Earth severs link with comet probe

Farewell to silent Philae

PARIS, July 27, (Agencies): Earth bid a final farewell to robot lab Philae on Wednesday, severing communications after a year-long silence from the pioneering probe hurtling through space on a comet.

Writing an extraordinary chapter in space history, the washing machinesized craft was the first to land on a comet — primeval rubble from the formation of the Solar System.

Philae sent home reams of data garnered from sniffing, tasting and prodding its new alien home hundreds of millions of kilometres (miles) from Earth.

Its plucky exploits captured the imagination of children, and many adults, who followed its successes and tribulations via Twitter and an animated cartoon series.

But after more than 12 months without news, it was decided to preserve all remaining energy available to Philae’s orbiting mothership Rosetta, the European Space Agency (ESA) announced in a blog entitled: “Farewell, silent Philae”.

Rosetta will remain in orbit around comet 67P/Churyumov-Gerasimenko for another two months.

It will crashland on September 30 to join Philae in their final resting place, concluding an historic quest for cometary clues to the origins of life on Earth.

Communication

“Today communication with Philae was stopped,” Andreas Schuetz of German space agency DLR told AFP from ground control in Cologne on Wednesday.

“This is the end of a ... fascinating and successful mission for the public and for science.”

Part of a 1.3-billion-euro ($1.4-billion) ESA mission, Philae was launched into space in March 2004, riding piggyback on Rosetta.

The pair travelled some 6.5 billion km (four billion miles) — aided by gravity boosts from Earth and Mars — before entering 67P’s orbit in August 2014.

Three months later, Rosetta sent the 100-kilogramme (220-pound) probe down to the comet surface — starting a nail-biting deep-space saga.

Philae’s harpoons failed to fire into the comet surface, and it bounced several times.

The tiny robot ended up in a ditch shadowed from the Sun’s batteryreplenishing rays, but managed to run about 60 hours of experiments and send home valuable data before entering standby mode.

As 67P neared the Sun on its elongated orbit, Philae got a battery boost and emerged from hibernation in June 2015, sending a two-minute message via Rosetta, eliciting great excitement on Earth.

But after eight intermittent communications, the lander fell permanently silent on July 9, 2015.

Rosetta has continued to monitor the comet, but without catching sight of its long-lost charge, even from as close as 10 km away.

In February, ground controllers said they believed Philae was in eternal hibernation — though they opted to keep an ear open just in case.

Wednesday’s final break, at 0900 GMT, means “abandoning all hope of receiving anything more from Philae,” said Philippe Gaudon of France’s CNES space agency.

“It’s time for me to say goodbye,” said Philae’s Twitter account, announcing communications “will be switched off forever...”

As the comet moves further and further away from the Sun — some 520 million km by end July — Rosetta needs to save energy for her final weeks.

“We need to maximise the power available to Rosetta’s scientific instruments, and thus had no choice but to turn off the ESS,” ESA senior science advisor Mark McCaughrean told AFP.

The ESS is the Electrical Support System on board Rosetta, used to send home the results of Philae’s science experiments and status reports.

Dwindle

“The power will only dwindle further, and so now the focus turns fully to Rosetta, whose amazingly succesful scientific mission will come to an end on 30 September,” said McCaughrean.

“Everyone involved will be extremely sad, of course, but equally enormously proud of what has been achieved by this unique space mission.”

Scientists will be busy for years analysing the data sent back by Philae and Rosetta.

Comets are deemed to be balls of primitive dust and ice left from the early years of the Solar System.

Their makeup interests scientists who speculate that comets may have seeded Earth — possibly other planets as well — with the ingredients for life.

The Rosetta probe will be crashlanded on Comet 67P on Friday 30 September, the European Space Agency has confirmed.

The manoeuvre, which is expected to destroy the satellite, will bring to an end two years of investigations at the 4km-wide icy dirt-ball.

Flight controllers plan to have the cameras taking and relaying pictures during the final descent.

Sensors that “sniff” the chemical environment will also be switched on.

All other instruments will likely be off.

Flight dynamics experts

have still to work out the fine details, but Rosetta will be put into a tight ellipse around the comet and commanded to drop its periapsis (lowest pass) progressively. A final burn will then put the satellite on a collision course with the duckshaped object.

Mission managers have previously talked about bringing Rosetta down in a place dubbed “Agilkia” — the location originally chosen to land its surface robot, Philae, in November 2014.

In the event, Philae bounced a kilometre away, but Agilkia’s relatively flat terrain is an attractive option still, although other targets are being studied.

Having swept around the Sun last August, Comet 67P is currently on a trajectory that is taking it away from the inner Solar System towards the orbit of Jupiter.

Today, the probe is nearly half a billion km from the Sun.

This means the amount of light falling on Rosetta’s solar panels is gradually diminishing; and, as a consequence, it has less power day by day to run its instruments and sub-systems.

Engineers would soon have to put the satellite into hibernation mode if they wanted to use it long term — during 67P’s next encounter with the Sun in a few years’ time.

But having already spent 12 years in space, battling huge temperature swings and damaging radiation, not to mention a much-reduced fuel load — there is little confidence Rosetta will still be operable so far into the future.

The crash-landing on the other hand offers the opportunity to get some very close-in science to complement the more distant remote sensing it has been doing.

Controllers will try to maintain contact with the satellite for as long as possible during the final descent.