‘Seven hours of terror’ to comet fall
A man-made object will land on a comet for the first time later on Wednesday, if the European Space Agency’s Philae probe can negotiate a perilous seven-hour descent from its Rosetta mother ship on to the irregular nucleus of Comet 67P.
The washing-machine-sized Philae left Rosetta on Wednesday morning. Confirmation of the successful separation was received at the control centre in Darmstadt shortly after 9am GMT. The radio signal had taken 28 minutes to travel 511m km back to earth.
ESA scientists have dubbed Philae’s descent to the comet “seven hours of terror” – an echo of the “seven minutes of terror” endured by their Nasa counterparts before the successful landing of the Curiosity rover on Mars in 2012.
If anything, the Philae landing will be even more perilous. While Curiosity dropped on to a relatively smooth Martian surface, Philae has to land on a duck-shaped lump of ice, dust and rock just 4km wide, strewn with boulders and shooting out unpredictable jets of gas.
Some problems were detected during the final check before separation but the team decided to go ahead anyway. “The cold gas thruster on top of the lander does not appear to be working so we will have to rely fully on the harpoons [to anchor it to the surface] at touchdown,” said Stephan Ulamec, Philae lander manager. “We’ll need some luck not to land on a boulder or a steep slope.”
The €1.3bn Rosetta mission achieved its first big feat in August after the spacecraft entered orbit around the comet – full name 67P/Churyumov-Gerasimenko – as it hurtled toward the sun at 55,000km per hour. The Rosetta spacecraft has covered 6.5bn km in a 10-year voyage from Earth.
Soon after 4pm GMT, all being well, mission scientists will receive confirmation that Philae has landed and secured itself to the cometary surface with ice screws and a pair of harpoons. Anchoring is needed because 67P’s gravitational pull is too weak to hold it firmly in place. Its first images of the surface should arrive minutes later.
The biggest uncertainty is how actively 67P will be shooting out gas and dust as Philae descends. “A sudden increase in activity could affect the . . . exact location where Philae will land,” said Andrea Accomazzo, Rosetta flight director. “That’s what makes this a risky operation.”
Philae will start scientific investigations of the comet as soon as it is in place. Various instruments will look at the physics and chemistry of the surface, while drills extract subsurface samples and deliver them to the probe’s onboard laboratory for further analysis.
Scientists are looking forward eagerly to the results because cometary material is believed to have changed little since the formation of the solar system 4.5bn years ago.
For instance, a comparison of the chemical signature of the ice on 67P and the water in Earth’s oceans will provide new evidence about the origins of terrestrial water – how much was delivered by comets bombarding the young planet and how much came from the Earth’s interior.
Although the initial science phase will last for just three days – the lifetime of Philae’s primary batteries – mission scientists hope its solar panels will enable it to study the change in conditions as it approaches the sun, heating up and becoming ever more active.
Rosetta’s celestial journey
March 2004 – Rosetta’s expedition begins with launch from Kourou in French Guiana. The three-tonne spacecraft is first inserted into a parking orbit before being sent towards the outer Solar System.
March 2005 – The spacecraft re-encounters Earth in a manoeuvre that accelerates the spacecraft using planetary gravity, the first of four planet ‘fly-bys’.
February 2007 – Rosetta flies 250km above the surface of Mars and loses contact with Earth for 37 minutes as it goes behind the shadow of the red planet in a risky manoeuvre dubbed “The Billion Euro Gamble”.
November 2007 – During a second Earth fly-by the spacecraft is briefly designated as a minor planet due to it being misidentified as an asteroid.
November 2009 – Rosetta passes by Earth for the last time, using the planet’s gravitational pull in a “slingshot effect” to propel itself further along its 6.5bn km journey.
May 2011 – After passing by the asteroid belt and performing a large deep-space manoeuvre, the spacecraft goes into hibernation, reaching a maximum distance from the Earth of 1bn km.
May 2014 – After waking up from deep space hibernation at the start of the year, Rosetta’s thrusters begin to brake so the spacecraft can match Comet 67P/Churyumov-Gerasimenko’s speed and orbit.
November 2014 – Four months after entering into 67P’s orbit, Rosetta is scheduled to make history by sending its robotic lander Philae on to the comet’s surface.
Source - http://www.ft.com/intl/cms/s/0...4feabdc0.html#slide0