The long trek (Rosetta, Philae)

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Comet 67P, Philae, Rosetta

http://www.esa.int/spaceinvideos/content/view/embedjw/421241
Click for Video – Reconstructing Philae’s flight

12 November 2015

One year since Philae made its historic landing on a comet, mission teams remain hopeful for renewed contact with the lander, while also looking ahead to next year’s grand finale: making a controlled impact of the Rosetta orbiter on the comet.

Rosetta arrived at Comet 67P/Churyumov–Gerasimenko on 6 August 2014, and after an initial survey and selection of a landing site, Philae was delivered to the surface on 12 November.

After touching down in the Agilkia region as planned, Philae did not secure itself to the comet, and it bounced to a new location in Abydos. Its flight across the surface is depicted in a new animation, using data collected by Rosetta and Philae to reconstruct the lander’s rotation and attitude.

In the year since landing, a thorough analysis has also now been performed on why Philae bounced.

There were three methods to secure it after landing: ice screws, harpoons and a small thruster. The ice screws were designed with relatively soft material in mind, but Agilkia turned out to be very hard and they did not penetrate the surface.

The harpoons were capable of working in both softer and harder material. They were supposed to fire on contact and lock Philae to the surface, while a thruster on top of the lander was meant to push it down to counteract the recoil from the harpoon.

Attempts to arm the thruster the night before failed: it is thought that a seal did not open, although a sensor failure cannot be excluded.

Then, on landing, the harpoons themselves did not fire. “It seems that the problem was either with the four ‘bridge wires’ taking current to ignite the explosive that triggers the harpoons, or the explosive itself, which may have degraded over time,” explains Stephan Ulamec, Philae lander manager at the DLR German Aerospace Center.

“In any case, if we can regain contact with Philae, we might consider an attempt to retry the firing.”

The reason is scientific: the harpoons contain sensors that could measure the temperature below the surface.

Despite the unplanned bouncing, Philae completed 80% of its planned first science sequence before falling into hibernation in the early hours of 15 November when the primary battery was exhausted. There was not enough sunlight in Philae’s final location at Abydos to charge the secondary batteries and continue science measurements.

The hope was that as the comet moved nearer to the Sun, heading towards closest approach in August, there would be enough energy to reactivate Philae. Indeed, contact was made with the lander on 13 June but only eight intermittent contacts were made up to 9 July.

The problem was that the increasing sunlight also led to increased activity on the comet, forcing Rosetta to retreat to several hundred kilometres for safety, well out of range with Philae.

However, over the past few weeks, with the comet’s activity now subsiding, Rosetta has started to approach again. This week it reached 200 km, the limit for making good contact with Philae, and today it dips to within 170 km.

(Click on link and read entire article for more of this fascinating story.)

http://www.esa.int/Our_Activities/Space_Science/Rosetta/The_long_trek

Rosetta mission extended

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comet, Comet 67P, Rosetta, spacecraft

 

23 June 2015The adventure continues: ESA today confirmed that its Rosetta mission will be extended until the end of September 2016, at which point the spacecraft will most likely be landed on the surface of Comet 67P/Churyumov-Gerasimenko.

Rosetta was launched in 2004 and arrived at the comet in August 2014, where it has been studying the nucleus and its environment as the comet moves along its 6.5-year orbit closer to the Sun. After a detailed survey, Rosetta deployed the lander, Philae, to the surface on 12 November. Philae fell into hibernation after 57 hours of initial scientific operations, but recently awoke and made contact with Rosetta again.

Rosetta’s nominal mission was originally funded until the end of December 2015, but at a meeting today, ESA’s Science Programme Committee has given formal approval to continue the mission for an additional nine months. At that point, as the comet moves far away from the Sun again, there will no longer be enough solar power to run Rosetta’s set of scientific instrumentation efficiently.

“This is fantastic news for science,” says Matt Taylor, ESA’s Rosetta Project Scientist. “We’ll be able to monitor the decline in the comet’s activity as we move away from the Sun again, and we’ll have the opportunity to fly closer to the comet to continue collecting more unique data. By comparing detailed ‘before and after’ data, we’ll have a much better understanding of how comets evolve during their lifetimes.”

Comet on 5 June 2015 – NavCam

Comet 67P/Churyumov-Gerasimenko will make its closest approach to the Sun on 13 August and Rosetta has been watching its activity increase over the last year. Continuing its study of the comet in the year following perihelion will give scientists a fuller picture of how a comet’s activity waxes and wanes along its orbit.

The extra observations collected by Rosetta will also provide additional context for complementary Earth-based observations of the comet. At present, the comet is close to the line-of-sight to the Sun, making ground-based observations difficult.

As the activity diminishes post-perihelion, it should be possible to move the orbiter much closer to the comet’s nucleus again, to make a detailed survey of changes in the comet’s properties during its brief ‘summer’.

In addition, there may be an opportunity to make a definitive visual identification of Philae. Although candidates have been seen in images acquired from a distance of 20 km, images taken from 10 km or less after perihelion could provide the most compelling confirmation.

During the extended mission, the team will use the experience gained in operating Rosetta in the challenging cometary environment to carry out some new and potentially slightly riskier investigations, including flights across the night-side of the comet to observe the plasma, dust, and gas interactions in this region, and to collect dust samples ejected close to the nucleus.

As the comet recedes from the Sun, the solar-powered spacecraft will no longer receive enough sunlight to operate efficiently and safely, equivalent to the situation in June 2011 when the spacecraft was put into hibernation for 31 months for the most distant leg of its journey out towards the orbit of Jupiter.

In addition, Rosetta and the comet will again be close to the Sun as seen from the Earth in October 2016, making operations difficult by then.

However, with Rosetta’s propellant largely depleted by that time, it makes little sense to place the spacecraft in hibernation again.

“This time, as we’re riding along next to the comet, the most logical way to end the mission is to set Rosetta down on the surface,” says Patrick Martin, Rosetta Mission Manager.

“But there is still a lot to do to confirm that this end-of-mission scenario is possible. We’ll first have to see what the status of the spacecraft is after perihelion and how well it is performing close to the comet, and later we will have to try and determine where on the surface we can have a touchdown.”

If this proposed scenario were played out, then the spacecraft would be commanded to spiral down to the comet over a period of about three months.

It is expected that science operations would continue throughout this period and be feasible up to very close to the end of mission, allowing Rosetta’s instruments to gather unique data at unprecedentedly close distances.

Once the orbiter lands on the surface, however, it is highly unlikely to be able to continue operations and relay data back to Earth, bringing to an end one of the most successful space exploration missions of all time.

http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_mission_extended

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 Rosetta’s MIRO Instrument Maps Comet Water

This image, by the Rosetta navigation camera, was taken from a distance of about 53 miles (86 kilometers) from the center of Comet 67P/Churyumov-Gerasimenko on March 14, 2015. The image has a resolution of 24 feet (7 meters) per pixel and is cropped and processed to bring out the details of the comet’s activity.

Since last September, scientists using NASA’s Microwave Instrument for Rosetta Orbiter (MIRO) on the European Space Agency’s Rosetta spacecraft have generated maps of the distribution of water in the coma of comet 67P/Churyumov-Gerasimenko, as the comet’s orbit brings it closer to the sun.

MIRO is able to detect water in the coma by measuring the direct emission from water vapor in the coma and by observing absorption of radiation from the nucleus at water-specific frequencies as the radiation passed through the coma.

For the rest of the article, click here:
http://www.nasa.gov/feature/rosettas-miro-instrument-maps-comet-water

Comet update / images

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Comet 67P, Rosetta

Images of Comet 67P/Churyumov-Gerasimenko taken from the Rosetta spacecraft:

Excerpt from update 20 April 2015:

The comet’s activity has been significantly increasing over the last weeks and months.

As the comet moves closer to the Sun along its orbit, its nucleus gets warmer and warmer. Frozen gases sublimate from its surface, carrying dust particles with it and enshrouding the nucleus in a dense coma.

With only four months to go until perihelion – the closest point to the Sun – this process is well underway, with pronounced dust jets seen at all times on the comet’s day side.

Montage of images:

The 13 April 2015 CometWatch entry is dedicated to Comet 67P/C-G’s activity – this stunning montage of images is showcased as our ‘Space Science Image of the Week’.

Visit the site below for more information and remarkable images.

http://blogs.esa.int/rosetta/2015/04/13/cometwatch-activity-31-january-25-march/