Philae makes historic landing on a comet!

[Peter Lemkin]

Rosetta mission: Philae makes historic landing on comet

The Philae lander travelling towards the comet, in a picture taken by the Rosetta spacecraft. Photograph: Handout/Reuters

The signal broke a seven-hour wait of agonising intensity and sparked scenes of jubilation at the European Space Agency's mission control in Darmstadt. The team in charge of the Rosetta mission had achieved what at times seemed an impossible task by landing a robotic spacecraft on a comet for the first time in history.
The safe landing gives scientists their first chance in history to ride a comet and study close up what happens as its activity ramps up as it gets closer to the sun.
The feat marks a profound success for ESA, which launched the Rosetta spacecraft more than 10 years ago from its Kourou spaceport in French Guiana. Since blasting off in March 2004, Rosetta and its lander Philae have travelled more than six billion kilometres to catch up with the comet which orbits the sun at speeds up to 135,000km/h.
The moment came shortly after 1600 GMT when Philae called home. It had fired harpoons to secure itself on the comet and twisted in ice screws fitted to its feet. "We are there, we are sitting on the surface," said a jubilant Stephan Ulamec, Philae lander manager at the DLR German Space Centre.
Andrea Accomazzo, Rosetta flight operations director, said: "We cannot be happier than we are now."
Touch down for the lander played out 510 million kilometres from Earth on a comet hurtling through space at 18km/s. At so vast a distance, even radio signals travelling at the speed of light take nearly half an hour to travel from Earth to the spacecraft, making realtime control of the landing impossible. Instead, the entire descent was precalculated, uploaded and run automatically.
The £1bn mission, named after the Rosetta stone which enabled scholars to decipher the language of ancient Egypt, aims to unlock the mysteries of comets made from material predating the birth of the solar system. In the data Rosetta and Philae gather, researchers hope to find answers to questions of how the solar system formed and whether comets carried water and even complex organic molecules to planets, preparing the stage for life on Earth.
Landing Philae on the comet's surface was never going to be easy. When ESA managers got their first closeup of the comet in July, its unusual rubber duck shape left some fearing that a safe touchdown was impossible. The shape was not the only problem. The comet's surface was hostile: hills and spectacular jutting cliffs gave way to cratered plains strewn with boulders. If Philae landed on anything other than even ground it could topple over leaving it stranded and defunct.
Rosetta spent weeks flying around the comet to create a surface map from which mission controllers could choose a landing site. They faced a trade-off: the site had to be fairly flat and clear of boulders, but with a good view of the whole comet and plenty of sunlight to charge the lander's batteries once down. From a shortlist of five potential landing spots, scientists and engineers unanimously voted for a 1 sq km region on the comet's "head" later named Agilkia.
At the start of the mission, ESA officials assumed the comet would be potato shaped and rated their chances of a successful landing at 75%. After seeing the shape and terrain of their target close up, those odds fell to around 50%, but climbed again as technical staff learned more about the landing site.
The confidence did not last long though. On Tuesday night, hours before Philae had left its mother ship, the chances of a safe landing took another dip. Overnight, a thruster on the lander failed to respond to commands sent from Earth. Engineers tried for hours to correct the fault but to no avail. The malfunction threatened to abort the mission, but at 0235 GMT on Wednesday mission controllers decided to go ahead with the landing regardless.
The nitrogen thruster, facing upwards from the top of the lander, was designed to fire for 60 seconds as Philae touched down to prevent it from bouncing off the comet's surface where the gravitational pull is several hundred thousand times weaker than on Earth.
For the mission team, the seven-hour descent, during which Philae fell at walking speed towards the comet's surface, was a nail-biting experience. The lander separated from its mothership at 0835 GMT with confirmation received on Earth at 0903. For the early part of the 20km descent, Philae was expected to be out of contact with Rosetta. Around 1100 GMT the mother ship reacquired a signal from the lander, which duly unfurled its legs and began to take pictures. The first image taken just 50 seconds after separation revealed a look back at the mother ship, one of its 14m-long solar arrays clearly visible, as Philae fell silently to its destination.
One hour from touchdown, Philae was on the right course. Ulamec of the DLR German Space Centre said everything looked "fantastic". Telemetry from the lander showed that it was rotating, but not enough to cause problems.
From its orbit around the comet, the Rosetta probe will take more high-resolution images and gather information on the body's density, temperature and chemical make-up. It will also capture dust and gas released in ever more violent jets from the comet's nucleus as it nears the sun.
Secured on the surface, the lander can drill down 20cm and collect samples of subsurface material for on-the-spot testing. On board Philae are 10 instruments, including one from the Open University named Ptolemy which will bake pieces of comet material and analyse the gases given off to build up a picture of the comet's composition. Another instrument, the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT), will reveal the comet's internal structure by passing radio waves through the icy body to Rosetta on the other side.
The Rosetta mission is planned to run until December 2015, but if enough fuel remains in the spacecraft's tanks, mission controllers may extend its life by six months and give the mother ship more high-risk tasks, such as flying through one of the gas and dust jets streaming from the comet. Philae has initial battery power to last 40 hours but will then switch to rechargeable ones replenished by sunlight.
The lander could continue working until March next year, when the electronics will become too warm to work properly. Even when Philae packs up, it may still cling on to the comet, perhaps for several 6.45-year-long laps around the sun, before enough material erodes from the comet's surface for the lander to lose its grip.

[Peter Lemkin]

In a few hours there will new photos from the surface...but here is close up of the landing location.

[Lauren Johnson]

The harpoons did not fire and the lander as yet is not secured to the comet. Re-firing the harpoons could cause the lander to fly back into space.

[Peter Lemkin]

The harpoons did not fire and the lander as yet is not secured to the comet. Re-firing the harpoons could cause the lander to fly back into space.

They think that may be the situation - not totally clear yet. Also, there have been some telemetry problems - but they are not yet worried about them. I imagine they'll find a way...maybe firing the harpoons one at a time, rather than all at once - or some other variant. Without the harpoons it should still be able to do a lot of science - but not as much as with - and not for as long a time......

It is really amazing. I've been trying to watch the livestream on Livestream or ESA's website, but nearly a million people are also trying to watch and the signal is not forthcoming live...but I've been able to watch some minutes later at all that has happened. The craft on the comet has supposedly taken some photos, but they haven't requested they be sent yet, as they are using the bandwidth for the other problems right now. It looks like a battered multi-scoop icecream.

One can find many amazing photos on the ESA website HERE. Sadly, most of them are too large to upload here...but I'll try to upload a few.

[Lauren Johnson]

I watched the last press briefing of the day. The preliminary theory is that when the harpoons did not fire, the land gently bounced back in the air and may have tumbled. Now they think it is back on the surface. Right now it is speculation by the controllers as they continue to analyze data.

[Peter Lemkin]

I watched the last press briefing of the day. The preliminary theory is that when the harpoons did not fire, the land gently bounced back in the air and may have tumbled. Now they think it is back on the surface. Right now it is speculation by the controllers as they continue to analyze data.

As long as it is upright and/or not damaged it still should be good for the mission.....we wait to hear!.....

[Lauren Johnson]

I watched the last press briefing of the day. The preliminary theory is that when the harpoons did not fire, the land gently bounced back in the air and may have tumbled. Now they think it is back on the surface. Right now it is speculation by the controllers as they continue to analyze data.

As long as it is upright and/or not damaged it still should be good for the mission.....we wait to hear!.....

I don't think they can do any work under the surface unless attachment is secure. Hopefully it is at least upright and other science can be completed. Yah, wait and see.

[Magda Hassan]

It is an amazing and wondrous thing watching the comet landing but I think there is so much to do here too.

[Peter Lemkin]

Rosetta mission controllers must decide whether to risk making lander hop from shadow of cliff blocking sunlight to its solar panels

Rosetta mission's Philae lander: follow latest developments

• 
  

• Ian Sample and Stuart Clark in Darmstadt
  
  
• The Guardian, Thursday 13 November 2014 18.30 GMT
  

How Esa scientists believe Philae has landed on the comet on its side. Photograph: European Space Agency/Reuters

The robotic lander that touched down on a comet on Wednesday came to rest on its side in the shadow of a cliff, according to the first data beamed home from the probe.
Pictures from cameras on board the European Space Agency's Philae lander show the machine with one foot in the sky and lodged against a high cliff face that is blocking sunlight to its solar panels.
The precarious resting place means mission controllers are faced with some tough decisions over whether to try and nudge the spacecraft into a sunnier spot. If successful, that would allow Philae to fully recharge its batteries and do more science on the comet, but any sudden move could risk toppling the lander over, or worse, knock it off the comet completely.
The washing machine-sized lander was released by its Rosetta mother ship at 0835am GMT on Wednesday morning and touched down at a perfect spot on the comet's surface. But when anchoring harpoons failed to fire, the probe bounced back off into space. So weak is the gravitational pull of the comet that Philae soared 1km into the sky and did not come down again until two hours later. "We made quite a leap," said Stephan Ulamec, the Philae lander manager.
In the time it took the probe to land for the second time, the comet had rotated, bringing more treacherous terrain underneath. The spacecraft bounced a second time and finally came to a standstill on its side at what may be the rim of an enormous crater. Technically, the agency pulled off not only the first landing on a comet in history, but the second and third too.
"We bounced twice and stopped in a place we've not entirely located," said Jean-Pierre Bibring, Philae's lead scientist. Teams of scientists are now trying to work out where the probe is. What mission controllers do know is that they are not where they hoped to be. "We are exactly below a cliff, so we are in a shadow permanently," Bibring added.
Space lander sends first image of landing video With most of Philae in the dark, the lander will receive only a fraction of the solar energy that Esa had hoped for. The spacecraft needs six or seven hours of sunlight a day but is expected to receive just one and a half. Though it can operate for 60 hours on primary batteries, the probe must then switch to its main batteries which need to be recharged through its solar arrays. If Philae's batteries run out it will go into a hibernation mode until they have more power.
The spacecraft was designed with landing gear that could hop the probe around, but from its awkward position on its side the option is considered too risky.
Though caught in a tight spot, the Philae lander's systems appear to be working well. The Rosetta spacecraft picked up the lander's signal on Thursday morning and received the first images and more instrument data from the surface of the comet.
One of Philae's major scientific goals is to analyse the comet for organic molecules. To do that, the lander must get samples from the comet into several different instruments, named Ptolemy, Cosac and Civa. There are two ways to do this: sniffing and drilling. Sniffing involves opening the instruments to allow molecules from the surface to drift inside. The instruments are already doing this and returning data.
Panoramic view around the point of Philae's final touchdown on the surface of comet 67P, taken when Rosetta was about 18km from centre of comet. Parts of Philae's landing gear can be seen in this picture. Photograph: European Space Agency/AFP/Getty Images Drilling is much riskier because it could make the lander topple over. Newton's third law of motion says that for every action there is an equal and opposite reaction. In the minuscule gravity of the comet, any movement on Philae will cause motion. The drill turning one way will make Philae want to turn the other. Pushing down into the surface will push the lander off again. "We don't want to start drilling and end the mission," said Bibring.
But the team has decided to operate another moving instrument, named Mupus, on Thursday evening. This could cause Philae to shift, but calculations show that it would be in a direction that could improve the amount of sunlight falling on the probe. A change in angle of only a few degrees could help. A new panoramic image will be taken after the Mupus deployment to see if there has been any movement.
Meanwhile, the Rosetta orbiter team will continue to try to pinpoint Philae's position. This will be done with images from the mother ship's Osiris wide-angle camera and its Concert radar instrument. The Concert instrument communicates with Philae and is designed to beam radar through the interior of the comet to reveal the internal structure. When Rosetta is directly overhead, Concert can also help to pinpoint the lander's position. "When we see where we are, we can decide what to do next," said Bibring.
But time is tight, the first 24 hours of the battery life will soon be gone. It is expected to be completely drained sometime on Saturday. "We are running against the clock," admits Bibring, "Don't put the emphasis on failure, it is gorgeous where we are."

[Magda Hassan]

Might as well risk it. The batteries will get flat pretty soon if the panels cannot collect light then they wont be able to move anyway and will lose all their data too.