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  ESA's Rosetta probe and lander to Comet 67P

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Author Topic:   ESA's Rosetta probe and lander to Comet 67P
Robert Pearlman
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posted 07-18-2005 06:00 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
European Space Agency release
Rosetta Overview

Rosetta is the first mission designed to orbit and land on a comet. It consists of an orbiter, carrying 11 science experiments, and a lander, called 'Philae', carrying 10 additional instruments, for the most detailed study of a comet ever attempted.

Rosetta gets its name from the famous Rosetta stone that led to the deciphering of Egyptian hieroglyphics almost 200 years ago. Similarly, scientists hope that Rosetta will unlock the mysteries of how the Solar System evolved.

Objective

To rendezvous with Comet 67P/Churyumov-Gerasimenko where it will study the nucleus of the comet and its environment for nearly two years, and land a probe on its surface.

Mission

Rosetta is en route to Comet 67P/Churyumov-Gerasimenko, where it will make the most detailed study of a comet ever attempted. It will follow the comet on its journey through the inner Solar System, measuring the increase in activity as the icy surface is warmed up by the Sun. The lander will focus on the composition and structure of the comet nucleus material. It will also drill more than 20cm into the subsurface to collect samples for inspection by the lander's onboard laboratory.

What's special?

Comets are considered the primitive building blocks of the Solar System, and likely helped 'seed' the Earth with water, and maybe even life. By studying the nature of the comet’s dust and gas, Rosetta will help scientists learn more about the role of comets in the evolution of the Solar System.

Rosetta will be the first mission ever to orbit a comet's nucleus and land a probe on its surface. It will also be the first spacecraft to fly alongside a comet as it heads towards the inner Solar System, watching how a frozen comet is transformed by the warmth of the Sun.

Rosetta is the first space mission to journey beyond the main asteroid belt and rely solely on solar cells for power generation, rather than the traditional radio-isotope thermal generators. The new solar-cell technology used on the orbiter's two giant solar panels allows it to operate over 800 million kilometers from the Sun, where sunlight levels are only 4 percent of those on Earth.

Spacecraft

The main spacecraft measures 2.8 by 2.1 by 2.0 m with two 14 meter long solar panels. It carries instruments for remote sensing and radio science, and instruments to study the composition, mass distribution and dust flux of the comet’s nucleus, as well as the comet plasma environment and its interaction with the solar wind.

The orbiter's 11 scientific instruments are accommodated on one side of the spacecraft, which will permanently face the comet during the operational phase of the mission.

Until its release, the 100kg Philae lander is carried on the opposite side of the orbiter to the large high-gain antenna dish. As Philae touches down on the comet, two harpoons will anchor it to the surface; the self-adjusting landing gear will ensure that it stays upright, even on a slope, and then the lander's feet will drill into the ground to secure it to the comet’s surface in the low gravity environment. Philae carries nine scientific instruments, including a drill to sample subsurface material.

Journey

Rosetta launched on March 2, 2004 by an Ariane 5 G+ from Europe's spaceport in Kourou, French Guiana. To place it on the required orbit to rendezvous with Comet 67P/ Churyumov-Gerasimenko it will receive four gravity assist maneuvers: three from Earth (March 4, 2005, Nov. 13, 2007 and Nov. 13, 2009) and one from Mars (Feb. 25, 2007).

Rosetta will also pass by and image two asteroids: 2867 Steins on Sept. 5, 2008 and 21 Lutetia on July 10, 2010.

The spacecraft will enter deep space hibernation in July 2011 and will be woken up in January 2014, before rendezvousing with Comet 67P/ Churyumov-Gerasimenko in May 2014. It will follow the comet around the Sun and as it moves back out towards the orbit of Jupiter.

The lander, Philae, will be delivered to the comet's surface in November 2014.

spaceuk
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Rosetta ticking along... from ESA:
The spacecraft will remain in Passive Cruise Mode until 26 July 2006. During the entire period, the spacecraft will be monitored on the basis of weekly ground station passes.

Operations for the Mars swing-by (February 2007) will start in August 2006, with another payload passive checkout (PC3), an intense tracking campaign around the Trajectory Correction Manoeuvre (DSM-2) in September, and the first payload Active Checkout (PC4) in November/December.

micropooz
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ESA release
Rosetta successfully swings-by Mars — next target: Earth

At 03:57 CET today, mission controllers at ESOC, ESA's Space Operations Centre in Germany, confirmed Rosetta's successful swingby of Mars, a key milestone in the 7.1-thousand-million km journey of this unique spacecraft to its target comet in 2014.

The gravitational energy of Mars helped Rosetta change direction, while the spacecraft was decelerated with respect to the Sun by an estimated 7887 km/hour. The spacecraft is now on the correct track towards Earth - its next destination planet whose gravitational energy Rosetta will exploit in November this year to gain acceleration and continue on its trek.

Robert Pearlman
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posted 02-25-2007 09:35 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Stunning image taken by the CIVA imaging instrument on Rosetta's Philae lander just 4 minutes before closest approach at a distance of some 1000 km from Mars.

A portion of the spacecraft and one of its solar arrays are visible in nice detail. Beneath, an area close to the Syrtis region is visible on the planet's disk.

Credits: CIVA / Philae / ESA Rosetta

Robert Pearlman
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posted 11-14-2007 10:22 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
On the subject of Rosetta and Earth, from ESA:

Robert Pearlman
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posted 09-04-2008 04:16 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
ESA's Rosetta spacecraft will make a historic encounter with asteroid (2867) Steins on September 5, 2008.
Rosetta Steins fly-by timeline

The Rosetta spacecraft control room is buzzing with anticipation as Rosetta closes in on asteroid 2867 Steins. The fly-by timeline includes a series of critical events, culminating with closest approach - expected at 20:58 CEST, 5 September 2008.

At the time of closest approach, Rosetta is planned to be 800 km from the asteroid, passing by at a speed of 8.6 km/s relative to Steins. Both Rosetta and Steins will be illuminated by the Sun, providing an excellent opportunity for science observations.

Between 40 and 20 minutes before closest approach, Rosetta will be flipped and the spacecraft will switch to a specially designed asteroid fly-by mode, an optimal configuration that supports the intensive observation and tracking activity of the on-board instruments.

Although most scientific observations will take place in the few hours around closest approach, several instruments will be switched on for a longer time around the event.

ESA's Cebreros deep space antenna (DSA 2) in Cebreros, Spain, will be used for communications with Rosetta in the two days preceding closest approach. When the spacecraft is not visible from Cebreros or New Norcia, NASA's DSN (Deep Space Network) ground stations at Goldstone, Canberra and Madrid will provide support for tracking and for science operations.

Around closest approach, Rosetta will be 2.41 Astronomical Units, or about 360 million km, from Earth. Radio signals sent to and from the spacecraft will have a 20 minute one-way travel time.

Timeline of nominal fly-by events

Note: All event times are stated in ground time, CEST.

Time-Event
1 September
02:20-Instruments switched on (except OSIRIS which was already on for the navigation campaign)
4 September
07:20-11:20-Slot for possible trajectory correction manoeuvre (36 hours before closest approach)
13:20-18:20-Last opportunity to acquire images for optical navigation campaign
5 September
07:20-10:20-Slot for possible trajectory correction manoeuvre (12 hours before closest approach)
10:20-Navigation cameras switch to tracking mode - initially both used, then use CAM 'A' only (to be decided)
11:00-Uplink fly-by commands for asteroid fly-by mode (AFM). Includes an update to the command profile already on board & the final updated AFM commands (only if 1 CAM at least is tracking)
20:18-20:38-Spacecraft flip over
20:39-Spacecraft switches automatically to asteroid fly-by mode
20:56-Sun illuminates Rosetta from the back and the asteroid fully
20:58-Closest approach, at a planned distance of 800 km from the asteroid
22:27-First post-fly-by acquisition of signal (AOS) - telemetry received via NASA's Goldstone ground station
22:30-Start of science data download via Goldstone
6 September
12:00-Live streaming of Rosetta Steins fly-by press conference from the European Space Operations Centre begins
13:00-Images from fly-by published on ESA web
15:00-End of press conference streaming
16:01-End of reception of first set of science data
The Rosetta Blog is now online, and will be updated throughout the fly-by of Steins with news and information direct from ESA's European Space Operations Centre.

Robert Pearlman
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ESA release
Rosetta Steins fly-by confirmed

The Rosetta control room at ESA's European Space Operations Centre, ESOC, received the first radio signal after closest approach to asteroid (2867) Steins at 22:14 CEST, confirming a smooth fly-by.

Closest approach took place at 20:58 CEST ground time, 20:38 CEST spacecraft time, at a distance of 800 km. Rosetta's relative speed with respect to Steins was 8.6 km/sec, or about 31 000 km/h. The exact time of closest approach will be confirmed over the next few days after a detailed analysis of telemetry data.

To optimise the science return from this historic encounter, a series of critical operations were executed before closest approach, some of which required the spacecraft flip over and change its orientation rapidly, pushing it to its design limits.

After the flip, at 20:39 CEST (ground time), Rosetta switched to the asteroid fly-by mode, during which its orientation was automatically controlled by the on-board navigation cameras. The asteroid was tracked continuously and kept it in the field of view of the imaging instruments.

At 20:48 CEST (ground time), while still in asteroid fly-by mode, Rosetta's high gain antenna was turned away from Earth and the science observations were carried out. Radio contact established again at 22:14 CEST and the first bit of telemetry was received through NASA's Goldstone antenna.

Science data download will start tomorrow morning, 6 September at about 02:00 CEST and continue through the night. Images and the preliminary results from the fly-by will be presented tomorrow at a press conference which be held at ESOC starting at 12:00 CEST. The press conference will be streamed on the web.

Robert Pearlman
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European Space Agency (ESA) release
Steins: A diamond in the sky

Asteroid Steins seen from a distance of 800 km, taken by the OSIRIS imaging system from two different perspectives. The effective diameter of the asteroid is 5 km, approximately as predicted. At the top of the asteroid (as shown in this image), a large crater, approximately 1.5-km in size, can be seen. Scientists were amazed that the asteroid survived the impact that was responsible for the crater.

The first images from Rosetta's OSIRIS imaging system and VIRTIS infrared spectrometer were derived from raw data this morning and have delivered spectacular results.

"Steins looks like a diamond in the sky," said Uwe Keller, Principal Investigator for the OSIRIS imaging system from the Max Planck Institut Fuer Sonnensystemforschung, Lindau.

Visible in the image are several small craters on the asteroid, and two huge ones, one of which is 2 km in diameter, indicating that the asteroid must be very old.

The images are 50 to 60 pixels in diameter, enough to characterise the shape and other characteristics of the body of the asteroid.

Rita Schulz, Rosetta Project Scientist, said, "In the images is a chain of impact craters, which must have formed from recurring impact as the asteroid rotated. The impact may have been caused by a meteoroid stream, or fragments from a shattered small body."

The chain is composed of about 7 craters. To determine the age of the asteroid, a count of the craters on the asteroid's surface has been started (the more the number of craters, the older the asteroid). So far, 23 craters have been spotted.

From the images, scientists will try and understand why the asteroid is unusually bright, and how fine grains of the surface regolith are. This will tell them more about how the asteroid formed.

Gerhard Schwehm, Mission Manager for Rosetta said, "It looks like a typical asteroid, but it is really fascinating how much we can learn from just the images. This is our first science highlight; we certainly have a lot of promising science ahead of us. I'm already looking forward to encountering our next diamond in the sky, the much bigger Lutetia."

The OSIRIS imaging system's Wide Angle Camera (WAC) worked perfectly through the fly-by.

The OSIRIS team expects that the images that they will retrieve from the Narrow Angle Camera (NAC) will be of comparable resolution. This will add to the detailed colour information and hence to knowledge of the surface composition.

Science team members noted that the Narrow Angle Camera (NAC) appears to have switched to safe mode a few minutes before closest approach, but switched back on after a few hours. The software is programmed to switch to safe mode when certain parameter thresholds are crossed to protect the camera. The team will concentrate investigating the reasons for this anomaly once the science data has been analysed.

After analysis of the Rosetta data, Steins will be one of the best-characterised asteroids so far.

View a movie of the flyby and 3-D images of Steins on ESA's website.

cspg
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Beautiful picture of Earth as the Rosetta spacecraft approaches our pale blue dot:
First view of Earth as Rosetta approaches home

This spectacular image of our home planet was captured by the OSIRIS instrument on ESA's Rosetta comet chaser on November 12 as the spacecraft approached Earth for the third and final swingby. Closest approach is due at 08:45 CET, 13 November 2009. Follow Rosetta's progress at ESA's dedicated Rosetta site and via the Rosetta Blog.


Credits: ESA MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

The image was acquired with the OSIRIS narrow-angle camera from a distance of 633 000 km on 12 November 2009 at 13:28 CET. The resolution is 12 km/pixel.

Three images with an orange, green, and blue filter were combined to create this one. The illuminated crescent is centered roughly around the South Pole (South at the bottom of the image). The outline of Antarctica is visible under the clouds that form the striking south-polar vortex. Pack ice in front of the coastline with its strong spectacular reflection is the cause for the very bright spots on the image.

The OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) is a wide-angle camera and a narrow-angle camera to obtain high-resolution images of the comet's nucleus and the asteroids that Rosetta passes on its voyage to Comet 67P/Churyumov-Gerasimenko. It will help in identifying the best landing sites.

SpaceAholic
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A reminder that Rosetta flyby of asteroid Lutetia will occur tomorrow (10 July) - monitor via an ESA live webcast of the event.
Rosetta lines up for spectacular asteroid flyby

On 10 July, ESA's Rosetta will fly past 21 Lutetia, the largest asteroid ever visited by a satellite. After weeks of manoeuvres and a challenging optical navigation campaign, Rosetta is perfectly lined up to skim by at 3162 km at 18:10 CEST.

Rosetta is expected to pass Lutetia at a relative speed of 54 000 km/hr, when both are located some 454 million km from Earth. As Lutetia is a major scientific target of Rosetta's mission, most of the orbiter and lander instruments will be on for flyby, studying the asteroid's surface, dust environment, exosphere, magnetic field, mass and density.

The OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) camera system is expected to obtain visible-spectrum images before and at closest approach. The powerful imaging system is operated by the Max Planck Institute for Solar System Research, Germany. Although most scientific observations will be performed in the few hours around closest approach, several instruments will be on several days before or after.

Challenging optical navigation technique

Since 31 May, the navigation cameras and the OSIRIS scientific imaging system have been used in a challenging optical navigation campaign aimed at visually tracking Lutetia and determining its orbit with more accuracy.

Initially, images were taken twice a week; since late June, images have been taken daily and this will continue until 9 July.

The results of the optical navigation campaign have been used to programme a series of Trajectory Correction Manoeuvres (TCM), or thruster burns, to nudge Rosetta onto the optimum trajectory. After the last TCM on 18 June, analysis of the spacecraft's orbit indicated that remaining manoeuvre slots (one week, three days, 40 hours and 12 hours before flyby) will most likely not be used.

Intense preparations for a deep-space encounter

Preparations for Lutetia flyby have been underway for a number of months by scientists and engineers at ESA, the German Aerospace Center (DLR) and two dozen institutes and universities in Europe and the USA. In the past weeks, activities at the Agency, and especially within the mission's science and operations teams, have intensified.

"There are several special configurations for Rosetta, including a special 'Asteroid Fly-by Mode' in which the spacecraft can operate autonomously and use its cameras to guide its attitude. It's been a challenge, but we are looking forward to an excellent flyby," said Andrea Accomazzo, Rosetta Spacecraft Operations Manager at ESOC, ESA's European Space Operations Centre, Darmstadt, Germany.

Scientists at ESAC, ESA's European Space Astronomy Centre, in Spain, have generated a series of coordinated commands for individual instruments so that observations can be conducted autonomously as Rosetta passes the asteroid. These will be radioed up to Rosetta in advance of the flyby, which will be conducted without ground station contact.

About four hours before closest approach, mission controllers at ESOC will issue commands that will flip Rosetta over and ready the spacecraft to enter Asteroid Fly-by Mode. During this mode, the orientation of the spacecraft is automatically driven by the navigation cameras to continuously keep the asteroid in the field of view of the imaging instruments.

ESA-NASA cooperation for tracking Rosetta

Increased ground tracking support has been scheduled throughout the fly-by period. In addition to ESA's 35m deep-space stations at New Norcia, Australia, and Cebreros, Spain, NASA's 70m Deep Space Network (DSN) stations at Goldstone, California, Canberra, Australia, and Madrid, Spain, will assist in relaying commands and data. The two agencies often work together and regularly share tracking station resources.

Time-line of critical events 10 July

Note: Times shown are ground event times in Central European Summer Time (CEST = UTC/GMT + 2 hours). Spacecraft event time is 25 mins and 21 secs earlier. All times are estimates and may change.

Watch the live fly-by webcast from ESA/ESOC, 10 July 2010, starting 18:00 CEST.

TimeEvent
00:00:00Start of tracking - NASA/DSN Goldstone (GDS)
00:25:05Start - Rosetta's NAVCAM asteroid tracking
05:30:00End of tracking - NASA /DSN Goldstone (GDS)
05:33:00Start of tracking - ESA/ESTRACK New Norcia station (NNO)
08:00:00Final telecommands for flyby ready from ESA Flight Dynamics team
10:00:00Uplink of updated final fly-by commands
10:20:00Start of tracking - NASA/DSN Canberra (CAN)
12:20:00End of tracking - NASA/DSN Canberra (CAN)
13:05:00Start of tracking - ESA/ESTRACK Cebreros (CEB) & NASA/DSN Madrid (MAD)
14:30:00End of tracking - ESA/ESTRACK Cebreros station (CEB)
15:26:00End of tracking - ESA/ESTRACK New Norcia station (NNO)
13:50:07Start Rosetta flip manoeuvre
14:30:07End Rosetta flip manoeuvre
15:10:07Start asteroid closed-loop tracking - Rosetta on self-navigation
18:00:00Start media event live from ESA/ESOC
18:05:07Stop - radio communications via high-gain antenna - Loss of signal (earliest)
18:10:07Closest approach to Lutetia
18:20:07End asteroid closed-loop tracking
18:45:07Resume radio communications via high-gain antenna - Acquisition of signal (latest)
18:47:00Media event pause
20:05:35Start science data downlink
23:00:00Resume media event - Science team presents data
23:45:00End media event
23:55:00End of tracking - NASA/DSN Madrid (MAD)

Robert Pearlman
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European Space Agency (ESA) photo release
First pre-flyby images now available

Largest view of Lutetia shows asteroid at a distance of 80,000 km.

Credit: ESA

Robert Pearlman
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European Space Agency (ESA) release
Rosetta triumphs at asteroid Lutetia

Asteroid Lutetia has been revealed as a battered world of many craters. ESA's Rosetta mission has returned the first close-up images of the asteroid showing it is most probably a primitive survivor from the violent birth of the Solar System.


Credit: ESA
Lutetia at Closest approach.
The flyby has been a spectacular success with Rosetta performing faultlessly. Closest approach took place at 18:10 CEST, at a distance of 3162 km.

The images show that Lutetia is heavily cratered, having suffered many impacts during its 4.5 billion years of existence. As Rosetta drew close, a giant bowl-shaped depression stretching across much of the asteroid rotated into view. The images confirm that Lutetia is an elongated body, with its longest side around 130km.

The images come from OSIRIS instrument, which combines a wide angle and a narrow angle camera. At closest approach, details down to a scale of 60 metres can be seen over the entire surface of Lutetia.


Credit: ESA
At a distance of 36000km the OSIRIS Narrow Angle Camera (NAC) took this image catching the planet Saturn in the background.
"I think this is a very old object. Tonight we have seen a remnant of the Solar System's creation," says Holger Sierks, OSIRIS principal investigator, Max Planck Institute for Solar System Research, Lindau.

Rosetta raced past the asteroid at 15 km/s completing the flyby in just a minute. But the cameras and other instruments had been working for hours and in some cases days beforehand, and will continue afterwards. Shortly after closest approach, Rosetta began transmitting data to Earth for processing.

Lutetia has been a mystery for many years. Ground-based telescopes have shown that the asteroid presents confusing characteristics. In some respects it resembles a C-type asteroid, a primitive body left over from the formation of the Solar System. In others, it looks like an M-type asteroid. These have been associated with iron meteorites, are usually reddish in colour and thought to be fragments of the cores of much larger objects.

The new images and the data from Rosetta's other instruments will help to decide but not tonight. Compositional information will be needed for that.


Credit: ESA
Zoom in on a possible landslide and boulders at the highest resolution.
Rosetta operated a full suite of instruments at the encounter, including remote sensing and in-situ measurements. Some of the payload of its Philae lander were also switched on. Together they looked for evidence of a highly tenuous atmosphere, magnetic effects, and studied the surface composition as well as the asteroid's density. They also attempted to catch any dust grains that may have been floating in space near the asteroid for on-board analysis. The results from these instruments will come in time.

The flyby marks the attainment of one of Rosetta's main scientific objectives. The spacecraft will now continue to its primary target, comet Churyumov-Gerasimenko. It will rendezvous with the comet in 2014, mapping it and studying it. It will then accompany the comet for months, from near the orbit of Jupiter down to its closest approach to the Sun. In November 2014, Rosetta will deploy Philae to land on the comet nucleus. "Wunderbar!" says David Southwood, ESA Director of Science and Robotic Exploration, "It has been a great day for exploration, a great day for European science. The clockwork precision is a great tribute to the scientists and engineers in our Member States in our industry and, not least, in ESA itself. Roll on 2014 and our comet rendezvous."

But for now, analysing the Lutetia data will now become the focus for the Rosetta instrument teams. Just twenty-four hours ago, Lutetia was a distant stranger. Now, thanks to Rosetta, it has become a close friend.

Robert Pearlman
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European Space Agency release
The most important alarm clock in the Solar System

At 10:00 GMT (4 a.m. CST) on Monday (Jan. 20), the most important alarm clock in the Solar System will wake up ESA's sleeping Rosetta spacecraft.

Rosetta is chasing comet 67P/Churyumov Gerasimenko and, since its launch in 2004, has made three flybys of Earth and one of Mars to build up enough speed and get on a trajectory towards the comet. It has also encountered asteroids Steins and Lutetia along the way.

Operating on solar energy alone, the spacecraft was placed into a deep space slumber in mid-2011 as it cruised far from the Sun and out towards the orbit of Jupiter. To prepare for its long sleep, Rosetta was oriented so that its solar arrays faced the Sun and put into a once per minute spin for stability.

The only devices left running were its computer and several heaters.

Thirty-one months later, Rosetta's orbit has brought it back to within 'only' 673 million kilometres of the Sun, and there is finally enough solar energy to power the spacecraft fully again. It is time to wake up.

Rosetta's computer is programmed to carry out a sequence of events to re-establish contact with Earth on 20 January, starting with an 'alarm clock' at 10:00 GMT.

Immediately after, the spacecraft's startrackers will begin to warm up, taking around six hours.

Then its thrusters will fire to stop the slow rotation. A slight adjustment will be made to Rosetta's orientation to ensure that the solar arrays are still facing directly towards the Sun, before the startrackers are switched on to determine the spacecraft's attitude.

Once that has been established, Rosetta will turn directly towards Earth, switch on its transmitter and point its high-gain antenna to send its signal to announce that it is awake.

Because of Rosetta's vast distance — just over 807 million kilometres from Earth — it will take 45 minutes for the signal to reach the ground stations. The first opportunity for receiving a signal on Earth is expected between 17:30 GMT and 18:30 GMT (1:30 p.m. and 2:30 p.m. CST).

Deep space tracking dishes will be listening out for the signal, starting with NASA's 'big ears' — the 70 m-diameter station at Goldstone, California, followed by, as the Earth rotates, the Canberra station in eastern Australia. ESA's New Norcia 35 m antenna, in Western Australia, would be next in line to await the signal's arrival.

Whenever the signal is received, it will be relayed immediately to ESOC, ESA's Operations Centre in Darmstadt, Germany.

This exciting moment will be announced to the world straightaway via the @ESA_Rosetta twitter account.

Once mission controllers have verified Rosetta's health, each of its scientific instruments will be switched back on and checked out, an effort that will take several months as the spacecraft continues to eat up the remaining 9 million kilometres separating it from the comet.

In May, Rosetta will make a major manoeuvre to line up for arriving at its target comet in August. If all goes well, it will become the first space mission to rendezvous with a comet, the first to attempt a landing, and the first to follow a comet as it swings around the Sun.

Comets are considered to be the primitive building blocks of the Solar System and likely helped to 'seed' Earth with water, and perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through its comprehensive, close-up study of comet 67P/Churyumov-Gerasimenko, Rosetta aims to unlock the secrets within.

Robert Pearlman
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European Space Agency release
ESA's 'sleeping beauty' wakes up from deep space hibernation

It was a fairy-tale ending to a tense chapter in the story of the Rosetta space mission this evening as ESA heard from its distant spacecraft for the first time in 31 months.

Rosetta is chasing down Comet 67P/Churyumov-Gerasimenko, where it will become the first space mission to rendezvous with a comet, the first to attempt a landing on a comet's surface, and the first to follow a comet as it swings around the Sun.

Since its launch in 2004, Rosetta has made three flybys of Earth and one of Mars to help it on course to its rendezvous with 67P/Churyumov-Gerasimenko, encountering asteroids Steins and Lutetia along the way.

Operating on solar energy alone, Rosetta was placed into a deep space slumber in June 2011 as it cruised out to a distance of nearly 800 million km from the warmth of the Sun, beyond the orbit of Jupiter.

Now, as Rosetta's orbit has brought it back to within 'only' 673 million km from the Sun, there is enough solar energy to power the spacecraft fully again.

Thus today (Jan. 20), still about 6 million miles (9 million km) from the comet, Rosetta's pre-programmed internal 'alarm clock' woke up the spacecraft. After warming up its key navigation instruments, coming out of a stabilising spin, and aiming its main radio antenna at Earth, Rosetta sent a signal to let mission operators know it had survived the most distant part of its journey.

The signal was received by NASA's Goldstone ground station in California at (12:18 p.m. CST) 18:18 GMT, during the first window of opportunity the spacecraft had to communicate with Earth.

It was immediately confirmed in ESA's space operations centre in Darmstadt and the successful wake-up announced via the @ESA_Rosetta twitter account, which tweeted: "Hello, World!"

"We have our comet-chaser back," says Alvaro Giménez, ESA's Director of Science and Robotic Exploration. "With Rosetta, we will take comet exploration to a new level. This incredible mission continues our history of 'firsts' at comets, building on the technological and scientific achievements of our first deep space mission Giotto, which returned the first close-up images of a comet nucleus as it flew past Halley in 1986."

"This was one alarm clock not to hit snooze on, and after a tense day we are absolutely delighted to have our spacecraft awake and back online," adds Fred Jansen, ESA's Rosetta mission manager.

Comets are considered the primitive building blocks of the Solar System and likely helped to 'seed' Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through its comprehensive, in situ study of Comet 67P/Churyumov-Gerasimenko, Rosetta aims to unlock the secrets contained within.

"All other comet missions have been flybys, capturing fleeting moments in the life of these icy treasure chests," says Matt Taylor, ESA's Rosetta project scientist. "With Rosetta, we will track the evolution of a comet on a daily basis and for over a year, giving us a unique insight into a comet's behaviour and ultimately helping us to decipher their role in the formation of the Solar System."

But first, essential health checks on the spacecraft must be completed. Then the eleven instruments on the orbiter and ten on the lander will be turned on and prepared for studying Comet 67P/Churyumov-Gerasimenko.

"We have a busy few months ahead preparing the spacecraft and its instruments for the operational challenges demanded by a lengthy, close-up study of a comet that, until we get there, we know very little about," says Andrea Accomazzo, ESA's Rosetta operations manager.

Rosetta's first images of 67P/Churyumov-Gerasimenko are expected in May, when the spacecraft is still 2 million km from its target. Towards the end of May, the spacecraft will execute a major manoeuvre to line up for its critical rendezvous with the comet in August.

After rendezvous, Rosetta will start with two months of extensive mapping of the comet's surface, and will also make important measurements of the comet's gravity, mass and shape, and assess its gaseous, dust-laden atmosphere, or coma. The orbiter will also probe the plasma environment and analyse how it interacts with the Sun's outer atmosphere, the solar wind.

Using these data, scientists will choose a landing site for the mission's 100 kg Philae probe. The landing is currently scheduled for 11 November and will be the first time that a landing on a comet has ever been attempted.

In fact, given the almost negligible gravity of the comet's 4 km-wide nucleus, Philae will have to use ice screws and harpoons to stop it from rebounding back into space after touchdown.

Among its wide range of scientific measurements, Philae will send back a panorama of its surroundings, as well as very high-resolution pictures of the surface. It will also perform an on-the-spot analysis of the composition of the ices and organic material, including drilling down to 23 cm below the surface and feeding samples to Philae's on-board laboratory for analysis.

The focus of the mission will then move to the 'escort' phase, during which Rosetta will stay alongside the comet as it moves closer to the Sun, monitoring the ever-changing conditions on the surface as the comet warms up and its ices sublimate.

The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow the comet throughout the remainder of 2015, as it heads away from the Sun and activity begins to subside.

"We will face many challenges this year as we explore the unknown territory of comet 67P/Churyumov-Gerasimenko and I'm sure there will be plenty of surprises, but today we are just extremely happy to be back on speaking terms with our spacecraft," adds Matt Taylor.

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NASA release
NASA Instruments Begin Science on European Spacecraft Set to Land on Comet

Three NASA science instruments aboard the European Space Agency's (ESA) Rosetta spacecraft, which is set to become the first to orbit a comet and land a probe on its nucleus, are beginning observations and sending science data back to Earth.

Launched in March 2004, Rosetta was reactivated January 2014 after a record 957 days in hibernation. Composed of an orbiter and lander, Rosetta's objective is to arrive at comet 67P/Churyumov-Gerasimenko in August to study the celestial object up close in unprecedented detail and prepare for landing a probe on the comet's nucleus in November.

Rosetta's lander will obtain the first images taken from a comet's surface and will provide the first analysis of a comet's composition by drilling into the surface. Rosetta also will be the first spacecraft to witness at close proximity how a comet changes as it is subjected to the increasing intensity of the sun's radiation. Observations will help scientists learn more about the origin and evolution of our solar system and the role comets may have played in seeding Earth with water, and perhaps even life.

"We are happy to be seeing some real zeroes and ones coming down from our instruments, and cannot wait to figure out what they are telling us," said Claudia Alexander, Rosetta's U.S. project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "Never before has a spacecraft pulled up and parked next to a comet. That is what Rosetta will do, and we are delighted to play a part in such a historic mission of exploration."

Rosetta currently is approaching the main asteroid belt located between Jupiter and Mars,. The spacecraft is still about 300,000 miles (500,000 kilometers) from the comet, but in August the instruments will begin to map its surface.

The three U.S. instruments aboard the spacecraft are the Microwave Instrument for Rosetta Orbiter (MIRO), an ultraviolet spectrometer called Alice, and the Ion and Electron Sensor (IES). They are part of a suite of 11 science instruments aboard the Rosetta orbiter.

MIRO is designed to provide data on how gas and dust leave the surface of the nucleus to form the coma and tail that gives comets their intrinsic beauty. Studying the surface temperature and evolution of the coma and tail provides information on how the comet evolves as it approaches and leaves the vicinity of the sun.

Alice will analyze gases in the comet's coma, which is the bright envelope of gas around the nucleus of the comet developed as a comet approaches the sun. Alice also will measure the rate at which the comet produces water, carbon monoxide and carbon dioxide. These measurements will provide valuable information about the surface composition of the nucleus.

The instrument also will measure the amount of argon present, an important clue about the temperature of the solar system at the time the comet's nucleus originally formed more than 4.6 billion years ago.

IES is part of a suite of five instruments to analyze the plasma environment of the comet, particularly the coma. The instrument will measure the charged particles in the sun's outer atmosphere, or solar wind, as they interact with the gas flowing out from the comet while Rosetta is drawing nearer to the comet's nucleus.

NASA also provided part of the electronics package for the Double Focusing Mass Spectrometer, which is part of the Swiss-built Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. ROSINA will be the first instrument in space with sufficient resolution to be able to distinguish between molecular nitrogen and carbon monoxide, two molecules with approximately the same mass. Clear identification of nitrogen will help scientists understand conditions at the time the solar system was formed.

U.S. scientists are partnering on several non-U.S. instruments and are involved in seven of the mission's 21 instrument collaborations. NASA's Deep Space Network (DSN) is supporting ESA's Ground Station Network for spacecraft tracking and navigation.

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European Space Agency Rosetta Blog
The dual personality of comet 67P/C-G

This week's images of comet 67P/Churyumov-Gerasimenko reveal an extraordinarily irregular shape. We had hints of that in last week's images and in the unscheduled previews that were seen a few days ago, and in that short time it has become clear that this is no ordinary comet. Like its name, it seems that comet 67P/C-G is in two parts.

What the spacecraft is actually seeing is the pixelated image shown below, which was taken by Rosetta's OSIRIS narrow angle camera on 14 July from a distance of 12 000 km.

A second image and a movie show the comet after the image has been processed. The technique used, called "sub-sampling by interpolation", only acts to remove the pixelisation and make a smoother image, and it is important to note that the comet's surface features won't be as smooth as the processing implies. The surface texture has yet to be resolved simply because we are still too far away; any apparent brighter or darker regions may turn out to be false interpretations at this early stage.

But the movie, which uses a sequence of 36 interpolated images each separated by 20 minutes, certainly provides a truly stunning 360-degree preview of the overall complex shape of the comet. Regardless of surface texture, we can certainly see an irregular shaped world shining through. Indeed, some people have already likened the shape to a duck, with a distinct body and head.

Although less obvious in the 'real' image, the movie of interpolated images supports the presence of two definite components. One segment seems to be rather elongated, while the other appears more bulbous.

Dual objects like this – known as 'contact binaries' in comet and asteroid terminology – are not uncommon.

Indeed, comet 8P/Tuttle is thought to be such a contact binary; radio imaging by the ground-based Arecibo telescope in Puerto Rico in 2008 suggested that it comprises two sphere-like objects. Meanwhile, the bone-shaped comet 103P/Hartley 2, imaged during NASA's EPOXI flyby in 2011, revealed a comet with two distinct halves separated by a smooth region. In addition, observations of asteroid 25143 Itokawa by JAXA's Hayabusa mission, combined with ground-based data, suggest an asteroid comprising two sections of highly contrasting densities.

Is Rosetta en-route to rendezvous with a similar breed of comet? The scientific rewards of studying such a comet would be high, as a number of possibilities exist as to how they form.

One popular theory is that such an object could arise when two comets – even two compositionally distinct comets – melded together under a low velocity collision during the Solar System's formation billions of years ago, when small building blocks of rocky and icy debris coalesced to eventually create planets. Perhaps comet 67P/C-G will provide a unique record of the physical processes of accretion.

Or maybe it is the other way around – that is, a single comet could be tugged into a curious shape by the strong gravitational pull of a large object like Jupiter or the Sun; after all, comets are rubble piles with weak internal strength as directly witnessed in the fragmentation of comet Shoemaker-Levy 9 and the subsequent impacts into Jupiter, 20 years ago this week. Perhaps the two parts of comet 67P/C-G will one day separate completely.

On the other hand, perhaps comet 67P/C-G may have once been a much rounder object that became highly asymmetric thanks to ice evaporation. This could have happened when the comet first entered the Solar System from the Kuiper Belt, or on subsequent orbits around the Sun.

One could also speculate that the striking dichotomy of the comet's morphology is the result of a near catastrophic impact event that ripped out one side of the comet. Similarly, it is not unreasonable to think that a large outburst event may have weakened one side of the comet so much that it simply gave away, crumbling into space.

But, while the interpolated images are certainly brilliant, we need to be closer still to see a better three-dimensional view – not to mention to perform a spectroscopic analysis to determine the comet's composition – in order to draw robust scientific conclusions about this exciting comet.

Rosetta Mission Manager Fred Jansen comments: "We currently see images that suggest a rather complex cometary shape, but there is still a lot that we need to learn before jumping to conclusions. Not only in terms of what this means for comet science in general, but also regarding our planning for science observations, and the operational aspects of the mission such as orbiting and landing.

"We will need to perform detailed analyses and modelling of the shape of the comet to determine how best we can fly around such a uniquely shaped body, taking into account flight control and astrodynamics, the science requirements of the mission, and the landing-related elements like landing site analysis and lander-to-orbiter visibility. But, with fewer than 10 000 km to go before the 6 August rendezvous, our open questions will soon be answered."

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European Space Agency (ESA) photo release
Comet on 29 July 2014

The nucleus of Rosetta's target comet seen from a distance of 1,212 miles (1,950 km) on July 29, 2014.

One pixel corresponds to about 120 feet (37 m) in this narrow-angle camera view. The bright neck between the two lobes of the nucleus is becoming more and more distinct.

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European Space Agency (ESA) photo release
Comet at 1000 km

Rosetta sees the comet just five days before arrival.

This image was acquired Aug. 1 at 04:48 CEST (02:48 UTC) by the OSIRIS Narrow Angle Camera on board ESA's Rosetta spacecraft. The distance was approximately 1000 km. Note that the dark spot is an artifact from the onboard CCD.

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European Space Agency (ESA) photo release
Comet at 300 km

Rosetta navigation camera (NAVCAM) image taken on Aug. 3, 2014 at about 300 km from comet 67P/C-G. The Sun is towards the bottom of the image in the depicted orientation.

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European Space Agency (ESA) release
Rosetta arrives at comet destination

After a decade-long journey chasing its target, ESA's Rosetta has today (Aug. 6) become the first spacecraft to rendezvous with a comet, opening a new chapter in Solar System exploration.

Comet 67P/Churyumov–Gerasimenko and Rosetta now lie 405 million kilometers from Earth, about half way between the orbits of Jupiter and Mars, rushing towards the inner Solar System at nearly 55 000 kilometers per hour.

The comet is in an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will accompany it for over a year as they swing around the Sun and back out towards Jupiter again.

Above: This animation comprises 101 images acquired by the Navigation Camera on board ESA's Rosetta spacecraft as it approached comet 67P/C-G in August 2014. The first image was taken on 1 August at 11:07 UTC (12:07 CEST), at a distance of 832 km. The last image was taken 6 August at 06:07 UTC (08:07 CEST) at a distance of 110 km.

Comets are considered to be primitive building blocks of the Solar System and may have helped to 'seed' Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through a comprehensive,in situstudy of the comet, Rosetta aims to unlock the secrets within.

The journey to the comet was not straightforward, however. Since its launch in 2004, Rosetta had to make three gravity-assist flybys of Earth and one of Mars to help it on course to its rendezvous with the comet. This complex course also allowed Rosetta to pass by asteroids Šteins and Lutetia, obtaining unprecedented views and scientific data on these two objects.

"After ten years, five months and four days traveling towards our destination, looping around the Sun five times and clocking up 6.4 billion kilometers, we are delighted to announce finally 'we are here'," says Jean-Jacques Dordain, ESA's Director General.

"Europe's Rosetta is now the first spacecraft in history to rendezvous with a comet, a major highlight in exploring our origins. Discoveries can start."

Today saw the last of a series of ten rendezvous maneuvers that began in May to adjust Rosetta's speed and trajectory gradually to match those of the comet. If any of these maneuvers had failed, the mission would have been lost, and the spacecraft would simply have flown by the comet.

"Today's achievement is a result of a huge international endeavor spanning several decades," says Alvaro Giménez, ESA's Director of Science and Robotic Exploration.

"We have come an extraordinarily long way since the mission concept was first discussed in the late 1970s and approved in 1993, and now we are ready to open a treasure chest of scientific discovery that is destined to rewrite the textbooks on comets for even more decades to come."

The comet began to reveal its personality while Rosetta was on its approach. Images taken by the OSIRIS camera between late April and early June showed that its activity was variable. The comet's 'coma' — an extended envelope of gas and dust — became rapidly brighter and then died down again over the course of those six weeks.

In the same period, first measurements from the Microwave Instrument for the Rosetta Orbiter, MIRO, suggested that the comet was emitting water vapor into space at about 300 milliliters per second.

Meanwhile, the Visible and Infrared Thermal Imaging Spectrometer, VIRTIS, measured the comet's average temperature to be about –70ºC, indicating that the surface is predominantly dark and dusty rather than clean and icy.

Then, stunning images taken from a distance of about 12,000 km began to reveal that the nucleus comprises two distinct segments joined by a 'neck,' giving it a duck-like appearance. Subsequent images showed more and more detail — the most recent, highest-resolution image was downloaded from the spacecraft earlier today and will be available this afternoon.

"Our first clear views of the comet have given us plenty to think about," says Matt Taylor, ESA's Rosetta project scientist.

"Is this double-lobed structure built from two separate comets that came together in the Solar System's history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects."

Today, Rosetta is just 100 km from the comet's surface, but it will edge closer still. Over the next six weeks, it will describe two triangular-shaped trajectories in front of the comet, first at a distance of 100 km and then at 50 km.

At the same time, more of the suite of instruments will provide a detailed scientific study of the comet, scrutinizing the surface for a target site for the Philae lander.

Eventually, Rosetta will attempt a close, near-circular orbit at 30 km and, depending on the activity of the comet, perhaps come even closer.

"Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land," says Sylvain Lodiot, ESA's Rosetta spacecraft operations manager.

As many as five possible landing sites will be identified by late August, before the primary site is identified in mid-September. The final timeline for the sequence of events for deploying Philae – currently expected for 11 November – will be confirmed by the middle of October.

"Over the next few months, in addition to characterizing the comet nucleus and setting the bar for the rest of the mission, we will begin final preparations for another space history first: landing on a comet," says Matt.

"After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behavior from close quarters to give us a unique insight and realtime experience of how a comet works as it hurtles around the Sun."

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European Space Agency (ESA) photo release
Postcards from Rosetta

Stunning close up detail focusing on a smooth region on the 'base' of the 'body' section of comet 67P/Churyumov-Gerasimenko.

The image was taken by Rosetta's OSIRIS narrow-angle camera and downloaded today, 6 August. The image clearly shows a range of features, including boulders, craters and steep cliffs.

The image was taken from a distance of 130 km and the image resolution is 2.4 metres per pixel.

Close-up detail of comet 67P/Churyumov-Gerasimenko.

The image was taken by Rosetta's OSIRIS narrow-angle camera and downloaded today, 6 August. The image shows the comet's 'head' at the left of the frame, which is casting shadow onto the 'neck' and 'body' to the right.

The image was taken from a distance of 120 km and the image resolution is 2.2 metres per pixel.

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European Space Agency (ESA) release
Rosetta: Landing site search narrows

Using detailed information collected by ESA's Rosetta spacecraft during its first two weeks at Comet 67P/Churyumov-Gerasimenko, five locations have been identified as candidate sites to set down the Philae lander in November – the first time a landing on a comet has ever been attempted.

Before arrival, Comet 67P/Churyumov-Gerasimenko had never been seen close up and so the race to find a suitable landing site for the 100 kg lander could only begin when Rosetta rendezvoused with the comet on 6 August.

The landing is expected to take place in mid-November when the comet is about 450 million km from the Sun, before activity on the comet reaches levels that might jeopardise the safe and accurate deployment of Philae to the comet's surface, and before surface material is modified by this activity.

The comet is on a 6.5-year orbit around the Sun and today is 522 million km from it. At their closest approach on 13 August 2015, just under a year from now, the comet and Rosetta will be 185 million km from the Sun, meaning an eightfold increase in the light received from the Sun.

While Rosetta and its scientific instruments will watch how the comet evolves as heating by the Sun increases, observing how its coma develops and how the surface changes over time, the lander Philae and its instruments will be tasked with making complementary in situ measurements at the comet's surface. The lander and orbiter will also work together using the CONSERT experiment to send and detect radio waves through the comet's interior, in order to characterise its internal structure.

Choosing the right landing site is a complex process. That site must balance the technical needs of the orbiter and lander during all phases of the separation, descent, and landing, and during operations on the surface with the scientific requirements of the 10 instruments on board Philae.

A key issue is that uncertainties in the navigation of the orbiter close to the comet mean that it is only possible to specify any given landing zone in terms of an ellipse – covering up to one square kilometre – within which Philae might land.

For each possible zone, important questions must be asked: Will the lander be able to maintain regular communications with Rosetta? How common are surface hazards such as large boulders, deep crevasses or steep slopes? Is there sufficient illumination for scientific operations and enough sunlight to recharge the lander's batteries beyond its initial 64-hour lifetime, while not so much as to cause overheating?

To answer these questions, data acquired by Rosetta from about 100 km distance have been used, including high-resolution images of the surface, measurements of the comet's surface temperature, and the pressure and density of gas around the nucleus. In addition, measurements of the comet's orientation with respect to the Sun, its rotation, mass and surface gravity have been determined. All of these factors influence the technical feasibility of landing at any specific location on the comet.

This weekend, the Landing Site Selection Group (comprising engineers and scientists from Philae's Science, Operations and Navigation Centre at CNES, the Lander Control Centre at DLR, scientists representing the Philae Lander instruments and ESA's Rosetta team) met at CNES, Toulouse, to consider the available data and determine a shortlist of five candidate sites.

"This is the first time landing sites on a comet have been considered," says Stephan Ulamec, Lander Manager at DLR.

"Based on the particular shape and the global topography of Comet 67P/ Churyumov-Gerasimenko, it is probably no surprise that many locations had to be ruled out. The candidate sites that we want to follow up for further analysis are thought to be technically feasible on the basis of a preliminary analysis of flight dynamics and other key issues – for example they all provide at least six hours of daylight per comet rotation and offer some flat terrain. Of course, every site has the potential for unique scientific discoveries."

"The comet is very different to anything we've seen before, and exhibits spectacular features still to be understood," says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument.

"The five chosen sites offer us the best chance to land and study the composition, internal structure and activity of the comet with the ten lander experiments."

The sites were assigned a letter from an original pre-selection of 10 possible sites, which does not signify any ranking. Three sites (B, I and J) are located on the smaller of the two lobes of the comet and two sites (A and C) are located on the larger lobe.

Summary of the five candidate sites

  • Site A
    Site A is an interesting region located on the larger lobe, but with a good view of the smaller lobe. The terrain between the two lobes is likely the source of some outgassing. Higher-resolution imaging is needed to study potential surface hazards such as small depressions and slopes, while the illumination conditions also need to be considered further.

  • Site B
    Site B, within the crater-like structure on the smaller lobe, has a flat terrain and is thus considered relatively safe for landing, but illumination conditions may pose a problem when considering the longer-term science planning of Philae. Higher-resolution imaging will be needed to assess the boulder hazards in more detail. In addition, the boulders are also thought to represent more recently processed material and therefore this site may not be as pristine as some of the others.

  • Site C
    Site C is located on the larger lobe and hosts a range of surface features including some brighter material, depressions, cliffs, hills and smooth plains, but higher-resolution imaging is needed to assess the risk of some of these features. It is also well illuminated, which would benefit the long-term scientific planning for Philae.

  • Site I
    Site I is a relatively flat area on the smaller lobe that may contain some fresh material, but higher-resolution imaging is needed to assess the extent of the rough terrain. The illumination conditions should also allow for longer-term science planning.

  • Site J
    Site J is similar to site I, and also on the smaller lobe, offering interesting surface features and good illumination. It offers advantages for the CONSERT experiment compared with Site I, but higher-resolution imaging is needed to determine the details of the terrain, which shows some boulders and terracing.

The next step is a comprehensive analysis of each of the candidate sites, to determine possible orbital and operational strategies that could be used for Rosetta to deliver the lander to any of them. At the same time, Rosetta will move to within 50 km of the comet, allowing a more detailed study of the proposed landing sites.

By 14 September, the five candidate sites will have been assessed and ranked, leading to the selection of a primary landing site, for which a fully detailed strategy for the landing operations will be developed, along with a backup.

During this phase, Rosetta will move to within 20–30 km of the comet, allowing even more detailed maps of the boulder distributions at the primary and backup landing sites to be made. This information could be important in deciding whether to switch from primary to backup.

The Rosetta mission team are working towards a nominal landing date of 11 November, but confirmation of the primary landing site and the date will likely only come on 12 October. This will be followed by a formal Go/No Go from ESA, in agreement with the lander team, after a comprehensive readiness review on 14 October.

"The process of selecting a landing site is extremely complex and dynamic; as we get closer to the comet, we will see more and more details, which will influence the final decision on where and when we can land," says Fred Jansen, ESA Rosetta mission manager.

"We had to complete our preliminary analysis on candidate sites very quickly after arriving at the comet, and now we have just a few more weeks to determine the primary site. The clock is ticking and we now have to meet the challenge to pick the best possible landing site."

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European Space Agency (ESA) release
'J' marks the spot for Rosetta's lander

Rosetta's lander Philae will target Site J, an intriguing region on Comet 67P/Churyumov–Gerasimenko that offers unique scientific potential, with hints of activity nearby, and minimum risk to the lander compared to the other candidate sites.

Site J is on the 'head' of the comet, an irregular shaped world that is just over 4 km across at its widest point. The decision to select Site J as the primary site was unanimous. The backup, Site C, is located on the 'body' of the comet.

Above: Philae's primary landing site will target Site J, the centre of which is indicated by the cross in this OSIRIS narrow-angle image. (ESA)

The 100 kg lander is planned to reach the surface on 11 November, where it will perform indepth measurements to characterise the nucleus in situ, in a totally unprecedented way.

But choosing a suitable landing site has not been an easy task.

"As we have seen from recent close-up images, the comet is a beautiful but dramatic world – it is scientifically exciting, but its shape makes it operationally challenging," says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

"None of the candidate landing sites met all of the operational criteria at the 100% level, but Site J is clearly the best solution."

"We will make the first ever in situ analysis of a comet at this site, giving us an unparalleled insight into the composition, structure and evolution of a comet," says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument at the IAS in Orsay, France.

"Site J in particular offers us the chance to analyse pristine material, characterise the properties of the nucleus, and study the processes that drive its activity."

Above: Context image showing the location of the primary landing site for Rosetta's lander Philae. (ESA)

The race to find the landing site could only begin once Rosetta arrived at the comet on 6 August, when the comet was seen close-up for the first time. By 24 August, using data collected when Rosetta was still about 100 km from the comet five candidate regions had been identified for further analysis.

Since then, the spacecraft has moved to within 30 km of the comet, affording more detailed scientific measurements of the candidate sites. In parallel, the operations and flight dynamics teams have been exploring options for delivering the lander to all five candidate landing sites.

Over the weekend, the Landing Site Selection Group of engineers and scientists from Philae's Science, Operations and Navigation Centre at France's CNES space agency, the Lander Control Centre at DLR, scientists representing the Philae Lander instruments and ESA's Rosetta team met at CNES, Toulouse, France, to consider the available data and to choose the primary and backup sites.

A number of critical aspects had to be considered, not least that it had to be possible to identify a safe trajectory for deploying Philae to the surface and that the density of visible hazards in the landing zone should be minimal. Once on the surface, other factors come into play, including the balance of daylight and nighttime hours, and the frequency of communications passes with the orbiter.

The descent to the comet is passive and it is only possible to predict that the landing point will place within a 'landing ellipse' typically a few hundred metres in size.

A one square kilometre area was assessed for each candidate site. At Site J, the majority of slopes are less than 30º relative to the local vertical, reducing the chances of Philae toppling over during touchdown. Site J also appears to have relatively few boulders, and receives sufficient daily illumination to recharge Philae and continue science operations on the surface beyond the initial battery-powered phase.

Provisional assessment of the trajectory to Site J found that the descent time of Philae to the surface would be about seven hours, a length that does not compromise the on-comet observations by using up too much of the battery during the descent.

Above: Close-up of Philae's primary landing site J, which is located on the 'head' of Comet 67P/Churyumov–Gerasimenko. The image was taken by Rosetta's OSIRIS narrow-angle camera on 20 August 2014 from a distance of about 67 km. The image scale is 1.2 metres/pixel. (ESA)

Both Sites B and C were considered as the backup, but C was preferred because of a higher illumination profile and fewer boulders. Sites A and I had seemed attractive during first rounds of discussion, but were dismissed at the second round because they did not satisfy a number of the key criteria.

A detailed operational timeline will now be prepared to determine the precise approach trajectory of Rosetta in order to deliver Philae to Site J. The landing must take place before mid-November, as the comet is predicted to grow more active as it moves closer to the Sun.

"There's no time to lose, but now that we're closer to the comet, continued science and mapping operations will help us improve the analysis of the primary and backup landing sites," says ESA Rosetta flight director Andrea Accomazzo.

"Of course, we cannot predict the activity of the comet between now and landing, and on landing day itself. A sudden increase in activity could affect the position of Rosetta in its orbit at the moment of deployment and in turn the exact location where Philae will land, and that's what makes this a risky operation."

Once deployed from Rosetta, Philae's descent will be autonomous, with commands having been prepared by the Lander Control Centre at DLR, and uploaded via Rosetta mission control before separation.

During the descent, images will be taken and other observations of the comet's environment will be made.

Once the lander touches down, at the equivalent of walking pace, it will use harpoons and ice screws to fix it onto the surface. It will then make a 360° panoramic image of the landing site to help determine where and in what orientation it has landed.

The initial science phase will then begin, with other instruments analysing the plasma and magnetic environment, and the surface and subsurface temperature. The lander will also drill and collect samples from beneath the surface, delivering them to the onboard laboratory for analysis. The interior structure of the comet will also be explored by sending radio waves through the surface towards Rosetta.

"No one has ever attempted to land on a comet before, so it is a real challenge," says Fred Jansen, ESA Rosetta mission manager. "The complicated 'double' structure of the comet has had a considerable impact on the overall risks related to landing, but they are risks worth taking to have the chance of making the first ever soft landing on a comet."

The landing date should be confirmed on 26 September after further trajectory analysis and the final Go/No Go for a landing at the primary site will follow a comprehensive readiness review on 14 October.

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European Space Agency (ESA) release
Rosetta to deploy lander on November 12

The European Space Agency's Rosetta mission will deploy its lander, Philae, to the surface of Comet 67P/Churyumov–Gerasimenko on Nov. 12.

Philae's landing site, currently known as Site J, is located on the smaller of the comet's two 'lobes', with a backup site on the larger lobe. The sites were selected just six weeks after Rosetta arrived at the comet on Aug. 6, following its 10-year journey through the Solar System.

In that time, the Rosetta mission has been conducting an unprecedented scientific analysis of the comet, a remnant of the Solar System's 4.6 billion-year history. The latest results from Rosetta will be presented on the occasion of the landing, during dedicated press briefings.

The main focus to date has been to survey 67P/Churyumov–Gerasimenko in order to prepare for the first ever attempt to soft-land on a comet.

Site J was chosen unanimously over four other candidate sites as the primary landing site because the majority of terrain within a square kilometre area has slopes of less than 30º relative to the local vertical and because there are relatively few large boulders. The area also receives sufficient daily illumination to recharge Philae and continue surface science operations beyond the initial 64-hour battery-powered phase.

Over the last two weeks, the flight dynamics and operations teams at ESA have been making a detailed analysis of flight trajectories and timings for Rosetta to deliver the lander at the earliest possible opportunity.

Two robust landing scenarios have been identified, one for the primary site and one for the backup. Both anticipate separation and landing on Nov. 12.

For the primary landing scenario, targeting Site J, Rosetta will release Philae at 08:35 GMT/09:35 CET at a distance of 22.5 km from the centre of the comet, landing about seven hours later. The one-way signal travel time between Rosetta and Earth on Nov. 12 is 28 minutes 20 seconds, meaning that confirmation of the landing will arrive at Earth ground stations at around 16:00 GMT/17:00 CET.

If a decision is made to use the backup Site C, separation will occur at 13:04 GMT/14:04 CET, 12.5 km from the centre of the comet. Landing will occur about four hours later, with confirmation on Earth at around 17:30 GMT/18:30 CET. The timings are subject to uncertainties of several minutes.

Final confirmation of the primary landing site and its landing scenario will be made on Oct. 14 after a formal Lander Operations Readiness Review, which will include the results of additional high-resolution analysis of the landing sites conducted in the meantime. Should the backup site be chosen at this stage, landing can still occur on Nov. 12.

A competition for the public to name the primary landing site will also be announced during the week of Oct. 14.

The Rosetta orbiter will continue to study the comet and its environment using its 11 science instruments as they orbit the Sun together. The comet is on an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will accompany the comet for more than a year as they swing around the Sun and back to the outer Solar System again.

The analyses made by the Rosetta orbiter will be complemented by the in situ measurements performed by Philae's 10 instruments.

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European Space Agency release
Farewell 'J', hello Agilkia

The site where Rosetta's Philae lander is scheduled to touch down on Comet 67P/Churyumov–Gerasimenko on 12 November now has a name: Agilkia.

The landing site, previously known as 'Site J', is named for Agilkia Island, an island on the Nile River in the south of Egypt. A complex of Ancient Egyptian buildings, including the famous Temple of Isis, was moved to Agilkia from the island of Philae when the latter was flooded during the building of the Aswan dams last century.

The name was selected by a jury comprising members of the Philae Lander Steering Committee as part of a public competition run 16–22 October by ESA and the German, French and Italian space agencies.

Agilkia was one of the most popular entries – it was proposed by over 150 participants. The committee selected Alexandre Brouste from France as the overall winner. As a prize, Mr Brouste will be invited to ESA's Space Operations Control Centre in Darmstadt, Germany, to follow the landing live.

Although perhaps not quite as complicated as navigating Rosetta and Philae towards the comet, the task of choosing a name was by no means simple. More than 8000 entries from 135 countries were received in one week, showing great creativity and cultural diversity.

"The decision was very tough," says Prof. Felix Huber of the DLR German Aerospace Center, chair of the Steering Committee.

"We received so many good suggestions on how to name Site J, and we were delighted with such an enthusiastic response from all over the world. We wish to thank all participants for sharing their great ideas with us."

Participants proposed names in a variety of languages, both ancient and modern; some were even in Esperanto. There were also some interesting acronyms, curious sequences of digits, and onomatopoeiac words.

The entries covered a tremendous range of themes, from abstract concepts to the names of places on Earth. As with the winning entry, many suggestions echoed the Egyptian origins of Rosetta and Philae, named in recognition of milestones in decoding hieroglyphics, the sacred writing system of ancient Egypt.

Many names dated back to the history of our planet's exploration, as those journeys into the unknown are the natural forebears of Rosetta and Philae. Mythological names from all over the globe were also proposed, including gods and goddesses of water, fertility, life and creation, relating closely to the fundamental themes investigated by the mission.

Other names were drawn from ancient history and prehistory, while others recalled milestones in the history of science, particularly the history of our understanding of comets.

The progress of the Space Age was also honoured by many entries. There were many references to science fiction, celebrating the work of Jules Verne, Arthur C. Clarke and Douglas Adams, among others.

Fictional characters from films, television shows, literary and musical works were also proposed. Some even referred to the virtual astronauts of the Kerbal Space Program, a popular online space exploration game.

Several entries acknowledged the Rosetta mission as an endeavour achieved through the cooperation of many European countries, while others referred to its groundbreaking technical and scientific achievements.

And, of course, there was no shortage of more humorous entries, many referring to the resemblance of the comet's nucleus to a rubber duck, a potato or even the cartoon dog, Snoopy.

But the final choice is Agilkia, which is how the landing site on the comet will be referred to by ESA and its mission partners.

"And it couldn't be a more appropriate name," comments Fred Jansen, ESA Rosetta mission manager. "The relocation of the temples of Philae Island to Agilkia Island was an ambitious technical endeavour performed in the 1960s and 1970s to preserve an archaeological record of our ancient history.

"In eight days' time, Philae will be deployed from the orbiter onto Agilkia. On 12 November, we'll be attempting a unique comet landing, an even more ambitious endeavour to unlock secrets of our most remote origins."

About the landing

Rosetta will release Philae at 08:35 GMT/09:35 CET on 12 November at a distance of 22.5 km from the centre of the comet, with a scheduled landing about seven hours later at Agilkia.

Taking into account the signal travel time from Rosetta on 12 November, confirmation of landing is expected on Earth at around 16:00 GMT/17:00 CET.

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European Space Agency (ESA) release
Rosetta and Philae separation confirmed

The Philae lander has separated from the Rosetta orbiter, and is now on its way to becoming the first spacecraft to touch down on a comet.

Separation was confirmed at ESA's Space Operation Centre, ESOC, in Darmstadt, Germany at 3:03 a.m. CST (0903 GMT) on Wednesday (Nov. 12). It takes the radio signals from the transmitter on Rosetta 28 minutes and 20 seconds to reach Earth, so separation actually occurred in space at 2:35 a.m. CST (0835 GMT).

The first signal from Philae is expected in around two hours, when the lander establishes a communication link with Rosetta. Philae cannot send its data to Earth directly — it must do it via Rosetta.

Once the link has been established, the lander will relay via Rosetta a status report of its health, along with the first science data. This will include images taken of the orbiter shortly after separation.

The descent to the surface of Comet 67P/Churyumov–Gerasimenko will take around seven hours, during which the lander will take measurements of the environment around the comet. It will also take images of the final moments of descent.

Confirmation of a successful touchdown is expected in a one-hour window centred on 11:02 a.m. CST (1702 GMT). The first image from the surface is expected some two hours later.

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'Philae is on the comet!' ESA probe makes historic first touchdown on comet

A small European space probe has become the first manmade object in history to touch down on the surface of a comet

And it may have done it twice.

Philae, the European Space Agency's three-legged lander, successfully fell to the surface of Comet 67P/Churyumov-Gerasimenko after a seven-hour, suspenseful descent on Wednesday (Nov. 12). The unprecedented touchdown was confirmed at 11:03 a.m. EST (1603 GMT), 28 minutes and 20 seconds after it occurred, given the time needed for the lander's signal to reach Earth.

"We're there and Philae is talking to us," Stephan Ulamec, the director of the Philae landing team at the DLR German Aerospace Center, said just moments after cheers erupted in the control room. "We are sitting on the surface. We are on the comet."

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European Space Agency photo release
Welcome to a comet

Rosetta's lander Philae is safely on the surface of Comet 67P/Churyumov-Gerasimenko, as these first two CIVA images confirm. One of the lander's three feet can be seen in the foreground. The image is a two-image mosaic.

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ESA's Philae probe 'bounced' twice during historic comet landing

The first space probe to touch down on the surface of a comet did so three times before it finally came to rest in the shadow of a cliff.

The European Space Agency (ESA) on Thursday (Nov 13) released photos captured by the Rosetta mission's Philae lander showing the three-legged probe was on the surface of Comet 67P/Churyumov-Gerasimenko. The probe, which on Wednesday separated from the Rosetta spacecraft and descended for seven hours to the comet's surface, did, in fact, land, but where exactly is still not known.

"We understood that we... bounced two times and finally stopped at a place we haven't entirely located," said Jean-Pierre Bibring, the Philae lander's lead scientist. "We sort of got close to the place that we are, where we think we are, which is not very close to [where] we wanted to [be], but not very far away."

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Philae falls silent: European comet lander goes to sleep as its power runs out

"I'm feeling a bit tired, did you get all my data? I might take a nap..."

And with that, the European Space Agency's (ESA) Philae lander, the first probe to land on a comet, went to sleep.

The status update, posted on Twitter by its mission team on Friday evening (Nov. 14), signaled the likely end for the probe. With its batteries depleted and not enough sunlight reaching its solar panels to recharge, the Philae lander fell into an "idle mode," with all of its science instruments and most of its systems shut down.

"[It] performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered," said Stephan Ulamec, the lander's manager, from the European Space Operations Center in Darmstadt, Germany.

See here for discussion of ESA's Rosetta probe and Philae lander to Comet 67P.

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