Image: Cassini
NASA
The Cassini orbiter, shown here in an artist's conception, has been returned to full operation, just in time for a flyby of the Saturnian moon Enceladus.
updated 11/24/2010 9:16:01 PM ET 2010-11-25T02:16:01

NASA reawakened the Cassini spacecraft from a forced hibernation while in orbit around Saturn on Wednesday, after three weeks of stalled science work due to a computer glitch.

All of the probe's science instruments have been reactivated, and the spacecraft is in good health, just in time to record observations of Saturn's icy moon Enceladus during a close flyby set for Nov. 30, NASA officials said. [ Cassini's Greatest Hits: Photos of Saturn]

Cassini had been operating in a protective standby mode — called "safe mode" — since Nov. 2 because of an ill-timed flip of a data bit in Cassini's command and data system computer.

The unexpected bit flip prevented Cassini's main computer from registering a vital instruction, and the spacecraft went into standby mode as a result.

"Engineers have traced the steps taken by the computer during that time and have determined that all spacecraft responses were proper, but still do not know why the bit flipped," NASA officials said in an update released Wednesday.

The computer glitch marked the sixth time that Cassini has gone into safe mode since its launch in 1997. During these periods, the probe beams engineering and spacecraft health data to its mission operations center at NASA's Jet Propulsion Laboratory in Pasadena, Calif., but cannot perform science observations.

The glitch prevented Cassini from studying Titan, Saturn's largest moon, during a Nov. 11 flyby of the cloud-covered satellite.

The upcoming Nov. 30 flyby will bring Cassini within about 30 miles (48 kilometers) of the surface of Enceladus, Saturn's sixth-largest moon. The frigid world has icy geysers jetting from its south pole and — possibly — a bubbly, subsurface ocean of liquid water.

Cassini will fly near Enceladus' north polar region on this flyby, and then will perform another rendezvous just like it three weeks later. The twin encounters will mark the spacecraft's second-closest approach to Enceladus (Cassini dipped to within 16 miles, or 25 kilometers, of the moon in October 2008).

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During the Enceladus flyby, Cassini will use its instruments to take gravity measurements of the icy moon. The results will be compared with those from an earlier flyby of Enceladus' south pole to better understand the moon's interior structure, according to NASA officials.

Cassini will also sample the charged-particle environment around Enceladus and snap images in visible light and other parts of the spectrum during the close encounter, they added.

The Cassini spacecraft arrived at Saturn in 2004 to study the dazzling planet and its rings, and to deliver the European-built Huygens probe to land on Titan. Cassini completed its primary mission in 2008 and is now in a second phase that extends through May 2017.

The mission is a collaborative effort between NASA, the European Space Agency and the Italian Space Agency.

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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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