Comet-Chasing Spacecraft Sends First Signal in 31 Months

The comet-chasing Rosetta spacecraft sent its first signal back to Earth after a 31-month hibernation on its decade-long mission into deep space.

Scientists at the European Space Agency’s mission control in Darmstadt, Germany, jumped up and cheered when the signal registered at about 7:20 p.m. local time, according to a webcast of the proceedings. It came during the agency’s predicted 1-hour window and more than 8 hours after the craft’s alarm clock woke it up from a hibernation period far in space.

“We made it!” Rosetta Spacecraft Operations Manager Andrea Accomazzo said on the webcast. “The signal from Rosetta is up there, you can see it on the screen. It’s a big success for everybody.”

The Rosetta mission is the first attempt to orbit and land a probe on a comet, and researchers hope to glean more about the role of comets in the evolution of the solar system. Made from dirty ice, dust and gas, they are considered building blocks that likely helped seed Earth with water and possibly even life. Its target is the Churyumov-Gerasimenko comet, which it’s due to reach in August.

After receiving the alarm call, the craft began a 6-hour wakeup procedure that included switching on some heaters to warm the units that control the direction it points, ESA’s head of mission operations, Paolo Ferri, said earlier today in an interview. Then the instruments had to halt the rotation of the craft, point an antenna to Earth and transmit a signal.

NASA’s monitoring station in Goldstone, California, was used to pick up the signal.

Airbus Project

Rosetta’s scientists will now test all of its subsystems and activate each of the craft’s scientific instruments in turn between now and April, according to Ferri. In May, they’ll begin to slow the craft down to a pace of a few meters per second from 1 kilometer per second, he said.

“Then we will be starting the final approach, and in August we can basically say we are in orbit around the comet,” Ferri said. “That’s when we start our phase of detailed characterization of the comet and we take pictures and we measure the gravity potential.”

Astrium, now part of Airbus Defence and Space, was the main contractor for the spacecraft launched on March 2, 2004. After reaching the Churyumov-Gerasimenko comet, Rosetta is then scheduled to orbit until the end of 2015, placing its lander, called Philae, on the icy mass, this November after identifying a suitable site. Rosetta has 11 packages of scientific instruments, and Philae 10.

Two Harpoons

“The mission is staying around the comet, studying it and seeing its evolution as it gets closer to the sun,” said Ferri.

When the lander is in place, it will shoot two harpoons into the comet to anchor it. The main craft will be “flying over the landing site, collecting signals, storing them on board and periodically pointing the antenna to Earth to send them back,” he said.

While Philae would be the first probe to touch down on a comet and beam data back, ESA’s first deep-space mission, Giotto, was sent to investigate Halley’s Comet in 1986. The U.S. National Aeronautics and Space Administration has also launched two missions to study comets in the past 20 years.

NASA’s Work

In 2005, NASA fired a projectile from its Deep Impact spacecraft into the comet Tempel 1. It monitored the ejected material using two instruments on the main craft, and the projectile beamed data back until nearly the point of impact.

In early 2006, the agency’s Stardust spacecraft returned samples to Earth that were collected during a seven-year round trip to the comet Wild 2. The mission had used a tray of silica gel to trap particles flying off the comet.

ESA’s Giotto in 1986 passed near the nucleus of Halley’s comet, capturing images of the nucleus and discovering the first evidence of organic material in a comet. In 1992, the same craft passed near a second comet, Grigg-Skjellerup.

Rosetta is currently about 670 million kilometers (416 million miles) from the sun and more than 800 million kilometers from earth, according to ESA. Its planned hibernation began in June 2011 because it was too far from the sun for its solar panels to generate sufficient energy. Since then, only the computer and some heaters have been active to ensure the craft didn’t freeze.

“For mission control, not having the signal of the spacecraft is the worst thing that you can have,” Ferri said. “When we have a signal, we know what is the status. Even if there are problems with the spacecraft we can intervene. Even though it was planned, 2 1/2 years without contact is very bad.”

Rosetta is box-shaped with a pair of 14-meter solar panels, giving it a total span of 32 meters (105 feet). The craft is named after the Rosetta Stone, a slab of basalt inscribed in different languages that helped historians to decipher Egyptian hieroglyphics.

The Churyumov-Gerasimenko comet orbits the sun every 6.6 years at a distance that ranges from 186 million kilometers to 857 million kilometers. Discovered in 1969, the comet has a nucleus estimated to be four kilometers in diameter. The Paris-based European Space Agency was formed in 1973 and has 20 member countries, including the U.K., Germany and France.

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