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Rosetta's pioneering Philae comet lander reactivated

Posted: April 1, 2014

Europe's Rosetta spacecraft has returned an image of its distant comet target as ground controllers received the first signals from probe's piggyback Philae lander Friday after hibernating nearly three years in a power-saving sleep mode.

Artist's concept of the Philae lander. Photo credit: DLR
Since the Rosetta spacecraft emerged from hibernation in January, engineers have checked the probe's systems and found them in good condition, according to Andrea Accomazzo, Rosetta's spacecraft operations manager at the European Space Agency.

Rosetta is heading toward an August rendezvous with Comet 67P/Churyumov-Gerasimenko, an inner solar system comet that completes one circuit of the sun every six-and-a-half years.

Ground teams started activating Rosetta's science instruments March 17, successfully switching on the spacecraft's primary science camera, ultraviolet spectrometer, and a plasma sensor suite to study the environment around the comet.

On Friday, the $1.7 billion mission's German-built Philae lander woke up and radioed Earth.

"Philae is operational and ready for the next few months," said Stephan Ulamec, Philae project manager at DLR, the German space agency.

Philae will be ejected from the Rosetta mothership in November to latch itself onto the comet's icy surface with harpoons and screws. The lander has its own suite of science instrumentation to take the first-ever photos and measurements from a comet's surface.

Engineers plan a four-week commissioning phase for Philae to check on its health and activate the lander's 10 instruments.

"We will analyse this data thoroughly, so we can find out whether Philae has survived the long flight and hibernation intact," Ulamec said in a DLR press release.

Before Friday, controllers last received data from Philae on June 8, 2011, when Rosetta entered hibernation. Since Rosetta woke up in January, the craft sent back preliminary temperature measurements from Philae.

Artist's concept of the Philae lander mounted on the Rosetta spacecraft. Photo credit: DLR
The first data packets from Philae arrived on Earth at 1440 GMT (10:40 a.m. EDT) Friday through a NASA tracking antenna in California, which fed the telemetry to the lander's control center in Germany.

Philae's 10 instruments will be activated and tested throughout April. By May, all of the mission's science payloads will be commissioned, including the 11 instruments aboard the Rosetta mothership.

So far, Rosetta's scientific camera has finished its round of testing since the spacecraft woke up in January. The Optical, Spectroscopic and Infrared Remote Imaging System, developed by the Max Planck Institute for Solar System Research in Germany, took the first pictures of the comet since hibernation on March 20 and 21.

"Finally seeing our target after a 10 year journey through space is an incredible feeling," said Holger Sierks, OSIRIS principal investigator at the Max Planck Institute. "These first images taken from such a huge distance show us that OSIRIS is ready for the upcoming adventure."

Churyumov-Gerasimenko was about 5 million kilometers, or 3.1 million miles, from Rosetta when the pictures were taken earlier this month.

The rest of Rosetta's instruments are still being tested.

A series of engine burns in May will adjust Rosetta's course toward the comet, burning much of the spacecraft's remaining fuel. Rosetta is now on a trajectory to miss the comet by approximately 50,000 kilometers, or about 31,000 miles.

The trajectory correction maneuvers in May will guide Rosetta within 100 kilometers, or about 60 miles, of Churyumov-Gerasimenko by the first week of August, according to ESA.

Rosetta's OSIRIS narrow-angle camera took this image of Comet 67P/Churyumov-Gerasimenko on March 21. The comet is indicated by the small circle next to the bright globular star cluster M107. Photo credit: ESA/MPS for OSIRIS-Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Officials have penciled in Philae's landing on Churyumov-Gerasimenko for Nov. 11, but the date could be adjusted a few days based on the probe's landing site and conditions around the comet.

Philae will operate for at least two days on the comet, and it carries solar arrays to recharge its battery if comet's unpredictable dust environment cooperates.

"Landing on the surface is the cherry on the icing on the cake for the Rosetta mission on top of all the great science that will be done by the orbiter in 2014 and 2015," said Matt Taylor, Rosetta's project scientist, in a blog post on ESA's website. "A good chunk of this year will be spent identifying where we will land, but also taking vital measurements of the comet before it becomes highly active. No one has ever attempted this before and we are very excited about the challenge!"

One of Philae's instruments will drill into the comet's surface, collect a sample and feed it into an on-board oven for analysis.

Scientists do not know what environment awaits Rosetta and Philae at the comet.

Controllers will cautiously approach Churyumov-Gerasimenko with Rosetta, taking cues on how to navigate around the comet based on the amount of debris observed by the spacecraft's two main cameras.

The flexible approach allows officials to keep a safe distance from the comet if the ice and dust are deemed too hazardous.

Rosetta will follow the comet for at least a year while it makes its closest approach to the sun, watching Churyumov-Gerasimenko "wake up" as sunlight and heating trigger the comet's volatile jets of water vapor and gas.

Scientists are eager to better understand comets because they may have seeded Earth with water and the building blocks of life soon after the genesis of the solar system.

"They are time capsules," said Mark McCaughrean, senior advisor in ESA's science and robotic exploration directorate, in a press conference in December. "They are remnants of the birth of the solar system. They go back to the beginning of the solar system more than 4.6 billion years ago."

Follow Stephen Clark on Twitter: @StephenClark1.