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0805 GMT (3:05 a.m. EST)
A potential problem with a rocket thruster designed to keep the Philae lander from bouncing off comet 67P/Churyumov-Gerasimenko after touchdown Wednesday will make the probe's daring descent even more challenging, officials said.

Read our full story.

0706 GMT (2:06 a.m. EST)
Sylvain Lodiot, Rosetta's spacecraft operations manager, reports the final "go" decision has been made to release the Philae lander. The mothership is now slewing into the correct orientation to deploy the lander in about two hours.
0644 GMT (1:44 a.m. EST)
The pre-separation thruster maneuver by Rosetta has been completed, according to Paolo Ferri, head of mission operations at the European Space Operations Center.

A final "go/no go" decision point by the Rosetta team is expected shortly.

0640 GMT (1:40 a.m. EST)
Stephan Ulamec, head of DLR's Philae lander team, says there is a problem with the cold gas thruster on the landing craft. This means the probe may have to rely on harpoons and ice screws to stabilize itself at touchdown.

Despite the problem, the lander team is "go" for deployment of Philae in a few hours.

Meanwhile, the Rosetta spacecraft is maneuvering now to fly to the correct location for release of Philae.

0554 GMT (12:54 a.m. EST)
The upcoming maneuver to send Rosetta to the correct location for deployment of the Philae lander is set 0630 GMT (1:30 a.m. EST), according to an ESA blog post.
0510 GMT (12:10 a.m. EST)
The two "go/no go" decisions overnight -- verifying the readiness of commands, the Rosetta spacecraft and Philae lander -- all concluded with a green light to proceed with the landing.

Rosetta is gearing up for a critical rocket burn soon to drive the probe toward the comet on the correct trajectory for release of Philae.

1918 GMT (2:18 p.m. EST)
The next "go/no go" decision point is expected at 0000 GMT (7 p.m. EST), when the European Space Operations Center in Darmstadt, Germany, will verify the Rosetta spacecraft is ready for Wednesday's landing and all commands in the landing sequence are ready.
1904 GMT (2:04 p.m. EST)
Preparations for Wednesday's comet landing are proceeding as planned after passing the first "go" milestone this evening. This "go/no go" decision was to be taken after confirming Rosetta was on the correct trajectory ahead of the deployment of the Philae lander.

A "pre-delivery" maneuver is planned less than 12 hours from now to nudge Rosetta toward the comet for release of the Philae lander.

1715 GMT (12:15 p.m. EST)
Navigators in Europe and the United States are measuring the Rosetta spacecraft's exact position in space this evening ahead of the first of four predetermined "go/no go" decision points.

The go/no go milestones are designed to ensure the Rosetta and Philae spacecraft, landing sequence commands, and trajectory solutions are all ready for Wednesday's descent.

Andrea Accomazzo, ESA's Rosetta flight director, says controllers at the European Space Operations Center in Darmstadt, Germany, and at NASA's Jet Propulsion Laboratory in California go through separate navigation procedures to independently determine Rosetta's position in space at any given time.

Engineers compare the navigation data to ensure each team came up with accurate information.

The navigation numbers will be presented by 8:30 p.m. local time in Darmstadt (1930 GMT; 2:30 p.m. EST) to ensure Rosetta is where it was predicted to be ahead of a critical rocket maneuver early Wednesday to put the spacecraft in the correct position to release the lander for its descent to comet 67P/Churyumove-Gerasimenko.

1635 GMT (11:35 a.m. EST)
Europe's Philae lander — still latched inside its mothership — has been activated and should be ready for release Wednesday to begin a daring first-ever descent to a comet, the mission’s flight director said Tuesday.

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1520 GMT (10:20 a.m. EST)
Rosetta flight director Andrea Accomazzo says the Philae lander is ready for a daring descent and touchdown Wednesday on comet 67P/Churyumov-Gerasimenko. The European craft is making the world's first attempt to land on a comet.

See the video of the interview.

1100 GMT (6:00 a.m. EST)
The European Space Agency's Rosetta mission stars with Game of Thrones actor Aidan Gillan and actress Aisling Franciosi in a short film released recently to promote the spacecraft’s exploration of comet 67P/Churyumov-Gerasimenko.

Read our full story.

This week marks the pinnacle of the professional careers of many scientists, when the European Space Agency plans to put down a three-legged robotic lander on a comet, a risky first-of-a-kind endeavor that could rewrite textbooks on the history of the solar system.

Read our full story.

European scientists have selected an aim point for the landing of Philae, a small probe riding piggyback on the Rosetta spacecraft set for the first-ever descent to a comet's nucleus in November.

Read our full story.

Scientists have narrowed a list of candidate landing sites for the Philae lander, a piggyback probe on Europe's Rosetta mission that will attempt the first ever descent to a comet this fall and latch onto its jagged surface.

Read our full story.

Rosetta's ten-year journey from the launch pad to comet 67P/Churyumov-Gerasimenko took the spacecraft by planets and asteroids, offering a preview of the probe's capabilities and whetting the appetites of researchers waiting for the mission's scientific payoff.

See photos from Rosetta's decade in space.

After a 10-year, 3.7-billion-mile chase, Europe's Rosetta spacecraft finally caught up with its target Wednesday, firing its main engine to precisely match orbits with comet 67P/Churyumov-Gerasimenko, giving the spacecraft a ringside seat as the icy relic falls into the inner solar system and comes to life in the warmth of the sun.

Read our full story.

See photos of the comet from Rosetta.

Initial observations from an imaging spectrometer aboard Europe's Rosetta spacecraft show the comet it is chasing has a dark, dusty surface instead of one covered in ice, scientists said Friday.

Read our full story.

On course for an historic rendezvous next week, the European Space Agency's Rosetta spacecraft is revealing new details of the oddball comet the probe has pursued for more than a decade.

Read our full story.

Closing in to begin a thorough investigation in August, a camera on Europe's Rosetta comet-chasing probe has revealed its target has a few surprises in store for scientists.

Read our full story.

SUNDAY, JULY 6, 2014
The European Space Agency's Rosetta spacecraft is one month from pulling alongside an icy comet and beginning the most comprehensive survey of a comet yet attempted.

Read our full story.

Europe's Rosetta spacecraft has returned an image of its distant comet target as ground controllers received the first signals from probe's piggyback Philae lander Friday after hibernating nearly three years in a power-saving sleep mode.

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A first look at the European Space Agency's Rosetta spacecraft after its reactivation last week shows the probe endured an unprecedented power-saving hibernation with few problems, giving engineers confidence the mission can continue the final leg of its decade-long pursuit of a little-known comet thought to harbor the building blocks of life.

Read our full story.

Fresh out of an unprecedented power-saving sleep mode, Europe's comet-chasing Rosetta spacecraft awakened and phoned home Monday on the way to an enigmatic ball of rock and ice for a daring close-up inspection later this year.

Read our full story.

2047 GMT (3:47 p.m. EST)
A first look at Rosetta's telemetry shows everything looks good. ESA says more details will be released tomorrow.
2038 GMT (3:38 p.m. EST)
ESA says ground controllers are receiving full telemetry from the Rosetta spacecraft for the first time in 31 months.
1910 GMT (2:10 p.m. EST)
Fresh out of an unprecedented power-saving sleep mode, Europe's comet-chasing Rosetta spacecraft awakened and phoned home Monday on the way to an enigmatic ball of rock and ice for a daring close-up inspection later this year.

Read our full story.

1851 GMT (1:51 p.m. EST)
The first commands to Rosetta in 31 months have been transmitted to the spacecraft as it flies more than 500 million miles from Earth.

The initial commands will tell Rosetta to downlink more detailed telemetry with crucial information on the health of the spacecraft's systems.

1830 GMT (1:30 p.m. EST)
"I think that's been the longest hour of my life," says Andrea Accomazzo, Rosetta's spacecraft operations manager.
1818 GMT (1:18 p.m. EST)
Rosetta is alive! A signal from the spacecraft is being received in the control center!
1757 GMT (12:57 p.m. EST)
In the above live video feed from the Rosetta control room in Darmstadt, Germany, you see a representation of the signal being detected by NASA's Goldstone tracking station in California. When Rosetta's signal is received, a spike will appear in the middle of the view.
1733 GMT (12:33 p.m. EST)
The window for receiving signals from Rosetta is now open, but exactly when controllers hear from the spacecraft is unpredictable.

"Our nominal window to receive the signal is opening right now," says Andrea Accomazzo, spacecraft operations manager at the control center in Darmstadt, Germany. "So from any minute now we could expect the signal from Rosetta coming back.

"We are still receiving only noise, but at any time could come the signal."

Rosetta is in uncharted territory. It's the first mission to go into hibernation for such a long period of time without any contact with Earth.

"It's the first mission that did anything like this," Accomazzo said. "It's not something we felt comfortable with, but we had no other choice."

Rosetta had to enter hibernation because it flew so far from the sun that its solar panels could not generate enough electricity to power all of its systems. While Rosetta slept, the probe was put into a slow spin to keep its solar arrays pointing toward the sun, and the spacecraft periodically switched on heaters to keep its internal components warm.

1701 GMT (12:01 p.m. EST)
If everything on-board Rosetta is working as expected, the spacecraft's radio transmitter should now be switched on to dispatch its first post-wakeup signals to Earth.

The next official update from the Rosetta control center should come at 1730 GMT (12:30 p.m. EST).

1625 GMT (11:25 a.m. EST)
By now, Rosetta should have warmed up its star trackers, acquired a field of stars to determine its orientation and stopped the slow spin it was put in before entering hibernation in June 2011.

Next up should be activation of the on-board transmitter and pointing of the 2.2-meter (7.2-foot) high gain antenna toward Earth, followed by the sending of the signal confirming it survived its 31-month sleep mode.

The initial signal won't contain much information on Rosetta's status -- it comes down at just 7.8 bits per second. But it will tell ground controllers, who are anxiously awaiting the signal in Darmstadt, Germany, that Rosetta is alive.

More detailed telemetry will be sent to Earth later tonight and tomorrow.

1435 GMT (9:35 a.m. EST)
The 70-meter (230-foot) diameter antenna at NASA's tracking site in Goldstone, Calif., is now aimed toward the spot in the sky where Rosetta should be after wakeup this morning.

Officials don't expect to hear anything from Rosetta for at least another three hours, but there is a slight chance signals could be received early.

1000 GMT (5:00 a.m. EST)
Wake up Rosetta! The spacecraft's on-board timer should be triggering a preprogrammed wakeup sequence now.
0940 GMT (4:40 a.m. EST)
Although Rosetta's on-board alarm goes off at exactly 1000 GMT (5 a.m. EST), it will take several hours before controllers get the first signals from the probe confirming its health.

Officials expect to receive news from Rosetta between 1730 and 1830 GMT (12:30-1:30 p.m. EST). Only then will we know Rosetta weathered its unprecedented 31-month hibernation well.

Rosetta's timer was set to wake up the spacecraft at 1000 GMT (5 a.m. EST) today before engineers put the spacecraft into hibernation in June 2011.

During the hibernation, Rosetta was put into a slow spin to keep the solar arrays pointed toward the sun.

"The first thing the spacecraft will do is switch on heaters and wake up the star trackers," said Paolo Ferri, head of mission operations at the European Space Operations Center in Darmstadt, Germany.

Ferri said it takes six hours to warm up the star trackers, then Rosetta will fire thrusters to stop its hibernation spin and determine its position in space, establishing "three-axis attitude control" before pointing its solar arrays toward the sun and turning its 7.2-foot-diameter high gain antenna toward Earth.

"Once it knows which attitude it's in, it knows where the Earth is," Ferri said.

ESA expects Rosetta will turn on its S-band transmitter around 1700 GMT (12 p.m. EST), but with 500 million miles separating the spacecraft and Earth, it will take 45 minutes for the carrier signal to reach a receiver at NASA's tracking station in Goldstone, Calif.

"There is a large uncertainty on the order of several hours on the actual timing of the expected signal," Ferri said.

Then ESA will send up a command for Rosetta to begin sending down more detailed telemetry to allow controllers to fully evaluate the probe's condition.

Europe's Rosetta spacecraft is in the final hours of a 31-month slumber, quietly bolting through deep space waiting for a wakeup alarm to go off Monday.

European Space Agency officials say the wakeup will launch Rosetta into a year of firsts: rendezvousing with a little-known comet beyond the orbit of Mars, maneuvering into a series of jagged, imprecise orbits, surviving blasts from dust and ice crystals, then ejecting a hitchhiking robot named Philae to latch onto the comet with harpoons and ice screws.

Such a tricky encounter, set to begin this summer, has never been tried before.

Rosetta's operators must "forget what we know about operating around Earth or Mars," said Paolo Ferri, head of mission operations at the European Space Operations Center in Darmstadt, Germany.

"Most of the things I've described nobody's ever done before," Ferri said. "It is the first time we've rendezvoused with a comet. Flybys are comparably much easier... It's the first time we've tried landing on a comet. There was a landing on an asteroid in the past, but it [was] certainly not as ambitious as ours."

Rosetta is helping pioneer a power-saving sleep mode, hibernating as the probe reaches its farthest point from the sun -- 490 million miles -- and reducing the draw of its computers, payloads and communications system on the craft's solar arrays.

NASA's Pluto-bound New Horizons mission is following a similar routine, but for different reasons. The plutonium power generator on New Horizons is not taxed as the probe gets farther from the sun, but mission managers opted to put it into hibernation to reduce wear-and-tear and operating costs.

"We came to such a distance from the sun that even our large solar arrays and our high-technology solar cells were not enough to keep our spacecraft active," Ferri said.

Ground controllers put the comet-chasing probe into hibernation in June 2011, switching off the spacecraft's instruments and transmitter before putting Rosetta into a slow spin for stability.

The only things left running on Rosetta were the computer and several heaters to keep the spacecraft from freezing, according to ESA.

Officials are anxious to receive the first signals from Rosetta in 31 months.

"Since the 8th of June 2011, we have had no signal from the spacecraft," Ferri said. "This was planned. It's not something we liked doing, but this is what the last two-and-a-half years were about. Silence."

Rosetta's wakeup will come at 1000 GMT (5 a.m. EST) on Jan. 20, but the spacecraft will take a few hours to get its bearings and radio home. By Monday evening, European time, officials expect to know Rosetta's status.

Then begins a multi-month activation and checkout procedure, including the power-up of Rosetta's science instruments and the Philae lander. By May, scientists expect Rosetta will have located its target -- Comet 67P/Churyumov-Gerasimenko -- in the sights of its navigation camera.

Europe's Rosetta mission departed Earth in 2004 on a long-distance journey to a comet. Along the way, Rosetta encountered two asteroids, visited Mars and flew by Earth three times to get natural gravity boosts into the outer solar system and set course for a rendezvous with comet 67P/Churyumov-Gerasimenko in 2014.

We will have live coverage throughout the final phase of Rosetta's chase of the comet, beginning Monday when an on-board alarm will awaken the probe from a 31-month slumber. The unprecedented deep space hibernation was necessary because the craft's solar panels could not generate enough electricity for all of Rosetta's systems at such large distances from the sun.

See our Rosetta launch coverage from March 2004.

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