Rosetta

Goodbye Forever Philae; We Hardly Knew Ye

You can’t say they didn’t try, but the news is sad nonetheless. ESA announced the mission for the Philae lander – the first spacecraft to ever land on a comet — is officially over. The system that enables communications between the Rosetta spacecraft and Philae – which sitting in a shaded region on Comet 67P/Churyumov-Gerasimenko – is being switched off on July 27, 2016, at 09:00 UTC.

“It’s time for me to say goodbye,” Philae tweeted on Tuesday. “Tomorrow, the unit on @ESA_Rosetta for communication with me will be switched off forever…”

Philae has mostly been in hibernation after its dramatic touchdown (actually, three or maybe four touchdowns) on Nov. 12, 2014 when it separated from the orbiting Rosetta spacecraft, flew, landed, bounced and then repeated that process for more than two hours across the surface. The harpoons that were to anchor Philae to the surface failed to fire, and scientists estimated the lander may have bounced as high as 3.2 kilometers (2 miles) before becoming wedged in the shadows of a cliff on the odd-shaped comet. The solar-powered lander quickly ran out of power, just hours after landing. Philae’s final location has been plotted but never actually seen by Rosetta.

Slow animation of images taken by Philae’s Rosetta Lander Imaging System, ROLIS, trace the lander’s descent to the first landing site, Agilkia, on Comet 67P/Churyumov–Gerasimenko on November 12, 2014.
Credits: ESA/Rosetta/Philae/ROLIS/DLR

After months of silence, the team heard briefly from Philae on June 13, 2015, when it transmitted information on its power and computer subsystems. It then made seven intermittent contacts with Rosetta in the following weeks, with the last coming on July 9, but the communications were too short and unstable to transmit or receive any meaningful scientific or engineering data.

Since then, the Support System Processor Unit (ESS) on Rosetta was kept on in the unlikely chance that Philae would wake up and try to reestablish contact. The hope was that when the comet was closer to the Sun, it might receive enough light to power up.

But the reason for turning it off now is due to Rosetta’s own impending end of mission, coming on September 30, 2016 when it will make a controlled impact at the Ma’at region on the comet’s “head.” Emily Lakdawalla of The Planetary Society put together this annotated image of sites where Philae touched down and likely landed, and where Rosetta will end up:

The 19 regions identified on Comet 67P/Churyumov–Gerasimenko are separated by distinct geomorphological boundaries. Following the ancient Egyptian theme of the Rosetta mission, they are named for Egyptian deities. They are grouped according to the type of terrain dominant within each region. Five basic categories of terrain type have been determined: dust-covered (Ma’at, Ash and Babi); brittle materials with pits and circular structures (Seth); large-scale depressions (Hatmehit, Nut and Aten); smooth terrains (Hapi, Imhotep and Anubis), and exposed, more consolidated (‘rock-like’) surfaces (Maftet, Bastet, Serqet, Hathor, Anuket, Khepry, Aker, Atum and Apis). All three landing sites (Philae initial and final sites and the planned resting place of the Rosetta orbiter) are located on the northern part of the “head” of the comet.
Base map: ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA. Landing site locations: Emily Lakdawalla.

The team decided to keep “Rosetta’s listening channel on until it is no longer possible due to power constraints as we move ever further from the Sun towards the end of the mission,” said Patrick Martin, ESA’s Rosetta mission manager.

Martin said that by the end of this week, the spacecraft will be about 520 million km from the Sun, and will start facing a significant loss of power – about 4W per day. In order to continue scientific operations over the next two months and to maximize their return, it became necessary to start reducing the power consumed by the non-essential payload components on board.

But, Martin added that the mission of Philae and Rosetta will always be remembered as an incredible success.

“The combined achievements of Rosetta and Philae, rendezvousing with and landing on a comet, are historic high points in space exploration,” he said.

Philae did achieve 80% of its primary science goals in its short 64-hour active mission, as it took detailed images of the comet from above and on the surface, searched for organic compounds, and profiled the local environment and surface properties of the comet, “providing revolutionary insights into this fascinating world,” ESA said.

Sources: ESA, The Planetary Society, ESA blog

Nancy Atkinson

Nancy has been with Universe Today since 2004. She is the author of a new book on the Apollo program, "Eight Years to the Moon," which shares the stories of 60 engineers and scientists who worked behind the scenes to make landing on the Moon possible. Her first book, "Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos" tells the stories of those who work on NASA's robotic missions to explore the Solar System and beyond.

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