saturn's moons, mapping the surface hidden beneath the moon's opaque atmosphere. Green areas represent water ice, while yellow areas have higher concentrations of hydrocarbons. The white spot is a methane cloud. (NASA) Back to slideshow navigation
  13. Ripples in the ring

    Scallops in the ring on the left side of this image were likely caused by a Saturnian moon rolling along the edge. One bright ringlet is visible within the gap, and at least one other faint ringlet can be made out. "This is textbook ring physics, right there, in one image," says Cassini imaging team leader Carolyn Porco. (NASA - SSI) Back to slideshow navigation
  14. Wisps in space

    A close-up of one of Saturn's rings shows a wispy pattern of ripples that may have been stirred up by a moonlet's orbit. Such unprecedented views of ring details are possible because of the Cassini camera's resolution. (NASA TV) Back to slideshow navigation
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