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Humans have never landed anything on a comet's surface. That may change tomorrow.

The European Space Agency's Rosetta mission is poised to send out a small probe to land on a comet known as 67P/Churyumov-Gerasimenko. Rosetta spent 10 years chasing the comet before arriving in August.

Catching up with 67P in time to watch it swing around the sun is an achievement, but Karl Battams, a researcher at the Naval Research Laboratory, says scientists want to do more. "I think it's kind of part of human nature to go up to something and touch it," he says.

And that's where Rosetta's refrigerator-sized lander comes in. Known as Philae, it will attempt to float down to the comet's surface and make contact. "It's our remote hands," Battams says.

Strictly speaking, scientists have made contact with a comet before.

In 2005, a NASA probe called Deep Impact slammed into a comet's surface. But the spacecraft was destroyed in the process.

This time, the lander will attempt to gently touch down at about walking speed. That won't be easy. "There are some very steep cliffs, there are huge boulders," Battams says. "It's truly an alien landscape"

The landscape of 67P came as a surprise to those who built the probe.

"We expected some more-or-less-roundish potato shape," says Stephan Ulamec, from Germany's aeronautics and space agency, DLR, and the lander's project manager.

That view held right up until midsummer, when the comet started coming into focus. Instead of a potato, researchers saw a bizarre, two-lobed structure peppered with cliffs, boulders and craters.

"The more we saw the terrain and how rough the terrain is, we saw, of course, this is an extremely difficult target to land on," Ulamec says.
They're not even sure what the ground is like. It might be hard, or it might be soft and sandy.

And that's why this lander comes with harpoons.

"We've chosen these harpoons for anchoring because they would work in hard material just like in soft material," Ulamec says.
Moments after its feet touch down, the harpoons will fire, along with some thrusters to keep the lander grounded. Then screws in the feet will try to get a grip.

It's a good plan, but only if the lander comes down on a flat spot. Philae is designed to hold its ground on an impressive 30-degree grade, but it could hit a cliff or a boulder, says Hermann Böhnhardt of the Max Planck School for Solar System Science.

The spacecraft is nearly 30 light-minutes from Earth, so controllers can't steer. They simply must let it fall. "We need quite a bit of luck [to have] a successful landing in the end," he says.

If it is successful, Battams says, the lander will provide a wealth of scientific knowledge.

"It sounds basic, but they're going to stick a thermometer on the surface of the comet and say, 'Hey, how hot is the surface of a comet?' " he says.

The lander will also drill into 67P, check it for seismic activity, and work with the Rosetta spacecraft to create an image of the interior. Plus, it should deliver some amazing photos.

The descent will take seven hours. Battams says the wait will be excruciating: "There's going to be a lot of sweaty palms, and tapping of fingers on desks, like, 'Well, did it, did it, did it?' "
12 November 2014
ESA’s Rosetta mission has soft-landed its Philae probe on a comet, the first time in history that such an extraordinary feat has been achieved.

After a tense wait during the seven-hour descent to the surface of Comet 67P/Churyumov–Gerasimenko, the signal confirming the successful touchdown arrived on Earth at 16:03 GMT (17:03 CET).

The confirmation was relayed via the Rosetta orbiter to Earth and picked up simultaneously by ESA’s ground station in Malargüe, Argentina and NASA’s station in Madrid, Spain. The signal was immediately confirmed at ESA’s Space Operations Centre, ESOC, in Darmstadt, and DLR’s Lander Control Centre in Cologne, both in Germany.

The first data from the lander’s instruments were transmitted to the Philae Science, Operations and Navigation Centre at France’s CNES space agency in Toulouse.

“Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet’s surface,” noted Jean-Jacques Dordain, ESA’s Director Gene

“With Rosetta we are opening a door to the origin of planet Earth and fostering a better understanding of our future. ESA and its Rosetta mission partners have achieved something extraordinary today.”

“After more than 10 years travelling through space, we’re now making the best ever scientific analysis of one of the oldest remnants of our Solar System,” said Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

“Decades of preparation have paved the way for today’s success, ensuring that Rosetta continues to be a game-changer in cometary science and space exploration.”

“We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander,” said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

“In the next hours we’ll learn exactly where and how we’ve landed, and we’ll start getting as much science as we can from the surface of this fascinating world.”

Rosetta was launched on 2 March 2004 and travelled 6.4 billion kilometres through the Solar System before arriving at the comet on 6 August 2014.

“Rosetta’s journey has been a continuous operational challenge, requiring an innovative approach, precision and long experience,” said Thomas Reiter, ESA Director of Human Spaceflight and Operations.

“This success is testimony to the outstanding teamwork and the unique knowhow in operating spacecraft acquired at the European Space Agency over the decades.”

The landing site, named Agilkia and located on the head of the bizarre double-lobed object, was chosen just six weeks after arrival based on images and data collected at distances of 30–100 km from the comet. Those first images soon revealed the comet as a world littered with boulders, towering cliffs and daunting precipices and pits, with jets of gas and dust streaming from the surface.

Following a period spent at 10 km to allow further close-up study of the chosen landing site, Rosetta moved onto a more distant trajectory to prepare for Philae’s deployment.

Five critical go/no-go decisions were made last night and early this morning, confirming different stages of readiness ahead of separation, along with a final preseparation manoeuvre by the orbiter.

Over the next 2.5 days, the lander will conduct its primary science mission, assuming that its main battery remains in good health. An extended science phase using the rechargeable secondary battery may be possible, assuming Sun illumination conditions allow and dust settling on the solar panels does not prevent it. This extended phase could last until March 2015, after which conditions inside the lander are expected to be too hot for it to continue operating.

Science highlights from the primary phase will include a full panoramic view of the landing site, including a section in 3D, high-resolution images of the surface immediately underneath the lander, on-the-spot analysis of the composition of the comet’s surface materials, and a drill that will take samples from a depth of 23 cm and feed them to an onboard laboratory for analysis.

The lander will also measure the electrical and mechanical characteristics of the surface. In addition, low-frequency radio signals will be beamed between Philae and the orbiter through the nucleus to probe the internal structure.

The detailed surface measurements that Philae makes at its landing site will complement and calibrate the extensive remote observations made by the orbiter covering the whole comet.

“Rosetta is trying to answer the very big questions about the history of our Solar System. What were the conditions like at its infancy and how did it evolve? What role did comets play in this evolution? How do comets work?” said Matt Taylor, ESA Rosetta project scientist.

“Today’s successful landing is undoubtedly the cherry on the icing of a 4 km-wide cake, but we’re also looking further ahead and onto the next stage of this ground-breaking mission, as we continue to follow the comet around the Sun for 13 months, watching as its activity changes and its surface evolves.”

While Philae begins its close-up study of the comet, Rosetta must manoeuvre from its post-separation path back into an orbit around the comet, eventually returning to a 20 km orbit on 6 December.

Next year, as the comet grows more active, Rosetta will need to step further back and fly unbound ‘orbits’, but dipping in briefly with daring flybys, some of which will bring it within just 8 km of the comet centre.

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 it throughout the remainder of 2015, as they head away from the Sun and activity begins to subside.

“It’s been an extremely long and hard journey to reach today’s once-in-a-lifetime event, but it was absolutely worthwhile. We look forward to the continued success of the great scientific endeavour that is the Rosetta mission as it promises to revolutionise our understanding of comets,” said Fred Jansen, ESA Rosetta mission manager.

Deployment was confirmed at 09:03 GMT (10:03 CET) at a distance of 22.5km from the centre of the comet. During the seven-hour descent, which was made without propulsion or guidance, Philae took images and recorded information about the comet’s environment.

“One of the greatest uncertainties associated with the delivery of the lander was the position of Rosetta at the time of deployment, which was influenced by the activity of the comet at that specific moment, and which in turn could also have affected the lander’s descent trajectory,” said Sylvain Lodiot, ESA Rosetta Spacecraft Operations Manager.

“Furthermore, we’re performing these operations in an environment that we’ve only just started learning about, 510 million kilometres from Earth.”

Touchdown was planned to take place at a speed of around 1 m/s, with the three-legged landing gear absorbing the impact to prevent rebound, and an ice screw in each foot driving into the surface.

But during the final health checks of the lander before separation, a problem was detected with the small thruster on top that was designed to counteract the recoil of the harpoons to push the lander down onto the surface. The conditions of landing – including whether or not the thruster performed – along with the exact location of Philae on the comet are being analysed.

The first images from the surface are being downlinked to Earth and should be available within a few hours of touchdown.
November 2014 may well be remembered as the time when humanity first landed a robotic probe on the nucleus of a comet.

Fittingly, the mission that accomplished this remarkable feat is called "Rosetta." In 1799, French soldiers discovered an ancient Egyptian tablet, inscribed in 196 BC with writing in three different languages. Ultimately, this script on the Rosetta Stone, in combination with writing on an obelisk on the Nile River island of Philae, helped to unlock understanding of Egyptian hieroglyphs. This writing told of a far more ancient Egypt.

Similarly, the modern-day creators of the Rosetta mission hope its exploration will unlock comets -- ancient nuclei of rock and ices that are keys to understanding the formation of our solar system.

Scientists also hope the mission will provide an insight into Earth's earliest years. Comets bombarded the young Earth. Did they bring with them much of the water that still exists on our home planet, as well as the organic molecules that life needed in order to arise on Earth?

November 2014 is significant for another reason -- the SETI Institute will celebrate its 30th birthday on November 20. Why is this relevant to the Rosetta mission? The SETI Institute's mission is to explore, understand, and explain the origin and nature of life in the universe. In many ways, the SETI Institute's goal is the same as Rosetta's -- but on a much larger stage.

The word "life" for a researcher at the SETI Institute can be anything from a single-celled organism to a technological life form far more advanced than humans.

It is the latter life form -- extraterrestrial intelligence -- that people typically associate with the SETI Institute. And the search for such intelligence stands in remarkable parallel to the spirit of Rosetta.

Just as the discovery and study of the Rosetta Stone aided understanding of ancient Egypt, the detection and study of evidence from another technological civilization would place our own in a universal context. It could even give us a look into the future of our own species.

Daily news reports tell of potential disaster that could befall civilization, be it in the form of global warming, a rapidly mutating virus, or an impact by a cousin of the very object that Philae will land on. Finding concrete evidence that technological societies have survived long-term elsewhere would be reassuring, even inspirational.

While searches for signs of intelligent life have been ongoing for more than three decades with no detection, we have barely scratched the surface of such a quest. There are several hundred billion stars in our galaxy, and a similar number of galaxies in the known universe, all containing their own billions of stars.

Recent results from the Kepler mission have shown that between 10 and 20% of our neighborhood's stars have planets that could be habitable.

To date, our searches for the intelligent life that might have grown up around those stars amounts to one scoop of sand compared to all of the sand on all of the beaches in the world. Be not discouraged by lack of detection to date. We must dig deeper and more thoroughly.

However, the SETI Institute researchers search for more than just the endgame intelligent life. They also work to fill in all gaps in the story of life, its origins, and its evolution. While the discovery of intelligent life elsewhere in the universe is similar to the end of a well-written novel, appreciation of that ending is greatly enhanced when you read the other chapters in the book.

To write those chapters, SETI researchers study extremophile life forms on this planet -- organisms that live beneath ice-covered lakes in Antarctica, inside the hot springs of Yellowstone in the United States, and in the high-elevation deserts of Chile. These studies inform us about whether life likely arose on other, less hospitable planets, how to recognize that life, and how life here has evolved.

Institute scientists also investigate whether strange life may inhabit other nearby worlds. Imagine finding biology on Saturn's moon Titan, with its lakes of methane. Such life would indeed be very different from what we're used to. Its discovery would throw open the window of possibilities for biological beings elsewhere.

How often does life make the leap from microbe to intelligence?

Evidence now indicates that the basic building block of intelligence emerged on this planet some billion years ago, with increasingly intelligent life being present in the intervening years.

Institute researchers study how non-human intelligent life on Earth communicates, hoping to grasp the fundamental elements of communication -- those we might find in the "languages" of extraterrestrial communicators -- both within and across species.

We are just beginning to understand and appreciate the levels and variety of intelligence that exist on this planet, and the myriad ways that other animals can and do communicate. Institute scientists play a key role in these fields, seeking both to understand the evolution of Earthly intelligence and to grasp the daunting complexity of how we might recognize and understand a message from beyond our planet.

However, public funding for science education programs, while steady in magnitude, is inadequate for the task. Government funding of space exploration is also in jeopardy.

But it's these things -- engaging science teachers, iconic images of manned space missions on TV -- that inspire young people to thirst for knowledge of the universe around us, and to enter into scientific fields of research and study.

As such, one of our main missions at the SETI Institute is to help educate the public and to instil a vigor for knowledge and exploration in the youth. Inspiring the next generation of scientific thinkers and explorers is paramount to our mission and our work.

I believe that not only will the Rosetta mission help us understand where we come from and what our history is, but also help in inspiring a new generation to follow in the footsteps of Carl Sagan and Frank Drake.

As we all celebrate the success of the Rosetta mission, those of us at the SETI Institute will continue into the fourth decade of the Institute's existence in pursuit of our mission -- understanding the origin of life on this planet and finding evidence of it on other worlds.
European Space Agency controllers will not give up on Philae.

They will continue to listen for the little probe in the days ahead, hopeful that it will somehow become active again.

On each pass overhead, the Rosetta satellite will try to detect and lock on to any sort of blip being transmitted from below.

The mission has faced up to the odds before, and won. It bounced and probably scraped across the surface during its historic touchdown on Wednesday.

Philae survived all that. People will now want to believe it can hunker down in the darkness and ride out its present predicament.

It would be very useful to know where exactly the probe is right now on the surface of Comet 67P.

This would give controllers a better sense of whether it is ever likely to come back to life.

The robot's own pictures show it to be rammed up against walls that throw a deep shadow over its solar panels for most of 67P's 12-hour day.

But the conditions that currently prevent Philae from charging its batteries could change.

It is not inconceivable that as the comet moves in closer to the Sun, the amount of light made available to the probe will increase, in amount and in intensity.

There could be structural changes on the comet, too. Obstructions that look hard and imposing today could crumble in time as 67P warms and becomes more active.

The jets of gas and dust that are generated as the comet's internal ices are heated could disturb the robot in such a way that it is bumped to a more favourable lighting location.

For sure, Philae will be very cold in the long nights it is experiencing, but the assessment of the thermal status of the probe is encouraging. It can survive.

If this is the last we hear from the robot, history will be very quick to judge this mission as an astonishing success.

Yes, the robot had some systems failures in its landing mechanisms, but it would be churlish in the extreme to dwell on these shortcomings.

The robot delivered almost 100% of its primary goals, returning the first-ever pictures and other science data from the surface of a comet.

And it has been a blast. This past week's events really caught the world's attention.

So how about we do it again? This is the dream certainly of many who control Philae's mothership, Rosetta.

It will continue to orbit and observe 67P for at least another year, but after that there is a desire to put the satellite on the surface of the comet as well.

"I would like to land on the surface of the comet with the full spacecraft - definitely," says European Space Agency flight director Andrea Accomazzo.

"In the end, we can design an approach trajectory to the comet. We just slow down the spacecraft and it falls on to the comet.

"The touchdown will not be as soft as the lander. There's no landing gear; the spacecraft would be mechanically damaged. But we can do it."

And Paolo Ferri, Esa's head of mission operations, added: "We would plan such a manoeuvre so that we could follow Rosetta down to the surface. But once it touches down, we cannot control anymore the attitude. So, the antenna will not be pointing to the right direction.

"We would lose the contact when it touches down, but we would still be able to control it down to the last metre, to get signal, measurements and pictures. It would be spectacular. That's the right way to die."

You can hear more from Accomazzo and Ferri in the BBC Radio 4 Frontiers special we recorded from mission control on Wednesday night - if you haven't already caught the programme.

And there'll be a special Sky At Night edition dedicated to Philae's exploits on BBC Four television this Sunday at 2100 GMT
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