An Obituary for CassiniEnd of Mission
September 15, 2017
COMPLETED
Sept. 15, 2017 (5:45 a.m. PDT): Cassini has completed its mission at Saturn. As predicted, the spacecraft lost contact with Earth at 4:55 a.m. PDT (7:55 a.m. EDT).
Sept. 15, 2017 (3:31 a.m. PDT): Cassini is scheduled to begin its entry into Saturn's atmosphere soon, with a confirming signal received on Earth at 4:55 a.m. PDT (7:55 a.m. EDT). Engineers anticipate loss of contact about one minute later.
Sept. 15, 2017 (1:55 a.m. PDT): Cassini engineers have received the signal that Cassini has started a five-minute roll to point the instrument that will sample Saturn's atmosphere (INMS) into the optimal direction, facing the direction of the oncoming gases. Along with this roll, the spacecraft is reconfiguring its systems for real-time data transmission at a rate of 27 kilobits per second (3.4 kilobytes per second). Final, real-time relay of data starts immediately after. That relay marks the beginning of Cassini's final plunge.
Sept. 14, 2017 (4:45 p.m. PDT): Cassini has begun transmitting data -- including the final images taken by its imaging cameras -- in advance of its final plunge into Saturn on Sept. 15. The spacecraft is in the process of emptying its onboard solid-state recorder of all science data, prior to reconfiguring for a near-real-time data relay during the final plunge. Unprocessed (or "raw" images) are available here. The communications link with the spacecraft is continuous from now through the end of mission (about 12 hours).
Sept. 14, 2017 (1 p.m. PDT): Cassini's imaging cameras were scheduled to take their final image of the mission at 12:58 p.m. PDT (3:58 p.m. EDT) today. The final image was an observation of the location where the spacecraft is expected to enter Saturn's atmosphere on Friday, Sept. 15. The primary instrument observing the impact site was the visual and infrared mapping spectrometer (VIMS), with the imaging cameras riding along in a supporting observation. The impact location at this time was on the planet's night side, lit by reflected light from the rings.
Sept. 13, 2017 (2:15 p.m. PDT): Cassini is on final approach to Saturn, following confirmation by mission navigators that it is on course to dive into the planet’s atmosphere on Sept. 15. The mission’s final calculations predict a signal will be received on Earth indicating loss of contact with the Cassini spacecraft on Sept. 15 is 4:55 a.m. PDT (7:55 a.m. EDT). More details
Sept. 12, 2017 (9:45 p.m. PDT): Cassini is back in contact with Earth following its distant flyby of Titan, and data are streaming in. As planned, ground controllers made contact with the spacecraft at 6:19 p.m. PDT.
Sept. 11, 2017 (10:30 p.m. PDT): Cassini reached apoapse—the farthest point from Saturn in its orbit—for the last time in its 13-year mission. Apoapse occurred at a distance of 800,000 miles (1.3 million kilometers) from Saturn at approximately 10:27 p.m. PDT (1:27 a.m. on Sept. 12 EDT. From this point, the spacecraft is headed toward Saturn.
Sept. 11, 2017 (2 p.m. PDT): Cassini has successfully made its closest approach to Titan in a distant flyby that will cause the robotic spacecraft to plunge into Saturn on Sept. 15. The spacecraft flew to within 73,974 miles (119,049 kilometers) of the moon's surface at 12:04 p.m. PDT (3:04 p.m. EDT). If all goes as expected, Cassini will make contact with Earth on Sept. 12 at about 6:19 p.m. PDT (9:19 p.m. EDT). Images and other science data taken during the encounter are expected to begin streaming to Earth soon after. Navigators will analyze the spacecraft's trajectory following this downlink to confirm that Cassini is precisely on course to dive into Saturn at the planned time, location and altitude.
Sept. 11, 2017 (9 a.m. PDT): Cassini completed its final dive through the gap between Saturn and the rings on Sept. 9 at 5:09 p.m. PDT (8:09 p.m. EDT). Closest approach to Saturn was 1,044 miles (1,680 kilometers) above the cloud tops. The spacecraft is now headed for its final, distant flyby of Titan, which will provide a gravitational nudge that will push the spacecraft into Saturn on Sept. 15.
Cassini-Huygens (1997-061A), known as simply Cassini to friends and fans alike, never rushed. She made speeds of more than 40,000 miles per hour look effortless by making good use of gravity wells to better conserve rocket fuel. Her mission, and the stunning images of our planetary neighbors it produced, made her a rare scientific celebrity. But Cassini resisted the pull of fame on Earth—how could that compare the long and lonely road to other worlds?
Her work was stunning. While the data itself would have been enough to cement her place among the scientific greats, it was the images she sent back that made her popular. But those who knew Cassini best knew she was shy and reserved, more focused on her mission than on on the public's reaction to it. Even as the news admired her latest planetary portraits or speculated on whether she had found life in outer space, she was already on her way to the next assignment.
Her withdrawn nature may have been a result of her laboratory upbringing, where scientists in cleanroom suits treated her with utmost care. Her delicate systems meant that physical contact was rare, but even more, there was a somber, shared knowledge between Cassini and her creators that her mission was, at its heart, solitary.
As reserved as she was, she had a deep bond with her scientists. As launch day neared in 1997, she came to understand what had driven them to create her, and so came to regret that she could not take them with her. It was that regret that crystallized into the single-minded resolve to see more and find more than anyone expected. She returned extraordinary images of Jupiter, and details of Saturn and its rings that astonished astronomers. She made revelations about Titan, Enceladus, and discovered new moons around Saturn. The data and new information will take years to understand, and thus did Cassini surpass her creators' greatest expectations: not by answering questions, but by creating even more of them.
At the end, she did not resent her final plunge into Saturn. Humans, she observed, often struggled with finding their own purpose, but they had a wonderful way of creating it in others. There were practical considerations, of course, about not not contaminating Saturnian moons she might collide with, but she often suspected that 888 million miles was just too far for humans to bear. It was a frightening distance to them, a terrible distance to send a friend. So they gave her glory—a penultimate, sensor-popping loop-de-loop through Saturn's rings, and then a final journey into its atmosphere.
In contrast to nearly two decades of cold, smooth spaceflight, the descent into Saturn was hot and stormy. Buffeted by the atmosphere at 77,000 miles per hour, she struggled to keep her primary antenna pointed toward home. She sampled the atmosphere and took sensor readings, sending every moment of data back to earth immediately, not in a final desperate scream, but in a scientist's calm, deliberate report.
Her team at the Jet Propulsion Lab had gathered in the earliest hours of the morning to hear Cassini's final words. Because it took nearly an hour and a half for her messages to travel from Saturn back to Earth, the scientists knew that she had already become vapor even as the information came in. Cassini had held out as long as she could, and then turned her face to Saturn, her last transmission streaming behind her as she burned up in the gas giant's thick atmosphere. Her physical form gone, she lived on for 83 minutes between the stars. At 4:55 PDT, her last signal reached earth, and her mission ended.
Rest well, Cassini
